Populations of the estuarine fish Fundulus heteroclitus indigenous to contaminated sites exhibit heritable resistance to some of the toxic effects of early life-stage exposure to polychlorinated biphenyls (PCBs). This evolved tolerance provides evidence of strong selection by PCBs, and it suggests other potential genetic effects of these stressors on resident populations. Environmental contaminants have the potential to affect the genetic structure of populations and to reduce genetic diversity, but species life-history traits, particularly patterns of migration and dispersal, also influence the distribution of genetic variation among populations. Therefore, the present was conducted to determine whether genetic diversity or genetic structure is altered in populations of F. heteroclitus indigenous to 18 sites in Massachusetts (USA) and Rhode Island (USA), representing a steep gradient of sediment PCB contamination and culminating in a Superfund site at New Bedford Harbor (NBH; MA, USA). Allele frequencies at enzymatic loci were used to assess genetic structure and diversity. Selection experiments using a highly toxic PCB congener (3,3',4,4',5-pentachlorobiphenyl) were conducted to determine if genetic patterns at field sites could be associated with contaminant exposures. Although allele frequencies clearly reflected a pattern of isolation by distance, the results indicated neither significant loss of genetic diversity nor alteration of allele frequencies for populations of F. heteroclitus in NBH.

This study was conducted to assess the effects of zinc and lead on genetic variability of minnow populations (Gambusia affinis, Pimephales notatus, and Fundulus notatus) sampled from two creeks, one receiving mine drainage (Willow Creek) and one reference (Brush Creek), in the Tri‐State Mining District in Kansas. Zinc and lead concentrations were greater in water samples taken from sites in Willow Creek compared to sites sampled in Brush Creek. Although total numbers of fish captured from Willow Creek were smaller than numbers taken from Brush Creek, there were no differences in these fish communities for estimates of species diversity, richness, and evenness. Genetic differentiation within creeks was rare. However, there was significant differentiation between creeks for allozymes of the enzymes glucose phosphate isomerase (Gpi) in F. notatus and P. notatus, malate dehydrogenase (Mdh) in G. affinis, and phosphogluconate dehydrogenase (Pgdh) in F. notatus. Proportions of heterozygous genotypes of P. notatus and G. affinis were higher in Willow Creek compared to Brush Creek. In vitro experiments were conducted to assess the effects of zinc and lead on sensitivity of enzyme staining during electrophoresis. Results indicated allozyme sensitivity to zinc for Gpi and Pgdh loci, but not for products of the Mdh locus. No sensitivity to lead was noted for allozymes. The significant differentiation between creek populations and the results of the in vitro tests indicate a selective effect of zinc on allozymic distributions of these fishes. These results provide additional support for the use of genetic structure and variability as a bioindicator of heavy metal contamination.

Historically, sediments and floodplain soils of the Tittabawassee River (TR; MI, USA) have been contaminated with polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated biphenyls (PCBs). Median concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) based on 2006 World Health Organization tetrachlorodibenzo-p-dioxin toxic equivalency factors (TEFs) in the diet of mink (Mustela vison) ranged from 6.8 x 10(-1) ng TEQ/kg wet weight upstream of the primary source of PCDF to 3.1 x 10(1) ng TEQ/kg wet weight downstream. Estimates of toxicity reference values (TRVs) derived from laboratory studies with individual PCDDs/PCDFs and PCB congeners or mixtures of those congeners, as well as application of TEFs, were compared to site-specific measures of mink exposure. Hazard quotients based on exposures expressed as concentrations of TEQs in the 95th percentile of the mink diet or liver and the no-observable-adverse-effect TRVs were determined to be 1.7 and 8.6, respectively. The resident mink survey, however, including number of mink present, morphological measures, sex ratios, population age structure, and gross and histological tissue examination, indicated no observable adverse effects. This resulted for multiple reasons: First, the exposure estimate was conservative, and second, the predominantly PCDF congener mixture present in the TR appeared to be less potent than predicted from TEQs based on dose-response comparisons. Given this, there appears to be great uncertainty in comparing the measured concentrations of TEQs at this site to TRVs derived from different congeners or congener mixtures. Based on the lack of negative outcomes for any measurement endpoints examined, including jaw lesions, a sentinel indicator of possible adverse effects, and direct measures of effects on individual mink and their population, it was concluded that current concentrations of PCDDs/PCDFs were not causing adverse effects on resident mink of the TR.

Few studies have determined the toxicity of perfluoralkyl substances (PFAS) to aquatic invertebrates. We exposed Chironomus dilutus to 6 different PFAS to assess single-chemical toxicity and relative or proportional toxicity among substances. A 10-d range-finding test was conducted to inform 20-d assays for the following PFAS: perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid (PFHxS), and perfluoroheptanoic acid (PFHpA). A 20-d binary mixture study of PFOS+PFHxS followed the single-chemical tests. Measurement endpoints for 20-d tests included larval survival and biomass. Log-logistic concentration response models were used to estimate 10, 20, and 50% effect concentrations (EC20, EC50) for PFOS, PFHxS, and PFOA. Survival EC50s for PFOS, PFHxS, and PFOA were 2.49, 3860, and 192 000 µg/L, respectively, whereas survival EC20s were 1.70, 913, and 119 000 µg/L for PFOS, PFHxS, and PFOA, respectively. Biomass as a combined survival and growth endpoint resulted in EC20s of 1.89, 896, and 137 000 µg/L for PFOS, PFHxS, and PFOA, respectively. Maximum concentrations tested (no-observed-effect concentrations) for PFNA, PFBS, and PFHpA were 2 to 3 orders of magnitude greater than the PFOS EC50s and showed no toxicity to C. dilutus, even at exposure concentrations well above what would be considered environmentally relevant. The binary mixture of 2.5 µg/L PFOS+1000 µg/L PFHxS showed reduced survival compared to controls and some indication of potential additive or synergistic interaction between PFOS and PFHxS. Overall, the present study supports previous studies showing PFOS to be the most toxic PFAS to aquatic life and suggests that PFOS could be more toxic to the freshwater midge than previously reported.

Concentrations of dioxin-like compounds, primarily polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs), in soils and sediments downstream of Midland, Michigan (USA) were greater than upstream sites and prompted a site-specific hazard assessment of tree swallows breeding in the associated floodplains. Potential for adverse population-level effects from site-specific contaminant exposures were evaluated at study areas (SAs) along the Tittabawassee and Saginaw rivers downstream of Midland. The site-specific multiple lines of evidence approach to hazard assessment included endpoints for dietary- and tissue-based exposures, and population productivity measurements for tree swallows ([TS]; Tachycineta bicolor) measured during the 2005, 2006, and 2007 breeding seasons. Exposure to dioxin-like compounds in TS eggs were some of the greatest recorded and were similar among all upstream and downstream study sites. Conversely, concentrations in nestlings from SAs were significantly greater compared to reference areas (RAs). The pattern of relative concentrations of PCDD/DFs in eggs and nestlings at RAs was dominated by dioxin congeners, whereas at SAs it was dominated by furan congeners. No statistically significant differences were noted in exposure to PCDD/DFs or in population-level responses when compared among locations, and total clutch failures were rare. Hatching success and fledging success were weakly negatively correlated with concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) in individual eggs and nestlings, respectively. On-site concentrations of TEQs in floodplain soils were some of the greatest ever reported in the environment, and several lines of evidence indicate potential population-level effects on TS overall reproductive productivity.