MERCURY VOLATILIZATION FROM WETLANDS SEDIMENTS

Field and laboratory experiments show that photochemistry is the dominant factor controlling volatilization fluxes of gaseous elemental mercury from sparsely or non-vegetated wetlands sediments. Sediment-air mercury volatilization fluxes measured at an urban/industrial (Secaucus High School Marsh, New Jersey Meadowlands) and a regional background (Great Bay estuary, Tuckerton, New Jersey) site peaked at midday and were below detection or negative at night. Cumulative mercury fluxes exhibited strong positive correlations with cumulative solar radiation (r² = 0.97, p < 0.01) consistent with a light-driven mercury volatilization efficiency of about 15 ng Hg mol PAR^-1 or about 0.06 ng Hg kJ^-1. The role of UV and visible light in the volatilization of Hg from air-exposed sediments was examined using a dynamic flux chamber. Sediments were collected from a highly Hg-contaminated site (Berry’s Creek estuary), the less mercury-impacted Raritan and Passaic River estuaries, and from mudflats of the freshwater Tivoli South Bay in New York. Mercury volatilization from sediments was 5 to 20 times higher in the presence of visible plus UV-A light than in the dark. Removal of UV light caused Hg volatilization to decrease and UV-A generally drove greater mercury fluxes that UV-B. Across sediment sample, Hg volatilization was inversely related with sediment acid-volatile sulfide concentration (r² = 0.8, p = 0.02), suggesting that mercury sulfide complexes or solids are not the photochemically active form of mercury in these sediments.