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 biphenyls (PCBs) were measured using GC-MS SLM analysis in dissolved, colloidal and particulate phases of sea water samples collected seasonally over a three-year period. Sample preparation used sequential membrane filtration and ultrafiltration prior to solid phase extraction (SPE) of the dissolved phase. Chlorinated pesticides and PCBs were rarely detected. Herbicides were found primarily in the dissolved and colloidal phases. Atrazine was ubiquitous over the entire northwestern Gulf of Mexico 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.