Trichloroacetic Acid as a Biomarker of Exposure to Disinfection By-Products in Drinking Water: A Human Exposure Trial in Adelaide, Australia. (Research Articles)
Froese, Kenneth L., Sinclair, Martha I., Hrudey, Steve E., Environmental Health Perspectives
We addressed the need for a biomarker of ingestion exposure to drinking water disinfection byproducts by performing a human exposure trial. We evaluated urinary excretion of trichloroacetic acid (TCAA) as an exposure biomarker using 10 volunteers who normally consume their domestic tap water. We recruited the volunteers at a water quality research laboratory in Adelaide, Australia. Participants maintained a detailed consumption and exposure diary over the 5-week study, We also analyzed tap water and first morning urine (FMU) samples for TCAA, and tap water for chloral hydrate (CH). We documented both interindividual and intraindividual variability in TCAA ingestion and urinary excretion, and both were substantial. With a TCAA-free bottled water intervention, we used creatinine-adjusted urinary TCAA levels to estimate urinary TCAA excretion half-lives for three of the participants. We observed correspondence over time between estimated TCAA excretion, calculated from TCAA + CH ingestion levels, and measured TCAA urinary excretion. This study demonstrates the merits and feasibility of using TCAA in FMU as an exposure biomarker, and reveals remaining concerns about possible alternate sources of TCAA exposure for individuals with low drinking water ingestion exposure. Key words: disinfection by-products, drinking water, exposure assessment, haloacetic acids, trichloroacetic acid.
Environ Health Perspect 110:679-687 (2002). [Online 28 May 2002] http://ehpnet1.niehs.nih.gov/docs/2002/110p679-687froese/abstract.html
The question of whether disinfection byproducts (DPBs) in drinking water pose any health risk to humans has been an ongoing issue since the discovery of DPBs in 1974. Although toxicology experiments with individual DPBs are necessary to establish plausible mechanisms of toxic action, epidemiologic studies of human populations are necessary to establish whether actual DPB exposures from drinking water pose a human health risk. Such studies have historically been focused on cancer outcomes, but more recently a number of studies have addressed the possibility of adverse reproductive outcomes (1-12).
The ability of epidemiologic studies to address these health questions has been seriously limited by inadequate individual assessment of exposure to DPBs (13,14). A major prospect for improved exposure assessment for epidemiologic studies of adverse reproductive outcomes is to validate a biomarker of exposure to DPBs. Desirable characteristics of potential biomarkers of DPB exposure have been discussed by Froese et al. (15).
To date, the only DPBs evaluated for use as biomarkers of exposure have been the trihalomethanes (THMs) and the haloacetic acids (HAAs). Weisel et al. (16) found that most background breath samples from a cohort of women who had participated in the Klotz and Pyrch (8) study were nondetectable for THMs in exhaled breath. Measurable levels of THMs were obtained in post-shower breath samples, and these breath values correlated with water levels of THMs. However, breath levels of THMs as a biomarker of exposure to DPBs do not persist for sufficient time to integrate exposure measurement over more than minutes to hours, at most. Likewise, measurable THM exposures are limited to inhalation and dermal exposure from showering or bathing. THM levels in breath will not reflect ingestion exposure because of rapid first-pass metabolism of ingested THMs in the liver. THMs in blood were demonstrated to be feasible for evaluating background THM exposure (17), but blood sampling is an invasive procedure.
The potential of two HAAs, dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), as DPB biomarkers in urine was examined with a cross-sectional study of a cohort of 49 women, who provided 42 valid samples (16,18). That study found that DCAA was rapidly metabolized and that urine levels showed no difference between low-exposure and high-exposure groups. …