Selenium, Mercury, and Their Molar Ratio in Sportfish from Drinking Water Reservoirs.

Tara Johnson,Thomas Kwak,W Cope,Catherine Leprevost

doi:10.3390/ijerph15091864

Abstract

Mercury (Hg) bioaccumulates in aquatic ecosystems and may pose a risk to humans who consume fish. Selenium (Se) has the ability to reduce Hg toxicity, but the current guidance for human consumption of fish is based on Hg concentration alone. The purpose of the present study was to examine the relationship between Se and Hg in freshwater sportfish, for which there is a paucity of existing data. We collected three species of fish from different trophic positions from two drinking water reservoirs in central North Carolina, USA, to assess Hg and Se concentrations in relation to fish total length and to compare two measures of the protective ability of Se, the Se:Hg molar ratio and Se health benefit value (HBVSe), to current guidance for Hg. According to the Se:Hg molar ratio, all of the low trophic position fish sampled and the middle trophic position fish sampled from one of the reservoirs were safe for consumption. The same number of fish were considered safe using the HBVSe. More fish were deemed unsafe when using the Se:Hg molar ratio and HBVSe than were considered unsafe when using the U.S. Environmental Protection Agency (USEPA) Hg threshold. These findings suggest that the measures of Se protection may be unnecessarily conservative or that the USEPA Hg threshold may not be sufficiently protective of human health, especially the health of sensitive populations like pregnant or nursing mothers and young children. Future examination of the Se:Hg molar ratio and HBVSe from a variety of fish tissue samples would help refine the accuracy of these measures so that they may be appropriately utilized in ecological and human health risk assessment.

Highlights

Mercury (Hg) is a naturally occurring element that exists in the environment in various states, including elemental, inorganic, and organic
The increase in Hg concentration appeared to reflect the increase in total length from one species to the and within each species, and supported the previous finding that length is correlated with Hg concentration [7]
We found that Hg concentration increased with total length (p < 0.05 for crappie and largemouth bass in both reservoirs) and that many more fish in Lake Michie exceeded the U.S. Environmental Protection Agency (USEPA) fish residue criterion than in Jordan Lake

Summary

Introduction

Mercury (Hg) is a naturally occurring element that exists in the environment in various states, including elemental, inorganic, and organic. The biogeochemical processes that transition Hg into and out of its various states and transport it throughout the environment can occur naturally, but anthropogenic actions, in particular the burning of coal for electricity, impact these natural processes [1]. Hg is a widespread contaminant in aquatic ecosystems resulting from wide-scale combustion of coal for electricity with variation among water bodies [2] and leading to fish consumption advisories throughout the USA and abroad [3,4]. Hg in the organic form of methylmercury (hereafter Hg) poses the greatest threat to aquatic organisms, such as fish, invertebrates, and waterfowl, and to the humans that consume them. Dietary exposure to Hg occurs through ingestion of contaminated fish and can result in bioaccumulation within species

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