Ecological applications of mercury stable isotopes: From organism level to ecosystem-exchange for mercury

Abstract

Mercury is a toxic and bioaccumulative trace metal that poses serious health threats to humans and wildlife. There are multiple uncertainties concerning mercury sources and exposure pathways to aquatic food webs and exchange for mercury between aquatic and terrestrial ecosystems. Fortunately, the measurement of natural abundances of mercury stable isotopes in environmental samples is beginning to shed new light on the sources and processes for mercury on multiple ecological levels. Here, we illustrate the scientific process of how we have come to use mercury stable isotopes to identify sources and processes of mercury in diverse aquatic ecosystems. First, we draw results from a series of controlled feeding experiments, which have been conducted to understand mercury isotope dynamics during internal distribution and bioaccumulation on an organism level. The absence of mercury isotope fractionation during internal processes has allowed the scientific communities to use fish mercury isotope ratios as a monitoring tool to identify both natural and anthropogenic sources of mercury in aquatic ecosystems. Second, we illustrate the results from previous applications of mercury stable isotopes in lake and lacustrine-terrestrial transition food webs to elucidate ecological variability in mercury sources as well as mercury movements between terrestrial and aquatic ecosystems. In addition to anthropogenic influences, natural ecological processes such as the emergence of aquatic insects can induce substantial amount of mercury movement from aquatic to terrestrial ecosystems. Lastly, we discuss the future prospects of using mercury stable isotopes for ecological applications and introduce complementary tools that can be coupled to enhance the ecological cycling of mercury in aquatic ecosystems.