Challenging the assumptions

chemicals and ionizing radiation. While an earlier study by other researchers did not find any correlation between increased placental UGT activity and maternal cigarette smoking, this study found a strong correlation for mothers who were both drug abusers and smokers. This suggests that illicit drugs compound the problems associated with smoking. The study also reports the discovery of a previously unknown placental biochemical marker activity. Among maternal drug abusers, P1OH correlated consistently with ECOD activity but not with EROD activity. However, P1OH correlated with EROD or testosterone hydroxylase activity only among the-cigarette smoking controls. The authors suggest that because ECOD and EROD activity always exhibit a positive correlation in normal cigarette smoking conditions., this may be evidence that in normal conditions a "silent" cytochrome P450 gene form may be responsible for P1OH activity. This change in the steroid metabolism profile in vitro suggests that maternal drug abuse may alter normal hormonal balance during pregnancy. The use of illicit drugs by pregnant women may disrupt placental metabolism and exacerbate the effects of smoking. The authors suggest that these findings may mean that the combination of illicit drugs with certain prescribed medications could also complicate the expression of placental metabolizing enzymes. They urge that term placentas from mothers using any medication or illicit drug be evaluated after delivery in terms of total metabolizing activity in vitro and any possible link to adverse responses in later development of the infant. For decades, scientists have agreed that cancer risks are best estimated by extrapolating from the high-dose effects observed in a cohort of atomic bomb survivors over the course of the subjects' lives. In this issue, Alice Stewart, a retired professor of epidemiology from the University of Birmingham in Great Britain, questions the traditional assumptions used to form cancer risk assessments: namely, that the only late effect of radiation is cancer, that there is no cancer risk at the radiation levels typically faced by nuclear workers, that the risk for leukemia far exceeds that for solid tumors, and that radiosensitivity is higher at the beginning of adult life than at the end [EHP 108:93-96]. Stewart also presents the alternative view that, in addition to cancer, high-dose exposures to radiation may also result in irreversible damage to the immune system. New research using a cohort of atomic bomb survivors questions how assessments of cancer risk from radiation exposure are made. Stewart's views challenge the assumptions …