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(28-09) Chemical Softening and Chlorination: Implications on Drinking Water Exposure Assessment of Pesticides. Pisigan, Rodolfo*,1, Speth, Thomas2, 1 Office of Pesticide Programs, U.S. EPA, Washington, DC2 National Risk Management Research Lab., U.S. EPA, Cincinnati, OH ABSTRACT- The removal and transformation of pesticides in drinking-water treatment plants is important in evaluating the drinking water exposure assessment of pesticides. A laboratory study was conducted to determine the effects of chemical softening and disinfection by chlorination on the concentrations of certain organophosphate, carbamate, organochlorine, triazine, amide, dinitroaniline, and uracil pesticides in drinking water. Raw well water from a treatment plant was spiked with 20 - 100 ug/L of pesticides. In the softening jar tests, the raw water with 9 pesticides was treated with 150 and 300 mg/L of lime which corresponded to conventional and magnesium softening conditions. In the chlorination jar tests, the same raw water with another set of different pesticides was chlorinated at Uniform Formation Conditions. Before and after treatment, the concentrations of the pesticides were analyzed by GC/MS, GC/ECD, and HPLC with fluorescence detector. Thiodicarb, malathion, and methomyl were removed by softening by 90 - 99%. Softening removed about 20% of phorate while no removal was observed for captan, iprodione, trifluralin, bentazon, or dichlorprop. Significant removals (90-99%) by chlorine treatment were observed for bromacil, chlorpyrifos, metribuzin, molinate, aldicarb, and prometryne. About 50% of the combined concentration of endosulfan I and II was removed. Lower removals of hexazinon( 6%) and lindane (3%) were observed. Hydrolytic and oxidative transformations were responsible for the concentration decreases. Some transformation products may have different toxicological properties that need to be considered for drinking water exposure assessment. Oxons potentially generated from organophosphate oxidation may persist in the treated water and consequently may pose a health concern. Key words: Softening, Chlorination, Pesticides, Assessment |
