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 test results from styrene-exposed workers [Mutti et al. (1984). American Journal of Industrial Medicine, 5, 275-286] were used to quantify neurotoxicity, defined as the percent of tested workers who responded abnormally to > or = 1, > or = 2, or > or = 3 out of a battery of eight tests. Exposure was based on previously published results on mean urinary mandelic- and phenylglyoxylic acid levels in the workers, converted to air styrene levels (15, 44, 74, or 115 ppm). Nonstyrene-exposed workers from the same region served as a control group. Maximum-likelihood estimates (MLEs) and BMDs at 5 and 10% response levels of the exposed population were obtained from log-normal analysis of the quantal data. The highest MLE was 9 ppm (BMD = 4 ppm) styrene and represents abnormal responses to > or = 3 tests by 10% of the exposed population. The most health-protective MLE was 2 ppm styrene (BMD = 0.3 ppm) and represents abnormal responses to > or = 1 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 > or = 1, > or = 2, or > or = 3 tests, 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 LOAEL, a segment of the worker population may be adversely affected. The benchmark approach will be useful for styrene noncancer risk assessment purposes by providing a more accurate estimate of potential risk that should, in turn, help to reduce the uncertainty that is a common problem in setting exposure levels.
Rabovsky
J
J
Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Oakland 94612-1499, USA. jrabovsk@oehha.ca.gov
Fowles
J
J
Hill
M D
MD
Lewis
D C
DC
D000395:Air Pollutants, Occupational / Q000032:analysis / Q000633:toxicity; D006801:Humans; D009498:Neurotoxins / Q000008:administration & dosage / Q000032:analysis / Q000633:toxicity*; D019055:No-Observed-Adverse-Effect Level; D016273:Occupational Exposure; D018570:Risk Assessment / Q000379:methods*; D020058:Styrene / Q000008:administration & dosage / Q000032:analysis / Q000633:toxicity*
D000395:Air Pollutants, Occupational; D009498:Neurotoxins; D020058:Styrene