Abstract
Speciation and reactivity of mercury were examined in Berry's Creek estuary downstream of a highly mercury-contaminated U.S. EPA Superfund site during the summers of 2002 and 2003. Surface water samples from Berry's Creek estuary, its confluence with the Hackensack River, and upstream of that confluence were analyzed for total (THg), particulate (PHgT), and dissolved (DHg) mercury, total and particulate monomethylmercury (MeHg), dissolved gaseous mercury (DGM), and bacterial merA gene and transcript abundances. Surface water concentrations of THg in Berry's Creek estuary (210-6800 pM) are among the highest in North America. A downstream gradient of Hg contamination is a permanent feature of Berry's Creek estuary, and the upper estuary appears to be a perennial source of Hg to the lower estuary and the Hackensack River. MeHg concentrations in Berry's Creek surface waters ranged from 2 to 14 pM, with the highest concentrations occurring at a midestuary site 2 km downstream of the tide gate. The suspended particle phase dominated Hg and MeHg speciation throughout this system, accounting for > 90% of THg in Berry's Creek estuary and 35-94% of THg in the Hackensack River. Concentrations of DGM in Berry's Creek estuary (0.1-1.0 pM) are similar to levels of DGM in other much less contaminated estuaries (0.04-0.75 pM). In addition, expression levels of the bacterial mercuric reductase gene, merA, a gene of the inorganic Hg(II)-regulated, mercury resistance (mer) operon, were low throughout Berry's Creek estuary. Thus, despite very high concentrations of mercury in Berry's Creek estuary, relatively low concentrations of DGM and merA gene expression levels indicate limited bioavailability of inorganic Hg in the estuary's surface waters. A system-wide limitation on the bioavailability of inorganic Hg, together with bacterial demethylation activity, may account for observed MeHg concentrations that, although elevated, are lower than expected given the concentrations of THg in this estuary.