Chronic Exposure Studies with Monomethylhydrazine

The manufacture and use of monomethylhydrazine MMH as a rocket fuel has increased over the past 10 years. The acute health hazards from handling this highly reactive compound are well defined, but although its usage is increasing little is known about its chronic exposure effects. The current industrial threshold limit value TLV of 0.2 ppm was established by analogy with hydrazine and unsymmetrical dimethylhydrazine. A series of 6-month MMH chronic exposures to four animal species was undertaken to evaluate the safety factor and appropriateness of the current TLV for health of workmen. The results of these experiments showed that MMH produces a dose-related hemolytic anemia with Heinz body formation for which there appears to be no threshold effect level. The anemia is reversible with removal from further exposure at least up to a level of 5 ppm intermittent exposure. For use in establishing continuous exposure limits for confined spaces such as missile silos, consideration should be given to variations in concentration which could considerably shift the exposed people down the effect curve. Consideration should also be given to the effect of MMH on people with preexisting blood dyscrasias or hemolytic traits.