Identifying public water facilities with low spatial variability of disinfection by-products for epidemiological investigations

Abstract

Background and Aims: Epidemiological studies of disinfection by-products (DBPs) and reproductive outcomes have been hampered by misclassification of exposure. In most epidemiological studies conducted to date, all persons living within the boundaries of a water distribution system have been assigned a common exposure value based on facility-wide averages of trihalomethane (THM) concentrations. Since THMs do not develop uniformly throughout a distribution system, assignment of facility-wide averages may be inappropriate. One approach to mitigate this potential for misclassification is to select communities for epidemiological investigations that are served by distribution systems with consistently low spatial variability of THMs. Methods and Results: A feasibility study was conducted to develop methods for community selection using the Information Collection Rule (ICR) database, assembled by the US Environmental Protection Agency. The ICR database contains quarterly DBP concentrations collected between 1997 and 1998 from the distribution systems of 198 public water facilities with minimum service populations of 100 000 persons. Facilities with low spatial variation of THMs were identified using two methods; 33 facilities were found with low spatial variability based on one or both methods. Because brominated THMs may be important predictors of risk for adverse reproductive outcomes, sites were categorised into three exposure profiles according to proportion of brominated THM species and average TTHM concentration. The correlation between THMs and haloacetic acids (HAAs) in these facilities was evaluated to see whether selection by total trihalomethanes (TTHMs) corresponds to low spatial variability for HAAs. TTHMs were only moderately correlated with HAAs (r = 0.623). Conclusions: Results provide a simple method for a priori selection of sites with low spatial variability from state or national public water facility datasets as a means to reduce exposure misclassification in epidemiological studies of DBPs.

Spatial and seasonal variability of tap water disinfection by-products within distribution pipe networks

“…All THM species were higher during summer, except for TCM, resulting in the absence of a season effect on the sum of the four THM species (total THM). Inevitably, certain studies showed higher total THM levels in tap water during summer Toroz and Uyak, 2005;Wei et al, 2010), where THM levels were higher either (i) in late summer (Villanueva et al, 2007;Symanski et al, 2004;Hinckley et al, 2005;Porter et al, 2005), or (ii) in late spring to early summer (Lewis et al, 2006). Keegan et al (2001) reported no seasonal effect on water total THM levels, corroborating our results.…”

Evaluation of Drinking Water Disinfectant Byproducts Compliance Data as an Indirect Measure for Short-Term Exposure in Humans

“…Temporal analysis of monthly mean concentrations of regulated THMs and HAAs measured at residential locations in this study suggest that May and June are high months of DBP formation in this system, which is consistent with other surface water systems with similar seasonal patterns of rainfall [14,43,44,45,46,47]. Treatment stations A, B, and D show high mean monthly concentrations in May (June in some cases, e.g., THMs in station D and HAAs in stations B and D).…”

Association of Brominated Trihalomethane and Haloacetic Acid Exposure With Fetal Growth and Preterm Delivery in Massachusetts

“…We recognize that the full extent of spatial variability may not be captured by existing DBP sample locations in some PWSs and that other approaches for quantifying the degree of spatial variability should be considered for different DBP metrics. 38 Nevertheless, our THMBr results seem robust to the impact of spatial variability in aggregated exposure measures.…”