Use of urinary trichloroacetic acid as an exposure biomarker of disinfection by-products in cancer studies.

Urinary trichloroacetic acid (TCAA) has been proposed as a valid exposure biomarker for ingested disinfection by-products (DBP) for reproductive studies. However, it has never been used in epidemiologic studies on cancer. We investigate the performance of urinary TCAA as a biomarker of DBP exposure in the framework of an epidemiologic study on cancer. We conducted home visits to collect tap water, first morning void urine, and a 48h fluid intake diary among 120 controls from a case-control study of colorectal cancer in Barcelona, Spain. We measured urine TCAA and creatinine, and 9 haloacetic acids and 4 trihalomethanes (THM) in tap water. Lifetime THM exposure was estimated based on residential history since age 18 plus routine monitoring data. Robust linear regressions were used to estimate mean change in urinary TCAA adjusted by covariates. Among the studied group, mean age was 74 years (range 63-85) and 41 (34%) were females. Mean total tap water consumption was 2.2l/48h (standard error, 0.1l/48h). Geometric mean urine TCAA excretion rate was 17.3pmol/min [95%CI: 14.0-21.3], which increased 2% for a 10% increase in TCAA ingestion and decreased with total tap water consumption (-17%/l), water intake outside home (-32%), plasmatic volume (-64%/l), in smokers (-79%), and in users of non-steroidal anti-inflammatory drugs (-50%). Urinary TCAA levels were not associated with lifetime THM exposure. In conclusion, our findings support that urine TCAA is not a valid biomarker in case-control studies of adult cancer given that advanced age, comorbidites and medication use are prevalent and are determinants of urine TCAA levels, apart from ingested TCAA levels. In addition, low TCAA concentrations in drinking water limit the validity of urine TCAA as an exposure biomarker.