MERCURY METHYLATION IN PRISTINE AND ANTHROPOGENICALLY IMPACTED ESTUARIES IN THE NORTHEASTERN US

Sediment cores were taken from 11 northeastern US sites and analyzed for bulk and porewater total mercury (THg), methylmercury (MeHg) and ancillary biogeochemical parameters (organic matter content, porewater DOC and sulfide concentrations). Methylmercury is a known neurotoxin that can affect human health through fish consumption; inorganic mercury (Hg^II) is converted into MeHg mainly in sediments by sulfate reducing bacteria. Methylation has been shown to be affected by physical and biogeochemical factors. The work presented here has the goal to investigate mercury methylation through a gradient of contamination from Wells Maine to Hackensack New Jersey. Methylation and demethylation rates were measured by injecting stable isotopes (²⁰⁰Hg, ²⁰¹Hg and Me¹⁹⁹Hg) into intact cores and incubating for 2 to 7 hours, and cores were then sectioned in 2 cm intervals and flash frozen. THg concentrations span over three orders of magnitude with the lowest concentrations (0.02±0.00 nmol g^-1) found in the pristine sites of Wells ME and the highest concentrations (7.54±1.82 nmol g^-1) in Hackensack NJ (located downstream of Ventron/Velsicol superfund site where 30-400 tons of mercury compounds were released from 1929 to 1974). Here we show that the methylation potential (nmol Hg L^-1 day ^-1), defined as the sediment’s capacity to convert Hg^II into MeHg, is dependent on the interplay between sediments binding capacity and input of mercury, hence both pristine and heavily contaminated sites show the same proficiency to methylate Hg. However, despite a high methylation potential, contaminated sites still show significantly lower %MeHg (about 0.2% in Hackensack NJ and up to 3% in Wells ME) as MeHg production does not compensate for high “legacy” THg content.