Chlorpyrifos transformation by aqueous chlorine in the presence of bromide and natural organic matter.

The aqueous chlorination of chlorpyrifos (CP) was investigated in the presence of bromide and natural organic matter (NOM), which were identified as naturally occurring aqueous constituents that could affect CP transformation rates to the toxic product chlorpyrifos oxon (CPO). Bromide can be oxidized by chlorine to form hypobromous acid (HOBr), which was found to oxidize CP at a rate that was 3 orders of magnitude faster than was the case with chlorine: k HOBr,CP=1.14 (+/-0.21)x10(9) M(-1) h(-1) and k HOCl,CP=1.72x10(6) M(-1) h(-1), respectively. Similar to previous findings with the hypochlorite ion, hypobromite (OBr-) was found to accelerate the hydrolysis of CP and CPO: kOBr,CP=965 (+/-110) M(-1) h(-1) and kOBr,CPO=1390 (+/-160) M(-1) h(-1), respectively. Treated water from the Athens-Clarke County (ACC) water treatment plant in Athens, GA, was used in some of the experiments as a NOM source. A mechanistic model was used to adequately predict the loss of CP as well as the formation of CPO and the hydrolysis product 3,5,6-trichloro-2-pyridinol (TCP) in the presence of the ACC water.