Dimethylmercury: A Source of Monomethylmercury in Fog Mechelle Johnson, BS in progress, Math and Science, Kirkwood Community College, Cedar Rapids, IA and Kenneth Coale, PhD, Chemical Oceanography, Moss Landing Marine Laboratories, Moss Landing, CA

Dimethylmercury (DMHg) and monomethylmercury (MMHg) are two naturally occurring neurotoxins found in marine systems. MMHg bioaccumulates in tissues causing increased concentrations in the food web. Recent studies show that maritime advective fog transports MMHg from the oceans to land where terrestrial biota also accumulate this neurotoxin. Gaseous evasion of DMHg has recently been proposed as a potential source of MMHg to fog, but the mechanism of its conversion remains unknown. In this study we show that photodemethylation is a factor in the conversion of DMHg to MMHg, thus a potential source of MMHg in fog. Seawater samples were collected from a CTD rosette in two upwelling zones in the northeastern Pacific Ocean. Samples were incubated both in the sunlight and in darkness and DMHg was subsequently analyzed. The difference between light and dark-incubated samples inform the lability of MMHg to photolysis. Results show whereas photodemethylation doesn’t occur in natural seawater, it does occur at significant rates under acidic conditions. Since fog water is acidic, these findings suggest photodemethylation may occur atmospherically, once absorbed in fog. These experiments inform the source and cycling of mercury from oceans to terrestrial ecosystems.