Olfactory toxicity of methyl iodide in the rat.

The monohalomethanes (methyl iodide, methyl bromide and methyl chloride) are widely used industrial methylating agents with pronounced acute and chronic toxicity in both experimental animals and man. Recently inhalation exposure of rats to methyl bromide has been shown to result in severe olfactory toxicity. This study examined the effects on the rat nasal cavity of inhalation of methyl iodide (100 ppm for 0.5-6 h), and demonstrated that methyl iodide is a more potent olfactory toxin than methyl bromide. Within the nasal cavity the olfactory epithelium was the principle target tissue, and it was only at high doses (600 ppm.h) that limited damage to transitional epithelium occurred. The squamous and respiratory epithelia were consistently unaffected. Within olfactory epithelium the sustentacular cells were the primary cellular target and damage to sensory cells appeared to be a secondary event. Methyl iodide induced olfactory damage was reversible, and 2 weeks after exposure almost complete repair had taken place.