A health risk benchmark for the neurologic effects of styrene: Comparison with NOAEL/LOAEL approach

Benchmark dose (BMD) analysis was used to estimate an inhalation benchmark concentration for styrene neurotoxicity. Quantal data on neuropsychologic t est results from styrene-exposed workers [Mutti et al. (1984). American Jou rnal of Industrial Medicine, 5, 275-286] were used to quantify neurotoxicit y, defined as the percent of tested workers who responded abnormally to gre ater than or equal to1, greater than or equal to2, or greater than or equal to3 out of a battery of eight tests. Exposure was based on previously publ ished results on mean urinary mandelic- and phenylglyoxylic acid levels in the workers, converted to air styrene levels (15, 44, 74. or 115 ppm). Nons tyrene-exposed workers from the same region served as a control group. Maxi mum-likelihood estimates (MLEs) and BMDs at 5 and 10% response levels of th e exposed population were obtained from log normal analysis of the quantal data. The highest MLE was 9 ppm (BMD = 4 ppm) styrene and represents abnorm al responses to greater than or equal to 3 tests by 10% of the exposed popu lation. The most health-protective MLE was 2 ppm styrene (BMD = 0.3 ppm) an d represents abnormal responses to greater than or equal to1 test by 5% of the exposed population. A no observed adverse effect level/lowest observed adverse effect level (NOAEL/LOAEL) analysis of the same quantal data showed workers in all styrene exposure groups responded abnormally to greater tha n or equal to1, greater than or equal to2, or greater than or equal to3 tes ts, compared to controls, and the LOAEL was 15 ppm. A comparison of the BMD and NOAEL/LOAEL analyses suggests that at air styrene levels below the LOA EL, a segment of the worker population may be adversely affected. The bench mark approach will be useful for styrene noncancer risk assessment purposes by providing a more accurate estimate of potential risk that should, in tu rn, help to reduce the uncertainty that is a common problem in setting expo sure levels.