SPATIAL AND TEMPORAL TRENDS OF PESTICIDE-RESIDUES IN WATER AND PARTICULATES IN THE MISSISSIPPI RIVER PLUME AND THE NORTHWESTERN GULF-OF-MEXICO

Selected herbicides, chlorinated pesticides and polychlorinated biphen yls (PCBs) were measured using GC-MS SLM analysis in dissolved, colloi dal and particulate phases of sea water samples collected seasonally o ver a three-year period. Sample preparation used sequential membrane f iltration and ultrafiltration prior to solid phase extraction (SPE) of the dissolved phase. Chlorinated pesticides and PCBs were rarely dete cted. Herbicides were found primarily in the dissolved and colloidal p hases. Atrazine was ubiquitous over the entire northwestern Gulf of Me xico coastal shelf area in spring, summer and fall. Highest herbicide concentrations occurred in summer and fall, except for alachlor, which was only detected in spring run-off.