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Copper (Cu) complexation by humic acids (HA) is expected to decrease Cu bioavailability for aquatic organisms as predicted by metal bioavailability models, such as the biotic ligand model (BLM). This has been confirmed for non-feeding organisms such as marine invertebrate embryos or microalgae, but for filter-feeding organisms such as the mussel Mytilus edulis, Cu bioaccumulation was higher in the presence of HA, suggesting that part of the Cu-HA complexes were available for uptake. This study shows the dynamic modeling of Cu accumulation kinetics in the gills and rest of the soft-body of M. edulis in the absence and presence of HA. Assuming that truly dissolved Cu is taken in the body via the gills following BLM premises, and including uptake of Cu-HA aggregates via the gut into the rest compartment, this two-compartmental model could successfully explain the observed bioaccumulation data. This modeling approach gives strong evidence to the hypothesis that Cu-HA aggregates can be ingested by mussels leading to Cu absorption in the digestive system., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Copper uptake and accumulation by the marine mussel Mytilus edulis were studied at different Cu concentrations in chemically defined artificial seawater in the presence and absence of fulvic acids. Both short-term uptake of Cu by excised mussel gills and Cu accumulation in whole mussels after 24 h of exposure decreased in the presence of fulvic acids compared with their absence at similar dissolved Cu concentrations. Calculations of Cu speciation based on previous measurements of labile Cu by anodic stripping voltammetry demonstrated that Cu uptake and accumulation depended on the concentration of labile Cu, in agreement with the free ion activity model. No evidence of a significant uptake of Cu-fulvic acid complexes was observed., (Copyright © 2012 SETAC.)

Four experiments were conducted with natural coastal phytoplankton assemblages exposed to [Cu] within the range 5-80 microg L(-1). The effect of Cu on several biological variables such as chlorophyll a concentration, particle size distribution, O2-production and fluorescence variables recorded by a Fast Repetition Rate fluorometer was monitored during 72 h. Variable fluorescence (Fv) was the most sensitive and rapid among all the variables tested. This work contributes to reinforce the use of fluorescence endpoints in ecotoxicological studies by proving their ecological relevance through relationships found between fluorescence and population-level responses as growth rate and gross O2 production. The lowest calculated EC10 was 2.65 microg L(-1), concentration commonly exceeded in polluted waters., (Copyright (c) 2010 Elsevier Inc. All rights reserved.)

Water samples of contrasting origin, including natural seawater, two sediment elutriates and sewage-influenced seawater, were collected and obtained to examine the effect of the dissolved organic matter (DOM) present on metal bioavailability. The carbon content (DOC) and the optical properties (absorbance and fluorescence) of the coloured DOM fraction (CDOM) of these materials were determined. Cu and Pb complexation properties were measured by anodic stripping voltammetry (ASV) and the effect of DOM on Cu and Pb bioavailability was studied by means of the Paracentrotus lividus embryo-larval bioassay. Sediment elutriates and sewage-influenced water (1) were enriched 1.4-1.7 times in DOC; (2) absorbed and reemitted more light; and (3) presented higher Cu complexation capacities (L(Cu)) than the natural seawater used for their preparation. L(Cu) varied from 0.08 microM in natural seawater to 0.3 and 0.5 microM in sediment elutriates and sewage-influenced water, respectively. Differences in DOC, CDOM and Cu complexation capacities were reflected in Cu toxicity. DOM enriched samples presented a Cu EC(50) of 0.64 microM, significantly higher than the Cu EC(50) of natural and artificial seawater, which was 0.38 microM. The protecting effect of DOM on Cu toxicity greatly disappeared when the samples were irradiated with high intensity UV-light. Cu toxicity could be successfully predicted considering ASV-labile Cu concentrations in the samples. Pb complexation by DOM was only detected in the DOM-enriched samples and caused little effect on Pb EC(50). This effect was contrary for both elutriates: one elutriate reduced Pb toxicity in comparison with the control artificial seawater, while the other increased it. UV irradiation of the samples caused a marked increase in Pb toxicity, which correlated with the remaining DOC concentration. DOM parameters were related to Cu speciation and toxicity: good correlations were found between DOC and Cu EC(50), while L(Cu) correlated better with the fluorescence of marine humic substances. The present results stress the importance of characterizing not only the amount but also the quality of seawater DOM to better predict ecological effects from total metal concentration data., (Copyright (c) 2009 Elsevier B.V. All rights reserved.)

Copper speciation in the presence of fulvic acids (FAs) was studied in chemically defined seawater by square wave anodic stripping voltammetry (SQWASV). A simple complexation model assuming a single type of ligand and a 1:1 reaction stoichiometry successfully explained the measured data. A conditional stability constant of 5.80 +/- 0.07 and a complexing capacity of 610 +/- 80 micromol Cu/g FAs were obtained. This conditional stability constant would correspond to 7.23 on a free copper ion basis. The complexation kinetics was easily followed by anodic stripping voltammetry (ASV) measurements, and complexation equilibria were not reached until approximately 12 h. Coupled to speciation studies, the toxicity of copper in the presence of FAs was studied with the sea urchin Paracentrotus lividus embryogenesis bioassay. A clear protective effect of FAs was observed on Cu toxicity, and this effect could be accurately explained by SQWASV Cu speciation measurements. Additional experiments in the presence of high Cu and FA concentrations were performed, and no extra toxicity of Cu-FA complexes was observed. These results are in agreement with metal bioavailability models and also underline the usefulness of ASV for determining copper bioavailability in the presence of natural organic matter.

In this investigation, we have tested the potential usefulness of variable fluorescence, i.e., the potential photochemical efficiency of photosystem II (F(v)/F(m)), determined with a fast repetition rate fluorometer (FRRF), as an indicator of the effect of metal pollution on natural phytoplankton assemblages. Phytoplankton populations were collected from an eutrophic embayment and exposed to different copper concentrations within the ppb range for 4 d. Enhanced photosynthesis was found for Cu concentrations of 10 and 20 microg/L, at very short exposure times (1 and 5 h). However, after 72 h even at 10 microg/L of Cu, F(v)/F(m)-values were significantly lower than those measured in the control. The highest Cu concentration tested (80 microg/L) caused a statistically significant decrease of F(v)/F(m) after 5 h. This response was contrasted with parallel determinations of chlorophyll a concentration, measurements of photosynthetic O2 production rates, and changes in the taxonomic composition and size structure of the microplankton communities. A reduction in overall particle size was found at Cu concentrations of 80 and 40 microg/L. Enhanced abundance of flagellates and the diatom Pseudonitzschia pungens was observed at 20 microg/L of copper. This study demonstrates the utility of this methodological approach as a rapid, nondestructive way for detecting trace-metal toxicity on natural phytoplankton.

The effects of humic acids (HA) on Cu uptake by the blue mussel (Mytilus edulis) were studied in chemically defined seawater. Short-term uptake by excised gills was studied and compared with whole-mussel Cu accumulation. Copper uptake in gills is not a saturable process within the time frame and concentration range tested, being a linear function of time (0-120 min) and Cu concentration (0-150 microg/L). For the whole mussel, Cu uptake is not linear with time (0-72 h) and Cu concentration (0-130 microg/L). The presence of HA (0-10 mg/L) clearly reduced Cu uptake by gills, but it did not have such an effect on whole-animal uptake. A simple complexation model obtained from voltammetric measurements was used to determine the noncomplexed (labile) fraction of Cu in the presence of HA to test the effect of speciation on Cu uptake. In most cases, Cu uptake by gills was better explained by labile Cu concentrations than by total Cu exposure concentrations, which is in agreement with the free-ion activity model. In whole-animal experiments, Cu uptake was not related to labile Cu concentrations in the presence of HA, indicating that Cu-HA complexes are at least partially available for uptake by the mussels.

The effects of humic acid (HA) on the toxicity of copper to sea urchin Paracentrotus lividus larvae were studied in chemically defined seawater. Square Wave Anodic Stripping Voltammetry (SWASV) was employed to study the complexation of copper in seawater medium. A simple complexation model assuming one ligand type and a 1:1 reaction stoichiometry successfully explained the inverse titration experiments. A conditional stability constant of 6.53+/-0.05 and a complexating capacity of 230+/-7 micromol Cu/g HA were obtained. Sea urchin bioassay tests with two endpoints, embryogenesis success and larval growth were carried out in order to study the toxicity of dissolved copper in both the presence and absence of HA. The toxicity data obtained fitted well into a logistic model, and the high sensitivity of both endpoints (EC(50) were 41.1 microg Cu/l and 32.9 microg Cu/l, respectively) encourages their use for biomonitoring. The HA had a clearly protective effect, reducing the toxicity of Cu to the sea urchin larvae. The labile copper, rather than the total copper concentrations, explained the toxicity of the Cu-HA solutions, and the Cu-HA complexes appeared as non-toxic forms. These results are in agreement with the Free Ion Activity Model, because the labile Cu concentrations in this buffered and chemically defined medium covary with the free ion activity of the Cu, validating the model to naturally occurring HA in the marine environment.

Abstract: The capacity of natural dissolved organic matter (DOM) produced during the onset, development and decay of a simulated bloom of the marine diatom Skeletonema costatum to complex free copper has been followed for a 2 week period. Copper binding capacity of the culture was measured by anodic stripping voltammetry (ASV) with a hanging mercury drop electrode (HMDE). The concentration of dissolved organic carbon (DOC) and two fluorophores, M (humic-like, Ex/Em: 320 nm/410 nm) and T (protein-like, Ex/Em: 280 nm/350 nm), were followed during the course of the incubation. Models using DOC concentrations alone could not accurately predict the complexing capacity of the culture, especially at the end of the bloom, and better predictions were obtained when fluorescence measurements were considered. They were helpful in characterising two types of copper ligands produced in the culture. The first type, traced by the fluorescence of peak T, was related to labile DOC directly exuded by phytoplankton. The second type, traced by the fluorescence of peak M, was the refractory humic-like material presumably produced in situ as a by-product of the bacterial degradation of phytogenic materials. During the onset and development of the bloom (days 0 to 7), the fluorescence of peak T explains 60–80% of the total complexing capacity of the culture, suggesting that exuded “protein-like” compounds among other exuded complexing agents efficiently complexed free copper. On the contrary, during the decay (days 8 to 13), these ligands were replaced by humic substances as the complexing agent for copper. [Copyright &y& Elsevier]