Tracing Legacy Mercury Sources in Aquatic Ecosystems Using Mercury Stable Isotopes.

Abstract

Mercury (Hg) is a neurotoxic pollutant that exists in both inorganic (Hg0, Hg2+) and organo-metallic (monomethyl mercury: MMHg) chemical forms. Inorganic Hg (IHg) has been released to aquatic environments during its historical use in mining and industry. In these environments IHg can be converted to MMHg, a potent developmental neurotoxin that bioaccumulates in the food web and can pose a risk to humans and wildlife. Therefore, identifying the distribution of legacy IHg sources, and understanding their transformation to MMHg is of great interest. In this dissertation, we report Hg stable isotope ratios in sediment and food webs from North American streams contaminated by legacy Hg sources. In Chapter 2 and 3, we use Hg isotopes in stream and estuarine sediment to fingerprint multiple Hg sources and trace their transport and deposition. In Chapters 4 and 5, we measure Hg isotopes in both sediment and aquatic food webs to identify MMHg formation, degradation and exposure pathways in streams and wetlands contaminated by historical gold and mercury mining. This work demonstrates that Hg stable isotope measurements can be used to trace the spatial and temporal distribution of legacy Hg sources and identify relevant biogeochemical processes and exposure pathways leading to MMHg bioaccumulation in aquatic environments.