The committee concludes that there continues to be inadequate/insufficient evidence to determine whether an association exists between solvent exposure and Alzheimer disease.
Review of over 300 studies of solvent exposure and neurobehavioral symptoms (such as fatigue, lack of coordination, and sensory disturbances) or neurobehavioral test results (such as results of tests of attention, reaction time, and visuomotor coordination) by IOM (2003) yielded only seven studies that had isolated former exposure from current exposure. The only way to identify chronic effects that continue past the period of active exposure is through studies that consider formerly (but not currently) solvent-exposed people. Of those studies, several (Mikkelsen et al. 1988; Parkinson et al. 1990; Hanninen et al. 1991; Daniell et al. 1993; Lundberg et al. 1995; Stollery 1996) found evidence of continued deficits in formerly solvent-exposed workers compared with reasonably constituted unexposed groups. Many studies compared painters or other solvent-exposed workers with people in similar occupations (such as carpentry) that did not have the same exposure history. The most specific and sophisticated evaluation of those previously exposed to solvents was conducted by Daniell et al. (1999), who found dose-dependent effects on neurobehavioral function some time after cessation of exposure. Although each of the studies found that one or more symptoms or test realms showed a deficit in function, there is not much consistency among the studies in which specific symptom or test was found to be affected, the comparison groups are not necessarily precisely comparable, and confounding factors were controlled to various degrees, so even relatively consistent evidence of some effects falls short of conclusive data. IOM concluded that there is limited/suggestive evidence of an association between past exposure to solvents and neurobehavioral outcomes, with the most support for decrements in visuomotor and motor function, for fatigue, for headache, and for difficulty in concentrating.
Recent studies have addressed the relationship between solvent exposure and neurobehavioral outcomes, including one focused on TCE (Reif et al. 2003) and one on PCE (Janulewicz et al. 2008). The study by Reif et al. (2003) evaluated neurobehavioral function in 184 adults who had been exposed through contaminated drinking water many years before testing. Higher exposure was associated with poorer performance on several tests (such as digit symbol and contrast sensitivity) and with increased symptoms (such as confusion, depression, and tension). The study of PCE (Janulewicz et al. 2008) addressed prenatal exposure in the Cape Cod water-contamination episode and evaluated school records for indications of learning or behavioral disorders. It found essentially no support of such an association. The studies of community water-supply contamination continue to provide mixed findings, as was found in the 2003 IOM report.
The committee concludes that there continues to be limited/suggestive evidence of an association between past solvent exposure and neurobehavioral outcomes.
IOM (2003) reviewed a series of studies of occupational solvent exposure that addressed an ill-defined combination of past and present solvent exposure in relation to measures of color discrimination.