Occupational styrene exposure and neurobehavioural functions: a cohort study with repeated measurements.

OBJECTIVE: Associations between occupational styrene exposure and cognitive as well as psychomotor functions were investigated with a view to answering three questions: (1) are the published results for neurobehavioural impairment reproducible, (2) if such effects exist, are they related to current or to chronic exposure and (3) if effects exist, are there reductions in the effects during an exposure-free period.
METHODS: Workers from a boat-building plant, some of whom were laminators, were investigated in groups of low (n = 83, mean mandelic acid MA + phenylglyoxylic acid PGA = 53 mg/g creatinine), medium (n = 101, 230 mg/g creat.) and high (n = 29, 928 mg/g creat.) levels of exposure to styrene. The mean job tenure was about 6 years. In addition, subgroups chronically exposed to low-short (n = 30, lifetime weighted average exposure mean 184 mg/g creat. for 6 years) and high-long (n = 16, 693 mg/g creat., 15 years) styrene levels were analyzed. The examinations were carried out during normal working days and during the company holidays. A symptom questionnaire and the tests Benton visual retention, symbol digit substitution and digit span for cognitive functions as well as choice reaction, aiming, peg board, tapping, and steadiness for psychomotor functions were administered. Co-variance analyzes with repeated measurements and linear regressions were used for statistical analysis. Co-factors were education, age, job tenure, long-term alcohol consumption, and German as mother tongue. In some cases also the activity as a laminator was considered.
RESULTS: Symptoms were not related to exposure. The tests for cognitive functions generally revealed (all variance analyses) no exposure-related associations. Only the linear regressions of Benton test results showed significant correlation with parameters of chronic exposure which was still evident as a tendency in the work-free and exposure-free period. Most tests for psychomotor functions also revealed no relationships with exposure. However, the peg board test results showed significant correlations with chronic exposure which disappeared during holidays. The activity as a laminator--considered in addition to exposure parameters--was significant as a factor to explain the variability of psychomotor variables.
CONCLUSION: Acute exposures to up to 40 ppm styrene and long-term exposures to about 27 ppm averaged over a period of 15 years were not identified as being associated with an elevated risk of developing impaired cognitive and psychomotor functions or increased symptom levels with the tests applied. This statement must be qualified by two exceptions: performances in the Benton test and in a finger dexterity test were associated with parameters of long-term exposure as a dose-response relationship, but not with current exposure.