Exogenous and endogenous determinants of blood trihalomethane levels after showering

Abstract

Background: We previously conducted a study to assess whether household exposures to tap water increased an individual's internal dose of trihalomethanes (THMs). Increases in blood THM levels among subjects who showered or bathed were variable, with increased levels tending to cluster in two groups.

Objectives: Our goal was to assess the importance of personal characteristics, previous exposures, genetic polymorphisms, and environmental exposures in determining THM concentrations in blood after showering.

Methods: One hundred study participants completed a health symptom questionnaire, a 48-hr food and water consumption diary, and took a 10-min shower in a controlled setting. We examined THM levels in blood samples collected at baseline and 10 and 30 min after the shower. We assessed the significance of personal characteristics, previous exposures to THMs, and specific gene polymorphisms in predicting postshower blood THM concentrations.

Results: We did not observe the clustering of blood THM concentrations observed in our earlier study. We found that environmental THM concentrations were important predictors of blood THM concentrations immediately after showering. For example, the chloroform concentration in the shower stall air was the most important predictor of blood chloroform levels 10 min after the shower (p < 0.001). Personal characteristics, previous exposures to THMs, and specific polymorphisms in CYP2D6 and GSTT1 genes were significant predictors of both baseline and postshowering blood THM concentrations as well as of changes in THM concentrations associated with showering.

Conclusion: The inclusion of information about individual physiologic characteristics and environmental measurements would be valuable in future studies to assess human health effects from exposures to THMs in tap water.

Keywords: CYP2D6; CYP2E1; GSTT1; disinfection by-products; drinking water disinfection; showering exposures; trihalomethanes.

Figure 1

THM concentrations in shower water. Data are presented by study ID number in numeric and chronologic order over the 12-week study period (n = 99).

Figure 2

THM concentrations in whole blood at baseline and 10 min postshowering. The capped bars are the minimum and maximum, the box extents indicate the 25th and 75th percentiles, the line inside the box marks the 50th percentile, and the + indicates the mean (n = 99).

Figure 3

Associations between the change in chloroform concentrations in whole blood (10 min postshower minus baseline) and THM concentrations in shower water (A) and the 10-min integrated shower air sample (B). The correlation (r²) between changes in chloroform concentrations in whole blood and in shower water was 0.60 (p < 0.001). The correlation between chloroform concentrations in water and the 10-min integrated shower air sample was 0.63 (p < 0.001) (n = 99).