ARSENIC RISK ASSESSMENT

We review recent publications by Hopenhayn-Rich et al, and Smith et al . regarding two critical issues in arsenic risk assessment: the role o f methylation in the dose-response relationship and the role of intern al cancers. Hopenhayn-Rich et al. applied simple linear regression to data from several studies to determine whether the percentage of inorg anic arsenic in urine increases with increasing dose. Although their r esults failed to show a correlation between percent inorganic arsenic and urinary arsenic concentration, their evaluation does not demonstra te the absence of a methylation threshold because of the relatively lo w level of arsenic in urine and the use of grab samples in evaluating methylating capacity. Using data from an epidemiological study in Taiw an, Smith et al. have indicated that arsenic could be an important ris k factor not only for skin cancer (the basis of the current EPA cancer slope factor), but also for several internal cancers including lung, liver, bladder, and kidney. We note the following deficiencies in the analysis of Smith et al: 1) the likely underestimated exposure estimat e due to lack of consideration on nonwater sources of arsenic and the undersestimate of water consumption, 2) lack of consideration of detox ification in estimating potential risks from low-level exposures typic al of the U.S. population, and 3) lack of consideration of key differe nces, particularly nutritional differences, between the Taiwanese and U.S. populations that could affect potential risks.