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CHLORPYRIFOS TRANSFORMATION BY AQUEOUS CHLORINE IN THE PRESENCE OF BROMIDE AND NATURAL ORGANIC MATTER
DUIRK, S. E., C. TARR, AND T. W. COLLETTE. CHLORPYRIFOS TRANSFORMATION BY AQUEOUS CHLORINE IN THE PRESENCE OF BROMIDE AND NATURAL ORGANIC MATTER. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. American Chemical Society, Washington, DC, 56(4):1328-1335, (2008).
Conditions for treatment of DW vary widely. However, most all processes involve some form of conventional treatment (filtration, etc.), and some form of disinfection. Also, systems sometimes use various other treatments, including softening by the addition of a base. Treatment processes can have profound effects on the pesticides and toxics that occur in DW sources. For example, hydrophobic chemicals may be partially removed by conventional treatment, however, percent removal can vary significantly depending on conditions. On the other hand, conventional treatment generally has little or no effect on hydrophilic chemicals.
If pollutants are not removed by conventional treatment, they may be altered by other treatment processes. For example, disinfection can transform some chemicals via oxidation; however, little is known about the identity of products formed by this process. Limited information shows that disinfection can yield products that are more toxic than the parent. Also, some chemicals are transformed via base-catalyzed hydrolysis during the softening process. The nature and extent of transformations vary greatly depending on treatment conditions.
EPA Program Offices recognize that treatment often has a large effect on pesticides and toxics that occur in DW sources; and they have articulated a need to incorporate these effects into risk assessments. This task will provide regulators with methods, tools, and databases to forecast the fate of pesticides and toxics during DW treatment. The early task outputs will be chemical-specific information from bench-scale studies that simulate disinfection and softening. However, all task efforts will be focused on the long-range goal of providing predictive models for chemical removal and transformation that cross chemical class and treatment conditions. Early experiments will provide information to elucidate transformation mechanisms. Next, we will investigate effects of varying treatment conditions and chemical speciation. This strategy will lead to broadly applicable tools for forecasting fate for a wide range of chemicals. Finally, we envision that the output of our predictive fate tools will be used as input into models developed under the ORD Computational Toxicology Initiative. In this fashion, the final contaminants and concentrations predicted by our models to occur in finished DW can then be considered for toxic potential. This will provide Program Offices with an integrated system for risk assessment and management for the pesticides and toxics in drinking water.
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 impact 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 three orders of magnitude faster than was the case with chlorine. Similar to previous findings with the hypochlorite ion, hypobromite (OBr) was found to accelerate the hydrolysis of CP and CPO. Treated water from the Athens Clarke County (ACC) water treatment plant in Athens, Georgia, USA 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.