Mercury and Selenium in Twelve Cutthroat Trout Tissues from High‐Elevation Colorado Lakes, USA: Intraspecific and Interspecific Comparisons

Abstract

AbstractTotal mercury (THg) and selenium (Se) concentrations were measured in 12 internal and external tissues of three different wild Cutthroat Trout Oncorhynchus clarkii populations occurring in pristine, high‐elevation lakes of Colorado, USA, within watersheds devoid of past and present mining activities. We have not found any comparable baseline data sets. The primary objective was to show how THg and Se bioaccumulate differentially among 12 tissues from Cutthroat Trout occurring in widely distant wilderness areas. A second objective was to compare THg and Se tissue levels in Cutthroat Trout from the pristine habitats to Cutthroat Trout populations elsewhere and to Brown Trout Salmo trutta from urbanized environments. The baseline tissue data from this investigation could be used to gauge other intraspecific and interspecific data sets. Results showed that both THg and Se concentrations were generally highest in the detoxifying organ tissues (liver, kidney, and spleen) and lowest in external tissues (skin and gill). In all three populations, THg levels were highest in kidney and second highest in spleen, while Se was highest in the liver. For 10 of 12 tissues, mean concentrations of THg were lower in Brown Trout from an urban setting than in the Cutthroat Trout from the pristine sites; testes and skin were the exceptional tissues. Threshold effect tissue concentrations of THg for muscle or ovary/eggs were not evident. None of the 34 Cutthroat Trout showed U.S. Environmental Protection Agency Se exceedances for ovary/eggs or muscle tissue. To show the relationship between THg and Se in each tissue, we calculated mean Se : Hg molar ratios, which were lowest in epaxial muscle in all three populations (range = 5.74–30.58), while kidney Se : Hg ratios were also in the low range (17.88–42.63). All tissues had a ratio greater than 1. In spite of atmospheric source‐inputs of both organometalloids to these pristine sites, the trout tissues appear to show no indication of deleterious trends.