NEUROPSYCHOLOGICAL EFFECTS OF EXPOSURE TO NAPHTHA AMONG AUTOMOTIVE WORKERS

The association between exposure to naphtha and neurobehavioural measu res was examined prospectively over one year among workers employed at an automotive plant that used naphtha to calibrate fuel injectors. Th e neurobehavioural tests included those that assess mood, basic intell igence, and functioning of the cerebral frontal lobes and limbic syste m and were designed so that acute, reversible, and chronic effects of solvent exposure could be assessed. Participants were 248 workers in J une 1988, and the testing was repeated on 185 of these workers in 1989 . Concentrations of naphtha at the plant ranged from six to 709 mg/m3, although exposure was greater in 1988 than in 1989. Duration of expos ure for individual subjects ranged from 0.8 to 7.3 years. Cross sectio nal data analyses showed significant associations between level of exp osure to naphtha and slower timed scores on trails A, and greater repo rts of negative affective symptoms on profile of mood states scales in 1988 but not 1989. Threshold model analyses of the 1989 data showed a n association between score on visual reproductions immediate recall a nd daily exposure to naphtha at or above 1050 h x mg/m3. Models of chr onic exposure showed no associations between chronic exposure and nega tive neurobehavioural outcome. Results suggest that naphtha produces m ild acute reversible effects on function of the central nervous system at or above daily exposures of 540 h x mg/ml (approximately 90 ppm/h) .