Evaluation of biomarkers of environmental exposures: urinary haloacetic acids associated with ingestion of chlorinated drinking water.

A study was conducted to determine if DCAA and TCAA urinary excretion rates are valid biomarkers of chronic ingestion exposure to these disinfection by-products of chlorination of drinking water. Entire first morning urine voids, time-of-visit urine samples, and tap water samples were collected from 47 female subjects. In addition, a 48-h recall questionnaire was administered to determine the amounts and types of liquids ingested by each subject as well as other exposures that could lead to DCAA and TCAA urinary excretion. The TCAA excretion rate for the first morning urine samples was significantly correlated with the estimated 48-h TCAA ingestion exposure for 25 subjects whose ingestion exposures primarily occurred at home, while the DCAA excretion rate was not correlated with the DCAA ingestion exposure. Thus, urinary TCAA appears to be a valid biomarker of chronic ingestion exposure to TCAA from chlorinated water, while urinary DCAA is not. It is proposed that the difference in the biological half-lives between these two compounds is the rationale for this finding. The biological half-life of TCAA is longer than successive exposure intervals; thus TCAA accumulates until it reaches a steady state. The half-life of DCAA is shorter than successive exposure intervals; thus DCAA is almost completely metabolized following an exposure and is eliminated from the body. This study suggests that biological half-life, exposure interval, and sample collection interval should be considered in selecting biomarkers and designing studies to validate them.