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Your Environment. Your Health.

Progress Reports: Dartmouth College: Methylmercury Production and Fate in Response to Multiple Environmental Factors

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
View this project in the NIH Research Portfolio Online Reporting Tools (RePORT)

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Progress Reports

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The primary aim of Drs. Celia Chen, Carol Folt, and Robert Mason’s jointly led project is to develop a mechanistic understanding for predicting fate and bioavailability of mercury (Hg), especially as methyl mercury (MeHg), in aquatic ecosystems to fish and shellfish, which are a vital link between human and environmental health.

The research team conducted a second season of field studies (Aim 1) in two Superfund sites, Callahan Mine in Brooksville, ME and the Berlin Hg site in Berlin, NH. Their studies in Callahan mine in summer 2011 extended the extent of their spatial sampling to include sites downstream of the metal source. Their previous results revealed that killifish and Atlantic silversides had elevated tissue concentrations (up to 300X higher) of copper, lead, zinc, and cadmium in the Goose Pond mine sites relative to reference sites at Horseshoe cove. Concentrations of the four metals in water were 4-8 times higher in the contaminated site than the reference site. The team presented their findings at a public meeting in Brooksville, ME organized by Mr. Ed Hathaway, the Remedial Project Manager (RPM) for the site.

In the Berlin Hg site, the team added an additional reference site above the Hg source on the Androscoggin River for a total of two sites above and 4 sites below the Hg source. They conducted sampling in coordination with the USGS, USEPA (RPM: Mr. Darryl Luce), and the USFWS. Data from the previous year indicated that certain predatory species increased in MeHg concentration at sites farther downstream from the Hg source. The sampling in 2011 allowed a more complete spatial coverage of common species groups across sites.

Experiments quantifying MeHg and HgII bioaccumulation in the benthic amphipod Leptocheirus plumulosus (Aim 2) have been conducted using stable isotopes of Hg in collaboration with the TEA core. In two different experiments, amphipods consistently bioaccumulated 105 times more MeHg from algae made available in the water column vs. from the sediments. The experiments demonstrate the importance of pelagic exposure to contaminants for these benthic infauna.

The researchers completed two month-long experiments to examine the effect of temperature on MeHg uptake by killifish fed equivalent amounts of food and found that MeHg bioaccumulation increased at higher temperatures (Aim 3). The effect was not explained by fish growth or amount of food ingested. Moreover, these results were consistent with field mesocosm experiments conducted in two field seasons where killifish at higher temperatures bioaccumulated higher levels of MeHg. These differences were not explained by variation in salinity, sediment MeHg, or organic carbon in sediments. These results provide both field and laboratory evidence that increased temperatures over ranges predicted to occur due to climate change can result in increased bioaccumulation of MeHg into estuarine food webs.

The research team also completed development of the MeHg “mer-lux bioreporter” (a genetically modified bacteria that emits light in response to the uptake of MeHg) to examine the impact of speciation on MeHg uptake. This innovation can be used to examine controls over both uptake of Hg into methylating organisms, uptake by demethylators as well as uptake at the base of the food chain.

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