Superfund Research Program
Methylmercury Production and Fate in Response to Multiple Environmental Factors
Project Leader: Celia Y. Chen
Grant Number: P42ES007373
Funding Period: 2000-2021
Final Progress Reports
Aims: The primary aim of this project is to develop a mechanistic understanding for predicting fate and bioavailability of Hg, especially as methylmercury (MeHg), in aquatic ecosystems to fish and shellfish, which are a vital link between human health and environmental health.
Studies and results: In early 2013 Dr.'s Chen, Folt, and Mason and their research team completed studies proposed in the application funded from 2008-2013. This included publications on mercury dynamics across a gradient of estuarine sites from contaminated to pristine. The team published findings on sediment biogeochemistry effects on methylmercury production and bioaccumulation in aquatic food webs rivers and estuaries.
Analysis of mercury methylation/demethylation experiments across a gradient of estuarine sites in ME and NH has revealed findings that alter the current paradigm about mercury methylation and organic carbon. Their finding was contrary to the accepted role of sediment organic matter as an inhibitor of methylation and suggests the importance of other site-specific factors in Hg methylation. This research indicates that Hg methylation could be even higher than previously thought in highly contaminated Superfund sites where both organic matter and mercury concentrations are elevated. Another manuscript that was just recently accepted shows that sulfur (S) is a better predictor of total Hg than the sediment organic matter across multiple estuaries. While organic matter and S are interchangeable in predicting total Hg in small scale studies, on a larger scale, S is the simplest and most effective variable to measure.
Across a contamination gradient in estuaries from ME to NJ, this project has shown that fish MeHg concentrations were better predicted by aqueous rather than sediment concentrations suggesting that the chemical flux of MeHg from sediments to the water column is important to bioaccumulation in these food webs leading to human exposure. In addition, the team's field and laboratory experiments show that MeHg bioaccumulation in the model fish species, Fundulus heteroclitus, increases with increasing temperature which has important implications for MeHg fate under climate change scenarios.
This project collaborated with the Research Translation Core (RTC) in leading the C-MERC (Coastal and Marine Mercury Ecosystem Research Collaborative) that produced in 2012 two special issues on Hg in the peer-reviewed journals, Environmental Health Perspectives and Environmental Research as well as a synthesis report entitled, "Sources to Seafood" for policy-makers. PI Chen took the report to the International Negotiating Conference for the Global Mercury Treaty in Geneva Switzerland in January 2013 and presented on C-MERC and the synthesis report at the International Conference on Mercury as a Global Pollutant in Edinburgh Scotland (July 2013). In addition, 10 posters and presentations -related to the Bioaccumulation and Trophic Transfer of Mercury in Aquatic Food Webs project were also presented at the ICMGP.
The team of researcher's completed their work with the Remediation Project Managers from USEPA Region 1 to investigate the fate of metals at the Berlin NH Hg Superfund site and the Brooksville ME Superfund site. Their research at the Berlin Superfund site indicates that the source of inorganic Hg into the adjacent river results in a local hotspot of inorganic mercury in sediments and water as well as increased bioaccumulation in aquatic invertebrates but other higher trophic level species do not appear to be affected (Buckman, in prep). The data from the Brooksville Superfund site indicates that metals (Cu, Zn, Cd, Pb) from the sediment and tailings pile are being bioaccumulated by forage fish in the adjacent estuary due to either constant flux of metals from the sediments or leaching from the tailings pile. Both studies demonstrate the importance of linking abiotic and biotic compartments in contaminated ecosystems in order to understand the potential for wildlife and human exposure to those contaminants.
In preparation for the renewal, if funded, the team conducted pilot field studies at estuarine sites in MD, CT, and ME to compare MeHg production and bioaccumulation in estuaries varying in seasonal temperature ranges and in sediment organic matter. They have also conducted MeHg bioaccumulation experiments across environmentally relevant temperature and salinity ranges using their model amphipod species, Leptocheirus plumulosus.
Significance: This project investigates the fate of metals, particularly Hg, in freshwater and estuarine ecosystems where fish that are consumed by humans bioaccumulate contaminants. Hg is the third most important contaminant on the CERCLA Priority List of Hazardous Substances and in its organic form, MeHg, is a potent toxin with neurological, immunological, and cardiovascular effects. Marine systems are the most important sources of human exposure to MeHg as consumption of marine fish and shellfish is the most common exposure vector. Therefore, it is of critical importance to understand the environmental and ecological factors controlling the transformation of inorganic mercury to MeHg and the bioaccumulation and trophic transfer in these aquatic food webs to fish that humans consume.
Plans: If funded, the team of researchers will begin to conduct studies proposed in the new aims of the renewal application.