complete (Bates, 1989). Where increased rates of cancer are involved, long-term follow-up will be needed.

One prospective study of a distinct group (such as Seventh Day Adventists —Euler et al., 1988—which have a stable population for which health outcomes can reliably be recorded) has been useful in identifying associations between total suspended particulates and respiratory symptoms and bronchitis, and between ozone levels and the incidence of asthma. Such studies are not applicable to hazardous-waste sites, however. Follow-up studies of residents of Love Canal, New York, chronically exposed for varying periods have been reported (Janerich et al., 1981). In general, these have not revealed striking long-term effects, although an increase in prevalence of low-birth-weight babies in Love Canal was linked to exposures from wastes deposited there (Vianna and Polan, 1984; Goldman et al., 1985).

There also are important data on children with chronic elevations of lead in their blood in whom subsequent effects have been detected with long-term follow-up studies. Follow-up studies of children known to have suffered from lead exposure showed that lead levels in umbilical cord blood predict a child's performance on the Bailey scales of mental development at 6 months and at 18 months of age (Bellinger et al., 1987). Exposure categories were in three groups, <5 µg/dL (micrograms per deciliter), 5-10 µg/dL, and >10 µg/dL. The fall-off in performance was significantly different between the lowest and highest exposure categories; in the middle it depended on economic circumstance, and poorer children performed worse than did others for the same lead level. Needleman et al. (1990) demonstrated that poorer school performance, reading problems, and deficits in intelligence tests persist into adolescence. Needleman's follow-up of children known to have been exposed to lead indicates an odds ratio of 5 for failure to graduate from high school and of 7 for reading disabilities (Needleman et al., 1990).

As noted in Chapter 3, lead is the commonest contaminant of hazardous-waste sites. It also is present in mining wastes, house paint, and urban soils contaminated by leaded gasoline and flaking house paint. Studies of the effects of lead are therefore clearly relevant to hazardous-waste site exposures, and they indicate the importance of ensuring that exposures of children to lead from hazardous-waste sites does not occur.

If adequate markers of exposure to developmental toxins can be secured (as was relatively easy in the case of lead), the outcome measurements can be sensitive enough to demonstrate significant long-term adverse effects. Unfortunately, markers of exposure often do

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