Using Raccoons as an Indicator Species for Metal Accumulation across Trophic Levels: A Stable Isotope Approach

The fact that raccoons (Procyon lotor) are an opportunistic omnivore has severely complicated interpretations of contaminant uptake patterns due to the inability to determine the trophic position an individual occupies. Moreover, few studies have examined the relationships between heavy metal bioaccumulation and trophic structure, especially in the terrestrial environment. In this study, the stable isotopes of nitrogen were used to characterize the feeding habits of the raccoon at the population level and to determine whether metal burden was related to trophic feeding structure within a well-defined ecosystem. Raccoon populations were isotopically distinct, and significant positive relationships existed between some trace element contents and δ15N of muscle when site was used as a covariable in a statistical model. Although the transfer of metals through terrestrial ecosystems is complex, our study showed that some of the variation in contaminant body burdens in raccoon populations can be attributed to trophic feeding position and that^{15}\text{N}/{}^{14}\text{N}$ratios of muscle tissue provide a quantitative measure of this process. The potential for using omnivores such as the raccoon, as a sentinel species for contaminant studies, should be explored further since the ambiguity of the relative trophic level an animal occupies can be directly estimated. This provides a more extensive sampling across trophic levels using a single species, which can have broad consequences for ecological risk assessments.