Application of a Finnish mutagenicity model to drinking waters in the U.S.

Recent epidemiological studies conducted in Finland have reported a positive correlation between the mutagenicity of chlorinated drinking waters and certain human cancers. In these studies, past exposure to drinking water mutagenicity was assessed using a model developed by Vartiainen et al. [1] based on data collected in Finland. In this model, mutagenicity, as determined in the Ames assay, is a function of the total organic carbon (TOC) concentration of the water, chlorine dose, and to a minor extent, the concentration of ammonia. A study has been initiated to assess the applicability of this model to source waters and water treatment practices in the United States. Water samples were collected from three full-scale treatment plants and one pilot-scale plant. All the plants used chlorine exclusively for disinfection. One full-scale plant used ground water. Surface water sources were used by the other plants. TOC and ammonia concentrations were determined analytically and chlorine doses were obtained from the treatment plants. The water samples were concentrated by XAD resin adsorption for testing in the Ames assay. The observed levels of mutagenicity in the finished waters were 1.5 to 2-fold higher than those predicted using the model as specified in Vartiainen et al. [1]. Consequently, further validation is needed prior to widespread use of the Finnish model to assess exposure to mutagenicity in chlorinated drinking waters in the United States.

Products identified at an alternative disinfection pilot plant.

Many drinking water utilities have recently changed or are seriously considering changing their disinfection practice from chlorine to some alternative treatment process. However, most of these utilities are changing their disinfectants without evaluating chemical impacts. Therefore, a research cooperative agreement was developed with Jefferson Parish, LA, to evaluate four parallel streams treated with four different disinfectants (chlorine, monochloramine, chlorine dioxide, and ozone.) These streams, along with a fifth parallel stream, which was not treated with a disinfectant (control), were passed through both sand and granular activated carbon (GAC). Ozonation reduced the total organic carbon (TOC) and total organic halide (TOX) concentration by 0.3 mg/L and 10 micrograms/L, respectively. The average concentration of TOC for the other disinfectants was comparable to that associated with the nondisinfected stream (3.3 mg/L). The average instantaneous TOX concentration for chlorine dioxide, chloramine, and chlorine disinfection after 30 min contact time increased by 60, 92, and 238 micrograms/L, respectively, from a nondisinfected concentration of 25 micrograms/L. The volatile organics most affected by disinfection (chlorination) were the trihalomethanes. No significant change in concentration was noted after disinfection for the other volatile organics evaluated, such as 1,2-dichlorethane, dichloromethane, trichloroethylene, 1,1,2-trichloroethane, and carbon tetrachloride. Ozonation produced an average concentration reduction of 11 to 84% for most of the nonvolatiles evaluated. Conversely, a concentration increase of 43 to 100% was noted, after chlorination, for some of the nonvolatile organics.