Combined effects of paired solvents on the rat's auditory system.

A number of volatile organic solvents have been shown to be ototoxic to rats, but there is little information regarding how solvents might act in this way when encountered in combination. To examine this issue, male Long Evans rats were exposed by inhalation to pairs of solvents known to be ototoxic when administered individually; those reported on here are trichloroethylene+toluene, mixed xylenes+trichloroethylene, xylenes+chlorobenzene, and chlorobenzene+toluene. Rats were exposed 8 h/day for 5 consecutive days, using complementary proportions of isoeffective concentrations of the solvents alone. Hearing was assessed by brainstem-evoked response audiometry. The effects were as predicted by a linear dose-addition model, indicating additive rather than synergistic or antagonistic interactions at the concentrations studied.