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The synergistic effects of simultaneous exposure to different risk factors (S´liwin´ska-Kowalska, 2003; Morata, 2002; Steyger, 2009) is a priority for preventionistic research. The European Directive 2003/10/CE, about occupational noise exposure, recommends highlighting, in the risk evaluation, the simultaneous exposure to noise and other ototoxic agents like vibration and organic solvents. A quantification criterion for risk evaluation due to synergic interaction between different ototoxic agents is missing.
Methods
The cochlear functionality was monitored before and after a working shift in volunteers in a glass-reinforced plastic factory by means of otoacoustic emission tests. Both TEOAE and DPOAE were measured using the ILO292 portable system. The styrene exposure was assessed by means of personal air monitoring and biomonitoring according to ACGIH. The quantitative determination of urinary Mandelic and Phenylglyoxylic acid was performed by HPLC/MS/MS with isotopic dilution. The styrene internal dose was also determined in saliva, an innovative matrix, by means of headspace GC/MS. Finally, the noise levels were measured using wearable phonometers. The correlations among cochlear functionality, urinary concentrations, salivary and environmental doses will be carefully studied.
Results
The first results show that workers dealing with glass reinforced plastic are exposed to styrene levels even exceeding the ACGIH TLVs. A good correlation was found between environmental and salivary doses. The OAE-based tests can effectively discriminate between different classes of exposure: statistically significant differences were found between workers exposed to high levels of noise and mild levels of styrene (class 1) and workers exposed to low levels of noise (Lex,8h around 80 dB(A)) and high levels of styrene (class 2). Both classes showed statistically significant differences with respect to non exposed volunteers.
Discussion
An high interdisciplinary approach should be used to assess multiple exposures, in particular to verify the possible synergistic effect of different risk agents. Results will allow to identify biomarkers predictive for cochlear damages.