Sister-chromatid exchanges in lymphocytes are increased in relation to longitudinally measured occupational exposure to low concentrations of styrene

A longitudinal investigation of styrene exposure was conducted among 48 workers employed at a reinforced plastic boat manufacturing facility. 8-h time-weighted average (TWA) exposures to styrene and concentrations of styrene in the breath were determined for each individual on 7 randomly chosen days during 1 year. Peripheral blood lymphocytes from each subject were analyzed for sister chromatid exchanges (SCEs) 2 times and micronuclei (MN) 4 times during this period. Individual mean SCEs ranged from 4.7 to 9.5 SCEs per cell with a population mean of 6.4 +/- 0.2 SCEs per cell. SCEs were found to be significantly increased with an overall observed increase of 11.7% related to increasing exposure to styrene (mean air concentration 64.2 mg/m3 +/- 71.5; range 0.88-235 mg/m3) and with cigarette smoking. Examination of the relative contribution of each variable to regression of SCEs showed that smoking contributed about 62% and styrene exposure contributed about 25% of the total variability. Intra-individual lymphocyte MN frequencies did not vary significantly over time nor was a gradient toward increased MN observed with styrene exposure. However, significant inter-individual differences in MN frequencies were observed. Females had significantly higher MN frequencies than did males; MN were also increased with age. This study is highly unusual in that it illustrates the ability to separately quantify the relative contribution of each of two variables--smoking and styrene exposure--to an increase in SCEs in lymphocytes of an exposed human population.