RE: "Arsenic Ingestion and Internal Cancers: A Review"

Bates et al. (1) conducted a very thorough review on arsenic ingestion and cancers. In assessing the role of humic subsstances in the studies in Taiwan, they state that the existence of humic substances has not been shown to be confined mainly to the blackfoot disease endemic area and that no correlation of the concentration of humic substances with arsenic levels, blackfoot disease, or any cancers has been shown. Accordingly, they consider it unlikely for humic substances to be a confounder of those studies. However, the largest survey of well water in Taiwan (2) showed that the existence of arsenic was not confined to the blackfoot disease endemic area either. According to Tseng's definition (3), the blackfoot disease endemic area covers only seven townships (districts), but 119 townships in Taiwan had wells a moderateto high arsenic level ( above 0.05 ppm), and 58 townships had wells with a high arsenic level ( above 0.35 ppm)(2). While all 10 townships having the hughest proportions (at least 8.2 percent) of wells with a high arsenic level had cases of blackfoot disease, only six of the 10 townships having the highest proportions (at least 46 .8 percent) of wells with a moderate-to-high arsenic level had reported cases of blackfoot disease. Among these six townships, five are among the 10 with the highest proportions of wells with a high arsenic level, and the other one had 7.7 percent (ranked 13th among 313 townships) of its wells with a high arsenic level (2). One of the speculations in the existence of a threshold concentration ( dose) of arsenic that causes blackfoot disease. In fact, there was an impression that townships having wells with arsenic above 0.35 ppm were more likely to hove cases of blackfoot disease (2). Therfore, the existence of arsenic was not confined mainly to the blackfoot disease area, and such a phenomenon does not exclude the association. For the same reason, if the carcinogenicity of arsenic has a threshold, the fact that the existence of humic substances in not confined to the areas with a high cancer occurrence does not exclude the association between humic substances and cancers. Actually, some evidence has suggested such a threstold (4,5).# 0675