AN ASSESSMENT OF A URINARY BIOMARKER FOR TOTAL HUMAN ENVIRONMENTAL EXPOSURE TO BENZO[A]PYRENE

Urinary banzo[a]pyrene (BaP) metabolite levels were compared to human environmental exposure to BaP through inhalation and dietary ingestion to assess the predictive validity of the exposure biomarker. These me asurements were made for 14 adult volunteers over 14 consecutive days, once during summer/fall, again during winter periods. Based on person al air monitoring, median potential inhalation doses of 11.0 and 2.3 n g/day were estimated for the winter and summer/fall studies, respectiv ely. A median potential ingested dose of 176 ng/day, estimated from '' duplicate plate'' sampling, exceeded inhalation by 6-and 122-fold for the winter and summer/fall studies, respectively. ''Total'' urinary Ba P metabolites were measured using a published ''reverse metabolism'' ( BaP) method of analysis. Median rates of urinary BaP metabolite elimin ation for the winter and summer/fall studies were 121 and 129 ng/day, respectively. The changes in inhaled and ingested potential doses were regressed on the change in urinary metabolite elimination from week 1 to week 2 to test the predictive validity of the biomarker measuremen t. The regression was statistically significant (r = 0.620, p = 0.015, n = 25) when body weight was included and two extreme values were rem oved. Consistent with the exposure measurements showing diet as the do minant route of exposure, most of the Variation in urinary metabolite elimination was explained by the ingested dose. It is concluded that t he measurement of urinary BaP by ''reverse metabolism'' is qualitative and of marginal predictive validity as an exposure biomarker due to t he method's low recoveries and the large unexplained variance.