Formation and removal of pesticides and pesticide transformation products during water treatment

A comprehensive suite of over 60 pesticides (herbicides, insecticides, and fungicides) representing a variety of classes at environmentally relevant concentrations (low µg/L) were screened for reactivity under typical drinking water conditions and dosages. The most common oxidants/transformation agents in water treatment systems were examined for reactivity including free and combined chlorine, chlorine dioxide, permanganate, ozone, hydrogen peroxide, ultraviolet radiation, and high pH (alkaline hydrolysis). Due to the broad nature of the study, pesticide compounds were analyzed as multiple mixes broken into two groups based on analytical methods, those analyzed by GC/ECD and those by LC/MS. Combinations of reactive disinfectant/oxidant and pesticide most likely to lead to significant degradate formation within water utilities were quantitatively identified. Results from the screening study portion of this work were prioritized based on reactivity, anticipated occurrence, anticipated toxicity implications, and other considerations. The most important systems were then studied in detail to determine major degradation products, kinetic rates, and other information specific to the disinfectant/oxidant - pesticide combination. One detailed system in particular, fipronil and several commonly utilized oxidants, was investigated. Findings indicate that fipronil is readily degraded by free chlorine, chlorine dioxide and permanganate but not by monochloramine. Furthermore, permanganate oxidation produces a degradation byproduct, fipronil sulfone, which accumulates within the system if no other oxidant is utilized. This body of work provides highly valuable information on the most reactive oxidant/pesticides systems, signifying the highest potential for degradation formation. Additionally, detailed information on a widely used insecticide is supplied. This work helps to direct future research and provides treatment facilities guidance as to relative removals of problematic pesticide compounds as well as an initial alert to future potential problems arising from degradate formation --Abstract, page iv