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Regulatory assessment of the bioaccumulation from water is commonly based on bioconcentration factors (BCFs) derived from fish flow-through tests. Such experiments require many laboratory animals and are time-consuming and costly. An alternative test setup for organic, neutral compounds using the amphipod Hyalella azteca was recently suggested, resulting in BCF values which show a strong correlation with fish BCF data. In the present study, the bioconcentration potential of the ionic compound laurate was elucidated in H. azteca. The sodium salt of 1-14 C laurate was applied to H. azteca in a flow-through and a semistatic approach. Because of rapid biodegradation, a semistatic approach with frequent medium replacements was required to ensure a stable medium concentration. Laurate was also rapidly metabolized by H. azteca. A large proportion of the total radioactivity measured in the amphipod tissue was not extractable, suggesting that mineralized laurate was accumulated in the calcified exoskeleton of H. azteca. This was confirmed in a further study using carbonate [14 C]. A lipid-normalized (5.0%) Hyalella BCF of 8.9 was calculated for laurate, measured as free fatty acids. The results of the bioconcentration studies with H. azteca confirm the low bioaccumulation potential of the test item previously observed in fish. However, more organic ionic compounds with various properties need to be tested to assess whether a general correlation between fish and Hyalella BCF data exists. Environ Toxicol Chem 2020;39:310-322. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

The authors investigated the chronic toxicity of aqueous Pb to the amphipod Hyalella azteca (Hyalella) in 42-d tests using 2 different diets: 1) the yeast + cereal leaf + trout pellet (YCT) diet, fed at the uniform low ration used in standard methods for sediment toxicity tests; and 2) a new diet of diatoms + TetraMin flakes (DT), fed at increasing rations over time, that has been optimized for use in Hyalella water-only tests. Test endpoints included survival, weight, biomass, fecundity, and total young. Lethal effects of Pb were similar for the DT and YCT tests (20% lethal concentration [LC20] = 13 μg/L and 15 μg/L, respectively, as filterable Pb). In contrast, weight and fecundity endpoints were not significantly affected in the DT test at Pb concentrations up to 63 µg/L, but these endpoints were significantly reduced by Pb in the YCT test-and in a 2005 test in the same laboratory with a diet of conditioned Rabbit Chow (RC-2005). The fecundity and total young endpoints from the YCT and RC-2005 tests were considered unreliable because fecundity in controls did not meet test acceptability criteria, but both of these tests still produced lower Pb effect concentrations (for weight or biomass) than the test with the DT diet. The lowest biotic ligand model-normalized effect concentrations for the 3 tests ranged from 3.7 μg/L (weight 20% effect concentration [EC20] for the RC-2005 test) to 8.2 μg/L (total young EC20 for the DT test), values that would rank Hyalella as the second or third most sensitive of 13 genera in a species sensitivity distribution for chronic Pb toxicity. These results demonstrate that toxicity tests with Hyalella fed optimal diets can meet more stringent test acceptability criteria for control performance, but suggest that results of these tests may underestimate sublethal toxic effects of Pb to Hyalella under suboptimal feeding regimes. Environ Toxicol Chem 2016;35:1825-1834. Published 2015 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and as such, is in the public domain in the United States of America.

In situ exposures with Hyalella azteca were used to assess impacts of current-use pesticides in Southern Ontario, Canada. Exposures were conducted over 2 growing seasons within areas of high pesticide use: 1 site on Prudhomme Creek and 3 sites on Twenty Mile Creek. Three sites on Spencer Creek, an area of low pesticide use, were added in the second season. Surface water samples were collected every 2 wk to 3 wk and analyzed for a suite of pesticides. Hyalella were exposed in situ for 1 wk every 4 wk to 6 wk, and survival and acetylcholinesterase (AChE) activity were measured. Pesticides in surface waters reflected seasonal use patterns: lower concentrations in spring and fall and higher concentrations during summer months. Organophosphate insecticides (chlorpyrifos, azinphos methyl, diazinon) and acid herbicides (2,4-dichlorophenoxyacetic acid [2,4-D], mecoprop) were routinely detected in Prudhomme Creek, whereas neutral herbicides (atrazine, metolachlor) dominated the pesticide signature of Twenty Mile Creek. Spencer Creek contained fewer pesticides, which were measured at lower concentrations. In situ effects also followed seasonal patterns: higher survival and AChE activity in spring and fall, and lower survival and AChE activity during summer months. The highest toxicity was observed at Prudhomme Creek and was primarily associated with organophosphates. The present study demonstrated that current-use pesticides in Southern Ontario were linked to in situ effects and identified sites of concern requiring further investigation.

The majority of sediment toxicity and aquatic bioaccumulation assessments are conducted using standardized species, such as Hyalella azteca, Chironomus dilutus, and Lumbriculus variegatus. The burrowing mayfly, Hexagenia sp., may serve as an ideal supplemental organism for both toxicity and bioaccumulation studies for several reasons. Hexagenia are recognized as sensitive species, have a long aquatic life stage (up to 2 yr), and have large bodies, which aid in retrieval from sediments and for residue analysis. The present study outlines the authors' established method for collecting and hatching eggs, raising nymphs, and using these animals for toxicity testing. Furthermore, the relative sensitivity of 3 size classes of Hexagenia to a representative contaminant (bifenthrin) was examined and compared with laboratory-derived median lethal concentrations for the more traditionally used Hyalella and Chironomus. Finally, sublethal end points, including immobilization and suspended solids, were defined for this species. This provides guidance for the use of this species in toxicological bioassays. Environ Toxicol Chem 2014;33:868–874. © 2013 SETAC

Proteomics has gained popularity in the field of ecotoxicology as a holistic tool for unraveling novel mechanisms of toxicity and elucidating subtle effects of contaminant exposure. The holoarctic amphipod Diporeia spp. is declining at precipitous rates in the Great Lakes, and we are evaluating the use of the well-studied amphipod model Hyalella azteca as a surrogate for Diporeia spp. This article presents proteomics data from both amphipod species exposed to atrazine (ATZ) and one of its metabolites, desethylatrazine (DEA; 3 and 30 µg/L for 21 and 42 d). We used a proteomics approach to determine whether these two species of amphipods responded similarly to the same chemicals and to understand better the mechanisms of toxicity of ATZ and DEA in aquatic invertebrates. We observed disruption in energy production and mitochondrial function as well as hormesis in exposed organisms. In addition, we identified a two proteins (GAPDH and HSP 90 kDa) that have been linked to hormonal disruptions, suggesting potential endocrine disruption. Finally, we found that H. azteca and Diporeia spp. responded with similar proteomic profiles after ATZ and DEA exposure, suggesting that H. azteca may be used as a surrogate model organism for Diporeia spp. Environ. Toxicol. Chem. 2011; 30:1197–1203. © 2011 SETAC

The relative sensitivity of four benthic invertebrates (Hyalella azteca, Chironomus riparius, Hexagenia spp., and Tubifex tubifex) was determined for Cd, Cu, and Ni in water-only and in spiked-sediment exposures. Survival (median lethal concentrations [LC50s] and the concentrations estimated to be lethal to 25% of test organisms [LC25s]), and endpoints for growth and reproduction (mean inhibitory concentrations [IC25s]) were compared. The sensitivities differed depending on the species and metal, although some trends emerged. In water-only exposures, H. azteca is the most sensitive species to cadmium and nickel, with mean LC50s of 0.013 and 3.6 mg/L, respectively; C. riparius is the most sensitive species to copper, with a mean LC50 of 0.043 mg/L. In the spiked-sediment exposures, the order in decreasing sensitivity to copper is Hyalella = Hexagenia < Chironomus < Tubifex for survival and growth/reproduction. For cadmium, the order in decreasing sensitivity is Hyalella = Chironomus < Hexagenia < Tubifex, and for nickel is Hyalella << Hexagenia < Chironomus < Tubifex. Chironomus riparius and Hexagenia spp. survival can be used to distinguish between toxicity caused by different metals. Species test responses in field-collected sediment(Collingwood Harbour, ON, Canada) were examined in an attempt to determine the causative agent of toxicity throughout, using the established species sensitivities. Sediment toxicity was categorized first by comparing species responses to those established for a reference database. Test responses in the field-collected sediment do not support causality by Cu, a suspected toxicant based on comparison of sediment chemistry with sediment quality guidelines.

Adult populations of Hyalella azteca, with similar reproductive potential, were exposed in the laboratory to a range of lindane concentrations below the 240-h adult LC50 (26.9 μg/L) for a period of 35 d. The reproductive status of each population was assessed through quantification of the precopulatory guarding behavior of Hyalella, the number of gravid females, and their brood sizes. At the end of the experiment, recruitment within the H. azteca populations was assessed, and the body lengths of individuals were measured using image analysis. By employing a range of integrated and quantifiable response criteria, the influence of lindane at the individual and at the population level was determined. A lowest observed effect concentration of 13.5 μg lindane/L was identified. The experimental results are discussed in relation to the reproductive strategies adopted within the treatment groups and with respect to previous toxicity data.

Hyalella azteca of different origins are maintained in many laboratories and are extensively used in toxicological bioassays. Quality assurance of interlaboratory toxicity data can only be made when the amount of genetic differentiation among laboratory populations is known. We assayed genetic variability at 16 enzymatic loci in H. azteca stocks from six laboratories (2 U.S. Environmental Protection Agency [USEPA], 1 U.S. Fish and Wildlife Service [USFWS], University of Mississippi, Environment Canada, Burlington, ON, Canada, and New York Department of Environmental Conservation), as well as an additional species, Hyalella montezuma (used as an outgroup). Three divergent groups were identified in laboratory stocks of H. azteca based on both Nei's genetic identity and modified Rogers' genetic distance. These three groups were differentiated genetically at a level characteristic of distinct species (Nei's I = 0.26–0.69) based on the comparison between H. azteca and H. montezuma. The high level of genetic differentiation among populations indicated that the Burlington and New York populations were distinct species of Hyalella. In order to enhance interlaboratory toxicity test comparisons, we recommend using genetically characterized populations of H. azteca.

Two freshwater amphipods, Hyalella azreca and Diporeia sp., were exposed to sediment spiked with radiolabeled fluoranthene at nomtnal c~ncentrattons of 0.1 (trace) to 1.270 nmol fluoranthenc/g dry weighl. In two experiments. uptake kinetics and mortaluy were determtned over 30-d exposures. Concentrations of fluoranthene in ,cdiment and pore water were also measured. Mean 'urvtval of H. azreca was generally high, greater than 90% after I 0 or 16 d. and greater than 74% after 30 d. Mean survival wa'. lower for Diporeia, _14% .after _a 30-d expo~ure to the highest sediment concentration in experiment 1. and 53% in experiment 2. 1tssuc conce?trattons tn Dtporeu~ were as htgh as 2 to 4 j.Lmollg wet weight, a body burden that could be expected to result in death by narcO\tS. Hya/el/a azreca dtd not typtcally accumulate more than I IJ.rnol/g wet weight, which is consistent with the lower ob,erved mortaltty. ~pparent steady-state biota-sediment accumulation factors (BSAFs, lipid- and organic-carbon-normalized) for scdtmcnt conccntrauons other than trace level tended to be higher for Diporeia (0.345 0.818) than for H. a::.reca (0.161-0.612). ~he BSAF'> fo~ trace lc~els tended to be l.owcr for both species (0.045 -0.436) in companson to higher sediment concentrations. for bothorgantsms. the tnternal concentration based on body residue was a more reliable mdicator of toxtcity than were equilibrium paruuontng prcdtcttOns.

This study evaluated the chronic toxicity of Ni-spiked freshwater sediments to benthic invertebrates. A 2-step spiking procedure (spiking and sediment dilution) and a 2-stage equilibration period (10 wk anaerobic and 1 wk aerobic) were used to spike 8 freshwater sediments with wide ranges of acid-volatile sulfide (AVS; 0.94–38 µmol/g) and total organic carbon (TOC; 0.42–10%). Chronic sediment toxicity tests were conducted with 8 invertebrates (Hyalella azteca, Gammarus pseudolimnaeus, Chironomus riparius, Chironomus dilutus, Hexagenia sp., Lumbriculus variegatus, Tubifex tubifex, and Lampsilis siliquoidea) in 2 spiked sediments. Nickel toxicity thresholds estimated from species-sensitivity distributions were 97 µg/g and 752 µg/g (total recoverable Ni; dry wt basis) for sediments with low and high concentrations of AVS and TOC, respectively. Sensitive species were tested with 6 additional sediments. The 20% effect concentrations (EC20s) for Hyalella and Gammarus, but not Hexagenia, were consistent with US Environmental Protection Agency benchmarks based on Ni in porewater and in simultaneously extracted metals (SEM) normalized to AVS and TOC. For Hexagenia, sediment EC20s increased at less than an equimolar basis with increased AVS, and toxicity occurred in several sediments with Ni concentrations in SEM less than AVS. The authors hypothesize that circulation of oxygenated water by Hexagenia led to oxidation of AVS in burrows, creating microenvironments with high Ni exposure. Despite these unexpected results, a strong relationship between Hexagenia EC20s and AVS could provide a basis for conservative site-specific sediment quality guidelines for Ni. Environ Toxicol Chem 2013;32:2495–2506. © 2013 SETAC

Fungicide application rates on row crop agriculture have increased across the United States, and subsequently, contamination of adjacent wetlands can occur through spray drift or field runoff. To investigate fungicide toxicity, Hyalella azteca amphipods were exposed to 2 fungicide formulations, Headline and Stratego, and their active strobilurin ingredients, pyraclostrobin and trifloxystrobin. Water-only exposures resulted in similar median lethal concentration (LC50; 20–25 µg/L) values for formulations and strobilurin ingredients, suggesting that toxicity is due to strobilurin ingredients. These values were below concentrations that could occur following spray drift over embedded cropland wetlands. When fungicides were added to overlying water of sediment-water microcosms, toxicity was reduced by 500% for Headline and 160% for Stratego, compared with water-only exposures, based on the total amount of fungicide added to the systems. In addition, when fungicides were added to sediment prior to the addition of water, the reduction in toxicity was even greater, with no toxicity occurring at environmentally relevant levels. Differences in toxicity among exposure groups were explained by dissipation from water as toxicity values based on measured water concentrations were within 20% between all systems. The present study reinforces previous studies that Headline and Stratego are toxic to nontarget aquatic organisms. However, the presence of sediment is likely to ameliorate some toxicity of fungicide formulations, especially if spraying occurs prior to wetland inundation. Environ Toxicol Chem 2013;32:1516–1525. © 2013 SETAC

Daphnia magna, Daphnia pulex, Hyalella azteca, and Gammarus lacustris were exposed to low dissolved oxygen concentrations in the laboratory. Acute and chronic exposures were conducted to develop data for use in the U.S. Environmental Protection Agency's (EPA's) water quality criteria document for dissolved oxygen. Daphnia magna had two 48-h LC50s (50% mortality) of 0.6 and 0.7 mg/L, a highest-adverse-effect concentration of 0.6, and a lowest-no-adverse-effect concentration of 0.9 mg/L O2 (based on reproduction). Daphnia pulex had a 48-h LC50 of 0.5, two 96-h LC50s of 0.4 and 0.7, a highest-adverse-effect concentration of 1.6, and a lowest-no-adverse-effect concentration of 2.1 mg/L O2 (based on reproduction). Hyalella azteca had 96-h and 30-d LC50s of 1.2 (based on reproduction). Gammarus lacustris had two 7-d LC50s of

The organophosphorous compound azinphosmethyl (AzMe) is applied extensively in northern Patagonia (southern Argentina) to manage codling moths (Cydia pomonella). This area is irrigated by fast-flowing channels that provide a favorable habitat for many species, including amphipods (Hyalella curvispina) and a field-mixed population of black flies (Simulium bonaerense, Simulium wolffhuegeli, and Simulium nigristrigatum). In the present study, AzMe susceptibility and carboxylesterase (CarbE) activity from both insecticide-exposed and nonexposed field populations were studied. The median lethal dose determined in codling moths from an insecticide-treated orchard was significantly higher (3.48 microg/insect) than that observed in those from an untreated orchard (0.69 microg/insect). Similarly, the median lethal concentration (LC50) determined in black flies collected from the treated area (0.021 mg/L) was significantly higher than that recorded in those from the untreated site (0.011 mg/L). For amphipods, both a subpopulation susceptible to AzMe (LC50, 1.83 microg/L) and a resistant one (LC50, 390 microg/L) were found in the treated area. Both subpopulations were more resistant to AzMe than the population from the untreated site (LC50, 0.43 microg/L). Significant differences (p0.001) in CarbE activities were observed between populations from pesticide-treated and untreated areas. Mean activities +/- standard deviation from treated and untreated sites were 0.21 +/- 0.16 and 0.016 +/- 0.008 micromol/min/mg protein, respectively, for codling moths; 2.17 +/- 1.71 and 0.81 +/- 0.35 micromol/min/mg protein, respectively, for black flies; and 0.27 +/- 0.10 and 0.14 +/- 0.07 micromol/min/mg protein, respectively, for amphipods. The results suggest that enhanced CarbE activity is one of the mechanisms that provide AzMe resistance in H. curvispina, Simulium spp., and C. pomonella populations from the insecticide-treated areas.

Four- and 10-week chronic toxicity tests were conducted using the freshwater amphipod Hyalella azteca and Cd-contaminated Chlorella sp. as a food source. Chlorella sp. was cultured in various Cd concentrations, filtered from solution, rinsed, dried, and ground into food flakes for the H. azteca. Unlike Cd toxicity from water sources, growth was found to be a more sensitive toxicological endpoint than survival, with calculated 50 and 25% effect concentrations (EC50s and EC25s, respectively) of 5.43 and 2.82 nmol/g, respectively, for Cd measured in food. Based on the regression of Cd in Chlorella sp. against Cd in filtered culture medium, the EC50 and EC25 corresponded to dissolved Cd concentrations of 11.30 and 5.09 nmol/L, respectively. Little or no bioaccumulation of Cd was found in the tissues of H. azteca that were fed contaminated food. These results demonstrate an apparent toxicological effect (either direct or indirect) of Cd-contaminated Chlorella sp. to H. azteca that is not associated with Cd accumulation. Toxicity of Cd-contaminated Chlorella sp. differs from waterborne Cd toxicity both in terms of the most sensitive endpoint (growth vs survival) and the relationship between toxicity and bioaccumulation. Unlike Cd toxicity through water exposure, Cd bioaccumulation by H. azteca cannot, therefore, be used to infer toxicity of Cd in a diet of Chlorella sp. Although the concentration of Cd in the algal culture medium that ultimately reduced growth of H. azteca in the present study was higher than Cd in water, which caused mortality to H. azteca in water-only tests during previous studies, further research regarding the contribution of dietary Cd to overall Cd toxicity is needed to verify that water-quality guidelines and risk assessments based on water-only exposures are fully protective.

The purpose of this study was to address four aspects of the kinetics of tributyltin (TBT) in the freshwater amphipod Hyalella azteca: time to steady state, route of uptake, depuration rates, and effect of gut clearance. The amphipods accumulated TBT rapidly, reaching steady state within 14 d. Body concentrations were similar between caged and sediment-exposed animals, indicating that the primary route of uptake is via dissolved TBT. However, the rate of uptake was significantly higher in sediment-exposed amphipods. During depuration, body concentrations of TBT exhibited a biphasic decline, with a stronger decrease over the first 24 h that is attributed primarily to gut clearance, followed by a more gradual decrease most likely due to excretion from the body. Gut contents contributed significantly to body concentrations of TBT, accounting for 30% of the initial total body burden in sediment-exposed amphipods. Half-lives of TBT in gut-cleared H. azteca were 8 d and 14 d for amphipods exposed to spiked water and spiked sediment, respectively. The results of this study have significant implications in the experimental design and interpretation of studies involving the effects of TBT in H. azteca.

Use of pyrethroid pesticides, which are highly toxic to aquatic organisms, has increased substantially over the past decade. In 2006, the pyrethroid pesticides cyfluthrin and permethrin were measured in Sacramento-San Joaquin (SSJ) Delta (CA, USA) water at 5 and 24 ng/L (pptr), respectively. To elucidate any interactions between the two pyrethroids, a 10-d laboratory exposure was performed with 7- to 14-d-old amphipods (Hyalella azteca). Cyfluthrin and permethrin were tested singly and in combination at detected levels and also at half and twice the detected levels, both with and without the addition of 25 ppb of piperonyl butoxide (PBO). Mortality in all treatments was significantly higher than in controls, with the median lethal concentration (LC50) for permethrin with PBO (13.9 ng/L) and the LC50s with and without PBO for cyfluthrin (5.7 and 2.9 ng/L, respectively) at or below levels measured in SSJ Delta water samples. The LC50 for permethrin alone was estimated to be 48.9 ng/L. To evaluate combined toxicity, logistic regression models containing terms for concentrations of cyfluthrin, permethrin, and PBO, as well as models containing all possible combinations of these terms and interactions, were run and compared using Akaike's information criterion. The most parsimonious set of models indicated slight antagonism between cyfluthrin and permethrin. Results indicate that a dissolved mixture of cyfluthrin and permethrin is toxic at environmentally relevant concentrations in the water column.

We evaluated the potential environmental risk of the herbicide Magnacide (Baker Petrolite, TX, USA) using native species from Argentina, representing the ecosystem at the Irrigation Corporation (CORFO) channels at the Colorado River mouth, Buenos Aires, Argentina. Six species including fish, toads, snails, crustaceans, and insects were selected to perform studies on acute toxicity and repeated exposure effects. Magnacide H susceptibility ranking was Bufo arenarum (lethal concentration 50 [LC50] = 0.023 mg/L), Onchorhynchus mykiss (LC50 = 0.038 mg/L), Heleobia parchappii (LC50 = 0.21 mg/L), Hyalella curvispina (LC50 = 0.24 mg/L), Simulium spp. (LC50 = 0.60 mg/L), and Chironomus spp. (LC50 = 2.83 mg/L). The risk limit of 10th percentile (0.013 mg/L) determined by probit analysis on sensitivity distribution was similar to the one calculated from literature data. Risk assessment based on field application data suggested lethal exposures for more than 70 to 90% of the species up to 20 km downstream from the application point. Repeated exposures to Magnacide H of amphibian larvae at the lowest-observed-effect concentration caused some effects during the first exposure, but without cumulative effects. Amphipods were insensitive to repeated exposures, showing no cumulative effects. Whether short-term exposures may result in long-term sublethal effects on the organism's life history was not addressed by these laboratory tests. In conclusion, tier 3 studies indicate that Magnacide H application schedule is extremely toxic for most native species at CORFO-Rio Colorado channels, representing a high potential risk in the environment. The real environmental impact must be addressed by field studies at tier 4 giving more information on population effects and communities.

The chronic toxicity of tributyltin (TBT) was examined by exposing two successive generations of the freshwater amphipod, Hyalella azteca, to sediments spiked with TBT. Survival was the most sensitive measure of effect, with lethal concentration resulting in 50% mortality (LC50) values on a water and body concentration basis ranging from 76 to 145 ng Sn/L and 2,790 to 4,300 ng Sn/g, respectively. Individual growth of amphipods was not negatively affected by TBT, and although reproduction might be more sensitive than survival, the data were too variable to use on a routine basis. There were no detectable TBT-induced differences in the response between first- and second-generation animals. The relationship between toxicity and bioaccumulation of TBT in H. azteca was determined and can be used as a tool to predict the toxicity of TBT in environmental samples. Body concentrations exceeding 2,000 ng Sn/g in H. azteca exposed to field-collected samples would indicate that chronic toxicity due to TBT is likely occurring in amphipod populations at those sites.

Methods are presented for using Daphnia magna, Hyalella azteca, Gammarus lacustris, Chironomus tentans and Hexagenia limbata to screen freshwater sediments for acute and chronic toxicity, bioaccumulation potential and in situ toxicity. The 48-h Daphnia tests are recommended as inexpensive, uncomplicated and sensitive acute methods. Hyalella and Chironomus are the recommended benthic test organisms, as they are easy to rear and test, they remain in intimate contact with the sediment and they exhibit high control survival. Verification studies (published elsewhere) evaluating the recommended methods and organisms are briefly summarized.

Freshwater sediments and water were spiked with cadmium (Cd) in the laboratory, and toxicity tests were conducted with the cladoceran Daphnia magna and the amphipod Hyalella azteca to determine if Cd in the sediment would cause increased toxicity. The 48-h LC50 values for Daphnia in tests without sediment were 36, 33, 24, and 40 micrograms/L total Cd. Calculated free-ion (Cd/sup 2 +/)LC50 values for the same tests were 28, 25, 18 and 31 micrograms/L. LC50 values (48-h) determined for total Cd(uncentrifuged water sample) in the sediment-containing beakers were 252, 69, and 122 micrograms/L for Daphnia. LC50 values for dissolved Cd(centrifuged 10,000 rpm) in the sediment-containing beakers were 61, 27, and 100 micrograms/L for Daphnia. Higher total Cd LC50 values indicate that Cd adsorbed to soluble organic material was not biologically available. No significant mortality of Daphnia or Hyalella occurred in the flow-through tests in which sediment contained the same levels of Cd as in the static tests. Mortality was similar in beakers with and without Cd-spiked sediment, indicating that Cd in the sediment and adsorbed to organic materials was not available to cause increased mortality.

Natural freshwater sediments from two Oregon sites were spiked with copper in the laboratory and two static toxicity tests were conducted with series of copper concentrations ranging from 59 to 10,600 mg/kg of dry sediment. Water (800 ml) was added to 1-liter test beakers over the sediment (200 ml) and repeatedly removed and replaced to lower the aqueous copper concentrations. When copper concentrations stabilized, i.e., attained equilibrium between water and sediment, the midge Chironomus tentans, the cladoceran Daphnia magna and the amphipods Hyalella azteca and Gammarus lacustris were introduced as test animals in solid-phase sediment toxicity bioassays. Based on dry-weight sediment copper concentrations, LC50 values (48-h for Daphnia, 10-d for other organisms) ranged from 681 to 2,296 mg/kg.

The cladoceran Daphnia magna, the amphipods Hyalella azteca and Gammarus lacustris, the annelid worm Lumbriculus variegatus and the fathead minnow Pimephales promelas were exposed to hexachlorobenzene (HCB) in flow-through tests ranging from 2 to 68 d in duration to determine the effects of HCB on survival, tissue bioconcentration and Hyalella and Lumbriculus growth and reproduction. No effects on survival, growth or reproduction were observed at concentrations of HCB up to saturation (5.0 μ/L) or at tissue HCB concentrations of up to 223 μg/g. Tissue HCB concentrations increased with increasing water concentrations, and tissue bioconcentration values were generally similar. Rapid uptake and change of tissue HCB concentration with change in water concentration occurred, with rapid depuration when the animals were no longer exposed to HCB in the water column, and tissue HCB concentrations were correlated closely with HCB water concentrations.

Fathead minnows (Pimephales promelas), the worm Lumbriculus variegatus and the amphipod Hyalella azteca were exposed in static tests to hexachlorobenzene (HCB) in water with and without HCB‒spiked sediment to evaluate the relative importance of water and sediment as routes of uptake. The concentration of HCB in water was maintained by passing air saturated with HCB vapor through the test vessels. The presence of HCB‒spiked sediment did not result in a significant increase in bioconcentration factor in two tests with H. azteca. The presence of HCB‒spiked sediment did significantly increase the bioconcentration factor in two tests with fathead minnows and in one of three tests with L. variegatus. The gas phase transfer method was efficient at maintaining a reasonably constant concentration of HCB in water. However, complete control of the aqueous phase activity of HCB through gas phase transfer was not achieved because of the source/sink capacity of the sediment, organisms and food.