Reactivity of several classes of pesticides with chlorine-containing disinfectants

Pesticide contamination of water resources has aroused wide concerns. The fate of pesticides during water treatment processes (especially disinfection) may affect the safety of drinking water since pesticides and their byproducts are usually toxic. Long-term exposure to these contaminants, even at low levels, may result in health problems. This work was to investigate the reactivity of 8 classes of pesticides, which are either commonly used or frequently detected in water sources, with three chlorine-containing disinfectants including free chlorine (NaOCl), monochloramine (NH2Cl) and chlorine dioxide (ClO2)Experiments were carried out at a disinfectant to pesticide molar ratio of 200: 1, pH 6.58 similar to 6.84, and ambient temperature (25 +/- 3 degrees C). Results show that bromacil, dimethoate, aldicarb, aldicarb sulfoxide and methiocarb were degraded quickly by NaOCl within 2 min, and 98% of oxamyl was degraded within 60 min. NH2Cl could only remove aldicarb and methiocarb within 1 and 4 min, respectively. ClO2 could degrade 100% of bromacil within 10 min, and 75% of aldicarb and 81% of methiocarb after 120 min. Fig. 1 shows the degradation curves of the pesticides mentioned above. However, all other pesticides could not react or exhibited low reactivity towards these disinfectants. Therefore, only a few pesticides may be degraded (or transformed) by these disinfectants during drinking water treatment, while most of the, pesticides will persist in the drinking water.