Screening Study and Byproduct Determination for Pesticide Degradation during Disinfection in Water Treatment

This study identifies combinations of over 60 pesticides and 8 common disinfectants (or conditions) including free chlorine, monochloramine, chlorine dioxide, permanganate, ozone, hydrogen peroxide, photo-oxidation with UV at 254 nm, and hydrolysis at pH 2, pH 7, and pH 12, that exhibit the potential for pesticide degradate formation. Initial parent pesticide concentrations were less than 25 µg/L, and treatment dosages were on the order of typical exposures used during water treatment. The reaction media was buffered Milli-Q water adjusted to pH 6.6 and 8.6. The reactivity of pesticide/oxidant pairs were categorized as highly reactive (\u3e50% parent removal), moderately reactive (20-50% parent removal), and slightly reactive (\u3c20% parent removal). The screening study results indicate the most reactive combinations of transformation agents and pesticides leading to degradates formation in water utilities. Based upon exposure (e.g., occurrence, usage), reactivity, toxicity and other criteria, several of the most important systems were studied in detail. The identity and pathway of the major metabolites were determined using Ion Trap LC/MS, GC/MS, and other techniques. The data presented helps identify situations of potentially harmful pesticide degradate formation in common drinking water treatment systems. Includes 19 references, table