Estimating National Exposures and Potential Bladder Cancer Cases Associated with Chlorination DBPs in U.S. Drinking Water.

BACKGROUND: Disinfection byproducts (DBPs) in public water systems (PWS) are an unintended consequence resulting from reactions between mostly chlorine-based disinfectants and organic and inorganic compounds in source waters. Epidemiology studies have shown that exposure to DBP (specifically trihalomethanes) was associated with an increased risk of bladder cancer. OBJECTIVE: Our goal was to characterize the relative differences in exposures and estimated potential bladder cancer risks for people served by different strata of PWS in the United States and to evaluate uncertainties associated with these estimates. METHODS: We stratified PWS by source water type (surface vs. groundwater) and population served (large, medium, and small) and calculated population-weighted mean trihalomethane-4 (THM4) concentrations for each stratum. For each stratum, we calculated a population attributable risk (PAR) for bladder cancer using odds ratios derived from published pooled epidemiology estimates as a function of the mean THM4 concentration and the fraction of the total U.S. population served by each stratum of systems. We then applied the stratum-specific PARs to the total annual number of new bladder cancer cases in the U.S. population to estimate bladder cancer incidence in each stratum. RESULTS: Our results show that approximately 8,000 of the 79,000 annual bladder cancer cases in the United States were potentially attributable to DBPs in drinking water systems. The estimated attributable cases vary based on source water type and system size. Approximately 74% of the estimated attributable cases were from surface water systems serving populations of >10,000 people. We also identified several uncertainties that may affect the results from this study, primarily related to the use of THM4 as a surrogate measure for DBPs relevant to bladder cancer. DISCUSSION: Despite significant reductions in exposure over the past several decades, our study suggests that ∼10% of the bladder cancer cases in the United States may still be attributed to exposure to DBPs found in drinking water systems. https://doi.org/10.1289/EHP9985.

On the use of total aerobic spore bacteria to make treatment decisions due to Cryptosporidium risk at public water system wells.

Spore reduction can be used as a surrogate measure of Cryptosporidium natural filtration efficiency. Estimates of log10 (log) reduction were derived from spore measurements in paired surface and well water samples in Casper Wyoming and Kearney Nebraska. We found that these data were suitable for testing the hypothesis (H0) that the average reduction at each site was 2 log or less, using a one-sided Student's t-test. After establishing data quality objectives for the test (expressed as tolerable Type I and Type II error rates), we evaluated the test's performance as a function of the (a) true log reduction, (b) number of paired samples assayed and (c) variance of observed log reductions. We found that 36 paired spore samples are sufficient to achieve the objectives over a wide range of variance, including the variances observed in the two data sets. We also explored the feasibility of using smaller numbers of paired spore samples to supplement bioparticle counts for screening purposes in alluvial aquifers, to differentiate wells with large volume surface water induced recharge from wells with negligible surface water induced recharge. With key assumptions, we propose a normal statistical test of the same hypothesis (H0), but with different performance objectives. As few as six paired spore samples appear adequate as a screening metric to supplement bioparticle counts to differentiate wells in alluvial aquifers with large volume surface water induced recharge. For the case when all available information (including failure to reject H0 based on the limited paired spore data) leads to the conclusion that wells have large surface water induced recharge, we recommend further evaluation using additional paired biweekly spore samples.