Mercury and methylmercury in Hudson River sediment: impact of tidal resuspension on partitioning and methylation

The Hudson River estuary is highly polluted with heavy metals, polychlorinated biphenyls (PCBs) and PAHs. The sediment of the estuary is subjected to substantial erosion and redeposition resulting in a complex redistribution of sediment annually. Understanding the fate of heavy metals during tidal resuspension is crucial to assessing the long-term fate of pollutants in the estuary. We examined the impact of sediment resuspension on Hg cycling within the estuarine turbidity maximum (ETM) of the Hudson River estuary. Concentrations of total mercury (T-Hg) in the ETM sediment averaged 5 nM g−1 in the upper 25 cm of sediment. We measured no desorption of Hg from the sediment during a tidal cycle. Therefore, release of mercury from the ETM of the Hudson River is dependent on sediment efflux. Methylmercury (MeHg) concentrations average 6.5 pM g−1 and although high for estuarine sediments, the percent T-Hg that is MeHg was lower than what has been observed in less contaminated systems. Mercury methylation is active throughout the upper 25 cm resulting in a large pool of MeHg in ETM sediment.