Ototoxicity in rats exposed to ethylbenzene and to two technical xylene vapours for 13 weeks.
Male Sprague-Dawley rats were exposed to ethylbenzene (200, 400, 600 and 800 ppm) and to two mixed xylenes (250, 500, 1,000 and 2,000 ppm total compounds) by inhalation, 6 h/day, 6 days/week for 13 weeks and sacrificed for morphological investigation 8 weeks after the end of exposure. Brainstem auditory-evoked responses were used to determine auditory thresholds at different frequencies. Ethylbenzene produced moderate to severe ototoxicity in rats exposed to the four concentrations studied. Increased thresholds were observed at 2, 4, 8 and 16 kHz in rats exposed to 400, 600 and 800 ppm ethylbenzene. Moderate to severe losses of outer hair cells of the organ of Corti occurred in animals exposed to the four concentrations studied. Exposure to both mixed xylenes produced ototoxicity characterized by increased auditory thresholds and losses of outer hair cells. Ototoxicity potentiation caused by ethylbenzene was observed. Depending on the mixed xylene studied and the area of the concentration-response curves taken into account, the concentrations of ethylbenzene in mixed xylenes necessary to cause a given ototoxicity were 1.7-2.8 times less than those of pure ethylbenzene. Given the high ototoxicity of ethylbenzene, the safety margin of less or equal to two (LOAEL/TWA) might be too small to protect workers from the potential risk of ototoxicity. Moreover, the enhanced ototoxicity of ethylbenzene and para-xylene observed in mixed xylenes should encourage the production of mixed xylenes with the lowest possible concentrations of ethylbenzene and para-xylene.
Gagnaire
François
F
Département Polluants et Santé, Institut National de Recherche et de Sécurité, Avenue de Bourgogne, BP 27, 54501 Vandoeuvre Cedex, France. francois.gagnaire@inrs.fr
Langlais
Cristina
C
Grossmann
Stéphane
S
Wild
Pascal
P
D000395:Air Pollutants, Occupational / Q000633:toxicity*; D000818:Animals; D001273:Atmosphere Exposure Chambers; D001299:Audiometry; D001555:Benzene Derivatives / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D007758:Ear, Inner / Q000187:drug effects* / Q000473:pathology; D005072:Evoked Potentials, Auditory / Q000187:drug effects*; D006198:Hair Cells, Auditory / Q000187:drug effects* / Q000473:pathology; D019570:Inhalation Exposure; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D014992:Xylenes / Q000633:toxicity*
D000395:Air Pollutants, Occupational; D001555:Benzene Derivatives; D014992:Xylenes; C004912:ethylbenzene