Search

Arthropods (including insects, crustaceans, and arachnids) rely on the synthesis of chitin to complete their life cycles (Merzendorfer 2011). The highly conserved chitin synthetic process and the absence of this process in vertebrates make it an exploitable target for pest management and veterinary medicines (Merzendorfer 2013; Junquera et al. 2019). Susceptible, nontarget organisms, such as insects and aquatic invertebrates, exposed to chitin synthesis inhibitors may suffer population declines, which may have a negative impact on ecosystems and associated services. Hence, it is important to properly identify, prioritize, and regulate relevant chemicals posing potential hazards to nontarget arthropods. The need for a more cost-efficient and mechanistic approach in risk assessment has been clearly evident and triggered the development of the adverse outcome pathway (AOP) framework (Ankley et al. 2010). An AOP links a molecular initiating event (MIE) through key events (KEs) to an adverse outcome. The mechanistic understanding of the underlying toxicological processes leading to a regulation-relevant adverse outcome is necessary for the utilization of new approach methodologies (NAMs) and efficient coverage of wider chemical and taxonomic domains. In the last decade, the AOP framework has gained traction and expanded within the (eco)toxicological research community. However, there exists a lack of mature invertebrate AOPs describing molting defect-associated mortality triggered by direct inhibition of relevant enzymes in the chitin biosynthetic pathway (chitin synthesis inhibitors) or interference with associated endocrine systems by environmental chemicals (endocrine disruptors). Arthropods undergo molting to grow and reproduce (Heming 2018). This process is comprised of the synthesis of a new exoskeleton, followed by the exuviation of the old exoskeleton (Reynolds 1987). The arthropod exoskeleton (cuticle) can be divided into 2 layers, the thin and nonchitinous epicuticle, which is the outermost layer of the cuticle, and the underlying chitinous procuticle. A single layer of epithelial cells is responsible for the synthesis and secretion of both cuticular layers (Neville 1975). The cuticle protects arthropods from predators and desiccation, acts as a physical barrier against pathogens, and allows for locomotion by providing support for muscular function (Vincent and Wegst 2004). Because the procuticle mainly consists of chitin microfibrils embedded in a matrix of cuticular proteins supplemented by lipids and minerals in insects (Muthukrishnan et al. 2012) and crustaceans (Cribb et al. 2009; Nagasawa 2012), chitin is a determinant factor for the appropriate composition of the cuticle and successful molting (Cohen 2001). A detailed overview of the endocrine mechanisms regulating chitin synthesis is given in Supplemental Data, Figure S1. The shedding of the old exoskeleton in insects is mediated by a sequence of distinct muscular contractions, the ecdysis motor program (EMP; Ayali 2009; Song et al. 2017a). Like the expression of chitin synthase isoform 1 (CHS-1), the expression of peptide hormones regulating the EMP is also controlled by ecdysteroids (Antoniewski et al. 1993; Gagou et al. 2002; Ayali 2009). Cuticular chitin is polymerized from uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) by the transmembrane enzyme CHS-1, which is localized in the epithelial plasma membrane in insects (Locke and Huie 1979; Binnington 1985; Merzendorfer and Zimoch 2003; Merzendorfer 2006). Because crustaceans are also dependent on the synthesis of chitin, the underlying mechanisms are believed to be similar, although less is known about different CHS isoforms and their localization (Rocha et al. 2012; Qian et al. 2014; Uddowla et al. 2014; Harðardóttir et al. 2019). Disruption of either chitin synthesis or the upstream endocrine pathways can lead to lethal molting disruption (Arakawa et al. 2008; Merzendorfer et al. 2012; Song et al. 2017a, 2017b). In the case of chitin synthesis inhibition, molting disruption can be referred to as "premature molting." If ecdysis cannot be completed because of decreased chitin synthesis, the organism may not successfully molt. Even if ecdysis can be completed on inhibition of chitin synthesis, the organism may not survive because of the poor integrity of the new cuticle. These effects are observed in arthropods following molting, which fail to survive subsequent molts (Arakawa et al. 2008; Chen et al. 2008) or animals being stuck in their exuviae (Wang et al. 2019) and ultimately dying as a result of insufficient food or oxygen intake (Camp et al. 2014; Song et al. 2017a). The term "premature molting" is used to differentiate from the term "incomplete ecdysis," which describes inhibition of ecdysis on a behavioral level, namely through reduction of the EMP (Song et al. 2017a). The present AOP describes molting-associated mortality through direct inhibition of the enzyme CHS-1. It expands the small but increasing number of invertebrate AOPs that have relevance to arthropods, the largest phylum within the animal kingdom (Bar-On et al. 2018). The development of this AOP will be useful in further research and regulatory initiatives related to assessment of CHS inhibitors and identification of critical knowledge gaps and may suggest new strategies for ecotoxicity testing efforts. Environ Toxicol Chem 2021;40:2112-2120. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC., (© 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.)

Anthropogenic sources increase freshwater salinity and produce differences in constituent ions compared with natural waters. Moreover, ions differ in physiological roles and concentrations in intracellular and extracellular fluids. Four freshwater taxa groups are compared, to investigate similarities and differences in ion transport processes and what ion transport mechanisms suggest about the toxicity of these or other ions in freshwater. Although differences exist, many ion transporters are functionally similar and may belong to evolutionarily conserved protein families. For example, the Na + /H + -exchanger in teleost fish differs from the H + /2Na + (or Ca 2+ )-exchanger in crustaceans. In osmoregulation, Na + and Cl - predominate. Stenohaline freshwater animals hyperregulate until they are no longer able to maintain hypertonic extracellular Na + and Cl - concentrations with increasing salinity and become isotonic. Toxic effects of K + are related to ionoregulation and volume regulation. The ionic balance between intracellular and extracellular fluids is maintained by Na + /K + -adenosine triphosphatase (ATPase), but details are lacking on apical K + transporters. Elevated H + affects the maintenance of internal Na + by Na + /H + exchange; elevated HCO 3 - inhibits Cl - uptake. The uptake of Mg 2+ occurs by the gills or intestine, but details are lacking on Mg 2+ transporters. In unionid gills, SO 4 2- is actively transported, but most epithelia are generally impermeant to SO 4 2- . Transporters of Ca 2+ maintain homeostasis of dissolved Ca 2+ . More integration of physiology with toxicology is needed to fully understand freshwater ion effects. Environ Toxicol Chem 2017;36:576-600. Published 2016 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., (Published 2016 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.)

Willapa Bay and Grays Harbor (WA, USA) comprise the largest region of commercial oyster cultivation on the Pacific Coast. The activities of 2 species of burrowing shrimp impair growth and survival of oysters reared on the intertidal mudflats. To maintain viable harvests, the oyster growers have proposed controlling the shrimp by applying the insecticide imidacloprid onto harvested beds. Green sturgeon (listed in the Endangered Species Act) forage on burrowing shrimp and could be exposed to imidacloprid in the sediment porewater and through consumed prey. Studies were conducted to evaluate the likelihood that green sturgeon would be exposed to imidacloprid and to characterize the subsequent environmental exposure. Comparisons between treated and untreated control beds following test application of the insecticide suggested that green sturgeon fed opportunistically on imidacloprid-impaired shrimp. The highest interpolated imidacloprid residue concentrations in field samples following chemical application were 27.8 µg kg(-1) and 31.4 µg kg(-1) in porewater and shrimp, respectively. Results from modeled branchial and dietary uptake, based on conservative assumptions, indicated that the porewater exposure route had the greatest contribution to systemic absorption of imidacloprid. The highest average daily uptake from porewater (177.9 µg kg(-1) body wt) was 9.5-fold greater than total dietary uptake (18.8 µg kg(-1) body wt). Concentrations and durations of exposure would be lower than the levels expected to elicit direct acute or chronic toxic effects., (© 2015 SETAC.)

The authors characterized global cytosine methylation levels in 2 different genotypes of the ecotoxicological model organism Daphnia magna after exposure to a wide array of biotic and abiotic environmental stressors. The present study aimed to improve the authors' understanding of the role of cytosine methylation in the organism's response to environmental conditions. The authors observed a significant genotype effect, an environment effect, and a genotype × environment effect. In particular, global cytosine methylation levels were significantly altered after exposure to Triops predation cues, Microcystis, and sodium chloride compared with control conditions. Significant differences between the 2 genotypes were observed when animals were exposed to Triops predation cues, Microcystis, Cryptomonas, and sodium chloride. Despite the low global methylation rate under control conditions (0.49-0.52%), global cytosine methylation levels upon exposure to Triops demonstrated a 5-fold difference between the genotypes (0.21% vs 1.02%). No effects were found in response to arsenic, cadmium, fish, lead, pH of 5.5, pH of 8, temperature, hypoxia, and white fat cell disease. The authors' results point to the potential role of epigenetic effects under changing environmental conditions such as predation (i.e., Triops), diet (i.e., Cryptomonas and Microcystis), and salinity. The results of the present study indicate that, despite global cytosine methylation levels being low, epigenetic effects may be important in environmental studies on Daphnia., (© 2015 SETAC.)

As the use of single-walled carbon nanotubes (SWNTs) increases over time, so does the potential for environmental release. This research aimed to determine the toxicity, bioavailability, and bioaccumulation of SWNTs in marine benthic organisms at the base of the food chain. The toxicity of SWNTs was tested in a whole sediment exposure with the amphipod Ampelisca abdita and the mysid Americamysis bahia. In addition, SWNTs were amended to sediment and/or food matrices to determine their bioavailability and bioaccumulation through these routes in A. abdita, A. bahia, and the estuarine amphipod Leptocheirus plumulosus. No significant mortality to any species via sediment or food matrices was observed at concentrations up to 100 ppm. A novel near-infrared fluorescence spectroscopic method was utilized to measure and characterize the body burdens of pristine SWNTs in nondepurated and depurated organisms. We did not detect SWNTs in depurated organisms but quantified them in nondepurated A. abdita fed SWNT-amended algae. After a 28-d exposure to [(14) C]SWNT-amended sediment (100 µg/g) and algae (100 µg/g), [(14) C]SWNT was detected in depurated and nondepurated L. plumulosus amphipods at 0.50 µg/g and 5.38 µg/g, respectively. The results indicate that SWNTs are bioaccessible to marine benthic organisms but do not appear to accumulate or cause toxicity., (Copyright © 2013 SETAC.)

The reproductive biology of amphipods is reviewed to update the knowledge of the male and female reproductive processes of oogenesis and spermatogenesis as well as the endocrine systems of amphipods with the aim of advancing studies of reproductive toxicology. The ovarian and reproduction cycles of female gammaridean amphipods are closely correlated with the molt cycle, which is under direct control by the steroid hormone 20-hydroxyecdysone. The ability of males to copulate and subsequently for females to ovulate is restricted to the early postmolt period of the females. New developments in our understanding of the molt cycle and the endocrine regulatory pathways for reproduction using genomics techniques on other crustacean species are also discussed. The arthropod sterol ponasterone A or xenobiotics such as the fungicide fenarimol have been shown to elicit endocrine disruption in some crustaceans by acting as an agonist for 20-hydroxyecdysone at the ecdysone receptor or by inhibiting the synthesis of 20-hydroxyecdysone, respectively, resulting in disruption of molting and reproduction. Recent studies suggest that cadmium can inhibit secondary vitellogenesis in amphipods. Experimental approaches for examining the metabolic pathways associated with ecdysteroid hormonal signaling or metabolism, exoskeleton maintenance and molting, and the regulation of vitellogenin in amphipods are discussed. This information should aid in the identification of useful biomarkers for reproductive toxicity., (Copyright © 2011 SETAC.)

The current study measured the concentrations of 14 polybrominated diphenyl ethers (PBDEs) and eight methoxylated polybrominated diphenyl ethers (MeO-PBDEs) in a marine food web and estimated their trophic magnification factors (TMFs), to highlight the differences between invertebrates, fish, and seabirds. Concentrations of PBDEs were orders of magnitude greater in seabirds (184.07 ± 161.63 ng/g lipid wt) compared with invertebrates and fish (19.01 ± 14.14 ng/g lipid wt). Although the congener profiles in invertebrates, fish, and juvenile seabirds were dominated by BDE-47, the contributions of BDE-99 and BDE-153 in adult seabirds were also significant. Unlike PBDEs, however, higher average MeO-PBDE concentrations were detected in fish (126.27 ± 189.27 ng/g lipid wt) and bivalves (15.96 ± 11.82 ng/g lipid wt) than in seabirds (2.61 ± 2.87 ng/g lipid wt). Correlations between lipid-normalized PBDE concentrations and trophic levels confirmed that seven PBDE congeners were magnified in the invertebrate-fish-seabird food web and that PBDE concentrations increased at a much greater rate across trophic levels in seabirds than in invertebrates and fish. This result indicates that estimating TMFs of PBDEs separately for seabirds, invertebrates, and fish is preferable. For MeO-PBDEs, no significant relationships were obtained in the invertebrate-fish-seabird food web., (Copyright © 2010 SETAC.)

In the present study, we used fresh preparations of mixed-cell populations to evaluate accumulation and toxicity of dissolved copper (1-100 microM) in isolated cells from posterior gills and hepatopancreas of the blue crab (Callinectes sapidus). For both gill and hepatopancreatic cells, significant increases in copper accumulation were observed after exposure to 50 or 100 microM copper. In gill cells, a linear increase in copper accumulation was observed over time. In hepatopancreatic cells, a maximum level of copper accumulation was achieved after 1 h of exposure, remaining unchanged up to 6 h. After 6 h of exposure, copper content in gill cells was 6.6-fold higher than that in hepatopancreatic cells. In both cell types, copper accumulation always followed a linear relationship with copper concentration in the incubation medium. Significant decreases in cell viability were observed after exposure to either 10 microM copper (gill cells) or 100 microM copper (gill and hepatopancreatic cells). Furthermore, an exponential rise to maximum-type relationship was observed between copper accumulation and toxicity in gill cells. Altogether, these findings indicate that the premise behind the biotic ligand model (BLM) approach is verified in isolated cells from posterior gills of the blue crab (i.e., toxicity is driven by copper accumulation in the biotic ligand, the gill cell). Therefore, these cells can be used as a model for the development of an in vitro BLM version for marine conditions. Isolated cells from the hepatopancreas, however, could be used as a model to better understand the mechanism of copper tolerance at a cellular level in crustaceans.

Arsenic is a proven carcinogen often found at high concentrations in association with gold and other heavy metals. The freshwater yabby, Cherax destructor Clark (Decapoda, Parastacidae), is a ubiquitous species native to Australia's central and eastern regions, with a growing international commercial market. However, in this region of Australia, yabby farmers often harvest organisms from old mine tailings dams with elevated environmental arsenic levels. Yabbies exposed to elevated environmental arsenic were found to accumulate and store as much as 100 microg/g arsenic in their tissues. The accumulation is proportional to the concentration of arsenic in the sediment and is high enough to be of concern for people who eat the yabbies. A comparison of arsenic levels in wild and lab-fed animals also was performed. Although there was no significant difference in the level of arsenic in the various organs of the wild animals, the animals purchased from a yabby farm showed a significantly higher arsenic concentration in their hepatopancreas (3.7 +/- 0.9 microg/g) compared to other organs (0.6-1.8 microg/g). Furthermore, after a 40-d exposure to food containing 200 to 300 microg/g inorganic arsenic, arsenate (As[V])-exposed animals showed a significant increase in tissue-specific arsenic accumulation, whereas arsenite (As[III])-exposed animals showed a lower, nonsignificant increase in As uptake, primarily in the hepatopancreas. These results have important implications for yabby growers and consumers alike.

The radiotracer technique was used to assess the influences of sediment-metal contact time or aging (up to two years) on the bioavailability and geochemical speciation of Cd and Zn in sediments. Bioavailability was quantified by measuring the assimilation efficiency of metals in two deposit-feeding invertebrates (sipunculans and soldier crabs) and the extraction by the sipunculans' gut juices. Sediment aging generally did not significantly affect the Cd speciation in the sediments, Cd assimilation, and Cd extraction. In contrast, sediment aging significantly affected the Zn distribution in different geochemical phases and the Zn bioavailability. With increasing aging, the Zn distributed in the carbonate phase decreased, whereas that in the reducible phase increased. Accordingly, the Zn gut-juice extraction decreased significantly. Two years of aging were not sufficient for Zn to be associated with the organic and residual phases. A significant positive correlation was found between Cd gut-juice extraction and assimilation efficiency. Gut-juice extraction of Cd and Zn generally increased with metal distribution in the exchangeable and carbonate phases but decreased with that in the reducible phase. Our results suggest that different metals are influenced by sediment aging differently and that geochemical speciation analysis is useful in studying the bioavailability of sediment-bound metals. This study may have implications for designing sediment toxicity tests using spiking techniques and for understanding the fates of anthropogenically derived metals in sediments.

In bioavailability studies, the biota sediment accumulation factor (BSAF) is invoked to describe the thermodynamic partitioning of a hydrophobic organic contaminant (HOC) between the organism lipid and the organic carbon fraction of the sedimentary matrix and accounts for differences in bioavailability among sediments. Bioaccumulation experiments were performed with Lumbriculus variegatus and Diporeia species exposed in seven sediments dosed with 2,4,5,2',4',5'-hexachlorobiphenyl (HCBP) and benzo[a]pyrene (BaP) or pyrene (PY) and 3,4,3',4'-tetrachlorobiphenyl (TCBP). The BSAF values for the nonplanar HCBP were consistent with equilibrium partitioning theory (EQP) and averaged 2.87 for L. variegatus and 1.45 for Diporeia, while the BSAF values for the planar compounds (BaP, PY, TCBP) were generally lower than estimated from EQP (<1). Correcting the BSAF values of the planar compounds for enhanced sorption due to black carbon improved the BSAF values for L. variegatus, generally resulting in values consistent with EQP, but substantial variation remained for Diporeia. The BSAF values for the planar compounds showed significant positive correlations with plant-derived carbon in sediments (lignin and pigments) but were more consistent for L. variegatus than for Diporeia. These correlations imply that compounds sorbed to plant-derived carbon are more bioavailable since this material is more likely ingested providing a second exposure route.

Brominated flame retardants (BFRs) were investigated for toxic effects both in vivo and in vitro in two invertebrate bioassays. Subchronic effects of tetrabromobisphenol A (TBBPA), tribromophenol (TBP), and four polybrominated diphenyl ethers ([PBDEs]; BDE-28, BDE-47, BDE-99, and BDE-100) on larval development of the marine copepod Acartia tonsa were studied. For TBBPA and TBP 5-d effective median concentration (EC50) values for inhibition of the larval development rate were 125 and 810 microg/L, respectively, whereas the PBDEs were much more potent with 5-d EC50 in the low microg/L range (1.2 microg/L for BDE-100; 4.2 microg/L for BDE-99; 13 microg/L for BDE-28; and 13 microg/L for BDE-47). These concentrations were up to two orders of magnitude below the 48-h LC50 for acute adult toxicity (108 microg/L for BDE-28; 400 microg/L for TBBPA; 520 microg/L for BDE-100; 705 microg/L for BDE-99; 1,500 microg/L for TBP; and 2,370 microg/L for BDE-47). To distinguish between general toxicological and endocrine-mediated toxic effects, the BFRs were assessed in vitro for ecdysteroid agonistic/antagonistic activity with the ecdysteroid-responsive Drosophila melanogaster B(II)-cell line. The pentabrominated diphenyl ethers BDE-99 and BDE-100 showed weak ecdysteroid antagonistic activity. Thus, these PBDEs may be regarded as potential endocrine disrupters in invertebrates. The combination of in vitro assays and subchronic biotests with ecologically important crustacean species is a rapid and cost-effective tool when screening for sublethal effects of BFRs and other chemicals.

Trophic transfer is the main process by which upper trophic level wildlife are exposed to selenium. Transfers through lower levels of a predator's food web thus can be instrumental in determining the threat of selenium in an ecosystem. Little is known about Se transfer through pelagic, zooplankton-based food webs in San Francisco Bay ([SFB], CA, USA), which serve as an energy source for important predators such as striped bass: A dynamic multipathway bioaccumulation model was used to model Se transfer from phytoplankton to pelagic copepods to carnivorous mysids (Neomysis mercedis). Uptake rates of dissolved Se, depuration rates, and assimilation efficiencies (AE) for the model were determined for copepods and mysids in the laboratory. Small (73-250 microm) and large (250-500 microm) herbivorous zooplankton collected from SFB (Oithona/Limnoithona and Acartia sp.) assimilated Se with similar efficiencies (41-52%) from phytoplankton. Mysids assimilated 73% of Se from small herbivorous zooplankton; Se AE was significantly lower (61%) than larger herbivorous zooplankton. Selenium depuration rates were high for both zooplankton and mysids (12-25% d(-1)), especially compared to bivalves (2-3% d(-1)). The model predicted steady state Se concentrations in mysids similar to those observed in the field. The predicted concentration range (1.5-5.4 microg g(-1)) was lower than concentrations of 4.5 to 24 microg g(-1) observed in bivalves from the bay. Differences in efflux between mysids and bivalves were the best explanation for the differences in uptake. The results suggest that the risk of selenium toxicity to predators feeding on N. mercedis would be less than the risk to predators feeding on bivalves. Management of selenium contamination should include food webs analyses to focus on the most important exposure pathways identified for a given watershed.

A diverse set of reference compounds suspected of having an endocrine-disrupting mode of action (i.e., testosterone, flutamide, ethinylestradiol, precocene, nonylphenol, fenoxycarb, and methoprene) were tested for acute toxicity to the estuarine mysid Neomysis integer (Crustacea: Mysidacea). Neomysis integer was very sensitive to all tested compounds, with 96-h median lethal concentrations in a narrow range between 0.32 and 1.95 mg/L. The pesticides methoprene and fenoxycarb, both synthetic insect juvenile hormone analogs, were most toxic to N. integer. In addition, the short-term sublethal effects of methoprene and nonylphenol (an estrogen agonist) on the energy and steroid metabolism of N. integer were evaluated. Both compounds significantly affected energy and testosterone metabolism of N. integer at concentrations below acute toxicity levels. Energy consumption in methoprene- and nonylphenol-exposed mysids was significantly induced at 100 microg/L, resulting in a lower cellular energy allocation in these animals. Testosterone phase I metabolism was affected at 10 microg/L, whereas glycosylation was the most important phase II pathway affected in mysids exposed to 100 microg/L of both compounds. Methoprene exposure resulted in a concentration-dependent increase in the metabolic androgenization ratio. Mysids exposed to nonylphenol at 10 microg/L had a significantly higher metabolic androgenization ratio. The present study indicates that energy and testosterone metabolism of mysids, as endpoints, are able to detect endocrine-disruptive activity of chemicals after short-term exposure to environmentally realistic levels of endocrine disruptors.

Toxicity identification evaluations (TIEs) were performed on seven produced water (PW) effluents from inland discharge facilities operated in Trinidad and Tobago, a Caribbean tropical country with one of the oldest commercial oil industries in the world. The research was performed to determine the presence and magnitude of toxicity and characterize which toxicants are responsible for observed effects. Marine effluent toxicity characterizations with Metamysidopsis insularis revealed high whole acute toxic-unit response for produced water ranged from 8.1 to > 17.0 acute toxic-unit (initial toxicity test) and 5.7 to 1,111 acute toxic-unit (baseline toxicity test). Toxicity test results for all sites except one, which had the highest toxicity, are comparative with similar studies on produced water. The toxicological causality of this complex mixture differed for each PW with nonpolar organics being consistently toxic in all samples. Other potential toxicants contributing to overall toxicity to a much lesser extent were metals, ammonia, and volatile organic compounds. With the use of sodium thiosulfate and filtration manipulations for only PW6 sample, there was very slight reduction in toxicity; therefore, oxidants and filterable materials were not a great contributing factor. Whole effluent toxicity also can be attributed to ionic imbalance and the very stable oil-in-water emulsion that consists of fine oil droplets (less than 0.1-10 microm with an average diameter of 2.5 microm). This investigation is the first of its type in Trinidad and demonstrates clearly the applicability of this test method and local test species for evaluating complex effluents in tropical environments.

The effects of dissolved humic acids (HAs) on the acute toxicities of the organophosphate pesticide chlorpyrifos and the organochlorine pesticide 4,4'-dichlorodiphenyltrichloroethane (DDT) were assessed by using freshwater crustaceans (Ceriodaphnia dubia) and saltwater crustaceans (Americamysis bahia). The effects of filtered Aldrich HAs (10-100 mg/L) on organism mortality were determined. Humic acids had no effect on mortality of A. bahia for either pesticide at a salinity of 20 parts per thousand, but greatly reduced the mortality of C. dubia for both pesticides in freshwater (0 parts per thousand). In the latter case, the effect was proportional to the HA concentration. The difference in toxicity mitigation as a function of salinity is believed to be due to conformational changes in the HA molecules, which impact pesticide-HA binding, rather than to organismal effects.

In aqueous media, ionic silver concentrations are low and transport occurs in the colloidal phase. In the aquatic environment, silver forms 1:1 complexes with thiol-containing compounds such as cysteine and glutathione. In order to quantitatively characterize the risk associated with silver in aquatic ecosystems, the bioavailabilities and toxicities of silver cysteinate and silver glutathionate were characterized. Static renewal bioassays were conducted with Ceriodaphnia dubia to estimate chronic toxicity, using mortality and reproduction as endpoints. Silver nitrate was the most lethal compound, with a median lethal concentration (8-d LC50) of 0.32 microg Ag/L (95% confidence interval [CI] = 0.19-0.54). The 48-h LC50 for AgNO3 was 0.5 microg/L and did not change significantly through 8 d. The presence of food in the bioassay did not change the 48-h LC50 for AgNO3. Silver glutathionate (AgGSH) and silver cysteinate (AgCys) induced less mortality during the 8-d bioassay. Silver cysteinate appeared to have the greatest effect on fecundity, with a no-observable-effect concentration (NOEC) less than 0.001 microg/L. Silver nitrate and AgGSH had lowest-observable-effect concentration (LOEC) values (nominal concentrations) of 0.01 and 0.6 microg/L, respectively. Results indicate that the ligand-bound silver in these laboratory studies is bioavailable and impairs reproduction of C. dubia at low aqueous concentrations.

The partitioning, bioavailability, and toxicity of cypermethrin in water-sediment systems was investigated. Cypermethrin adsorbed extensively and rapidly, with an overall mean organic carbon (OC) adsorption partition coefficient (Koc) of 350,000, and approximately 99% adsorption occurred within 24 h. Bioavailability was measured via body burdens of Daphnia magna and Chironomus tentans. Mean biota-sediment accumulation factors (BSAFs), that is, the concentration in the organism as a proportion of the concentration in the sediment, decreased with increasing OC content. The BSAF values were 0.31, 0.14, and 0.08 for D. magna and 0.63, 0.19, and 0.08 for C. tentans, in 1, 3, and 13% OC sediments, respectively. The 10-d median lethal sediment concentrations (LC50s) of cypermethrin were 3.6, 18, and 32 mg/kg for Hyalella azteca and 13, 67, and 62 mg/kg for C. tentans in 1, 3, and 13% OC sediments, respectively. Predictions of aqueous concentrations at the LC50 in sediments (based on Koc) compared well to each other and to effect concentrations from studies in water alone, suggesting that equilibrium partitioning theory could be used reasonably to predict and normalize the toxicity of cypermethrin across sediments of differing OC content.

The estuarine environment is characterized by frequent fluctuations in salinity. Consequently, organisms used for environmental monitoring of estuaries must be euryhaline so that their laboratory responses to chemical pollutants are measured under the full range of salinity exposures experienced in the field. Neomysis integer and Praunus flexuosus are two potential candidates for use in environmental monitoring of European estuaries. The present study assesses the effects of salinity on survival, trace metal accumulation, and toxicity to these two mysid species. Neomysis integer was more euryhaline, showing 100% survival at 1 to 40@1000 compared with P. flexuosus, which showed 100% survival at salinities of 10 to 40@1000. Toxicity of the free cadmium ion to both species was unaffected by salinity, and 96-h LC50s ranged from 4.8 to 15 micrograms Cd2+/L for N. integer and from 12.3 to 16 micrograms Cd2+/L for P. flexuosus. The 7-d LC50s ranged from 1.0 to 4.2 and 4.8 to 5.3 micrograms Cd2+/L for N. integer and P. flexuosus, respectively. No effect of exposure salinity was found on cadmium body burdens of mysids exposed for 7 d to 0.5 and 1.0 microgram Cd2+/L. The results are discussed in terms of possible effects of osmoregulatory mechanisms on trace metal uptake, accumulation, and toxicity.

High concentrations of Hg, Cd, Pb, Cu, and Zn were found in the euxinic sediment of the inner archipelago of Stockholm. In the sulfide-rich sediment, they are precipitated as metal sulfides with low dissolving capacity and bioavailability. In two experiments, the significance of acid-volatile sulfide (AVS) and dissolved sulfides for mobility, bioavailability, and toxicity of metals were studied by oxygenation of intact sediment cores. Influence of bioturbating deposit-feeding amphipods, that is, Monoporeia affinis, was examined on studied sediment processes. Results showed a low mobility of most metals except Cd and Zn. Bioturbation did not enhance mobility. Cd and Zn, released from the sediment, were not bioaccumulated in amphipods. In contrast, the less mobile metals Hg and Pb were bioaccumulated. A low toxicity of contaminated sediments, in terms of mortality and embryonic malformations of amphipods, was recorded. Results indicate that Cd, Zn, and Cu are comparatively unavailable after oxygenation of the metal sulfides. Similar results were recorded in contaminated sediments differing in redox potential, AVS, dissolved sulfides, and organic contents, suggesting that other metal ligands, in addition to AVS, are important for metal bioavailability and toxicity in anoxic and suboxic environments.