DISTRIBUTIONS AND PARTITIONING OF MERCURY AND METHYLMERCURY IN ESTUARIES OF THE NORTHEASTERN US

Elevated levels of methylmercury (MeHg) in fish is a global human health and environmental concern, and coastal systems, which are little studied, could be important conduits for the production and trophic transfer of MeHg. Water, sediment, and biota were sampled to study MeHg production and bioaccumulation in both contaminated and pristine estuaries from Maine to New Jersey in 2008 and 2009. Sediment measurements (core and grab samples) included solid phase and pore water MeHg and total mercury (Hg), rates of methylation using stable isotopes, organic matter content (LOI), pore water DOC, and sulfide (S^2-, AVS/CRS). Water column parameters (surface and bottom waters) included dissolved and particulate MeHg and total Hg, TSS, nutrients, and DOC. Sediment total Hg spanned 3 orders of magnitude among estuarine sites (0.01 to 20 nmol g^-1), and was well correlated with organic matter (LOI). Sediment MeHg ranged from 0.2 to 50 pmol g^-1 among locations, and both MeHg and total Hg were elevated in anthropogenically impacted areas (e.g., Mill Creek, NJ) as compared to rural/residential estuaries (e.g., Waquoit Bay, MA). Among intensively sampled locations (Wells, ME; Portsmouth, NH; Hackensack, NJ), water column filtered total Hg ranged from 0.3 pM to 3.5 pM and was highest at Portsmouth. Both filtered MeHg (<0.1 to 0.5 pM) and particulate MeHg (0.02 to 2.9 pM) were highest at Hackensack and reduced at Wells. Average sediment MeHg was highest (7.9 to 39 pmol g^-1; 0.4 to 0.6% of total Hg [%MeHg]) in cores (8 cm) from the contaminated Hackensack site, and less at Portsmouth (3.4 to 7.7 pmol g^-1; 0.2 to 0.3% MeHg) and Wells (0.2 to 2.6 pmol g^-1; 2.0 to 2.8% MeHg). Elevated %MeHg at the Wells site was associated with comparatively low levels of sediment total Hg (0.01 to 0.1 nmol g^-1) and reduced organic matter (0.5 to 3.7%). Increased production of MeHg in Wells sediments are indicated by lower pore water inorganic Hg (HgII) partitioning coefficients (K_D; 1.7 to 3.1 L kg^-1), indicating greater bioavailability of HgII to methylating bacteria. Preliminary observations suggest that organic matter is the main control over MeHg production among the geographically separated estuaries included in this study. We will discuss the relationships between water column and sediment constituents in the presentation.