Predictive meta‐regressions relating mercury tissue concentrations of freshwater piscivorous mammals

Abstract

Mercury (Hg) is a pollutant of global concern. Sentinel species such as river otter (Lontra canadensis) and mink (Neovison vison) are often used to monitor environmental concentrations in freshwater ecosystems. Tissue total Hg (THg) concentrations are frequently used as biomarkers of exposure. However, there is no comprehensive model relating Hg tissue concentrations in different tissues, making interstudy comparisons challenging. Our objective was to establish conversion factors relating fur, brain, liver, kidney, and muscle THg concentrations using mean concentrations and standard errors reported in the literature. We used data from more than 6000 samples, pooled across 16 studies and 96 sampling sites in North America and Europe. Sixteen regressions were derived for the river otter and mink models, which were statistically significant at a 95% confidence interval and yielded high explained variances. The models were validated using an external data set of individually measured THg tissue concentrations. The validated conversions were used to evaluate the current fur Hg screening guidelines of 20 µg/g and 30 µg/g. At both of these fur concentrations, brain concentrations are of concern for altering brain neurochemistry. We suggest a more conservative fur Hg screening guideline of 15 µg/g to protect sensitive furbearers. The conversion factors can be used to predict internal organ THg concentrations from fur measurements, eliminating the need for invasive tissue sampling. Environ Toxicol Chem 2017;36:2377-2384. © 2017 SETAC.

Mercury contamination in bats from the central United States

“…Twenty‐two bats (3.8%) in the present study exceeded this concentration. More recently, Eccles et al conducted a meta‐analysis of 6000 mink and otter samples from 16 studies and 96 sampling sites and recommended a screening guideline of 15 μg/g in fur for sensitive piscivorous mammals . Seven bats (1.2%) in the present study exceeded 15 μg/g in fur.…”

Distribution of organic and inorganic mercury across the pelts of Canadian river otter (Lontra canadensis)

“…Further, samples should be taken from the head/forelimb region of the pelt to be most reflective of internal THg concentrations when using the conversion factor outlined in Eccles et al . 9 . Implications of estimating internal THg concentrations with fur sampled from other regions include the over or underestimation of the internal THg concentrations.…”

“…Using the conversion between fur THg and organ THg developed in Eccles et al . 9 , the brain, kidney, liver, and muscle concentrations were estimated based on the THg concentration at every sample point in the topcoat and undercoat. The percent error was calculated for each organ at each sample point for topcoat and undercoat (Eq.…”

“…Tissues examined in previous biomarker studies of Hg exposure in river otters include brain, liver, kidney, muscle and fur. Mercury concentrations in all tissues are directly related to the concentrations of mercury found in the blood and fur 7–9 . Hair is advantageous because it is a minimally-invasive matrix and an important excretory pathway which provides temporal trends in Hg exposure at concentrations that can be upwards of two orders of magnitude higher than those in blood 10 .…”

“…Several studies have discussed the utility of fur THg concentrations to estimate the internal organ THg concentrations in these river otter and mink 15,16 , using predictive regression models. The accuracy of estimates generated by this model vary between 28.6–45.4% based on a normalized root mean squared error (NRMSE) for river otter depending on the tissue 9 . While these relationships did not appear to be age or sex dependent 8,16 , some of the unexplained variance could be attributed to differences in fur sample locations within each animal.…”