Mercury Levels, Speciation, and Fate in Gulf Islands National Seashore Aquatic Systems

Youn, Sejin; Bonzongo, Jean-Claude

The Gulf Islands National Seashore in southeastern USA gets on average about five million visitors every year. Amongst the multiple recreational activities attracting these visitors are both recreational and subsistence fishing. Unfortunately, mercury (Hg) levels in different environmental compartments of this park have not been studied and the potential for exposure to Hg by consumption of fish caught in the park’s waters remains unknown. Following the discovery of high Hg levels in fish caught from Mobile Bay in Alabama, and based on the location of the Gulf Islands National Seashore park, the National Park Service (NPS) decided to conduct a set of studies that would help park managers to take appropriate decisions with regard to health risks to people visiting the park. In this study, we hypothesized that “Hg reaching the park waters from both runoffs and atmospheric deposition could result in fish Hg levels above safe limits, and therefore, to human exposure if the aquatic systems in and around the park have high potentials for methyl-Hg (MeHg) production and accumulation”. This study was therefore initiated to assess both the levels and the extent of Hg contamination in different environmental compartments of selected sites within the park and to determine the potential for sediments collected from these sites to produce and accumulate MeHg. These objectives were addressed by a combination of field observational studies and laboratory investigations of Hg methylation and MeHg demethylation. Besides a few exceptions (e.g., sites with THg levels >10 ng/L), obtained results show rather low total Hg (THg) and MeHg levels in both water and sediment collected from most of the park units, with most of the determined concentrations falling within the range of background values reported in the literature. In addition, the ability of sampled sediments to produce and accumulate MeHg appears to be low as they tend to favor the degradation of MeHg over its production. Unfortunately, fish samples were not available for this first portion of the study. Despite the above observed favorable trends, our recommendation is that the complexity of Hg bioaccumulation and biomagnification processes in aquatic food chains warrants an investigation of Hg levels in fish and shellfish as the only effective way to address the issue of fish contamination in aquatic systems of the Gulf Islands National Seashore

Mercury Levels, Speciation, and Fate in Gulf Islands National Seashore Aquatic Systems

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