Mercury in Aquatic Systems of the Gulf Islands National Seashore, Southeastern USA

Abstract

This study reports on levels and speciation of mercury (Hg) in different environmental compartments of selected park units in the Gulf Islands National Seashore (USA), and on potential rates of methyl-Hg (MMHg) formation and degradation in sediments. In the aqueous phase, total (THg) and MMHg concentrations ranged from 0.19 to 14.26 ng/L (n=32) and <0.5 to 1.58 ng/L (n=32), respectively. In sediments, THg concentrations varied from 6.4 to 838 ng/g wet weight (n=32), while MMHg levels ranged from 1 to 17 ng/g (n=21). Potential rates of MMHg formation (M) and degradation (D) in sediments resulted in M/D ratios that were mostly <1, suggesting a low tendency for accumulation of produced MMHg in these sediments. Finally, the detection of THg concentrations averaging 168.18 ± 48 ng/g in tissues of Ulva prolifera points to the tendency of Hg bioaccumulation, and therefore, the need for investigation of Hg levels in fish and shellfish. Overall, our findings show that coastal waters and sediments with very low Hg concentrations could support Hg-contaminated biota, which should justify the need for stringent regulations on Hg introduction to natural systems at both local and regional levels. @JASEM