Mercury phase speciation in the surface waters of three Texas estuaries: Importance of colloidal forms

Abstract

Surface-water samples were collected from Galveston Bay, Corpus Christi Bay, Sabine Lake, and Laguna Madre and analyzed for Hg in the <0.45-mu m, 0.45-mu m-1-kDa, and <1-kDa fractions. Colloidal material was isolated with an Amicon cross-flow ultrafiltration system which was rigorously tested. Filter-passing Hg concentrations (< 0.45 mu m) ranged from 0.12 to 13.6 pM, with the highest values in Corpus Christi Bay. Within Galveston and Corpus Christi Bays, filter-passing Hg exhibited nonconservative estuarine mixing behavior. The colloidal Hg fraction ranged from 12 to 93% of the filter-passing pool and averaged 57 +/- 20%, indicating that a major portion of the operationally defined ''dissolved'' Hg is associated with submicron particles and macromolecules >1 kDa. Colloidal Hg covaries with colloidal organic C concentrations in Galveston Bay waters, suggesting that most of the filter-passing Hg pool is associated with large organic macromolecules. The log of the particle-water partition coefficient (K-d) ranged from 4.6 to 5.2, and covaried with suspended particulate matter concentrations, likely due to the presence of colloidal Hg