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Neurobehavioral assessment of chronic low-level methyl bromide exposure in the rabbit
Abstract:
The research reported here was intended to identify the concentration at which methyl bromide begins to produce neurotoxic effects in the rabbit, a species known to be sensitive to this compound. Rabbits were exposed via inhalation to 27 ppm methyl bromide over a period of 8 mo for a total exposure duration of 900 h. Biweekly neurobehavioral tests, consisting of the latency rates of the ulnar and sciatic nerves and the amplitude of the eyeblink reflex of the orbicularis oculi muscle, failed to uncover any untoward consequences of the exposures. The rabbits gained weight and otherwise appeared to be healthy. In contrast to reports available in the literature, these findings suggest that long-term exposures to methyl bromide, in the present concentration range, are tolerated by this species. Also detailed in this report is the course of recovery of a separate group of rabbits previously given subchronic exposures to 65 ppm methyl bromide. These animals developed severe neuromuscular losses and had impaired blink reflexes and body weights. The symptoms partially subsided within 6-8 wk after removal from the exposures, suggesting that recovery from a nonfatal but seriously debilitating exposure is possible.
Insights
Long-term exposure to 27 ppm methyl bromide did not cause neurotoxic effects in rabbits. However, rabbits previously exposed to 65 ppm methyl bromide showed partial recovery after exposure cessation.
Area of Science:
- Toxicology
- Neuroscience
- Environmental Health
Background:
- Methyl bromide is a fumigant with known neurotoxic potential.
- Rabbits are considered a sensitive species for studying methyl bromide toxicity.
Purpose of the Study:
- To determine the threshold concentration for methyl bromide-induced neurotoxicity in rabbits.
- To investigate the long-term effects of low-level methyl bromide exposure.
- To assess the recovery process following subchronic methyl bromide exposure.
Main Methods:
- Rabbits were exposed to 27 ppm methyl bromide via inhalation for 8 months (900 hours).
- Neurobehavioral tests included ulnar and sciatic nerve latency and orbicularis oculi muscle eyeblink reflex amplitude.
- A separate group of rabbits previously exposed to 65 ppm methyl bromide were monitored during recovery.
Main Results:
- No neurotoxic effects or adverse health outcomes were observed in rabbits exposed to 27 ppm methyl bromide.
- Rabbits in the 27 ppm group maintained healthy weight and appearance.
- Animals exposed to 65 ppm showed partial recovery of neuromuscular function, blink reflexes, and body weight after exposure cessation.
Conclusions:
- Long-term inhalation of methyl bromide at 27 ppm is tolerated by rabbits without apparent neurotoxicity.
- Recovery from severe neuromuscular deficits caused by subchronic methyl bromide exposure is possible.
- Findings suggest a higher tolerance to methyl bromide in rabbits than previously reported.