Sunlight-Mediated Emission of Elemental Mercury from Soil Amended with Municipal Sewage Sludge

Abstract

We studied the fate and atmospheric emission of mercury (Hg) from soil amended with municipal sewage sludge using a Teflon dynamic flux chamber. A sunlight-mediated, in situ reduction of oxidized Hg to volatile elemental mercury (Hg0) resulted in the atmospheric transport of Hg from land-applied sludge. The reduction of oxidized Hg to Hg0 occurred in a shallow layer of surface soil (<0.5 cm), where light penetration was possible. Sludge application increased soil Hg0 emission by 1−2 orders of magnitude, to a daily average emission rate of ∼100 ng m-2 h-1 greater than background. In the United States and Europe, municipal sewage sludge application to land may be responsible for the flux of ∼5 × 106 g yr-1 of Hg0 to the atmosphere. Considering that municipal sludge is used extensively as a soil amendment worldwide, the land application of sewage sludge warrants further study as a global source of atmospheric Hg. This research calls into question the stability of any land application of Hg-contaminated materials; all surface application of Hg waste represents a potential source of atmospheric Hg0.