Degradation of pesticides by chlorination during water purification

An attempt was made to detect pesticides remaining in river water and raw water for tap water supply, located in an agricultural area. As a result, 11 kinds of pesticides were detected. The residual pesticides in water were also degraded to by-products, since chlorine is a strong oxidant that does not exist in natural conditions. Organophosphate pesticides containing P = S bonds were easily degraded and produced oxons (P = O) as a primary by-product. Thiobencarb was also degraded by chlorination, producing chlorobenzyl alcohol, chlorotoluene, chlorobenzyl chloride, chlorobenzoic acid and chlorobenzyl aldehyde as chlorination by-products. Also, when thiobencarb was detected in raw water, the above by-products were detected in the filtered water in a purification plant for water supply. Therefore, the management and control of pesticides in drinking water and ambient water quality management should include testing for chlorination by-products.