Disinfection By-products: A Question of Balance

By all accounts, disinfection of drinking water is one of the major public health triumphs of the 20th century. No human endeavor, however, is without risk; more than 30 years ago it was determined that chlori­ nation of water resulted in formation of disinfection by­products (DBPs). Several of these, such as the trihalomethanes (THMs) and haloacetic acids (HAAs), were subsequently observed to produce cancer in animal models and to have other toxic end points, such as reproduc­ tive and developmental effects. Moreover, some of these end points have been associated with consumption of disinfected water in human populations; in particular, an elevated risk for bladder cancer has been observed in published epidemiology studies. Many governments have set limits on the amount of DBPs that may be present in drinking water produced by public systems. The U.S. Environmental Protection Agency (EPA), for exam­ ple, has regulatory limits of 80 μg total THMs and 60 μg total HAA per liter of water (Richardson et al. 2007). However, regula­ tions must also ensure that efforts to reduce DBPs do not result in water that is impaired due to microbial contamination: This is the microbe–DBP balanc­ ing act of minimizing risk while maximizing benefi­ cial effects. In this issue of EHP, a suite of four articles builds upon the hundreds of studies (see Richardson et al. 2007) reported since the first report of the genotoxicity of disinfected water (Loper et al 1978). These articles include a case–control study of gene–environment interaction in bladder can­ cer and three studies of DBP exposures in swimming pool water and biomarkers of their potential effects among swimmers. In the case– control study, Cantor et al. (2010) estimated associations between bladder cancer and individual DBP exposure estimates based on THM measurements in municipal water sources that were linked to residential history. The authors report that participants who carried a glutathione S­transferase zeta­1 (GSTZ1) rs1046428 poly morphism and were missing one or both copies of GSTT1 appeared to be par­ ticularly susceptible to bladder cancer when exposed to relatively high levels of THMs in water [odds ratio = 5.9 (95% confidence interval, 1.8–19.0) for > 49 μg versus ≤ 8 μg THMs/L]. The two susceptibil­ ity alleles occurred together in 29% of the Spanish study population (Cantor et al. 2010). Richardson et al. (2010) identified > 100 DBPs in water samples from two indoor pools in Barcelona, Spain (one chlorinated …