MERCURY ASSOCIATED WITH COLLOIDAL MATERIAL IN AN ESTUARINE AND AN OPEN-OCEAN ENVIRONMENT

We have used traditional filtration and tangential flow ultrafiltratio n to isolate mercury into 4 size fractions: particulate (> 0.4 mu m), high molecular weight (> 10 kD, 1kD = 1000 daltons), medium molecular weight (1-10 kD), and low molecular weight (< 1 kD). Samples with vary ing salinities were collected from the Ochlockonee River/Estuary in Ja nuary 1993 and 1994. A small set of open-ocean samples was collected a nd processed during the 1993 Baseline Survey Expedition for Trace Cont aminants in the Atlantic Ocean, sponsored by the Intergovernmental Oce anographic Commission (IOC). Concentrations of total dissolved Hg down the estuary ranged from 30 to 3 pM. Total dissolved Hg measurements f rom the IOC cruise ranged from 0.5 to 2.5 pM. Colloidal Hg (> 1 kD) re presented 35-87% of the total dissolved Hg within the estuary and 10-5 0% of the total dissolved Hg in the North Atlantic. Equilibrium Hg spe ciation modeling supports speculation that colloidal Hg is bound by th iol-type functional groups associated with the colloidal organic carbo n.