Concentrations of heavy metals and PCBs in the tissues of European beavers (Castor fiber) captured in northeastern Poland

Comparison of trace elements in tissue of beaver (Castor canadensis) and local vegetation from a rural region of southern Ontario, Canada

Beavers have been analyzed in several studies examining trace elements (TEs) in wildlife; however, most of these studies were undertaken in areas with known environmental pollutants. To understand and quantify natural enrichments of TEs in beaver tissue, samples of kidney, liver, muscle from 28 animals were compared with bark from 40 species of trees and shrubs, from the same, uncontaminated watershed. Pearson correlation and factor analysis show that conservative, lithophile elements such as Al, Ga, Th, and Y, all surrogates for mineral dust particles, explain 61% of the variation in the bark data. In contrast, Cd, Co, Cu, Mn, Mo, Ni, Rb, Se, Sr, and Tl in bark are independent of Al, and therefore most likely occur in non-mineral forms. Comparing tissue concentrations of beaver and bark, the organs are enriched in micronutrients such as Cu, Fe, Mo, Se, and Zn, but also non-essential, benign elements such as Cs and Rb, and potentially toxic elements such as Cd and Tl. Thus, the elements most enriched in beaver organs are those that apparently occur in biological form in the plant tissue. The elements enriched in these animals, relative to bark, appear to offer the most promise for monitoring environmental contamination by TEs using beavers. The majority of TEs of environmental relevance are most abundant in beaver kidney. However, monitoring studies must consider the variation in TE concentrations in beaver tissue, including those due to sex and age. Also, due consideration must be given to background concentrations of TEs in the vegetation composing the diet of the animals. The natural enrichment in the case of elements such as Cd, in beaver tissue relative to bark, is profound. These data establish critical baseline values for TEs in beavers in an unpolluted environment, thereby allowing for their use as model organisms in tracking how heavy metal pollutants may affect wildlife.

Ecotoxicoparasitology of mercury and trace elements in semi-aquatic mammals and their endoparasite communities

Many contaminants persist in the environment for decades or more, influencing ecosystem health. Environmental contamination with mercury (Hg) is a particular concern due to its ability to biomagnify in food webs and its lethal and sub-lethal effects in exposed organisms. Despite the known impacts of anthropogenic contamination, there remains a need for data on wildlife exposure to Hg and other contaminants, and the effects of exposure on wildlife health. The objectives of this study were to: 1) quantify differences in concentrations of mercury and other trace elements among three sympatric semiaquatic mammals of different assumed trophic position: North American river otter (Lontra canadensis), raccoon (Procyon lotor), and North American beaver (Castor canadensis), 2) compare trace element concentrations between animals captured on the Savannah River Site (SRS) in South Carolina, USA, where known inputs of Hg and other trace elements have occurred, and reference sites in South Carolina (SC) and Georgia (GA), USA, and 3) investigate the relationship between host trace element concentrations and endoparasite communities. River otters, beavers, and raccoons were sampled from the SRS, SC, and GA to quantify trace element concentrations in liver tissue and quantify endoparasite communities. Both species and sampling location were important factors determining hepatic trace element concentration, however, there was no consistent trend of elevated trace element concentrations among animals sampled on the SRS. Only Hg demonstrated biomagnification based on assumed trophic position, with river otters having the highest Hg concentrations among the sampled species. Additionally, the results suggest a possible relationship between host hepatic mercury concentration and endoparasite abundance, while hepatic selenium concentration may be related to endoparasite diversity. These findings further demonstrate how wildlife can accumulate anthropogenic contamination, although future research is needed to determine the mechanisms contributing to patterns observed between endoparasite communities and the contaminant concentrations of their mammalian hosts.

A geochemical perspective on the natural abundance of trace elements in beaver (Castor canadensis) from a rural region of southern Ontario, Canada

Chalcophile (Ag, Cd, Co, Cu, Mo, Ni, Pb, Se, Tl, Zn) and lithophile (Al, Ba, Ce, Cr, Cs, Fe, La, Li, Mn, Nd, Rb, Sr, V, Y) trace elements (TEs) were determined in kidney, liver and muscle of beaver (Castor canadensis) from a rural watershed in southern Ontario, Canada. To estimate the relative bioavailability of TEs in the landscape, they were also determined in the dissolved (<0.45 μm) fraction of water from the river where the animals were harvested. Concentration ratios (tissue/water) always showed the greatest enrichments for Cd (kidney, 1.1 × 10⁷; liver, 2.4 × 10⁶; muscle, 7.2 × 10⁵), most likely due to the metal binding properties of metallothioneins. Despite its potential toxicity, Tl also showed considerable enrichment: kidney, 4.2 × 10⁴; liver 1.2 × 10⁴; muscle 1.5 × 10⁴. Enrichments of Cs and Rb exceeded those of Tl in all three tissues, suggesting that the chemical similarity of their ionic species (Cs⁺, Rb⁺, Tl⁺) to K⁺ may be the key to their uptake. Lithophile elements of limited solubility in natural waters (Al, Ce, La, Nd) show moderate enrichments, despite the lack of physiological role. The smallest enrichments were found for Sr and Ba, the two TEs which are most abundant in the river. Of the TEs considered essential for animal nutrition, V was the least enriched in tissue relative to water (liver 19×, kidney, 33× and muscle 28×). Despite the lack of physiological function and absence of any known sources of contamination, Al, Ag, Cd, Ce, Cs, La, Pb, Rb, and Tl, are all enriched in beaver tissue, relative to water, by at least three orders of magnitude, due to natural processes. The widespread abundance of beaver in Canada combined with the growing need to manage their numbers in populated regions offer a unique opportunity for monitoring environmental quality in the riparian zone.

Beavers indicate metal pollution away from industrial centers in northeastern Poland

Heavy metals are persistent environmental contaminants, and wild animals are increasingly exposed to the harmful effects of compounds of anthropogenic origin, even in areas distant from industrial centers. We used atomic absorption spectrometry to determine levels of cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) in liver and kidney of wild Eurasian beavers (Castor fiber) in Poland. Cd concentrations in liver (0.21 ± 0.44 μg/g) and in kidney (2.81 ± 4.52 μg/g) were lower in juvenile than in adult beavers. Pb concentrations in liver (0.08 ± 0.03 μg/g) and kidney (0.08 ± 0.03 μg/g) were similar among all individuals, while both Cu and Zn levels were higher in liver (Cu 9.2 ± 4.5 μg/g; Zn 35.7 ± 3.5 μg/g) than in kidney (Cu 3.7 ± 1.1 μg/g; Zn 21.5 ± 2.7 μg/g). Cu levels also differed between juveniles and adults. We reviewed the literature reporting metal concentrations in beavers. Our results indicate metal contamination in beavers away from important industrial emission sources and suggest the natural environment should be regularly monitored to ensure their levels are below recommended, legal values.

The use of chemical markers for the identification of farm escapees in feral mink populations

Variations in the contaminant burden in feral and ranch mink, resulting from differences in their diet, may permit the identification of farm escapees. However, this is only possible in the case of contaminants that accumulate to significantly different levels in the two groups of animals. The main objective of this study was to identify chemical markers whose concentrations differ between feral and ranch mink, by analyzing the accumulation of 13 chemical elements in liver and kidney samples. Total mercury levels were up to 15-fold higher in kidney, and up to 7-fold higher in liver of feral mink compared with ranch mink. The majority of feral mink samples analyzed for mercury, contained concentrations that ranged from 1 to 5 μg/g in kidney (68 %) and from 1 to 5 μg/g in liver (70 %). In comparison, the organs of ranch mink had significantly lower levels of mercury: 95 % of kidney samples had concentrations below 1 μg/g and 82 % of liver samples had concentrations below 1 μg/g. Small geographical variations in Hg levels were observed in mink from the four studied feral populations. Significant differences in Cu concentrations between ranch and feral mink were also detected, with low variation within the two groups. Less pronounced differences were recorded for other chemical elements. These data suggest that Hg and Cu may be used as chemical markers for the identification of first generation mink farm escapees.