A sizable number of published scientific studies are relevant to the issue of parental occupational exposure to trichloroethylene and childhood cancer. The studies generally involve parental occupational exposures based on case-control studies. The committee did not have the time or resources to analyze all the studies, so it relied on a review paper (Colt and Blair 1998) and some new studies to illustrate the issues important in estimating the public health risk of parental exposure to occupational trichloroethylene and risk conveyed to their children. Chapter 2 provides guidelines for conducting a more rigorous review of the epidemiologic data.
The effects of parental occupational exposure on the risk of childhood cancer have been studied epidemiologically for more than 25 years. During that time, in most countries the nature of industry has changed in two important ways: through materials usage and levels of exposure. Specifically, trichloroethylene has been largely phased out as an industrial solvent. It is important to keep this in mind when reviewing the studies and their chronology. Colt and Blair (1998) reviewed information on parental exposure to solvents and the risk of childhood cancer. They summarized results from 48 published papers, virtually all of which were case-control studies. A few later papers have not clarified whether a relation exists (Shu et al. 1999; Schuz et al. 2000; McKinney et al. 2003; Infante-Rivard et al. 2005).
All studies used the case-control approach and therefore relied on questionnaire information, raising the usual methodological issues of the reliability of identifying specific exposures, selection of controls, and recall bias. Most studies relied on information about occupation and industry to infer exposures rather than questioning subjects about exposure to specific chemicals. Ages of the children studied varied from study to study. Often, only the mother was interviewed and asked about both her and her husband’s occupational history. It is very unlikely that women know about specific occupational exposures of their husbands, which is illustrated in two studies by Peters et al. (1981, 1985). In the first study, excess childhood brain cancer was associated with maternal and paternal exposure to chemicals, specifically to paint, and to work in the aerospace industry. An open-ended question addressed to the mother about specific chemicals to which either parent was exposed revealed little for the mothers and two mentions of trichloroethylene for the fathers. A follow-up study in which the fathers were interviewed revealed that five of them had exposure to trichloroethylene, whereas no control fathers did. Much like the community studies, the same occupations had other exposures to materials such as methylethylketone and other unspecified solvents. Following the approach of asking both parents about exposure to specific chemicals, Lowengart et al. (1987), in studying childhood leukemia, showed a risk associated with paternal exposure to