Assessing Mercury Levels in Fish Tissue, Duck Valley Reservation, Idaho and Nevada

Introduction

In May 2007, the U.S. Geological Survey collaborated with the Shoshone-Paiute Tribes to evaluate mercury concentration in rainbow trout from Mountain View, Lake Billy Shaw, Sheep Creek, and Wildhorse reservoirs. These reservoirs are valued trout fishery resources to the Tribes for commercial and recreational benefits that may be threatened by mercury contamination. Bioaccumulation of methylmercury in the aquatic food chain can yield concentrations in fish that are more than a million times greater than concentrations in water.

Due to mercury’s potential toxicity to humans, more information on the occurrence of mercury concentrations in fish will help to determine whether mercury poses a potential exposure risk to Tribal members and the general public. Sources of the mercury contamination are not well-quantified; however, they likely include coal-fired power plants, mining operations, and natural sources. Inorganic mercury from these sources is converted to organic forms by anaerobic bacteria in a process called methylation. Fish in shallow reservoirs and wetlands are particularly susceptible to bioaccumulation of mercury because they offer favorable habitats for the methylation process to occur.