Evaluation of Long-Term Occupational Exposure to Styrene Vapor on Olfactory Function

Abstract

The primary sensory neurons of the olfactory system are chronically exposed to the ambient environment and may therefore be susceptible to damage from occupational exposure to many volatile chemicals. To investigate whether occupational exposure to styrene was associated with olfactory impairment, we examined olfactory function in 2 groups: workers in a German reinforced-plastics boat-manufacturing facility having a minimum of 2 years of styrene exposure (15-25 ppm as calculated from urinary metabolite concentrations, with historical exposures up to 85 ppm) and a group of age-matched workers from the same facility with lower styrene exposures. The results were also compared with normative data previously collected from healthy, unexposed individuals. Multiple measures of olfactory function were evaluated using a standardized battery of clinical assessments from the Monell-Jefferson Chemosensory Clinical Research Center that included tests of threshold sensitivity for phenylethyl alcohol (PEA) and odor identification ability. Thresholds for styrene were also obtained as a measure of occupational olfactory adaptation. Styrene exposure history was calculated through the use of past biological monitoring results for urinary metabolites of styrene (mandelic acid [MA], phenylglyoxylic acid [PGA]); current exposure was determined for each individual using passive air sampling for styrene and biological monitoring for styrene urinary metabolites. Current mean effective styrene exposure during the day of olfactory testing for the group of workers who worked directly with styrene resins was 18 ppm styrene (standard deviation [SD] = 14), 371 g/g creatinine MA + PGA (SD = 289) and that of the group of workers with lower exposures was 4.8 ppm (SD = 5.2), 93 g/g creatinine MA+PGA (SD = 100). Historic annual average exposures for all workers were greater by a factor of up to 6x. No differences unequivocally attributable to exposure status were observed between the Exposed and Comparison groups or between performance of either group and normative population values on thresholds for PEA or odor identification. Although odor identification performance was lower among workers with higher ongoing exposures, performance on this test is not a pure measure of olfactory ability and is influenced by familiarity with the stimuli and their sources. Consistent with exposure-induced sensory adaptation, however, elevated styrene thresholds were significantly associated with higher occupational exposures to styrene. In summary, the present study found no evidence among a cross-section of reinforced-plastics workers that current or historical exposure to styrene was associated with a general impairment of olfactory function. When taken together with prior studies of styrene-exposed workers, these results suggest that styrene is not a significant olfactory toxicant in humans at current exposure levels.

Occupational styrene exposure and hearing loss: a cohort study with repeated measurements

“…Transforming the LWAE MA + PGA data into styrene air concentrations, one can assume 25-33 ppm as long-term exposure for the group exposed to high-long levels with job tenure of about 15 years (range up to 26 years). As outlined in section "past and current exposure" higher exposures of 80-100 ppm as average can be assumed for the time period before 1995 (Dalton et al 2007;Triebig et al 1985). Thus, (1) the cases with a hearing loss of more than 25 dB and (2) the group diVerences at 125-1,500 Hz and selectively at 8,000-12,500 Hz as well as (3) the "recovery eVects" at frequencies above 8,000 Hz are probably caused by styrene concentrations of more than 50 ppm as an average.…”

Olfactory dysfunction revisited: a reappraisal of work-related olfactory dysfunction caused by chemicals

“…This has already been frequently observed for volatile substances in industry or the laboratory and is correspondingly well documented [126]. Whereas the identification test revealed no differences between exposed and non-exposed individuals in the study published in 2003, the identification test published in 2007 resulted in a significant difference between the workers with high vs. low exposure [125]. Dalton et al state that the proportion of individuals showing poor values in the identification test is substantially higher in both groups (40 and 20%) than in the normal population (10%) [125].…”

“…Other epidemiological studies of workers in the glass fibre reinforced plastic industry revealed no relationship between styrene exposure and a general deterioration in olfactory function [124, 125]. In both studies the olfactory threshold for styrene was significantly higher among the exposed workers.…”

“…High concentrations of the two cytochrome P450 isoforms which are required for the conversion of styrene to styrene oxide were for example detected in respiratory fractions of rats and mice, but not in those of humans [165]. At styrene exposure concentrations resembling those of occupational exposure, mice and rats exhibit extensive damage, whilst humans exhibit no indication of a dose-dependent long-term change in olfactory function [124, 125, 127, 128]. …”

“…Whereas the identification test revealed no differences between exposed and non-exposed individuals in the study published in 2003, the identification test published in 2007 resulted in a significant difference between the workers with high vs. low exposure [125]. Dalton et al state that the proportion of individuals showing poor values in the identification test is substantially higher in both groups (40 and 20%) than in the normal population (10%) [125]. Even with the aid of multiple regression analysis, no association was demonstrated between the results of the identification test and the exposure values measured at present or in the past in the group of workers subject to high exposure.…”