Degradation of Pesticides by Chlorination According to Their Basic Structures

One hundred and one pesticides listed as “Complementary Items for Setting the Targets for Water Quality Management in Japan” were divided into 16 groups on the basis of their structures. The degradation of 96 pesticides and 5 oxidation by-products in chlorination was studied to determine the potential of the purification process. Pesticides containing sulfur (S) were easily degraded; for 38 pesticides out of 46 examined pesticides, only 50 % or less of their original concentration remained after 4 hours. On the other hand, pesticides without S were hardly degraded; for 45 pesticides out of 50 examined pesticides, more than 50 % of their original concentration remained even after 24 hours. Thus, the potential for degradation of the pesticides by chlorination can be approximated by the presence or absence of S in their chemical formulae. Oxons (P=O), which are oxidation by-products of organophosphate pesticides containing P=S, were hardly degraded. Therefore, oxons may remain in chlorinated water for a long time.