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USGS2024

Exposure to and biomarker responses from legacy and emerging contaminants along three drainages in the Milwaukee Estuary, Wisconsin, USA

Legacy contaminants and contaminants of emerging concern (CECs) were assessed in tree swallow ( Tachycineta bicolor ) tissue and diet samples from three drainages in the Milwaukee estuary, Wisconsin, USA, to understand exposures and possible biomarker responses. Two remote Wisconsin lakes were assessed for comparative purposes. Bioaccumulative classes of contaminants, such as polybrominated diphenyl ethers and per- and polyfluoroalkyl substances, while at higher concentrations than the reference lakes, did not vary significantly among sites or among the three drainages. Polycyclic aromatic hydrocarbons were assessed in diet and sediment and were from primarily pyrogenic sources. Ten biomarkers were assessed relative to contaminant exposure. Polychlorinated biphenyls (PCBs) were elevated above reference conditions at all Milwaukee sites but did not correlate with any measured biomarker responses. Only one site, Cedarburg, just downstream from a Superfund site, had elevated PCBs compared to other sites in the Milwaukee estuary. Few non-organochlorine insecticides or herbicides were detected in tree swallow liver tissue, except for the atrazine metabolite desethylatrazine. Few pharmaceuticals and personal care products were detected in liver tissue except for N,N -diethyl-meta-toluamide, iopamidol, and two antibiotics. The present study is one of the most comprehensive assessments to date, along with the previously published Maumee River data, on the exposure and effects of a wide variety of CECs in birds. Environ Toxicol Chem 2024;00:1–22. © 2024 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Wisconsin↗

USGS2024

Evaluation of chronic effects of potassium chloride and nickel on survival, growth, and reproduction of a unionid mussel (Lampsilis siliquoidea)

The ASTM International standard test method for freshwater mussels (E2455‐13) recommends 4‐week toxicity testing with juveniles to evaluate chronic effects on survival and growth. However, concerns remain that the method may not adequately address the sensitivity of mussels to longer term exposures (>4 weeks), particularly in relation to potential reproductive impairments. No standard method directly evaluates toxicant effects on mussel reproduction. The objectives of the present study were to (1) evaluate toxicity endpoints related to reproduction in fatmucket ( Lampsilis siliquoidea ) using two common reference toxicants, potassium chloride (KCl) and nickel (Ni); (2) evaluate the survival and growth of juvenile fatmucket in standard 4‐week and longer term (12‐week) KCl and Ni tests following a method refined from the standard method; and (3) compare the sensitivity of the reproductive endpoints with the endpoints obtained from the juvenile mussel tests. Reproductive toxicity tests were conducted by first exposing female fatmucket brooding mature larvae (glochidia) to five test concentrations of KCl and Ni for 6 weeks. Subsamples of the glochidia were then removed from the adults to determine three reproductive endpoints: (1) the viability of brooded glochidia; (2) the viability of free glochidia in a 24‐h exposure to the same toxicant concentrations as their mother; and (3) the success of glochidia parasitism on host fish. Mean viability of brooded glochidia was significantly reduced in the high KCl concentration (26 mg K/L) relative to the control, with a 20% effect concentration (EC20) of 14 mg K/L, but there were no significant differences between the control and any Ni treatment (EC20 > 95 µg Ni/L). The EC20s for viability of free glochidia after the additional 24‐h exposure and parasitism success were similar to the EC20s of brooded glochidia. The EC20s based on the most sensitive biomass endpoint in the 4‐week juvenile tests were 15 mg K/L and 91 µg Ni/L, similar to or greater than the EC20s from the reproductive KCl and Ni tests, respectively. When exposure duration in the juvenile tests was extended from 4 to 12 weeks, the EC20s decreased by more than 50% in the KCl test but by only 8% in the Ni test. Overall, these results indicate that a standard 4‐week test with juvenile mussels can prove effective for estimating effects in chronic exposures with different life stages although a longer term 12‐week exposure with juvenile mussels may reveal higher sensitivity of mussels to some toxicants, such as KCl.

Environmental Toxicology and Chemistry↗

USGS2024

Methylmercury effects on birds: A review, meta-analysis, and development of toxicity reference values for injury assessment based on tissue residues and diet

Birds are used as bioindicators of environmental mercury (Hg) contamination, and toxicity reference values are needed for injury assessments. We conducted a comprehensive review, summarized data from 168 studies, performed a series of Bayesian hierarchical meta-analyses, and developed new toxicity reference values for the effects of methylmercury (MeHg) on birds using a benchmark dose analysis framework. Lethal and sublethal effects of MeHg on birds were categorized into nine biologically relevant endpoint categories and three age classes. Effective Hg concentrations where there was a 10% reduction (EC10) in the production of juvenile offspring (0.55 µg/g wet wt adult blood-equivalent Hg concentrations, 80% credible interval: [0.33, 0.85]), histology endpoints (0.49 [0.15, 0.96] and 0.61 [0.09, 2.48]), and biochemical markers (0.77 [<0.25, 2.12] and 0.57 [0.35, 0.92]) were substantially lower than those for survival (2.97 [2.10, 4.73] and 5.24 [3.30, 9.55]) and behavior (6.23 [1.84, >13.42] and 3.11 [2.10, 4.64]) of juveniles and adults, respectively. Within the egg age class, survival was the most sensitive endpoint (EC10 = 2.02 µg/g wet wt adult blood-equivalent Hg concentrations [1.39, 2.94] or 1.17 µg/g fresh wet wt egg-equivalent Hg concentrations [0.80, 1.70]). Body morphology was not particularly sensitive to Hg. We developed toxicity reference values using a combined survival and reproduction endpoints category for juveniles, because juveniles were more sensitive to Hg toxicity than eggs or adults. Adult blood-equivalent Hg concentrations (µg/g wet wt) and egg-equivalent Hg concentrations (µg/g fresh wet wt) caused low injury to birds (EC1) at 0.09 [0.04, 0.17] and 0.04 [0.01, 0.08], moderate injury (EC5) at 0.6 [0.37, 0.84] and 0.3 [0.17, 0.44], high injury (EC10) at 1.3 [0.94, 1.89] and 0.7 [0.49, 1.02], and severe injury (EC20) at 3.2 [2.24, 4.78] and 1.8 [1.28, 2.79], respectively. Maternal dietary Hg (µg/g dry wt) caused low injury to juveniles at 0.16 [0.05, 0.38], moderate injury at 0.6 [0.29, 1.03], high injury at 1.1 [0.63, 1.87], and severe injury at 2.4 [1.42, 4.13]. We found few substantial differences in Hg toxicity among avian taxonomic orders, including for controlled laboratory studies that injected Hg into eggs. Our results can be used to quantify injury to birds caused by Hg pollution.

Environmental Toxicology and Chemistry↗

USGS2024

Acute toxicity of the lampricide 4-nitro-3-(trifluoromethyl)phenol to the Mussel (Obovaria subrotunda), its host (Percina maculata), and a surrogate mussel species (Obovaria olivaria)

The risk of lampricide applications (such as 4-nitro-3-[trifluoromethyl]phenol [TFM]) to nontarget fauna continues to be a concern within the Great Lakes Fishery Commission Sea Lamprey Control Program, especially among imperiled aquatic species—such as native freshwater mussels. The Grand River (Ohio, USA) is routinely treated for larval sea lampreys ( Petromyzon marinus ), and this river contains populations of the federally threatened mussel Obovaria subrotunda . Given this spatial overlap, information on the sensitivity of O. subrotunda to TFM is needed. Our objectives were to assess the toxicity of TFM to (1) adult Obovaria olivaria (a surrogate for O. subrotunda ), (2) glochidial larvae of O. olivaria and O. subrotunda , (3) juveniles of O. olivaria and O. subrotunda , and (4) adult Percina maculata (host for O. subrotunda glochidia). In acute toxicity tests, TFM was not toxic to glochidia and adult mussels at exposure concentrations that exceed typical treatment rates. Although significant dose–response relationships were observed in hosts and juveniles, survival was ≥95% ( Percina maculata ), ≥93% ( O. olivaria ), and ≥74% ( O. subrotunda ) at typical treatment rates. However, the steep slope of these dose–response relationships indicates that an approximately 20% difference in the treatment level can result in nearly an order of magnitude difference in survival. Collectively, these data indicate that routine sea lamprey control operations are unlikely to acutely affect these species or their host. However, given that many mussel species are long-lived (30–100 years), the risks posed by lampricide treatments in the Great Lakes would be further informed by research on the potential long-term effects of lampricides on imperiled species. Environ Toxicol Chem 2024;00:1–8. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.

Environmental Toxicology & Chemistry↗

USGS2024

Potential hazards of polycyclic aromatic hydrocarbons in Great Lakes tributaries using water column and porewater passive samplers and sediment wquilibrium partitioning

The potential for polycyclic aromatic hydrocarbon (PAH)-related effects in benthic organisms is commonly estimated from organic carbon-normalized sediment concentrations based on equilibrium partitioning (EqP). Although this approach is useful for screening purposes, it may overestimate PAH bioavailability by orders of magnitude in some sediments, leading to inflated exposure estimates and potentially unnecessary remediation costs. Recently, passive samplers have been shown to provide an accurate assessment of the freely dissolved concentrations of PAHs, and thus their bioavailability and possible biological effects, in sediment porewater and overlying surface water. We used polyethylene passive sampling devices (PEDs) to measure freely dissolved porewater and water column PAH concentrations at 55 Great Lakes (USA/Canada) tributary locations. The potential for PAH-related biological effects using PED concentrations were estimated with multiple approaches by applying EqP, water quality guidelines, and pathway-based biological activity based on in vitro bioassay results from ToxCast. Results based on the PED-based exposure estimates were compared with EqP-derived exposure estimates for concurrently collected sediment samples. The results indicate a potential overestimation of bioavailable PAH concentrations by up to 960-fold using the EqP-based method compared with measurements using PEDs. Even so, PED-based exposure estimates indicate a high potential for PAH-related biological effects at 14 locations. Our findings provide an updated, weight-of-evidence–based site prioritization to help guide possible future monitoring and mitigation efforts.

Illinois, Indiana, Michigan, Minnesota, New York, ↗

USGS2024

Egg mercury concentration and egg size varies with position in the laying sequence in two songbird species

In birds, mercury embryotoxicity can occur through the transfer of mercury from the female to her eggs. Maternal transfer of mercury can vary by egg position in the laying sequence, with first-laid eggs often exhibiting greater mercury concentrations than subsequently laid eggs. We studied egg mercury concentration, mercury burden (total amount of mercury in the egg), and egg morphometrics by egg position in the laying sequence for two songbirds: tree swallows ( Tachycineta bicolor ) and house wrens ( Troglodytes aedon ). Egg mercury concentration in the second egg laid was 14% lower for tree swallows and 6% lower for house wrens in comparison with the first egg laid. These results indicate that in both species, after an initial relatively high transfer of mercury into the first egg laid, a smaller amount of mercury was transferred to the second egg laid. This lower mercury concentration persisted among all subsequently laid eggs (eggs three to eight) in tree swallows (all were 14%–16% lower than egg 1), but mercury concentrations in subsequently laid house wren eggs (eggs three to seven) returned to levels observed in the first egg laid (all were 1% lower to 3% greater than egg 1). Egg size increased with position in the laying sequence in both species; the predicted volume of egg 7 was 5% and 6% greater than that of egg 1 in tree swallows and house wrens, respectively. This change was caused by a significant increase in egg width, but not egg length, with position in the laying sequence. The percentage of decline in mercury concentration with position in the laying sequence was considerably lower in tree swallows and house wrens compared with other bird taxonomic groups, suggesting that there are key differences in the maternal transfer of mercury into songbird eggs compared with other birds. Finally, we performed simulations to evaluate how within-clutch variation in egg mercury concentrations affected estimates of mean mercury concentrations in each clutch and the overall sampled population, which has direct implications for sampling designs. Environ Toxicol Chem 2024;00:1–11. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.

Environmental Toxicology and Chemistry↗

USGS2024

Bioconcentration of per- and polyfluoroalkyl substances and precursors in fathead minnow tissues environmentally exposed to aqueous film-forming foam-contaminated waters

Exposure to per- and polyfluoroalkyl substances (PFAS) has been associated with toxicity in wildlife and negative health effects in humans. Decades of fire training activity at Joint Base Cape Cod (MA, USA) incorporated the use of aqueous film-forming foam (AFFF), which resulted in long-term PFAS contamination of sediments, groundwater, and hydrologically connected surface waters. To explore the bioconcentration potential of PFAS in complex environmental mixtures, a mobile laboratory was established to evaluate the bioconcentration of PFAS from AFFF-impacted groundwater by flow-through design. Fathead minnows ( n = 24) were exposed to PFAS in groundwater over a 21-day period and tissue-specific PFAS burdens in liver, kidney, and gonad were derived at three different time points. The ∑PFAS concentrations in groundwater increased from approximately 10,000 ng/L at day 1 to 36,000 ng/L at day 21. The relative abundance of PFAS in liver, kidney, and gonad shifted temporally from majority perfluoroalkyl sulfonamides (FASAs) to perfluoroalkyl sulfonates (PFSAs). By day 21, mean ∑PFAS concentrations in tissues displayed a predominance in the order of liver > kidney > gonad. Generally, bioconcentration factors (BCFs) for FASAs, perfluoroalkyl carboxylates (PFCAs), and fluorotelomer sulfonates (FTS) increased with degree of fluorinated carbon chain length, but this was not evident for PFSAs. Perfluorooctane sulfonamide (FOSA) displayed the highest mean BCF (8700 L/kg) in day 21 kidney. Suspect screening results revealed the presence of several perfluoroalkyl sulfinate and FASA compounds present in groundwater and in liver for which pseudo-bioconcentration factors are also reported. The bioconcentration observed for precursor compounds and PFSA derivatives detected suggests alternative pathways for terminal PFAS exposure in aquatic wildlife and humans.

Environmental Toxicology and Chemistry↗

USGS2024

Evaluation of short-term mussel test for estimating toxicity

Effect concentrations of ammonia, nickel, sodium chloride, and potassium chloride from short-term 7-day tests were compared to those from standard chronic 28-day toxicity tests with juvenile mussels (fatmucket, Lampsilis siliquoidea ) to evaluate the sensitivities of the 7-day tests. The effect concentrations for nickel (59 µg Ni/L), chloride (316–519 mg Cl/L, a range from multiple tests), and potassium (15 mg K/L) obtained from the 7-day tests were within a range of effect concentrations for each corresponding chemical in the 28-day tests (41–91 µg Ni/L, 251–>676 mg Cl/L, 15–23 mg K/L), whereas the 7-day ammonia effect concentration (0.40 mg/L total ammonia nitrogen; TAN) was up to 3.3-fold greater than the 28-day effect concentrations (0.12–0.36 mg TAN/L) but with overlapped 95% confidence limits. These results indicate that the 7-day tests produced similar estimates compared to the 28-day tests. Further studies are needed to evaluate the 7-day test sensitivity using additional chemicals with different modes of toxic action. Environ Toxicol Chem 2024;00:1–6. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.

Environmental Toxicology and Chemistry↗

USGS2024

Inconsistent transcriptomic responses to hexabromocyclododecane in Japanese quail: A comparative analysis of results from four different study designs

Efforts to use transcriptomics for toxicity testing have classically relied on the assumption that chemicals consistently produce characteristic transcriptomic signatures that are reflective of their mechanism of action. However, the degree to which transcriptomic responses are conserved across different test methodologies has seldom been explored. With increasing regulatory demand for New Approach Methods (NAMs) that use alternatives to animal models and high‐content approaches such as transcriptomics, this type of comparative analysis is needed. We examined whether common genes are dysregulated in Japanese quail ( Coturnix japonica ) liver following sublethal exposure to the flame retardant hexabromocyclododecane (HBCD), when life stage and test methodologies differ. The four exposure scenarios included one NAM: Study 1—early‐life stage (ELS) exposure via a single egg injection, and three more traditional approaches; Study 2—adult exposure using a single oral gavage; Study 3—ELS exposure via maternal deposition after adults were exposed through their diet for 7 weeks; and Study 4—ELS exposure via maternal deposition and re‐exposure of nestlings through their diet for 17 weeks. The total number of differentially expressed genes (DEGs) detected in each study was variable (Study 1, 550; Study 2, 192; Study 3, 1; Study 4, 3) with only 19 DEGs shared between Studies 1 and 2. Factors contributing to this lack of concordance are discussed and include differences in dose, but also quail strain, exposure route, sampling time, and HBCD stereoisomer composition. The results provide a detailed overview of the transcriptomic responses to HBCD at different life stages and routes of exposure in a model avian species and highlight certain challenges and limits of comparing transcriptomics across different test methodologies.

Environmental Toxicology and Chemistry↗

USGS2011

Influence of dissolved organic carbon on toxicity of copper to a unionid mussel ( Villosa iris ) and a cladoceran ( Ceriodaphnia dubia ) in acute and chronic water exposures

Acute and chronic toxicity of copper (Cu) to a unionid mussel ( Villosa iris ) and a cladoceran ( Ceriodaphnia dubia ) were determined in water exposures at four concentrations of dissolved organic carbon (DOC; nominally 0.5, 2.5, 5, and 10 mg/L as carbon [C]). Test waters with DOC concentrations of 2.5 to 10 mg C/L were prepared by mixing a concentrate of natural organic matter (Suwannee River, GA, USA) in diluted well water (hardness 100 mg/L as CaCO 3 , pH 8.3, DOC 0.5 mg C/L). Acute median effect concentrations (EC50s) for dissolved Cu increased approximately fivefold (15–72 μg Cu/L) for mussel survival in 4-d exposures and increased about 11-fold (25–267 μg Cu/L) for cladoceran survival in 2-d exposures across DOC concentrations from 0.5 to 10 mg C/L. Similarly, chronic 20% effect concentrations (EC20s) for the mussel in 28-d exposures increased about fivefold (13–61 μg Cu/L for survival; 8.8–38 μg Cu/L for biomass), and the EC20s for the cladoceran in 7-d exposures increased approximately 17-fold (13–215 μg Cu/L) for survival or approximately fourfold (12–42 μg Cu/L) for reproduction across DOC concentrations from 0.5 to 10 mg C/L. The acute and chronic values for the mussel were less than or approximately equal to the values for the cladoceran. Predictions from the biotic ligand model (BLM) used to derive the U.S. Environmental Protection Agency's ambient water quality criteria (AWQC) for Cu explained more than 90% of the variation in the acute and chronic endpoints for the two species, with the exception of the EC20 for cladoceran reproduction (only 46% of variation explained). The BLM-normalized acute EC50s and chronic EC20s for the mussel and BLM-normalized chronic EC20s for the cladoceran in waters with DOC concentrations of 2.5 to 10 mg C/L were equal to or less than the final acute value and final chronic value in the BLM-based AWQC for Cu, respectively, indicating that the Cu AWQC might not adequately protect the mussel from acute and chronic exposure, and the cladoceran from chronic exposure.

Environmental Toxicology and Chemistry↗

USGS2024

Sensitivity of Alabama freshwater gastropod species to nickel exposure

Snails are effective bioindicators due to their prolific distribution, high level of endemism, and capacity to accumulate contaminants. Freshwater snails have unique ecological niches which are imperiled by land‐use change and the introduction of hazardous chemicals. To assess how environmental alterations affect gastropods, lab‐based studies are needed to characterize the toxicity of specific stressors. This can help guide policy decisions and remediation efforts. The aim of this research was to characterize acute toxicity of nickel (Ni) on endemic snails ( Somatogyrus georgianus [Walker, 1904], Elimia cahawbensis [Lea, 1861], and Elimia spp.) and measure the accumulation of Ni and mineral elements including calcium (Ca), magnesium, potassium, and sodium (Na). Snails were exposed to six concentrations (25–800 µg/L) of Ni for 96 h. Among the studied snail species, E. cahawbensis was the most sensitive to Ni, with the lowest lethal concentration where 50% of the organisms died (LC50) at 88.88 µg/L Ni after 96 h. The LC50 at 96 h for S. georgianus was 167.78 µg/L Ni, and 393.13 μg/L Ni for Elimia spp. Except for Elimia spp., mortality of the other two snail species corresponded to the whole‐body uptake of Ni. Nickel exposure also influenced Ca and Na uptake for Elimia spp. All three endemic species are potential candidate species for evaluating localized effects of human activities, and the present study provides a first step in characterizing how snails would be affected by environmental alterations. More research could further characterize potential effects of other human stressors on these endemic snail species. Future research into subindividual responses and routes of exposure can further elucidate variations in species sensitivity.

Alabama↗

USGS2011

Toxicity of methylmercury injected into eggs when dissolved in water versus corn oil

In a previous study, the embryotoxicity of methylmercury dissolved in corn oil was compared among 26 species of birds. Corn oil is not soluble in the water‐based matrix that constitutes the albumen of an egg. To determine whether the use of corn oil limited the usefulness of this earlier study, a comparison was made of the embryotoxicity of methylmercury dissolved in corn oil versus water. Mallard ( Anas platyrhynchos ) and chicken ( Gallus gallus ) eggs were injected with methylmercury chloride dissolved in corn oil or water to achieve concentrations of 0, 0.2, 0.4, 0.8, and 1.6 µg/g mercury in the egg on a wet weight basis. Hatching success at each dose of mercury was compared between the two solvents. For mallards, 16.4% of the eggs injected with 1.6 µg/g mercury dissolved in water hatched, which was statistically lower than the 37.6% hatch rate of eggs injected with 1.6 µg/g mercury dissolved in corn oil, but no differences in hatching success were observed between corn oil and water at any of the other doses. With chicken eggs, no significant differences occurred in percentage hatch of eggs between corn oil and water at any of the mercury doses. Methylmercury dissolved in corn oil seems to have a toxicity to avian embryos similar to that of does methylmercury dissolved in water. Consequently, the results from the earlier study that described the toxicity of methylmercury dissolved in corn oil to avian embryos were probably not compromised by the use of corn oil as a solvent.

Environmental Toxicology and Chemistry↗

USGS2011

Perfluorinated chemicals in surface waters and sediments from northwest Georgia, USA, and their bioaccumulation in Lumbriculus variegatus

Concentrations of perfluorinated chemicals (PFCs) were measured in surface waters and sediments from the Coosa River watershed in northwest Georgia, USA, to examine their distribution downstream of a suspected source. Samples from eight sites were analyzed using liquid chromatography‐tandem mass spectrometry. Sediments were also used in 28‐d exposures with the aquatic oligochaete, Lumbriculus variegatus , to assess PFC bioaccumulation. Concentrations of PFCs in surface waters and sediments increased significantly below a land‐application site (LAS) of municipal/industrial wastewater and were further elevated by unknown sources downstream. Perfluorinated carboxylic acids (PFCAs) with eight or fewer carbons were the most prominent in surface waters. Those with 10 or more carbons predominated sediment and tissue samples. Perfluorooctane sulfonate (PFOS) was the major homolog in contaminated sediments and tissues. This pattern among sediment PFC concentrations was consistent among sites and reflected homolog concentrations emanating from the LAS. Concentrations of PFCs in oligochaete tissues revealed patterns similar to those observed in the respective sediments. The tendency to bioaccumulate increased with PFCA chain length and the presence of the sulfonate moiety. Biota‐sediment accumulation factors indicated that short‐chain PFCAs with fewer than seven carbons may be environmentally benign alternatives in aquatic ecosystems; however, sulfonates with four to seven carbons may be as likely to bioaccumulate as PFOS.

Georgia↗

USGS2009

Enhanced reproduction in mallards fed a low level of methylmercury: An apparent case of hormesis

Breeding pairs of mallards ( Anas platyrhynchos ) were fed a control diet or a diet containing 0.5 µg/g mercury (Hg) in the form of methylmercury chloride. There were no effects of Hg on adult weights and no overt signs of Hg poisoning in adults. The Hg‐containing diet had no effect on fertility of eggs, but hatching success of eggs was significantly higher for females fed 0.5 µg/g Hg (71.8%) than for controls (57.5%). Survival of ducklings through 6 d of age was the same (97.8%) for controls and mallards fed 0.5 µg/g mercury. However, the mean number of ducklings produced per female was significantly higher for the pairs fed 0.5 µg/g Hg (21.4) than for controls (16.8). Although mercury in the parents' diet had no effect on mean duckling weights at hatching, ducklings from parents fed 0.5 µg/g Hg weighed significantly more (mean = 87.2 g) at 6 d of age than did control ducklings (81.0 g). The mean concentration of Hg in eggs laid by parents fed 0.5 µg/g mercury was 0.81 µg/g on a wet‐weight basis. At this time, one cannot rule out the possibility that low concentrations of Hg in eggs may be beneficial, and this possibility should be considered when setting regulatory thresholds for methylmercury.

Environmental Toxicology and Chemistry↗

USGS2011

Bioaccumulation dynamics and exposure routes of Cd and Cu among species of aquatic mayflies

Consumption of periphyton is a potentially important route of metal exposure to benthic invertebrate grazers. The present study examined the bioaccumulation kinetics of dissolved and dietary Cd and Cu in five species of mayflies (class Insecta). Artificial stream water and benthic diatoms were separately labeled with enriched stable metal isotopes to determine physiological rate constants used by a biokinetic bioaccumulation model. The model was employed to simulate the effects of metal partitioning between water and food, expressed as the bioconcentration factor (BCF), as well as ingestion rate (IR) and metal assimilation efficiency of food (AE), on the relative importance of water and food to metal bioaccumulation. For all test species, the contribution of dietary uptake of Cd and Cu increased with BCF. For a given BCF, the contribution of food to the body burden increased with k uf , the metal uptake rate constant from food that combined variation in IR and AE. To explore the relative importance of water and diet exposure routes under field conditions, we used estimated site‐specific aqueous free‐ion concentrations to model Cd and Cu accumulation from aqueous exposure, exclusively. The predicted concentrations accounted for less than 5% of the observed concentrations, implying that most bioaccumulated metal was acquired from food. At least for the taxa considered in this study, we conclude that consumption of metal‐contaminated periphyton can result in elevated metal body burdens and potentially increase the risk of metal toxicity.

Environmental Toxicology and Chemistry↗

USGS2009

Effects of egg order on organic and inorganic element concentrations and egg characteristics in tree swallows, tachycineta bicolor

The laying order of tree swallow eggs was identified from the Housatonic River, Berkshire County, Massachusetts, USA, and eggs were chemically analyzed individually to document possible effects of laying order on organic contaminant and inorganic element concentrations. Effects of laying order on other parameters such as egg weight, size, and lipid and moisture content also were assessed. Some effects of egg order on total polychlorinated biphenyls (PCBs) were detected, but the effect was not uniform across individual females or between years. In 2004, clutches with higher total PCBs tended to have concentrations decline across egg order, whereas clutches with lower concentrations of PCBs tended to increase across egg order. In contrast, in 2005, there was a tendency for concentrations to increase across egg order. Polychlorinated biphenyl concentrations were highly variable within and among clutches in both years. The directionality of egg order associations (i.e., slopes) for trace elements was element dependent, was positive for Mn and Zn, was negative for B, and had no slope for Cr. Whole egg weight increased across egg order. Percentage lipid was variable within a clutch, with no pattern common across all females. Percentage lipid was also correlated with organic contaminant concentration. In highly contaminated environments, higher lipid content could have the unanticipated corollary of having higher concentrations of lipophilic contaminants such as PCBs. To reduce the effect of high variation within a clutch when assessing contamination exposure, it is recommended that two eggs per clutch be collected and pooled for chemical analysis. We further recommend that, as long as the two eggs are randomly collected, the additional effort needed to identify and collect specific eggs is not warranted.

Massachusetts↗

USGS2006

Flow cytometry, morphometry and histopathology as biomarkers of benzo[a]pyrene exposure in brown bullheads (ameiurus nebulosus)

Brown bullheads were given a single intraperitoneal dose of 0, 5, 25 or 125 mg kg −1 benzo[ a ]pyrene (BaP), a carcinogenic polycyclic aromatic hydrocarbon, and evaluated over 18 months. Flow cytometric analyses of hepatocyte DNA content indicated an increase in DNA synthesis in BaP-exposed fish prior to day 14 post-exposure. Thereafter, all flow cytometric variables returned to initial levels. Histopathological evaluation of livers from fish sampled at 18 months revealed significant differences among treatments in the amount of hepatic macrophage ceroid pigmentation and basophilic staining intensity. No neoplasms or changes in blood cell DNA content were detected. Significant morphometric variations existed among fish, but differences between sexes overshadowed differences attributable to dose. Flow cytometry yielded no evidence of long-term DNA alterations from a single exposure to BaP; however, the differences detected by DNA analysis shortly after the toxic event suggest that flow cytometric cell cycle analysis may be useful for documenting continuing exposures.

Journal of Applied Toxicology↗

USGS2002

Impact of selenium and other trace elements on the endangered adult razorback sucker

A study was conducted with endangered the razorback sucker ( Xyrauchen texanus ) to determine if environmental exposure to selenium in flooded bottomland sites affected survival, growth, and egg-hatching success. Adults were stocked at three sites adjacent to the Colorado River near Grand Junction, Colorado, in July 1996: hatchery ponds at Horsethief Canyon State Wildlife Area (referred to here as Horsethief; the reference site), a diked tertiary channel at Adobe Creek, and North Pond at Walter Walker State Wildlife Area (WWSWA). Fish were collected in April 1997 and spawned. After two spawnings adults from the three sites were held at Horsethief for an 86-day selenium depuration period. Selenium concentrations at Horsethief were 1.4–3.0 μg/L in water, 0.8–0.9 μg/g in sediment, 4.5 μg/g in muscle plug, and 6.0 μg/g in eggs; at Adobe Creek, <0.7–4.5 μg/L in water, 1.2–2.5 μg/g in sediment, 16–20 μg/g in zooplankton, 9.6 μg/g in muscle plug, and 40 μg/g in eggs; and at North Pond, 3.2–17 μg/L in water, 16–94 μg/g in sediment, 32–48 μg/g in zooplankton, 14 μg/g in muscle plug, and 55 μg/g in eggs. During the depuration period, when adults from Adobe Creek and North Pond were held at Horsethief, the fish lost 7%–13% of their selenium burden in 59 days and 14%–21% in 86 days. Larvae from North Pond adults had the most deformities, followed by Adobe Creek adults, with the fewest deformities found in the Horsethief adults.

Colorado↗