Carcinogenic Interactions For Smoking And Occupational Inhaled Arsenic

Table 3 provides three examples of carcinogenicity from arsenic and smoking (Pershagen et al., 1981; Enterline, 1983; Pershagen, 1985). The first shows that the relative risk for lung cancer, comparing retired arsenic smelter workers to the male population in the state where the study was conducted, among nonsmokers is 5.1. If we compare smokers to nonsmokers among the general population of males, the relative risk is 7.2. If the effects were multiplicative then we would expect the arsenic-exposed workers who were smokers to have a relative risk of about 35. The actual relative risk is 20.7, indicating that there is interaction on the multiplicative scale: the effects of smoking and arsenic exposure are less than multiplicative. If we express these numbers on the additive scale, we obtain an excess relative risk (ERR) for arsenic exposure among nonsmokers of 4.1, an ERR for smoking in the general population of males of 6.2, and an expected ERR, under an additive model, of 11.3 (= background + arsenic ERR + smoking ERR). The actual ERR is 19.7, indicating a synergistic effect.

The second example in Table 3 also shows a synergistic effect, but in this Swedish study, the effects of smoking and arsenic exposure are multiplicative (predicted relative risk = 3 x 4.9 = 14.7; observed relative risk = 14.6). The third example, also from Sweden, suggests that residential exposure to arsenic (i.e., exposure among persons living near a smelter) has a multiplicative effect with smoking on lung cancer, whereas occupational exposure shows a less than multiplicative relationship with smoking vis-a-vis the induction of cancer. Both

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