MERCURY PHASE SPECIATION IN THE SURFACE WATERS OF 3 TEXAS ESTUARIES -IMPORTANCE OF COLLOIDAL FORMS

Surface-water samples were collected from Galveston Bay, Corpus Christ i 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 is olated with an Amicon cross-flow ultrafiltration system which was rigo rously tested. Filter-passing Hg concentrations (< 0.45 mu m) ranged f rom 0.12 to 13.6 pM, with the highest values in Corpus Christi Bay. Wi thin Galveston and Corpus Christi Bays, filter-passing Hg exhibited no nconservative estuarine mixing behavior. The colloidal Hg fraction ran ged from 12 to 93% of the filter-passing pool and averaged 57 +/- 20%, indicating that a major portion of the operationally defined ''dissol ved'' 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 po ol is associated with large organic macromolecules. The log of the par ticle-water partition coefficient (K-d) ranged from 4.6 to 5.2, and co varied with suspended particulate matter concentrations, likely due to the presence of colloidal Hg.