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

Abstract

In the absence of shorter term disinfectant byproducts (DBPs) data on regulated Trihalomethanes (THMs) and Haloacetic acids (HAAs), epidemiologists and risk assessors have used long-term annual compliance (LRAA) or quarterly (QA) data to evaluate the association between DBP exposure and adverse birth outcomes, which resulted in inconclusive findings. Therefore, we evaluated the reliability of using long-term LRAA and QA data as an indirect measure for short-term exposure. Short-term residential tap water samples were collected in peak DBP months (May-August) in a community water system with five separate treatment stations and were sourced from surface or groundwater. Samples were analyzed for THMs and HAAs per the EPA (U.S. Environmental Protection Agency) standard methods (524.2 and 552.2). The measured levels of total THMs and HAAs were compared temporally and spatially with LRAA and QA data, which showed significant differences (p < 0.05). Most samples from surface water stations showed higher levels than LRAA or QA. Significant numbers of samples in surface water stations exceeded regulatory permissible limits: 27% had excessive THMs and 35% had excessive HAAs. Trichloromethane, trichloroacetic acid, and dichloroacetic acid were the major drivers of variability. This study suggests that LRAA and QA data are not good proxies of short-term exposure. Further investigation is needed to determine if other drinking water systems show consistent findings for improved regulation.

Keywords: Haloacetic acids; Trihalomethanes; birth outcomes; disinfection byproducts; drinking water; exposure assessment; locational running annual average; temporal variability.

Figure 1

Schematic of the community water system used in this study. Initial distribution system evaluation (IDSE) monitoring sites from treatment stations A, C, and D were used to collect water samples for compliance reporting.

Figure 2

Temporal comparison of monitored (a) total THMs and (b) HAAs levels with LRAA compliance and QA data.

Figure 3

Spatial comparison of monitored (a) total THMs and (b) HAAs levels with LRAA compliance and QA data. The boxplots above utilize Tukey-style whiskers in that the upper whisker extends from the upper hinge (75th percentile) to the highest value that is within 1.5 × IQR (interquartile range) of the hinge and the lower whisker extends from the lower hinge (25th percentile) to the lowest value within 1.5 × IQR of the hinge. The black dots are outlier data points (outside the 1.5 × IQR range).

Figure 4

Spatial distribution of (a) individual THMs and (b) HAAs. BDCM = bromodichloromethane, TBM = bromoform, TCM = chloroform, and DBCM = dibromochloromethane. MCAA = monochloroacetic acid, DCAA = dichloroacetic acid, TCAA = trichloroacetic acid, MBAA = monobromoacetic acid, and DBAA = dibromoacetic acid. The boxplots above utilize Tukey-style whiskers in that the upper whisker extends from the upper hinge (75th percentile) to the highest value that is within 1.5 × IQR of the hinge and the lower whisker extends from the lower hinge (25th percentile) to the lowest value within 1.5 × IQR of the hinge. The black dots are outlier data points (outside the 1.5 × IQR range).