John Kern

Residue‐based mercury dose–response in fish: An analysis using lethality‐equivalent test endpoints

Dose-response relationships for aquatic organisms have been developed for numerous contaminants using external media exposures (water and sediment). Dose-response relationships based on internal concentrations (tissue residues) are limited. The present study reports Hg dose-response curves for early life stage and juvenile or adult fish based on published tissue-residue toxicity studies. These curves rely primarily on endpoints that can be directly related to mortality, such as survival, reproductive success, and lethal developmental abnormalities. These lethality-equivalent endpoints were linked using the common metric of injury. Uncertainties and potential applications of this mercury dose-response curve are discussed. Major uncertainties include lab to field extrapolations, biological endpoints selected by investigators, interspecific extrapolations, and the paucity of published early life stage residue (dose)-response information. To the extent this curve is based exclusively on laboratory toxicity tests and does not consider other potentially sensitive and ecologically important biological endpoints (e.g., growth and behavior), the magnitude of the adverse effects predicted by the curve may be underestimated.

Dietary exposure of mink (Mustela vison) to fish from the upper Hudson River, New York, USA: Effects on reproduction and offspring growth and mortality

The effects of feeding farm-raised mink (Mustela vison) diets containing polychlorinated biphenyl (PCB)-contaminated fish from the upper Hudson River (New York, USA) on adult reproductive performance and kit growth and mortality were evaluated. Diets contained 2.5 to 20% Hudson River fish, providing 0.72 to 6.1 µg ∑PCBs/g feed (4.8-38 pg toxic equivalents [TEQWHO 2005 ]/g feed). The percentage of stillborn kits per litter was significantly increased by dietary concentrations of 4.5 µg ∑PCBs/g feed (28 pg TEQWHO 2005 /g feed) and greater. All offspring exposed to dietary concentrations of 4.5 and 6.1 µg ∑PCBs/g feed (28 and 38 pg TEQWHO 2005 /g feed) died by 10 weeks of age, and all offspring exposed to 1.5 and 2.8 µg ∑PCBs/g feed (10 and 18 pg TEQWHO 2005 /g feed) died by 31 weeks of age, leaving juveniles in the control and 0.72 µg ∑PCBs/g feed (0.41- and 4.8 pg TEQWHO 2005 /g feed) groups only. The dietary concentration predicted to result in 20% kit mortality (LC20) at six weeks of age was 0.34 µg ∑PCBs/g feed (2.6 pg TEQWHO 2005 /g feed). The corresponding maternal hepatic concentration was 0.80 µg ∑PCBs/g liver, wet weight (13 pg TEQWHO 2005 /g liver, wet wt). Mink residing in the upper Hudson River would be expected to consume species of fish that contain an average of 4.0 µg ∑PCBs/g tissue. Thus, a daily diet composed of less than 10% Hudson River fish could provide a dietary concentration of ∑PCBs that resulted in 20% kit mortality in the present study.

Dietary exposure of mink (Mustela vison) to fish from the upper Hudson River, New York, USA: Effects on organ mass and pathology

The authors evaluated effects of feeding ranch mink (Mustela vison) diets containing polychlorinated biphenyl (PCB)-contaminated fish from the upper Hudson River (New York, USA) on adult and offspring organ mass and pathology. Diets contained 2.5 to 20% Hudson River fish, providing 0.72 to 6.1 µg ΣPCBs/g feed (4.8-38 pg toxic equivalents [TEQWHO 2005 ]/g feed). Absolute thyroid and adrenal gland masses were increased in adult females and 31-week-old juveniles, respectively, and absolute liver and heart masses were decreased in six-week-old kits exposed to dietary PCBs. Dietary concentrations of 0.72 µg ΣPCBs/g feed (4.8 pg TEQWHO 2005 /g feed) and greater induced mandibular and maxillary squamous epithelial proliferation in adult animals. The dietary concentration of ΣPCBs predicted to result in 20% incidence of the jaw lesion (EC20) was 2.3 µg ΣPCBs/g feed (15 pg TEQWHO 2005 /g feed), and the hepatic concentration was 2.8 µg ΣPCBs/g liver (89 pg TEQWHO 2005 /g liver). The EC20 values were greater than the dietary and hepatic concentrations predicted to result in a 20% increase in kit mortality (LC20) at six weeks of age (0.34 µg ΣPCBs/g feed or 2.6 pg TEQWHO 2005 /g feed and 0.80 µg ΣPCBs/g liver or 13 pg TEQWHO 2005 /g liver). However, the EC20 values reflect exposure of adults to PCBs for approximately six months, and the LC20 values reflect exposure of offspring from conception onward.

Type I errors linked to faulty statistical analyses of endangered subspecies classifications

Legal issues related to subspecies identification frequently occur through the implementation of the 1973 Endangered Species Act (ESA). A listing under the ESA requires management actions to ensure the continued existence of the taxa. However, these actions often have important social, economic, and political implications. We examined the statistical methods of morphological analysis used in subspecies identification. Methods are illustrated using the California gnatcatcher (Polioptila californica), which was incorrectly listed under the ESA due to misinterpretation of morphological data. We found that inferences based on tests of sample means (i.e., t-test, Hotelling’s T2-statistics), cluster analysis, and discriminant analysis were subject to high rates of false positives (identification of subspecies when none exist; Type I error). These simple tests ignore the common occurrence of spatial clines in animal tracts. Alternatively, spline-regression and step-regression procedures were found to be quite robust yet had high resolution in finding subspecies break locations.

Use of polychlorinated biphenyl and toxic equivalent concentrations in scat from mink(Neovison vison) fed fish from the upper Hudson River to predict dietary and hepatic concentrations and health effects

To evaluate health effects associated with consumption of fish contaminated with polychlorinated biphenyls (PCBs) from the upper Hudson River, farm-raised mink were fed diets containing fish collected from the river. Endpoints assessed included adult reproductive performance, offspring growth and mortality, and organ mass and pathology of adults and their offspring. Scat samples were collected from adult males at the time of necropsy and from adult females just prior to whelping. Scat samples were analyzed for PCBs, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). The present study provides the results of these analyses and compares ∑PCB and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalent (TEQ) concentrations in scat with dietary and hepatic concentrations associated with effects reported previously. Dry weight concentrations of ∑PCBs and ∑TEQs in scat generally increased with dietary concentration and reflected corresponding increases in hepatic concentrations of ∑PCBs and ∑TEQs. Maternal concentrations of ∑PCBs in scat expressed on a dry, wet, and lipid weight basis predicted to result in 50% kit mortality (LC50) were 1.0, 0.30, and 12 μg ∑PCBs/g. Concentrations of ∑PCBs in scat expressed on a dry, wet, and lipid weight basis predicted to result in 50% incidence of a previously reported jaw lesion (EC50) were 1.7, 0.48, and 24 μg ∑PCBs/g in adult females and 2.5, 0.87, and 19 μg ∑PCBs/g in adult males. Environ Toxicol Chem 2018;37:563-575.