Later, more carefully controlled studies showed nothing. Lacy-Hulbert, Metcalf, and Hesketh (1998) have provided a comprehensive review of this aspect of the EMF research.
In the United States in 1997, the National Research Council published a report that concluded that there was no evidence of any harmful health effects of EMFs. The same year Linet et al. (1997) published a major study in the
The most recent instantiation of the “EMFs cause cancer” claim is that the radiation from cellular phones causes brain cancer, especially in the brain tissue in the part of the brain closest to the phone itself. In 1992 a tragic case in which a woman died of brain cancer was highlighted in the media when her husband had become convinced that her use of a cellular phone had caused her cancer. He went on a crusade against cell phones that included suing the major cell phone manufacturers. (Somewhat surprisingly, Paul Brodeur does not appear in this part of the story). Keller (1993) has provided a good history of the early stages of this controversy. One result was that the stock of cell phone manufacturers plummeted in value. It also led to widespread worry among cell phone users.
At the time, no epidemiological studies had been done of cell phones. The publicity over this case, however, led to the initiation of several studies of the risks of cell phones. Muscat et al. (2000) studied 469 patients with primary cancerous brain tumors. These patients had not used cell phones at a greater frequency or for a greater time than a control group that did not have any brain cancer. Inskip et al. (2001) reported a similar study of 782 patients and also found that cell phone use was not related to brain cancer, nor was there any association between the side of the brain in which the tumor was located and the side of the head to which the phone had been held, if the patient had been a cell phone user. Finally, Johansen et al. (2001) examined cancer rates in 420,095 cell phone users in Denmark between the years 1982 and 1995. Within this huge sample, there was no greater incidence of brain tumors than would be expected. In addition to examining brain tumors, this study examined the incidence of cancer in all organs of the body. Overall, cell phone users had a significantly lower rate of cancer than expected. This was due to reduced rates of “lung cancer and other smoking related cancers” (p. 203). This effect, in turn, was probably due to the fact that cell phone users are somewhat more affluent than nonusers and thus tend to be more aware of real health risks such as smoking.
PCBs-A CASE OF ENVIRONMENTAL MASS HYSTERIA
Polychlorinated biphenyls (PCBs) are a class of chemicals that were used in numerous industrial processes until the 1970s. Through various routes, they entered the environment in small concentrations. The cause of most of the worry over PCBs is the fact that they are found in freshwater fish that are often eaten by humans. Specifically, it is claimed that exposure to PCBs in the workplace causes cancer and that the children of women who ate fish contaminated with PCBs show various physical and mental abnormalities. It is this latter claim that has caused the furor over PCBs because, while they are no longer found in the workplace, they are still present in the environment and, as noted, in fish. In the Hudson River Valley in New York State, worry about the effects of lingering PCBs is so great that the Environmental Protection Agency has ordered General Electric to spend hundreds of millions of dollars dredging the river bottom to remove contaminated soil. The important question thus becomes whether exposure to PCBs by eating PCB-contaminated fish really poses a hazard to human health.
Before discussing the research on the possible effects of PCBs on infants, it is appropriate to discuss the relationship between PCB exposure and cancer. While it is the case that giving massive doses of PCBs to animals can cause cancer, these doses are vastly greater than those to which any human would ever be exposed (Kimbrough 1993). Kimbrough et al. (1999) addressed the hypothesis that occupational levels of exposure to PCBs resulted in a greater incidence of cancer and other health problems. This study examined the causes of death of 1,157 industrial workers who had been exposed to high levels of PCBs as a consequence of their work. This sample is the largest ever studied in this regard. There was no increase in the rate of cancer among these workers.
The possible effects of PCBs on the children of women who ate fish with PCBs have been extensively studied. The results show a very minimal risk, if any. The earliest study to examine this issue was that of Fein et al. (1984), who found that, compared to infants of mothers who had not eaten PCB-contaminated fish, the infants of mothers who had showed a smaller birth weight, a smaller head circumference, and had lower “neuromuscular maturity.” These differences, while statistically significant, were very small. For example, the actual difference in head circumference was only 1.6 percent. Using the same group of infants, Jacobson et al. (1984) reported that the exposed children showed “worrisome” results on three out of seven measures of neonatal behavior at three days of age. The authors noted that their results “must be interpreted with caution” because such behavioral differences “are frequently transitory [and] their long-term developmental implications are uncertain” (p. 530). In a 1996 study Jacobson and Jacobson reported that greater prenatal exposure to PCBs was associated with significantly lower scores on five out of eleven measures of intelligence. Even on the five measures where the differences were statistically significant, they were tiny. The largest association had a correlation with an absolute value of .18. This means that only a little over 3 percent of differences among the children on this measure were due to PCB exposure.
Contrary to the findings noted above, Rogan et al. (1987) did not find any effect of exposure to PCBs or another chemical pollutant (DDE) on infant weight, head circumference, or how often the children suffered from various childhood illnesses. A later study (Gladden et al. 1988) examined various behavioral and intelligence variables in PCB and DDE exposed infants. Out of sixteen comparisons made, only two showed any effects of PCB exposure. In both cases, exposure was related to lower psychomotor development scores. As would be expected based on the quote from Jacobson et al. (1984) above that such findings are “transitory,” Gladden and Rogan (1991) found that, when tested at ages three to five, exposed children showed no effects of exposure. The small effects seen earlier had vanished.
Jacobson et al. (1985) reported an effect of PCB exposure in utero on a measure of visual recognition memory in infant. Gladen et al. (1988), however found no effect of PCB exposure on several measures of infant cognitive function.
Lonky et al. (1996) examined the relationship between prenatal PCB exposure and several measures of infant behavior. Infants were tested one and two days after birth. It is not at all clear from the published report just how many statistical comparisons were done, but in their Table 8 (p. 208), twenty-four are reported. Of these, only five were significant, the definition of significance being adjusted to take into account the number of tests performed. Nonetheless, if there really was an effect of PCBs, one would expect it to be more pervasive and show up in more than five out of twenty-four results. Making the interpretation of these results even more problematic is the fact that Lonky et al. did not analyze the actual scores on the tests from day one and day two; rather, they took the difference between day one and day two scores and analyzed these
Stewart et al. (2000) reported a slightly different analysis of what appears to be basically the same data reported by Lonky et al (1996). While Lonky et al. found PCB exposure to be associated with poorer performance on three out of seven measures of infant behavior, Stewart et al. found it associated with poorer performance on only two of seven measures. Publishing repeated analyses of the same data results in a spurious impression of replication.
Using older infants (between six and twelve months of age) Darvill et al. (2000) reported that PCB exposure impairs performance on a test of infant intelligence. But, as usual, the effects were inconsistent and very small, such that exposure to PCBs accounted for only about 2 percent of differences on test scores.
The Gladen et al. (1988) study was mentioned above, but I did not describe one of their most interesting
