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In this study, we investigate the broader impacts of microplastics on ecosystem health and ecological risks, specifically through altered assimilation efficiency of aquatic organisms, an individual-level effect that has garnered significant attention recently. The Ecopath with Ecosim model is employed to assess these impacts, focusing on Baiyangdian Lake, China. We examine three scenarios: no microplastics effects (EPScenario 1) and current and assumed high microplastics concentrations effects (EPScenario 2 and EPScenario 3). Results indicate that considering the adverse effects of microplastics on aquatic organisms' assimilation efficiency worsens Baiyangdian Lake's ecosystem health. "Bad" memberships are 0.459, 0.506 and 0.555 for EPScenarios 1–3, respectively. Ecosystem maturity is severely impacted, reducing it to less than half its original level due to decreased total respiration of consumers and increased total system throughput in the entire ecosystem. Furthermore, there are over 3% reductions in ecosystem function due to the decrease in the relative ascendency and over 18% reductions in food web structure caused by the decrease in Finn's cycling index and Finn's mean path length. A critical aspect of this research is the relationship between assimilation efficiency and microplastics dynamics in the food web. Diminished assimilation efficiency results in lower microplastics concentrations in detritus but increased levels in water. This shift significantly affects trophic transfer, reducing microplastics concentrations in organisms that primarily feed on detritus. Conversely, the accumulation of microplastics on plant surfaces in water elevates the concentrations in organisms that feed predominantly on plants. These dynamics are crucial for understanding the ecological risks associated with microplastics, which vary significantly based on the primary food sources of aquatic organisms. The risk escalates in food chains dependent on detritus and diminishes in those reliant on plant-based food chains. This insight is also vital in assessing human health risks related to dietary intake of microplastics from aquatic food sources, highlighting increased risks for consumers of herbivorous and filter-feeding fish. Overall, this research offers critical insights into the complex effects of microplastics on freshwater ecosystems, emphasizing assimilation efficiency's role in managing ecological and health implications. These findings have significant practical implications for ecosystem management, providing a basis for strategies to mitigate microplastic impacts on aquatic organisms and ecosystem health. Additionally, understanding these effects can inform public health initiatives by highlighting risks from consuming contaminated aquatic organisms. Effective management and policy measures can be also developed to reduce microplastic pollution, protecting both ecosystems and public health. • Evaluating microplastics (MPs) effect on ecosystem health and risk through decreasing assimilation efficiency. • MPs degrade ecosystem maturity significantly, harming function and food web structure. • MPs alter food chain trophic transfer patterns and vary ecological risks based on prey primary food sources. • Human dietary habits influence exposure risk to MPs. [ABSTRACT FROM AUTHOR]

Fish consumption is considered to be a major human exposure route for mercury (Hg), but assessing the actual Hg bioavailability from consumed fish is challenging. In this study, we conducted both in vivo bioavailability (using a mouse model) and in vitro bioaccessibility (using various gastrointestinal digestion methods) assessments of Hg from consumed fish. Lyophilized fish muscles which already absorbed Hg through natural incorporation were introduced to mice by active feeding. Assimilation efficiency (AE) was measured as a short-term kinetic parameter, while a 7-day accumulation of Hg in mice blood, liver and kidney was determined. The AEs of Hg in mice ranged between 82 and 96% and showed a positive relationship with MeHg in fish independent of the fish species. For long-term bioavailability tests in which the Hg retention in organs was measured after a 7-day exposure, most Hg was found to be accumulated in liver and kidney, resulting in a strong correlation between Hg dosage and accumulation in mice organs. The long-term absolute bioavailability of mice was comparable between the liver and kidney, but much lower in the blood. The calculated absolute total Hg bioavailability ranged between 38% and 99% and decreased as the Hg dosage increased. Results of bioaccessibility tests varied considerably among different methods, illustrating that there were limitations for the in vitro bioaccessibility assay to predict the digestive dynamics of Hg in mammalian gastrointestinal tract. Our study strongly demonstrated the expediency of direct determination of Hg bioavailability, but more bioaccessibility assessments should be explored and optimized as an alternative to traditional animal experimentation. Unlabelled Image • Dietary assimilation of Hg in the mice was high and positively related to MeHg in fish. • Hg accumulation in mice organs was strongly correlated with Hg dosage. • Absolute total Hg bioavailability decreased as the Hg dosage increased. • Bioaccessibility tests varied considerably among different methods • Direct determination of Hg bioavailability is preferred to bioaccessibility measurement. [ABSTRACT FROM AUTHOR]

Abstract Inter-population variations in growth rate can result from independent or interactive effects of genetic and environmental factors, and be induced by some physiological differences as well. Toad-headed lizards (Phrynocephalus vlangalii) from a higher-elevation population were shown to have a higher growth rate than those from a lower-elevation population. The physiological basis of growth rate variation in this species is not well understood. Here, we investigated the feeding performance and resting metabolic rate (RMR) of lower- and higher-elevation individuals at different test ambient temperatures to evaluate the role of differences in energy intake, assimilation efficiency and metabolic expenditure on growth rate variations. Within the range of 25−35 °C, lizard RMR increased with increasing test ambient temperature, but food intake, apparent digestive coefficient (ADC, food energy minus faecal energy divided by food energy), and assimilation efficiency (AE, food energy minus faecal and urinary energy divided by food energy) were less thermally sensitive in both populations. Higher-elevation lizards tended to eat more food and have a lower RMR than lower-elevation ones, despite the lack of differences in ADC and AE. Our result showed that more energy intake and reduced maintenance cost may be associated with the higher growth rate of higher-elevation lizards. Accordingly, inter-population differences in energy acquisition and expenditure could act as potential sources for geographic variation in growth rate. Highlights • High-elevation toad-headed lizards had greater food intake (but similar assimilation efficiency) than low-elevation ones. • High-elevation lizards had lower metabolic rates than low-elevation ones, probably reflecting lower maintenance cost. • More energy intake but lower maintenance cost could potentially lead to a higher growth rate for high-elevation lizards. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the trophic transfer of 137 Cs in marine and freshwater food chains, focusing on phytoplankton, zooplankton, and planktivorous fish. Algal concentration factors were 278 in freshwater and 69 in seawater. The weight-normalized uptake rate constants of 137 Cs were similar for both freshwater daphnids and marine copepods. Most of the 137 Cs in marine copepods was in the exoskeleton followed by polar and non-polar components. In freshwater daphnids, 137 Cs was highest in the polar fractions followed by exoskeleton and low amounts in the non-polar components. Fish that fed on contaminated marine copepods assimilated 137 Cs with an efficiency of 88%, while 91% was assimilated from freshwater daphnids. A bioaccumulation model demonstrated that diet accounted for ≤3% of the total body burden of 137 Cs in marine zooplankton and ≤12% in freshwater zooplankton, but ≥99% of the total body burden in fish. Rate constants of 137 Cs loss from fish following aqueous exposure were 0.2 d −1 and 0.4 d −1 in marine and freshwater conditions, respectively, but only 0.06 d −1 and 0.3 d −1 , respectively, following dietary exposure. This model also indicates that trophic transfer factors from zooplankton to fish are up to 2.2 for marine conditions and up to 0.6 for freshwater. 137 Cs is unusual among metals in that it enters marine food chains primarily from the aqueous phase into zooplankton, from which it is highly assimilated by fish, resulting in detectable 137 Cs in fish tissues. [ABSTRACT FROM AUTHOR]

The trophic transfer of radiocesium ( 134 Cs) was investigated in two tropical fish, the silver moony Monodactylus argenteus and the spotted scat Scatophagus argus . Juveniles of both species were exposed to dietary 134 Cs using the pulse-chase feeding methodology. The food was brine shrimp ( Artemia salina ) previously exposed to the dissolved radiotracer. Depuration kinetics of 134 Cs were followed for 45 d. Results showed that Cs was similarly efficiently assimilated by both species (AE > 50%). The estimated trophic transfer factors in the two species ranked from 1 to 2, suggesting that 134 Cs could be biomagnified in both omnivorous species. In complement, dissections of 7 body compartments were carried out at three different times in order to highlight 134 Cs organotropism. 134 Cs organotropism was similar in both species: more than 50% of 134 Cs was quickly distributed in the muscles and skeleton (after 3 days of depuration), which is likely related to the analogous behavior between Cs and K, an essential element for muscle contractions and bone formation. [ABSTRACT FROM AUTHOR]

Bioaccumulation of radiocaesium in many marine organisms occurs through complex trophic transfer mechanisms. The present study addresses the trophic transfer of 134 Cs in the widely distributed marine bivalve, the Manila clam Ruditapes philippinarum , by experimentally determining the assimilation efficiency (AE) and the specific role of food quality or diet on the AE in this marine invertebrate. Pulse-chase feeding experiments were carried out on this clam using the phytoplankton species Tetraselmis chuii , Phaeodactylum tricornutum and Isochrysis galbana . Depuration kinetics of 134 Cs over 21 days were analysed using a two-component exponential model. Observed assimilation efficiencies were consistently less than 10% but slightly varied among individuals fed on the three different phytoplankton species diets ( T. chuii : AE = 8.4 ± 0.6%; P. tricornutum : AE = 9.8 ± 0.5%; I. galbana : AE = 5.3 ± 0.6%), although no statistical differences were observed. Comparing results from these experiments with existing data from the literature on the same species exposed to caesium through seawater, it appears that trophic transfer processes are the main accumulation pathway, contributing up to 96% of the global 134 Cs bioaccumulation in this bivalve species. [ABSTRACT FROM AUTHOR]

Methods for accurately estimating within-field yield are essential to improve site-specific crop management and resource use efficiencies, which would be a major step toward sustainable intensification of agricultural systems. We set out to assess the accuracy of within-field soybean yields predicted by two data assimilation methods and to assess these methods' assimilation efficiency (AE). Yields were estimated by assimilating remotely sensed leaf area index (LAI) data from Sentinel-2 into a soybean crop growth model on a pixel basis. The LAI data was integrated into the model by Ensemble Kalman Filtering (EnKF) or by recalibrating with the Subplex algorithm (recalibration-based). An open-loop setting which only integrates information on the soil layers was used as a baseline scenario for quantifying the AE. We assessed both data assimilation techniques on eight fields (3067 pixels) in the Corn Belt region (Nebraska, Kansas and Kentucky) in the United States. The data set encompassed substantial variation in crop growth conditions: three growing seasons (2018, 2019 and 2020), rainfed and irrigated fields, and early and late planting dates. Ground truth yield acquired from combine monitors was used to validate the yield estimations. Agreement between predicted and observed yield at pixel level was two times higher for both data assimilation methods compared to the open-loop. The root mean square error (RMSE) was 476 kg.ha−1 (RRMSE of 10 %) in the recalibration-based method and 573 kg.ha−1 (RRMSE of 12 %) in the EnKF-based method. For both data assimilation methods, assimilating the LAI improved predictions for 68 % of the pixels. For a further 12 % of pixels, there was no accuracy improvement. For the remaining 20 %, AE was positive for one of the two assimilation methods. The high proportion of pixels with positive AE indicates the potential for overcoming the limitations in applying crop models at high spatial resolution by integrating a crop growth indicator. Assimilating an in-season indicator of crop growth (LAI) into a soybean model made it possible to adjust the simulation pathway, thereby greatly improving the accuracy of the yield estimations at the pixel level. This study elucidates the practical applications of data assimilation strategies for fine-scale within-field crop yield mapping. [Display omitted] • We assessed the efficiency by comparing assimilation methods against an open loop. • The assimilation of LAI into the soybean model improved by 42 % yield predictions. • We proved the usefulness of assimilating LAI to compensate for the lack of inputs. • This study provides insights to produce high-resolution yield maps. [ABSTRACT FROM AUTHOR]

Digestive physiology is important for understanding the feeding behaviour of organisms. Specifically, studies on the digestive physiology of frugivorous and nectarivorous birds are important for elucidating their preference patterns in the wild and the selective pressures they exert on fruit pulp and nectar. In this study, digesta transit times and digestive efficiencies of three species of birds, the Cape white-eyes ( Zosterops virens ), red-winged starlings ( Onychognathus morio ) and speckled mousebirds ( Colius striatus ) were investigated on equicaloric glucose or sucrose artificial fruit diets. Three concentrations, approximating the natural range of sugar concentrations in sugary, bird-dispersed fruits were used: low (6.6%), medium (12.4%) and high (22%). Digesta transit times of birds increased with an increase in concentration for all diets but were generally higher on glucose diets. Intake rates, on the other hand, decreased with an increase in sugar concentration. All species of birds failed to maintain a constant assimilated energy intake on glucose diets but mousebirds and white-eyes maintained it on sucrose diets. Apparent assimilation efficiencies of glucose diets for all species were comparable and typical of those found in other frugivorous birds. However, assimilation efficiencies for sucrose diets differed widely with red-winged starlings displaying very low assimilation efficiencies and as a consequence; they lost significant body mass on all sucrose diets. These results demonstrate the importance of digestive physiology in explaining fruit selection patterns in frugivorous birds and how a seemingly trivial physiological trait can have dire ecological consequences. [ABSTRACT FROM AUTHOR]

We evaluated the potential for biomagnification of endocrine disrupting chemicals (EDCs) such as nonylphenol (NP), octylphenol (OP), bisphenol A (BP), and natural estrogens such as estrone (E1) and 17β-estradiol (E2) in a benthic fish, Pleuronectes yokohamae . The assimilation efficiencies (AE) of most EDCs ranged from 88 to 96% suggesting that they were efficiently incorporated and assimilated into P. yokohamae , except for NP (50%). However, the biomagnification factor (BMF) values were <1.0 suggesting that the compounds were not biomagnifying. Additionally, three of the target EDCs were not detected (BP, E1 and E2). Glucuronidation activity towards BP (11.44 ± 2.5 nmol/mg protein/min) and E2 (12.41 ± 3.2 nmol/mg protein/min) was high in the intestine suggesting that EDCs were glucuronidated prior to excretion into bile. Thus, we conclude that biomagnification of dietary EDCs is reduced in P. yokohamae because of effective glucuronidation. [ABSTRACT FROM AUTHOR]

Grass-based suckling beef-derived foods occasionally exceed regulatory levels for polychlorinated biphenyls (PCBs) and dibenzo- p -dioxins/dibenzofurans (PCDD/Fs). Ensuring chemical safety requires understanding the cow-calf transgenerational PCB and PCDD/F fate. The current focus was on dairy cows, omitting transgenerational fate and suckling beef-related physiological effects. This study aimed to investigate PCB and PCDD/F absorption, distribution, metabolism, and excretion within 12 Simmental cows (six primiparous/six multiparous) and 12 calves fed with the milk of their respective mothers for 109 days prepartum until 288 days in milk (DIM), i.e., slaughter time. Eight cows were exposed to a grass silage-soil mixture. Four were decontaminated after DIM164 by receiving uncontaminated grass silage, which four control cows received. An input-output balance during gestation and lactation was computed from PCB, PCDD/F, and lipid inputs (solid feed/milk intakes), outputs (fecal/milk excretions), and body storage (initial/final burdens). At slaughter, PCB and PCDD/F tissue distribution, and lipid allometry were linked. Apparent PCB and PCDD/F absorption rates and metabolized fractions decreased with increasing chlorination. In calves, PCB absorption showed no effect due to chlorination (steady range: 71–87%). High-chlorinated PCB and PCDD/F absorption rates decreased when provided through soil. Cows excreted PCBs and PCDD/Fs via feces (50% relative to input) and milk (9%) and accumulated only 5% in their body, whereas calves accumulated the largest fraction of the total input in their bodies (44%). Cow physiology affected accumulation and excretion, as in primiparous cows, net body burden and milk assimilation efficiencies were higher and lower, respectively, than in multiparous. Liver-specific enrichment was observed in cows and calves (7.0- and 3.2-fold iPCB and dlPCB + PCDD/F TEQ, compared to empty body-based lipid concentrations), whereas iPCBs were also enriched in kidneys (3.1-fold) and muscles (1.5-fold). Consequently, adipose concentrations did not perfectly represent most edible beef tissues. This highlights the essence of integrating the interplay between physicochemical pollutant properties and animal physiology in transgenerational transfer assessments of PCBs and PCDD/Fs. [Display omitted] • Increasing PCB lipophilicity reduced the absorption rate in cows but not in calves. • Compared to POPs from grass silage, POPs from soil were less absorbed by cows. • Calf exposure to POPs occurred more via milk suckling than prenatal exposure. • Young calves (3 mo) had lower estimated metabolism rates than 10 mo calves and cows. • IPCBs are more concentrated in liver, kidneys and muscles than in adipose tissue. [ABSTRACT FROM AUTHOR]

We aimed to evaluate three defined monoalgal diets, Isochrysis galbana clone T-ISO, Tetraselmis suecica and Rhodomonas lens , as a food source for Mytilus galloprovincialis to ascertain which of the diets maximized the feeding, digestion and the assimilatory balance of nutrients and energy. Mussels fed with Rhodomonas yielded the highest clearance and ingestion rates (CR and IR), suggesting that the dimensions of Tetraselmis and T-ISO might have restricted their capture by the mussels’ gill. Absorption efficiency (AE), an indicator of digestibility, was significantly higher for Rhodomonas (69.6%) than for Tetraselmis (38.4%) or T-ISO (23.6%) diets. This could be explained by the greater proportion of refractive non-digestible material contained in Tetraselmis and T-ISO diets, together with the low digestibility of the cell wall of Tetraselmis . The Rhodomonas diet showed the highest protein content, which was reflected in the highest ingestion and absorption of proteins compared with the other diets. However, the amount of carbohydrates and lipids ingested did not match the amount absorbed, probably owing to inefficient carbohydrate digestion and lipids lost through metabolic fecal losses. The total energy absorbed was higher for Rhodomonas (34.5 Jh − 1 ) than for T-ISO (20.1 J h − 1 ) or Tetraselmis (13.9 J h − 1 ) diet. The optimal feeding and digestive behaviour obtained for mussels fed with Rhodomonas diet, coupled with its ideal size, volume, weight and biochemical composition, might provide a better coverage for the anabolic demands of proteins during the seasonal growth cycle, especially during shell formation, gametogenesis and byssogenesis. Statement of relevance We state that this manuscript is relevant for the field of bivalve aquaculture and hatchery. We recommend that the main criteria in selecting algae for culturing mussels should be based on choosing the suitable dimension (size, volume, weight) of algal cell depending on the feeding capacity of mussels, which might vary between species and life stages (larvae, adult). The second main criteria should be based on selecting algae with high digestibility and balanced biochemical composition, to obtain a high absorption of energy that covers the nutritional requirements of each life stage of the mussels. [ABSTRACT FROM AUTHOR]

Saprophagous macroarthropods are usually described as litter transformers that have low assimilation efficiencies and little direct effect on carbon mineralization. They are considered to enhance decomposition indirectly, by fragmenting leaf litter and increasing the surface area available for microbial colonization, thus stimulating microbial activity in their faeces. A review of experimental studies on the direct and indirect effects of macroarthropods on leaf litter decomposition does not confirm these views. (1) Laboratory estimates of assimilation efficiency are highly variable across studies, ranging from less than 5% to over 50%; this suggests that under field conditions that offer a variety of food choices, direct impacts of macroarthropods on carbon mineralization may be stronger than generally assumed. (2) Macroarthropod faeces are poor in easily assimilable organic compounds and rich in lignin; microbial respiration is only transiently stimulated in this material and, in the long term, there is no evidence of increased mass loss in faeces compared with intact leaf litter; faecal pellets are more akin to partially stabilized organic matter than to hotspots of microbial activity. (3) The overall impact of macroarthropods on microbial respiration in litter or soil-litter microcosms can be positive or negative; the results vary depending on animal abundance and litter type, but macroarthropod-microorganism interactions in unconsumed leaf litter may also be involved; recent studies have shown that macroarthropods grazing on fungi have complex, species-specific effects on fungal-mediated decomposition, which may partly explain the variability of microbial responses in microcosm experiments. (4) The most consistent effect of macroarthropods in decomposing leaf litter is an increased rate of nitrogen mineralization, which results predominantly from interactions with microorganisms and not from excretion; fresh macroarthropod faeces probably stimulate microfaunal activity, thereby increasing nitrogen release, although the actual mechanism remains unclear. It is concluded that soil macroarthropods play important roles in nutrient cycling, while their impact on carbon mineralization is much less clear. Significant alterations of carbon and nutrient dynamics may result from their interactions with fungi and more research is required in this area. [ABSTRACT FROM AUTHOR]

Abstract: The survival, growth, food availability and assimilation efficiency of the bottom-cultured sea cucumber Apostichopus japonicus were investigated at a subtropical fish farm in Dapeng Cove, Daya Bay, during an 8-month field study. Our aim was to assess the possibility of producing commercial-sized A. japonicus under fish farms and developing an integrated multi-trophic aquaculture (IMTA) system on the southern China coast. Survival of A. japonicus cultured at the fish farm and reference site (1km away from the fish farm) was 100% from December 9, 2011 through June 29, 2012, though all animals at both sites died at the July sampling because of anoxia caused by water stratification. Factors including time, culture site and stocking density had significant effects on the growth of A. japonicas. Growth during winter and early spring varied significantly with density and site; however, growth over the whole study period was significantly affected by time, site and the interactions between time/site and time/density. Specific growth rates of A. japonicus at the fish farm (0.40–0.71%) and reference site (0.15–0.54%) were always positive from winter through early spring (December to April). The faster growth recorded at the fish farm site during this period was mainly due to accessing more food of better quality from the surrounding environment. A. japonicus underwent aestivation and suffered weight loss with the increase of water temperature after the April sampling. Only A. japonicus cultured at low density (10indm−2) at the fish farm site reached a commercial size (>100g wet weight) during the entire study period. Organic matter contents of the foregut material were higher than the surrounding sediments, indicating that A. japonicus had a high food selection capability. The assimilation efficiency of A. japonicus in the experimental areas was relatively high, with average values of 13.78±5.83% at the fish farm and 15.13±7.75% at the reference site. This study demonstrated that fish farm debris can be efficiently used by A. japonicus, and bottom culture is an economical and environmentally friendly system of producing commercial-sized A. japonicus in subtropical fish farms in southern China. We recommend harvesting bottom-cultured A. japonicus specimens before May, thereby avoiding weight loss during aestivation. We also suggest improving product size through enhanced seed size and/or reducing stocking density. [Copyright &y& Elsevier]

Arsenic exists universally in freshwater and marine environments, threatening the survival of aquatic organisms and human health. To elucidate arsenic bioaccumulation and biotransformation processes in aquatic organisms, this review evaluates the dissolved uptake, dietary assimilation, biotransformation, and elimination of arsenic in aquatic organisms and discusses the major factors influencing these processes. Environmental factors such as phosphorus concentration, pH, salinity, and dissolved organic matter influence arsenic absorption from aquatic systems, whereas ingestion rate, gut passage time, and gut environment affect the assimilation of arsenic from foodstuffs. Arsenic bioaccumulation and biotransformation mechanisms differ depending on specific arsenic species and the involved aquatic organism. Although some enzymes engaged in arsenic biotransformation are known, deciphering the complicated synthesis and degradation pathway of arsenobetaine remains a challenge. The elimination of arsenic involves many processes, such as fecal excretion, renal elimination, molting, and reproductive processes. This review facilitates our understanding of the environmental behavior and biological fate of arsenic and contributes to regulation of the environmental risk posed by arsenic pollution. [ABSTRACT FROM AUTHOR]

Highlights: [•] We obtained the respiratory uptake efficiencies (E W) of 99 compounds by fish. [•] The relationship between the E W values and log K OW was analyzed. [•] The E W of the compounds increased with increasing the log K OW up to a log K OW of 5. [•] We derived an equation for predicting E W based on a two-phase resistance model. [Copyright &y& Elsevier]

Abstract: The assimilation efficiency of zooplankton is an essential parameter required to estimate energy transfer to higher trophic levels in marine ecosystems. However, little information is available for large oceanic copepods, especially the Neocalanus and Eucalanus species dominant in the subarctic Pacific. In this study, the assimilation efficiencies of the C5 stages of Neocalanus cristatus, Neocalanus flemingeri and Eucalanus bungii were evaluated using eight phytoplankton species as food. The average assimilation efficiencies of N. cristatus, N. flemingeri and E. bungii ranged between 45 and 66%, 44 and 66% and 34 and 65%, respectively. The assimilation efficiency was highly variable depending on the food phytoplankton species. In all species, the assimilation efficiency showed a significant negative relationship with the ash content of the phytoplankton (r 2 =0.79–0.87, p <0.001). The assimilation efficiency of large-body sized N. cristatus for large-sized diatoms was higher than for the other copepod species. In population models of N. cristatus, changes in assimilation efficiency affect the growth and survival rates of the population. The Lagrangian ensemble model (LEM) for N. cristatus showed that, for assimilation efficiencies less than 57%, the population could not be maintained. Because variations in assimilation efficiency may have significant effects on the copepod population, their variability should be incorporated into marine ecosystem models in the future. [Copyright &y& Elsevier]

Abstract: Differences between the bioavailability of cadmium in a periphyton diet and an artificial laboratory diet (TetraMin®) have important consequences for predicting bioaccumulation and toxicity in the freshwater amphipod Hyalella azteca. The assimilation efficiency (AE) of Cd was compared between periphyton and TetraMin® at low (1510 and 358nmol/g ash-free dry mass respectively) and chronically lethal (31,200 and 2890nmol/g ash-free dry mass respectively) Cd concentrations and in fresh and dry forms using a 109Cd radiotracer pulse-chase feeding technique. Assimilation efficiency of Cd from periphyton (AE=3–14%) was lower than that for TetraMin® (AE=44–86%) regardless of Cd concentration or food form. Ingestion rate (IR) was lower for dry than fresh forms of periphyton (0.042 and 0.16g AFDM/g H. azteca/day respectively) and TetraMin® (0.19 and 0.87AFDM/g H. azteca/day respectively) and depuration rate (k e ) did not differ statistically with food type, form or Cd concentration (0.032–0.094d−1). Biokinetic models with parameters of AE, IR and k e were used to estimate bioaccumulation from the separate food types. These estimates were compared to those from an independent chronic Cd saturation bioaccumulation model. While the model estimates did not concur, a sensitivity analysis indicated that AE and IR were the most influential biokinetic model parameters for Cd in periphyton and TetraMin® respectively. It was hypothesized that AE was underestimated for Cd in periphyton due to a non-adapted gut enzyme system and IR was overestimated for Cd in TetraMin® due to an initial rapid ingestion phase in H. azteca''s feeding habits. This research demonstrated the importance of using ecologically relevant food types in laboratory experiments and verifying acute biokinetic model predictions of dietary metal contribution with those derived from a chronic exposure which is more representative of a field exposure scenario. [Copyright &y& Elsevier]

Abstract: The kinetics of food processing by zooplankton affects both their energy budgets and the biogeochemical fate of their fecal pellets. We sampled 40 schools of krill across the Scotia Sea during spring, summer and autumn and found that in all 3 seasons, every aspect of their absorption and defecation varied greatly. The C content of fecal pellets varied from 0.85% to 29% of their dry mass (median 9.8%) and C egestion rates varied 75-fold. C:N mass ratios of pellets ranged from 4.9 to 13.2 (median 7.8), higher than values of 3.9 in the krill and 5.4 in their food, pointing to enhanced uptake of N. Pellet sinking rates equated to 27–1218md−1 (median 304md−1), being governed mainly by pellet diameter (80–600μm, mean 183μm) and density (1.038–1.391gcm−3, mean 1.121gcm−3). Pellets showed little loss of C or N in filtered seawater over the first 2 days and were physically robust. When feeding rates were low, slow gut passage time and high absorption efficiency resulted in low egestion rates of pellets that were low in C and N content. These pellets were compact, dense and fast-sinking. Conversely, in good feeding conditions much food tended to pass quickly through the gut and was not efficiently absorbed, producing C and N-rich, slow-sinking pellets. Such “superfluous feeding” probably maximises the absolute rates of nutrient absorption. Food composition was also important: diatom-rich diets depressed the C content of the pellets but increased their sinking rates, likely due to silica ballasting. So depending on how krill process food, their pellets could represent both vehicles for rapid export and slow sinking, C and N-rich food sources for pelagic scavengers. C egestion rates by krill averaged 3.4% of summer primary production (and ingestion rates would be 2–10-fold higher than this) so whatever the fate of the pellets, krill are an important re-packager within the food web. While salp pellets tend to sink faster than those of krill, it is the latter that tend to prevail in sediment traps. We suggest that this is because krill schools are more compact, producing “rain showers” of pellets that exceed the capacity of pelagic scavengers to reprocess them. [Copyright &y& Elsevier]

This study investigates the ability of the biodynamic model to predict the trophic bioaccumulation of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and zinc (Zn) in a freshwater bivalve. Zebra mussels were transplanted to three sites along the Seine River (France) and collected monthly for 11 months. Measurements of the metal body burdens in mussels were compared with the predictions from the biodynamic model. The exchangeable fraction of metal particles did not account for the bioavailability of particulate metals, since it did not capture the differences between sites. The assimilation efficiency (AE) parameter is necessary to take into account biotic factors influencing particulate metal bioavailability. The biodynamic model, applied with AEs from the literature, overestimated the measured concentrations in zebra mussels, the extent of overestimation being site-specific. Therefore, an original methodology was proposed for in situ AE measurements for each site and metal. [Copyright &y& Elsevier]

Abstract: Dietary metal uptake in fish is determined by metal bioavailability in prey and the metal requirements of the fish. In this study zebrafish were fed the intertidal polychaete worm Nereis diversicolor (3% wet weight day−1) collected from Ag, Cd and Cu-impacted Restronguet Creek (RC) or a reference site, Blackwater estuary (BW), for 21 days. On days 0, 7, 14 and 21 fish were fed a single meal of RC or BW N. diversicolor labeled with 110mAg or 109Cd for measurements of metal assimilation efficiency (AE). Zebrafish intestines were also taken for mRNA expression analysis of copper transporter 1 (ctr1), divalent metal transporter 1 (dmt1) and metallothionein 2 (mt2). No significant difference was observed in the AE of 109Cd in metal naïve fish at day 0 between RC and BW worms, 11.8±2.1 and 15.3±2.8%, respectively. However, AE of 110mAg was significantly greater in fish fed worms from BW compared to RC, 5±1.2% and 1.6±0.5%, respectively at day 0. Fractionation analysis of radiolabeled metal partitioned in N. diversicolor from RC revealed a greater proportion of Ag (40±1.1%) in a fraction containing protein and organelle bound metal, associated with high trophic availability, compared to BW polychaetes (24±2.5%). Lower AE of 110mAg from RC polychaetes is therefore unlikely due to speciation of 110mAg in N. diversicolor from RC, but to the high concentration of Cu, a potential Ag antagonist. Exposure to RC polychaetes significantly increased the AE of 110mAg (6.2±1%), but not 109Cd, from RC worms, after 21 days. AE of 110mAg and 109Cd was unaffected by pre-exposure to BW. Elevated concentration of intestinal Cu and increased expression of ctr1, dmt1 and mt2 after 14 days exposure in fish fed worms from RC suggest altered Cu handling strategy of these fish which may increase AE of Ag via shared Ag and Cu transport pathways. These data suggest metal exposure history of invertebrates may affect metal bioavailability to fish, and fish may alter intestinal uptake physiology during chronic dietary exposure with implications for the assimilation and toxicity of dietary metals. [Copyright &y& Elsevier]

Abstract: Elevated metal levels in fish are a concern for the fish themselves, their predators, and possibly humans who consume contaminated seafood. Metal bioaccumulation models often rely on assimilation efficiencies (AEs) of ingested metals and loss rate constants after dietary exposure (k efs). These models can be used to better understand processes regulating metal accumulation and can be used to make site-specific predictions of metal concentrations in animal tissues. Fish often consume a varied diet, and prey choice can influence these two parameters. We investigated the trophic transfer of As, Cd, Cr, Hg(II), and methylmercury (MeHg) from a benthic amphipod (Leptocheirus plumulosus) and an oligochaete (Lumbriculus variegatus) to killifish (Fundulus heteroclitus) using gamma-emitting radioisotopes. Except for MeHg, AEs varied between prey type. AEs were highest for MeHg (92%) and lowest for Cd (2.9–4.5%) and Cr (0.2–4%). Hg(II) showed the largest AE difference between prey type (14% amphipods, 24% worms). For Cd and Hg(II) k efs were higher after consuming amphipods than consuming worms. Tissue distribution data shows that Cd and Hg(II) were mainly associated with the intestine, whereas As and MeHg were transported throughout the body. Calculated trophic transfer factors (TTFs) suggest that MeHg is likely to biomagnify at this trophic step at all ingestion rates, whereas As, Cd, Cr, and Hg(II) will not. Data collected in this study and others indicate that using one prey item to calculate AE and k ef could lead to an over- or underestimation of these parameters. [Copyright &y& Elsevier]

Abstract: Cadmium is a non-essential toxic metal that is able to bioaccumulate in both flora fauna and has the potential to biomagnify in some food chains. However, the form in which cadmium is presented to consumers can alter the bioavailability and possibly the internal distribution of assimilated Cd. Previous studies in our laboratory highlighted differences in Cd assimilation among isopods when they were provided with a plant-based food with either Cd biologically incorporated into plant tissue or superficially amended with ionic Cd2+. Cd is known for its high affinity for sulphur ligands in cysteine residues which form the basis for metal-binding proteins such as metallothionein. This study compares Cd assimilation efficiency (AE) in Porcellio dilatatus fed with food amended with either cadmium cysteinate or cadmium nitrate in an examination of the influence of Cd speciation on metal bioavailability followed by an examination of the sub-cellular distribution using a centrifugal fractionation protocol. As hypothesized the AE of Cd among isopods fed with Cd(NO3)2 (64%, SE=5%) was higher than AE for isopods fed with Cd(Cys)2 (20%, SE=3%). The sub-cellular distribution also depended on the Cd species provided. Those isopods fed Cd(Cys)2 allocated significantly more Cd to the cell debris and organelles fractions at the expense of allocation to metal-rich granules (MRG). The significance of the difference in sub-cellular distribution with regard to toxicity is discussed. This paper demonstrates that the assimilation and internal detoxification of Cd is dependent on the chemical form of Cd presented to the isopod. [Copyright &y& Elsevier]

Abstract: Omnivory has an important role in the movement of energy, nutrients, and contaminants between benthic and pelagic food webs. While top-predator fish are known to supplement a mostly piscivorous diet with benthic organisms, a more obscure benthic–pelagic coupling occurs when benthic invertebrates forage on fish carcasses, referred to as necrophagy. The combination of these two benthic–pelagic links, top-predator fish feeding on benthic organisms that have fed on dead fish, can generate a trophic feedback cycle that conserves energy and nutrients and may have implications for biomagnification of methylmercury (MeHg) in fish. We investigated the role of necrophagy by crayfish (Procambarus clarkii), via a trophic feedback cycle, on the biomagnification of MeHg in largemouth bass (Micropterus salmoides), a cosmopolitan top predator fish known to feed on crayfish. Controlled laboratory tests quantified the uptake of MeHg by both organisms from artificial and natural food (whole crayfish or bass tissue). Assimilation efficiency (AE) of MeHg was greater for bass fed crayfish (79±0.5%) than those fed artificial food (60±3%). Furthermore, AE of MeHg was greatest for largemouth bass fed crayfish that fed on MeHg-dosed dead fish (i.e., trophic feedback cycle; 94±17%). A model, parameterized with results of the laboratory experiments, was used to make steady-state projections of MeHg biomagnification factors. Model projections also indicate that MeHg biomagnification would be greatest for largemouth bass from a trophic feedback cycle. These results suggest that food web ecology has an important role in determining MeHg levels in predatory fish and underscore the need for further investigation into the magnitude that necrophagy may affect MeHg biomagnification in aquatic systems. [Copyright &y& Elsevier]

Abstract: To evaluate the dietary uptake of polychlorinated biphenyls (PCBs) from live food, we investigated the dietary uptake and depuration kinetics of PCBs in a marine benthic fish (marbled sole, Pseudopleuronectes yokohamae) by using as food live sandworms (Perinereis nuntia) that were laboratory-exposed to field-collected PCB-contaminated sediment. Marbled sole were fed the PCB-contaminated sandworms for 28d and then uncontaminated sandworms for 56d. The assimilation efficiencies (AEs) of 84 PCB congeners via the gastrointestinal tract (GIT) to the muscle of the fish ranged from 0.21 to 0.78; whole-body AEs would be lower than those of muscle because of the lower PCB concentrations, on a lipid basis. The AEs determined in this study were lower than those in other studies that used PCB-spiked commercial pelletized food. The lower AEs found in this study might be attributable to differences in the food administered (live sandworms vs. commercial pellet food), possibly because of low digestibility of sandworm lipids by marbled sole. In addition, the AEs in this study tended to increase with increasing log octanol–water partition coefficients (K OW) up to about seven, although AEs in the other studies using commercial pelletized food did not increase with increasing log K OW. This result suggests the co-transport of highly hydrophobic PCB congeners along with lipids and fatty acids from the digested sandworms into the GIT epithelium cells. The growth-corrected half-lives of 26 PCB congeners in the muscle of fish ranged from 20 to 107d. [ABSTRACT FROM AUTHOR]

We test the hypothesis that accumulated metal in prey that is trophically available to one predator is not necessarily equally trophically available to another predator feeding on the same prey, given the variability between invertebrate digestive systems. We provided two predators, the neogastropod mollusc Hinia reticulata and the palaemonid decapod crustacean Palaemonetes varians , with the digestive glands and adductor muscles of four bivalves radiolabelled with Zn, Cd or Ag. The bivalves (the mussel Mytilus edulis , the clam Ruditapes philippinarum , the scallop Aequipecten opercularis , the oyster Crassostrea gigas) have different metal accumulation patterns with differential dependence on soluble and insoluble detoxification, as confirmed by fractionation of the prey tissues. We found no consistent significant difference between the AE of the two predators for the three trace metals accumulated in the same prey tissues. There were no significant correlations for either predator between percentages of metal in soluble form (or soluble form with organelle-associated metal) and percentage AE for any of the three metals, allowing the conclusion that both predators are assimilating each metal from more than the soluble and organelle-associated metal fractions. For neither predator did an increased percentage of Zn in the form of metal rich granules (MRG) affect its Zn AE, but increases in the percentages of both Cd and Ag bound to MRG decreased the AE of the relevant metal in P. varians but not H. reticulata. Thus the Cd and Ag in some Cd-rich and Ag-rich granules in the bivalve tissues are not as trophically available to P. varians as they are to H. reticulata. This interspecific difference confirms that the neogastropod has the stronger digestive and assimilative powers involving Cd and Ag bound in prey than the palaemonid decapod. [ABSTRACT FROM AUTHOR]

Abstract: Nickel (Ni) is a widespread contaminant present at toxic concentrations in aquatic systems in the vicinity of some mining and smelting operations. However, its accumulation by aquatic animals has been little studied and there are few biomonitors for this metal. Recently, larvae of the aquatic insect Chaoborus were shown to be effective as biomonitors for Ni concentrations in lakewater. Since animals are more effective as biomonitors when we understand how they take up their contaminants (from water or from food) and the rate at which they exchange contaminants with their surroundings, we set out to measure these parameters for Chaoborus. To achieve these goals, we exposed the components of a laboratory food chain (green alga, cladoceran, Chaoborus) to realistic Ni concentrations. We found that the majority (≈65%) of the Ni taken up by Chaoborus flavicans comes from lakewater, with the remainder coming from its planktonic prey (Daphnia magna). This result is consistent with the low mean efficiency (14%) with which C. flavicans assimilated Ni from its prey. To explain the low efficiency of Ni uptake from food we measured the subcellular distribution of Ni in prey, which predicted that the majority of the Ni in prey (≈55%) was available for assimilation by the predator. This potential Ni uptake efficiency was only reached in animals that ingested few prey, likely because their gut passage time was longer than those ingesting many prey. We also measured Ni uptake and loss by C. flavicans exposed to Ni in water then used these data to parameterize a mechanistic bioaccumulation model that allowed us to describe Ni exchange between this insect and water. Lastly, we used these model constants, along with field measurements of Ni in 10 Canadian lakes, to predict Ni concentrations in field populations of Chaoborus. Model predictions overestimated Ni concentrations in field populations by a factor of 4. We suggest that uncertainties in the rate constant for Ni uptake from water and a lack of measured Ni concentrations in the prey eaten by Chaoborus larvae in the field could explain this difference. [Copyright &y& Elsevier]

Abstract: Three aspects of the appendicularian O. dioica''s ecophysiology were measured here: 1) morphological parameters over a wide range of appendicularian sizes, including mature animals in order to document the morphological characteristics inducing reproduction; 2) clearance rate and assimilation efficiency using feeding incubations with different algal concentrations and 3) the effect of food concentration on growth, mortality and reproduction. The relationship between the body carbon weight and the clearance rate follows a power function, with an exponent of 0.91 (±0.07). The rate of particles retention increases with the food concentration following a Michaelis–Menten relationship (half-saturation constant = 151±22 µg C l−1, maximum clearance rate = 12±1 µg C µg C−1 d−1). The carbon assimilation efficiency decreases with the increasing food concentration. As a result, appendicularian growth which is limited in concentrations lower than 50 µg C l−1 is saturated above 100 µg C l−1. In immature animals the gonad represents less than 30% of the body volume whereas in mature individuals, its volume varies between 50% and 87% (mean 63%) suggesting that gonad/total volume ratio can be used as indicator of the maturation stages. The gonad weight in mature animals represents 70.3 (±4.6)% of the total body carbon weight. Two major maturity stages can explain the changes in energy allocation: i) the somatic growth, when less energy is invested in gonad growth when compared to the rest of the body and ii) the maturation phase where most of the assimilated matter is invested in gonad maturation. This process is rapid, lasting only few hours. For this reason we measured completely mature organisms that are generally not measured during the experimental work with appendicularians. In food-limited conditions, the gonad maturation process starts with smaller individuals and ends with smaller reproductive animals having the same gonad to total volume ratio than in unlimited food conditions. The results obtained in this study were used to model the life cycle of O. dioica (see Lombard, F., Sciandra, A. and Gorsky, G., 2009-this volume. Appendicularian ecophysiology. II. Modeling nutrition, metabolism, growth and reproduction of the appendicularian Oikopleura dioica.). [Copyright &y& Elsevier]

Abstract: Chronic exposure to polluted field conditions can impact metal bioavailability in prey and may influence metal transfer to predators. The present study investigated the assimilation of Cd, Hg and organic carbon by grass shrimp Palaemonetes pugio, collected along an impact gradient within the New York/New Jersey Harbor Estuary. Adult shrimp were collected from five Staten Island, New York study sites, fed 109Cd- or 203Hg-labeled amphipods or 14C-labeled meals and analyzed for assimilation efficiencies (AE). Subsamples of amphipods and shrimp were subjected to subcellular fractionation to isolate metal associated with a compartment presumed to contain trophically available metal (TAM) (metal associated with heat-stable proteins [HSP – e.g., metallothionein-like proteins], heat-denatured proteins [HDP – e.g., enzymes] and organelles [ORG]). TAM-109Cd% and TAM-203Hg% in radiolabeled amphipods were ∼64% and ∼73%, respectively. Gradients in AE-109Cd% (∼54% to ∼75%) and AE-203Hg% (∼61% to ∼78%) were observed for grass shrimp, with the highest values exhibited by shrimp collected from sites within the heavily polluted Arthur Kill complex. Population differences in AE-14C% were not observed. Assimilated 109Cd% partitioned to the TAM compartment in grass shrimp varied between ∼67% and ∼75%. 109Cd bound to HSP in shrimp varied between ∼15% and ∼47%, while 109Cd associated with metal-sensitive HDP was ∼17% to ∼44%. Percentages of assimilated 109Cd bound to ORG were constant at ∼10%. Assimilated 203Hg% associated with TAM in grass shrimp did not exhibit significant variation. Percentages of assimilated 203Hg bound to HDP (∼47%) and ORG (∼11%) did not vary among populations and partitioning of 203Hg to HSP was not observed. Using a simplified biokinetic model of metal accumulation from the diet, it is estimated that site-specific variability in Cd AE by shrimp and tissue Cd burdens in field-collected prey (polychaetes Nereis spp.) could potentially result in up to ∼3.2-fold differences in the dose of Cd assimilated by shrimp from a meal in the field. The results of this study also suggest that chronic field exposure can impact mechanisms of metal transport across the gut epithelium that do not influence carbon assimilation. Differences in the assimilation and subcellular partitioning of metal may have important implications for metal toxicity in impacted shrimp populations. [Copyright &y& Elsevier]

Radiolabelled experiments were carried out to measure necessary parameters in the development of a biodynamic ecotoxicological simulation model of Cd accumulation in the barnacle biomonitor Balanus amphitrite. The Cd uptake rate constant from the dissolved phase, the Cd assimilation efficiency (AE) from suspended particulate matter (SPM) and the efflux rate constant were obtained using 109Cd. A Cd uptake rate constant from the dissolved phase (k u) of 0.0072Lg¿1 h¿1 was determined for the barnacle under environmentally realistic dissolved Cd concentrations (maximum of 400ngL¿1). Cd AE from SPM was determined from the barnacle feeding on SPM with low and high chl a concentrations, resulting in AEs of 39.0% and 48.7%, respectively, and an efflux rate of 0.0072d¿1. The difference between the AEs resulted from differences in chl a:SPM ratios suggesting a general tendency of higher AE when SPM is enriched with chl a. These results reinforce that the accuracy of ecotoxicological models for metal accumulation in organisms depends on how representative the selected food items are of the organism¿s natural diet. [Copyright &y& Elsevier]

Abstract: Digestive assimilation efficiency is considered a trait with important implications for animal ecology. However, practically all studies have ignored the importance of sex differences in food assimilation efficiency (AE). Here, we investigated sex differences in dietary and physiological parameters in the Black-tailed Godwit Limosa limosa limosa feeding on rice seeds, a species with sexual dimorphism in body size and body mass. Gross daily food intake, gross energy intake, gross energy output and metabolizable energy intake did not vary significantly between sexes, but godwit females showed lower faeces energy density and higher AE than males. Mass-specific AE was similar in males and females, and the difference in AE could be attributed to the females'' greater body mass. We suggest that a differential AE could play a role in explaining sex differences in habitat or micro-habitat selection during the non-breeding season in bird species with sexual dimorphism in size. Finally, we addressed the question about assimilation efficiency accuracy in models that estimate prey acquisitions by declining shorebirds as the Black-tailed Godwit. [Copyright &y& Elsevier]

Abstract: Leopard tortoises (Stigmochelys pardalis) experience wide fluctuations in environmental conditions and unpredictable availability of food and water within the Nama-Karoo biome. It was hypothesised that tortoises fed two diets differing in preformed water and fibre content would have differing food intake, gut transit rate, assimilation efficiency, faecal and urinary water loss, and urine concentrations. It was predicted that tortoises fed these contrasting diets would attempt to maintain energy and water balance by altering their digestive parameters. Leopard tortoises fed lucerne (Medicago sativa) had a low food intake coupled with long gut transit times, which resulted in the lowest amount of faecal energy and faecal water lost. Tortoises fed tomatoes (Solanum lycopersicum) had higher food intake and faster gut transit times, but more energy and water was lost in the faeces. However, daily energy assimilated and assimilation efficiency were comparable between tortoises fed the two diets. Urine osmolality was significantly different between tortoises on the two diets. Results indicate that leopard tortoises can adjust parameters such as transit rate, food intake, water loss and urine osmolality to maintain body mass, water and energy balance in response to a high fibre, low water content and a low fibre, high water content diet. This study suggests that this digestive flexibility allows leopard tortoises in the wild to take advantage of unpredictable food and water resources. [Copyright &y& Elsevier]

Abstract: We examined the influence of macronutrient (nitrate and phosphate) additions on Ni uptake by phytoplankton (Prorocentrum donghaiense and Skeletonema costatum) and its subsequent transfer to marine copepods (Calanus sinicus and Labidocera euchaeta). Ni uptake by phytoplankton after 24h of exposure was markedly dependent on nutrient conditions, with a higher nutrient quota facilitating Ni accumulation in the algae. Trophic transfer was quantified by measurements of the Ni assimilation efficiency in C. sinicus and L. euchaeta, feeding on the algae under different nutrient treatments. Ni assimilation efficiency generally increased with an increase of nutrient concentration in the algae. A significant positive-correlation was found between the Ni assimilation efficiencies of the copepods and the %intracellular Ni in the algal cells. However, ambient nutritional conditions had little effect on the physiological turnover rate constant of Ni by copepods. Thus, nutrient enrichment may lead to an increase in Ni uptake and transfer in marine plankton. [Copyright &y& Elsevier]

Abstract: We employ a novel approach that combines pulse-chase feeding and multi-labelled stable isotopes to determine gut passage time (GPT), gut retention time (GRT), food ingestion rate (IR) and assimilation efficiency (AE) of three trace elements for a freshwater gastropod. Lettuce isotopically enriched in 53Cr, 65Cu and 106Cd was fed for 2h to Lymnaea stagnalis. The release of tracers in feces and water was monitored for 48h, during which unlabelled lettuce was provided ad libidum. The first defecation of 53Cr occurred after 5h of depuration (GPT), whereas 90% of the ingested 53Cr was recovered in the feces after 22.5h of depuration (GRT). 53Chromium was not significantly accumulated in the soft tissues upon exposure. In contrast, 65Cu and 106Cd assimilation was detectable for most experimental snails, i.e., 65/63Cu and 106/114Cd ratios in exposed snails were higher than those for controls. Food IR during the labelled feeding phase was 0.16±0.07gg−1 d−1. IR was inferred from the amount of 53Cr egested in the feces during depuration and the concentration of 53Cr in the labelled lettuce. Assimilation efficiencies (±95% CI) determined using mass balance calculations were 84±4% for Cu and 85±3% for Cd. The ratio method yields similar AE estimates. Expanding the application of this novel stable isotope tracer technique to other metals in a wide variety of species will provide unique opportunities to evaluate the interplay between digestive processes and dietary influx of metals. Understanding the biological processes that modulate dietborne metal uptake is crucial to assess the toxicity of dietborne metals. [Copyright &y& Elsevier]

Abstract: Munida gregaria is the most abundant galatheid crab species in the Beagle Channel (55 °S 68 °W) off Tierra del Fuego, Argentina. This species has two different and simultaneous feeding habits: predator and deposit feeder. The objectives of this work were to determine whether either of the two different feeding habits imply differences in assimilation and oxygen consumption. Subsamples of 40 and 20 crabs of each sex were randomly selected, transported to the laboratory, and used in assimilation and oxygen consumption experiments, respectively. Animals were placed in individual chambers at 8±1 °C. The assimilation experiment was conducted using four types of diet: isopods (CRU), algae (ALG), pulverized fish food (PFF), and particulate organic matter (POM). The crabs'' routine metabolism and postprandial oxygen consumption – or specific dynamic action SDA – were measured using Clark-type polarographic electrodes. Two kinds of food were offered: CRU and PFF to simulate both feeding habits. Assimilation in M. gregaria for both feeding habits presented values >90% for dry mass and energetic content. Consumption rate varied between 15 and 50 mgingested gDM −1, and was significantly higher for CRU and PFF diets. Females showed significantly higher consumption rates than males for all diets. On average, the routine metabolism of M. gregaria was 15±5 μlO2 h−1 g−1. Deposit feeding may confer energetic advantages to female M. gregaria, especially because this diet has a low energetic cost of assimilation. Deposits of high-energy content showed the highest consumption rates among four the experimental diets. In terms of mass and energy, the deposit diet also showed the highest assimilation efficiency. The postprandial oxygen consumption was lower in females and in the deposit feeding experiment. We suggest that females may prefer the deposit feeding habit to maximize their ingested energy, allowing them to devote more energy to reproduction. This is attained by a high consumption rate and by minimizing the energy used in assimilation. [Copyright &y& Elsevier]

Abstract: The assimilation of trace metals from food can be the main route of metal uptake into aquatic invertebrates. The assimilation efficiencies of zinc and cadmium from muscle tissue of a cephalopod mollusc (40% to 70% Zn, 64% to 83% Cd) and from a macrophytic alga (50% to 69% Zn, 39% to 50% Cd) were measured in juvenile penaeid prawns Penaeus indicus. Assimilated Zn and Cd were retained mostly in the hepatopancreas of the prawns, some metal being excreted (Zn k e 0.10 and 0.11 and Cd k e 0.004 and 0.009, from cephalopod muscle and alga, respectively). There were no significant differences between k es (efflux rate constants) of one metal from either diet. Given the high trace metal assimilation efficiencies measured here, it is highly probable that metal assimilation from food plays an important role in Zn and Cd accumulation in the body of P. indicus, particularly in estuarine stages of the life cycle, for estuaries are particularly prone to metal pollution and are likely to offer the prawns abundant metal-rich diets such as detrital material derived from local macrophytes. [Copyright &y& Elsevier]

Abstract: A nature-simulating culture system was used to explore the influence of salinity, the diurnal cycle and daylength on ingestion rate (IR) and assimilation efficiency (AE) of Meretrix meretrix. The clams used in the experiments were grouped into three sizes: small, with a shell length of 2.70±0.10 cm and a dry fresh weight of 0.35±0.04 g; medium, with a shell length of 4.00±0.05 cm and a dry fresh weight of 1.25±0.05 g; and large, with a shell length of 5.00±0.10 cm and a dry fresh weight of 2.45±0.10 g. The clams in all size groups demonstrated a common response pattern in IR and AE under salinities ranging from 18 to 34 ppt. The clams achieved the greatest IR within the salinity range 27 to 30 ppt. There was a marked reduction in IR outside this range. Of the salinities tested 18 ppt was the harshest stress to the feeding of M. meretrix. Between the salinities 24 to 34 ppt, changes in AE of the clam were the inverse of those observed in IR, suggesting that M. meretrix is able to compensate for the loss of IR by an increase in AE. Although the effect of both salinity and body size of the clam was significant on both IR and AE, salinity had evidently stronger influence than body size. All sizes of clam showed a three-phase diurnal feeding pattern: a high ingestion phase from 00:00 to 08:00, a low ingestion phase from 12:00 to 20:00, and a changing phase between low and high ingestion phases. The IR response to daylength comprised a high and constant feeding phase at daylengths from 0 to 16 h (longer darkness) and a declining and unstable feeding phase as daylength increased from 16 to 24 h (shorter darkness). All sizes of clams demonstrated an inverse adaptation to AE compared with IR, indicating that the clam is able to achieve a stable feeding physiology by compensating for daylength-induced variations in IR by changing AE. The ANOVA analysis also showed that both diurnal cycle and daylength affected IR and AE of the clam very significantly, body size did not, however. [Copyright &y& Elsevier]

Abstract: The kinetics of Cd trophic transfer from benthic diatoms to the Prosobranch mud snail Hydrobia ulvae was described experimentally in microcosms using Cd contaminated microalgae (0.71, 3.63 and 8.54 μg Cd mg Chl a −1). The depurated mud snails (2 ind. cm−2) were allowed to feed on the stable Cd pre-contaminated benthic diatoms at the concentration of 2 mg Chl a dm−3 to ensure that the algal food availability was not a limiting factor. Weight-specific ingestion rate (IR) and assimilation efficiency (AE) were calculated by an indirect mass-balance method on the basis of metal residues in the snail tissues, and metal loss (efflux rate, Δe) was estimated for the time intervals when a decrease or no change in the tissue metal concentrations occurred. A similar pattern of consumption was observed in all experiments: ingestion was rapid over the first 4 h, followed by slower ingestion period (between 4 and 16 h). The feeding behaviour of H. ulvae was not affected by the different diatom Cd concentrations. An analogous two-phasic pattern was observed in the tissue Cd concentration changes. Net accumulation of Cd in the snails was observed for the two highest exposures, indicating that the Cd threshold concentration in food above which metal is retained in the body, lies between 0.71 and 3.63 μg Cd mg Chl a −1. The respective 16-h AEs were 0.024% and 0.004% potentially due to rapid gut-passage of microalgae and/or diminished nutritional value of the food. The efflux rates, calculated for the last 12 h of exposure, were positively related to the concentration of Cd in the snail tissues and microalgae. This study demonstrated that trophic transfer should be considered as a source of Cd accumulation in snails and the ability of H. ulvae to enhance their rate of Cd elimination in response to elevated metal concentrations in the ambient environment is relevant for models predicting metal bioaccumulation and toxicity in coastal and estuarine systems. [Copyright &y& Elsevier]

Abstract: The uptake and assimilation efficiency of cadmium administered via the food in the shore crab Carcinus maenas were investigated together with elimination kinetics and seasonal variations in cadmium content. The majority of shore crabs assimilated between 41 and 86% of the cadmium administered in their food. More than 90% of the cadmium taken up from food was retained in midgut gland. Elimination of cadmium after uptake from one meal of radioactively labelled soft parts of blue mussels could be described by a three-compartment model (percent 109Cd-retained=64×e−0.001107× t +25×e−0.0385× t +11×e−0.888× t ). The biological half-life for cadmium in the most slowly exchanging compartment (containing 64% of the body burden) was 626 days. Groups of male and female shore crabs were collected from an uncontaminated site in the period May till October and the concentrations of cadmium in midgut gland and gills were determined. Male crabs had higher cadmium concentrations in the midgut gland in June and August (mean 2.7μg Cdg−1 dry weight) than they had in May, September and October (mean 1.7μg Cdg−1 dry weight). Females generally had slightly lower cadmium concentrations in the midgut gland than the males, except for a relatively high concentration in May. The cadmium concentrations in gills generally ranged between 0.3 and 0.5μg Cdg−1 dry weight) except for male values in October (mean 1μg Cdg−1 dry weight). Some of the seasonal changes in cadmium content of the crabs might plausibly be explained by changes in cadmium uptake from water, i.e. changes during the moult cycle and changes in cadmium uptake rates from water brought about by changes in ambient factors such as salinity and temperature. However, uptake of cadmium from water and transfer to the midgut gland take place at a rate that is two orders of magnitude too low to account for the increase in the cadmium concentrations in midgut gland in male crabs between May and June. The distribution of cadmium among tissues in crabs collected at uncontaminated sites also corresponds better with results obtained after administration of cadmium via the food than via water, and the exposure of the crabs to cadmium via the food is large enough to explain the increase in concentration between May and June. [Copyright &y& Elsevier]

Rates of uptake from solution and assimilation efficiencies of the trace metals Ag, Cd and Zn were investigated in the barnacle Balanus amphitrite after exposure in the laboratory for 19 days to low and high doses of added Ag and Cd in a diatom (Thalassiosira weissflogii) diet, the major route of metal uptake in barnacles. The hypothesis under test was that acute metal pre-exposure would affect the assimilation efficiency (AE) of that and other metals and their rate of uptake from solution. It was found that pre-exposure of the barnacles to atypically high dietary challenges of Cd and Ag did not cause changes in the rates of uptake of Cd, Ag or Zn from solution. Similarly, there was no clear consistent effect of dietary pre-exposure to Cd or Ag on the assimilation efficiency of Cd, Ag or Zn. The efflux rates of the metals were also comparable following the acute dietary exposure. Subcellular fractionation data indicated that the majority of the three metals were partitioned in the insoluble fraction, with very little in the soluble fraction consisting of metallothionein-like proteins and other (heat-sensitive) proteins. The lack of induction of increased Cd or Ag AE after pre-exposure in barnacles contrasts with results for mussels; this inconsistency is interpreted to result from differences in physiological accumulation patterns, the barnacles relying to an extreme extent on insoluble detoxification. [Copyright &y& Elsevier]

We investigated the assimilation efficiency (AE) of a piscivorous alcid, Rhinoceros Auklet (Cerorhinca monocerata), chicks when fed Japanese anchovy (Engraulis japonicus) and Japanese sand lance (Ammodytes personatus), which are their main prey species. The assimilation efficiency corrected for nitrogen retention (NR) of the chicks fed sand lance (81.6%) was significantly higher than those fed anchovy (78.0%). The values of assimilation efficiencies for both fish species are similar to those of fish-fed seabird adults and fledglings. [Copyright &y& Elsevier]

We examined the influences of different concentrations and species of Se (selenite, selenate, and seleno-l-methionine) in the ambient environment on the accumulation of inorganic Hg(II) and methylmercury (MeHg) by the diatom Thalassiosira pseudonana and the green mussel Perna viridis. At the experimental concentrations tested (<500 μg l−1), selenite and selenate did not significantly affect the uptake of either mercury species by the diatoms and the green mussels. The assimilation efficiency of Hg(II) and MeHg by the mussels from ingested diatoms was also independent of the inorganic Se loadings in the food particles. In contrast, selenomethionine significantly inhibited the uptake of MeHg and enhanced the uptake of Hg(II) by the diatoms and the mussels, but it did not affect the assimilation from the ingested diatoms. The influence of tissue body burden of Se in the green mussels following pre-exposure to selenite and selenomethionine for different periods (1–5 weeks) on the accumulation of Hg(II) and MeHg was further investigated. Our results showed that tissue Se concentrations did not significantly affect the dietary assimilation of mercury, but the influences on the aqueous uptake were variable. Our study thus, strongly highlights the specificity of the Se–Hg interaction in marine mussels for different Se and Hg species. Both dissolved and dietary uptake appeared to be equally important in the accumulation of Hg(II) and MeHg in the green mussels. [Copyright &y& Elsevier]

The potential impact of zebra mussel infestation on the dynamics of polychlorinated biphenyls (PCBs) in the Hudson River was determined by investigating the biodeposition and bioconcentration of PCBs, using algal food contaminated with 2,5,2′- and 2,4,2′,4′-chlorobiphenyls (CBPs) in the laboratory. Approximately 46–90% of the total food was ingested depending on the supply rate. The highest proportion of ingested congeners was found in biodeposits (64±11% for 2,5,2′-CBP, and 52±6% for 2,4,2′,4′-CBP), followed by tissues (17±3% for 2,5,2′-CBP, and 23±5% for 2,4,2′,4′-CBP), and the lowest in shells. The clearance rate decreased with increasing food concentration, but increased with dilution rate. On the other hand, ingestion rate (IR) increased with food concentration and dilution rate. IR also increased with food supply rate (food concentration×dilution rate) following the same linear function whether the supply rate was varied through food concentration or dilution rate. Therefore, the dilution rate- or food concentration-dependent variation in IR was due to the change in the food supply rate. IR was independent of the kind of PCB congeners. The trend of bioaccumulation in mussel tissues from food ingestion was similar to that of IR; bioaccumulation increased linearly with food supply rate, whether the supply rate was varied through the dilution rate or the food concentration. The bioaccumulation of 2,4,2′,4′-CBP was significantly higher than that of 2,5,2′-CBP (p<0.05). The bioaccumulation was linearly related to the IR or to the total amount of food ingested. Assimilation efficiency, PCB incorporated in the tissue per total ingested PCB, was higher for 2,4,2′,4′-CBP than for 2,5,2′-CBP (p<0.05). The congener concentration in biodeposits increased with food supply rate. However, the concentration of 2,5,2′-CBP was significantly greater than that of 2,4,2′,4′-CBP in a mirror image of bioaccumulation. These results indicate that zebra mussels may significantly alter PCB dynamics in the Hudson River through redeposition from the water column and through bioconcentration. [Copyright &y& Elsevier]

Influence of body temperature on food assimilation and locomotor performance was studied in adult white-striped grass lizards (Takydromus wolteri) from a population in Chuzhou (Anhui, Eastern China). Food passage time dramatically decreased with increase in body temperature within the range from 26°C to 34°C, and then nearly levelled at higher body temperatures. Lizards overall gained net mass at 26°C, 28°C and 30°C and lost mass at 32°C and 34°C. Daily production of faeces (mass-specific) was affected by body temperature and, when influence of variation in the total food energy intake was removed by an ANCOVA, lizards at 26°C were found to produce faeces that contained significantly lower energy as compared with those at higher body temperatures. The total energy of urates was affected by the total food energy intake, but an ANCOVA with the total food energy intake as the covariate showed that lizards at different body temperatures did not produce urates that differed in energy. Within the temperature range considered, daily production of urates (mass-specific), apparent digestive coefficient (ADC) and assimilation efficiency (AE) were not affected by body temperature, although both ADC and AE were apparently greater in lizards at 26°C. Both locomotor stamina and sprint speed increased with increase in body temperature within the range from 18°C to 30°C, and then decreased at higher temperatures. Inter-individual differences were a significant source of variation in locomotor performance. Except for ADC and AE, all traits examined were significantly affected by body temperature, although thermal sensitivities differed considerably among traits. Within the body temperature range considered, 26°C was the most suitable body temperature for somatic tissue growth, and 30°C was an optimal body temperature for locomotor performance. [Copyright &y& Elsevier]

We examined the assimilation of Cd, Cr, and Zn by the green mussel Perna viridis under complicated food conditions, including combinations of different compositions and concentrations of food (diatom and sediment), and variable food quantity and quality during particle digestion. At different combinations of food composition and quantity (5 mg l−1 and 20 mg−1, below and above the pseudofeces production), the Cd assimilation was significantly dependent on the food composition. The Cd assimilation efficiency (AE) decreased with increasing proportions of sediments in the diets, but its assimilation was not significantly affected by food concentration. In contrast, the assimilation of Cr and Zn decreased significantly with increasing food concentrations, whereas food composition did not significantly affect their AEs. Variations in metal gut passage time accounted partially for the difference in AEs among different combinations of food composition and quantity. By changing the type of particles during metal digestion, their AEs were maintained comparably at a low particle load (1 mg l−1), suggesting that variation of food quality during digestion did not affect metal assimilation. At a higher particle load (5 mg l−1), variation of food type during digestion affected the AEs of Cr and Zn. An increase in food concentrations from 1 to 15 mg l−1 during digestion resulted in a significant decrease in the AEs of Cr and Zn bound with either sediments or diatoms. Conversely, decreasing the food concentrations from 15 to 1 mg l−1 did not affect the AEs of metals, except for Zn bound with diatoms. Overall, our results highlighted the metal-specificity in their assimilation as influenced by complicated food environments, probably caused by different metal geochemical and biological behavior in the mussels. Feeding selectivity may have a greater control on the influx rate into the mussels than metal assimilation. [Copyright &y& Elsevier]

The effect of the concentration of tributyltin (TBT) in feed on the dietary bioaccumulation of tributyltin chloride (TBTCl) was studied in an 8-week uptake experiment and a 4-week elimination experiment using red sea bream (Pagrus major). The biomagnification factor (BMF) and the assimilation efficiency (AE) decreased from 0.30 to 0.15 and from 13% to 5.9%, respectively, as the TBT concentration in feed increased from 1.3 to 20 μg/g. The elimination rate constant (k2) was independent of the TBT concentration in the fish. Laboratory measurements of the BMF and AE of TBTCl underestimate actual field values if highly contaminated feed is used. Judging from the BMF and AE, the risk of the bioaccumulation of TBTCl through the food chain might be smaller than that of polychlorinated biphenyls. [Copyright &y& Elsevier]

Trace metal (Cd, Cr, Se, and Zn) uptake from the dissolved phase, assimilation efficiency from the dietary phase, and metal body burden, as well as the clearance rate, apparent water permeability and gill surface area were measured in the green mussel Perna viridis collected from two contrasting salinity sites in Hong Kong coastal waters with following acclimation in the laboratory at different salinities. The concentrations of metals were 1.2–6.4× greater in mussels collected from the low salinity site, i.e. Tai O, as compared with Tap Mun (high salinity) mussels. Influx of Cd and Zn from the dissolved phase increased with decreased salinity. Furthermore, Cr(VI) and Se (selenite) influx were also affected by decreased salinity, in particular below 17 psu, suggesting that speciation was not the only factor to effect metal uptake. Long-term acclimation to different salinity also had an effect on metal uptake. Mussels collected from Tap Mun (high salinity) accumulated metals 1.2–2.2× faster than mussels from Tai O (low salinity) at intermediate and high experimental salinities >17 psu. Metal assimilation efficiencies were unaffected by salinity variation, but gut passage times were significantly longer at low (10 psu) salinities, indicating some effect of lowered salinity on mussels gut physiology. Gill surface area, which was similar in both populations of mussels, and filtration rate, which was generally similar or higher in those groups with low metal uptake, could not explain the inter-population difference in metal accumulation. Although there was no significant difference, due to high inter-individual variability, the apparent water permeability of the Tap Mun population was on average about 1.6× greater compared with Tai O mussels, and may partially account for the difference in metal uptake between these two populations acclimated at salinity >17 psu. Thus, the effect of salinity on metal uptake is dependent on metal biogeochemistry as well as a range of physiological responses. There was a clear effect of acclimation to lowered salinity on metal uptake, which may have important implications for metal accumulation modelling, biomonitoring, and toxicity studies. [Copyright &y& Elsevier]

The trophic transfer of metals along the food chain has been recognized as an important issue in the study of water quality in recent years. Feeding experiments were conducted to examine the assimilation of three metals (Cd, Cr and Zn) by the zebrafish Danio reiro feeding on the freshwater zooplankton Daphnia magna. The zooplankton were exposed to radiotracers from both the aqueous and dietary phases for different duration, and then pulse-fed to the zebrafish for measurements of metal assimilation efficiency (AE). The calculated AEs were 3–8% for Cd, 2–39% for Cr, and 17–36% for Zn in the zebrafish. For Cd and Zn, there was no statistically significant difference between the two different radiolabeling routes (aqueous and dietary exposure). For Cr, the AEs were higher when it was accumulated by D. magna from the dietary source than when it was accumulated from the aqueous phase. The gut passage time (GPT) was 6–10 h for all metals, with less variation for Zn among the different treatments. There was no obvious relationship between metal GPT and metal AE, presumably due to the narrow range of variation of metal gut passage. About 5–36%, 20–31%, and 8–30% of the total Cd, Cr and Zn was found in the soft tissue of D. magna after the radiolabeling. A much higher fraction of Cd and Zn was found in the soft tissue of D. magna when the metals were accumulated from the dietary phase. No significant relationship between the metal AE and the metal distribution in the soft tissue of D. magna was however documented in this study. Our results demonstrated that there was major difference in metal AE in freshwater fish among different metals. Metal localization in prey organisms and GPT appear to have little influence on metal assimilation by the zebrafish. [Copyright &y& Elsevier]

Mercury (Hg) and methylmercury (CH 3 Hg) are found at trace levels in most marine waters. These species, particularly CH 3 Hg, then ominously bioaccumulate through marine food chains eventually reaching potentially harmful levels in top oceanic wildlife. Accordingly, it is important to measure and evaluate uptake at environmentally relevant concentrations where trophic transfer initiates; during uptake in primary producers, and consumption by plankton grazers. Experiments using cultured copepods (Acartia tonsa) and field zooplankton assemblages were performed with two different sized diatom species labeled with stable isotopes of inorganic Hg (200Hg) and CH 3 Hg (CH 3 199Hg) at different concentrations. We observed size-specific effects on algal uptake and transfer to copepods, in addition to effects of Hg species concentration. Prey size effects were likewise observed on copepod assimilation efficiencies (AE). Average AE of 200Hg for copepods feeding on smaller diatoms was 50%, and 39% for larger diatoms. The AEs were much greater for CH 3 199Hg, yielding 71% for the smaller and 88% for the larger diatoms. These experiments add evidence demonstrating a significant relationship between Hg and CH 3 Hg exposure concentration and subsequent algal uptake and transfer to zooplankton. Furthermore, results imply that facilitated uptake of CH 3 Hg into algae occurs at low (~pM) concentrations, which has been suggested but not confirmed in previous research. • Copepods more efficiently assimilated methylmercury than inorganic mercury. • Algal size can consequentially influence uptake for different mercury species. • The fraction of methylmercury transferred to zooplankton varies with algae species. • Uptake of mercury species into algae is active. • Demonstrated the usefulness of stable isotopes approaches. [ABSTRACT FROM AUTHOR]

This study investigated the effect of different plant litter types and developmental stages of the cockroach species Blaptica dubia on food consumption, animal growth, and excrement production. Three leaf litter species Alnus glutinosa , Acer platanoides , and Quercus robur were selected as model plants in a microcosm test in which plant litter was consumed by three different cockroach instar groups during five consecutive one-week intervals. At each interval, litter consumption, animal weight, and produced excrements were measured. The results showed slightly higher consumption of A. glutinosa compared to other leaf litter species in all three age/size groups of animals. Animals gained weight with time, especially Group B (medium-sized class animals) feeding on Alnus. The production of excrements was higher in Group C (big class animals) and increased in Alnus among litter species. Foliar litter consumption and excrement production rates were highest in B and C animal groups and in Alnus treatments; however, animal growth rates did not show a clear pattern, except for A. glutinosa. Measured energy contents showed highest values for animals, but slightly higher for leaves compared to excrements. Our results show that using energy budget parameters can help explain the relationship between litter type, cockroach sizes, and their consumption in this microcosm experiment. [ABSTRACT FROM AUTHOR]

A mathematical model was developed to represent the dynamics of predation and assimilation of ingested material by heterotrophic marine micro-zooplankton. Predation rate was made a rectangular hyperbolic function of prey carbon (C) concentration modified to simulate the prey selectivity that these organisms have been observed experimentally to exhibit in response to prey nutritional quality. We chose prey N:C ratio as an index of selectivity and related both the maximum predation rate (PM) and the assimilation efficiency (AE) to changes in prey nitrogen:carbon (N:C). Changes in PM simulated the phenomena of “surge feeding” and “prey rejection”. Changes in AE simulated sub-optimal assimilation of material from ingested prey, which in turn, served to decrease the ingestion rate on this material. The model was parameterised using laboratory data sets that followed ingestion of non-growing phytoplankton prey of different N:C ratio by a micro-flagellate predator. Investigative simulations in transient conditions, incorporating growing prey and hence with changing N:C ratio, indicated both PM and AE influenced the quantitative and temporal dynamics of C transfer to the higher trophic level. In particular, we noted that although various model formulations predicted similar trophic transfer of C, this was achieved on very different time scales. The inclusion of heterotrophic micro-zooplankton within food web models is a necessary step in accurate prediction of pelagic nutrient flux but requires physiological models carefully parameterised and tested in both steady state and transient conditions to ensure accurate simulation. [Copyright &y& Elsevier]