Application of diffusive gradients in thin films and core centrifugation methods to determine inorganic mercury and monomethylmercury profiles in sediment porewater.

A diffusive gradient in thin films (DGT) is an in situ sampling technique for the quantitative analysis of contaminant concentrations that is based on the diffusion and adsorption of contaminants on to resin gels. In the present study, a DGT technique was applied to measure total mercury (Hg) and monomethylmercury (MMHg) concentrations in lake and coastal sediment porewaters and compare them with those from ex situ sediment centrifugation. To calculate the total Hg and MMHg concentrations in porewater using the DGT method, the diffusion coefficients of Hg species in a diffusive gel medium was first determined, and then total Hg and MMHg depth profiles were measured using the experimentally determined diffusion coefficients. Using the diffusion coefficients for artificial lake and estuarine waters containing inorganic salts, rather than those for lake and estuarine waters containing Suwannee River humic acid (∼5 mg C L(-1) ), the DGT method demonstrated similar Hg and MMHg profiles to those using the centrifugation method. Based on the need for fine vertical resolution and high metal concentrations to be collected, DGT is suggested to be a reliable method for determining Hg(II) and MMHg depth profiles in sediment porewater.