Effect of water disinfection type on adverse fetal outcomes

Maternal Exposure to Tap Water Disinfection By-Products and Risk of Selected Congenital Heart Defects

BACKGROUND

The use of chlorine to treat drinking water produces disinfection by-products (DBPs), which have been associated with congenital heart defects (CHDs) in some studies.

METHODS

Using National Birth Defects Prevention Study data, we linked geocoded residential addresses to public water supply measurement data for DBPs. Self-reported water consumption and filtration methods were used to estimate maternal ingestion of DBPs. We estimated adjusted odds ratios and 95% confidence intervals using logistic regression controlling for maternal age, education, body mass index (BMI), race/ethnicity, and study site to examine associations between CHDs and both household DBP level and estimated ingestion of DBPs.

RESULTS

Household DBP exposure was assessed for 2717 participants (1495 cases and 1222 controls). We observed a broad range of positive, null, and negative estimates across eight specific CHDs and two summary exposures (trihalomethanes and haloacetic acids) plus nine individual DBP species. Examining ingestion exposure among 2488 participants (1347 cases, 1141 controls) produced similarly inconsistent results.

CONCLUSIONS

Assessing both household DBP level and estimated ingestion of DBPs, we did not find strong evidence of an association between CHDs and DBPs. Despite a large study population, DBP measurements were available for less than half of participant addresses, limiting study power.

Meta-analysis of small for gestational age births and disinfection byproduct exposures

BACKGROUND

Some epidemiological studies show associations between disinfection byproducts (DBPs) and adverse developmental outcomes.

OBJECTIVES

We undertook a meta-analysis of epidemiological studies on maternal exposure to trihalomethanes (THMs) and haloacetic acids (HAAs) and risk of small for gestational age (SGA) birth.

METHODS

We identified forty-five publications including two reports and five theses via a 2020 literature search. Nineteen study populations from 16 publications met the inclusion criteria and were systematically evaluated. Effect measures were pooled using random effects meta-analytic methods along with cumulative, sub-group and meta-regression analyses to examine between-study heterogeneity and variation in risk across different DBP measures.

RESULTS

We detected a small increased risk for SGA with exposure to the sum of four (i.e., THM4) THM4 (odds ratio (OR) = 1.07; 95%CI: 1.03, 1.11), chloroform (OR = 1.05; 95%CI: 1.01, 1.08), bromodichloromethane (OR = 1.08; 95%CI: 1.05, 1.11) and the sum of the brominated THM4 (OR = 1.05; 95%CI: 1.02, 1.09). Larger ORs were detected for the sum of five haloacetic acids (i.e., HAA5) (OR = 1.12; 95%CI: 1.01, 1.25), dichloroacetic acid (OR = 1.25; 95%CI: 1.01, 1.41) and trichloroacetic acid (OR = 1.21; 95%CI: 1.07, 1.37). We detected larger SGA risks for several THM4 among the prospective cohort and case-control studies compared to retrospective cohorts and for the SGA3/5% (vs. SGA10%) studies. The THM4 meta-regression showed associations between SGA and the total quality score based on categorical or continuous measures. For example, an OR of 1.03 (95%CI: 1.01, 1.06) was detected for each 10-point increase in the study quality score based on our systematic review.

CONCLUSIONS

We detected a small increased risk of SGA based on 18 THM4 study populations that was comparable to a previous meta-analysis of eight THM4 study populations. We also found increased risks for other THM4 and HAA measures not previously examined; these results were robust after accounting for outliers, publication bias, type of SGA classification, different exposure windows, and other factors.

Spatial variation of disinfection by-product concentrations: exposure assessment implications

The use of public water system (PWS) average trihalomethane (THM) and haloacetic acid (HAA) concentrations as surrogates of "personal" exposures in epidemiological studies of disinfection by-products (DBPs) may result in exposure misclassification bias from various sources of measurement error including intra-system variation of DBPs. Using 2000-2004 data from 107 PWSs in Massachusetts, we assessed two approaches for characterizing DBP spatial variability by identifying PWSs with low spatial variability (LSV) and examining differences in LSV across DBP groups and by type of source water and primary disinfectant. We also used spatial differences to examine the association between THM concentrations and indices of social disadvantage; however, we found no correlations or statistically significant differences based on the available data. We observed similar patterns for the percentage of quarterly sampling dates with LSV across different types of source water for all DBPs but not across disinfectants. We found there was little overlap between sites classified as having LSV across different DBP groups. In the main analysis, we found moderate correlations between both approaches (φ(THM4) = 0.55; φ(BrTHM) = 0.64; φ(HAA5) = 0.67); although Method 1 (based on concentration differences between samples) may be better suited for identifying PWSs for inclusion in epidemiological studies because it is more easily adapted to study-specific exposure gradients than Method 2 (based on categorical exposure percentiles). These data reinforce the need to consider different exposure assessment approaches when examining the spatial variation of multiple DBP surrogates as they can represent different DBP mixtures.