OSHA formerly had a 15-mg/m3 total particulate limit for malathion, with a skin notation; the ACGIH TLV for this substance is 10 mg/m3 as a TWA, also with a skin notation, and the NIOSH REL is 15 mg/m3. The proposed PEL was 10 mg/m3 (total particulate), with a skin notation. The final rule establishes a 10 mg/m3 TWA limit for total malathion particulate and includes a skin notation; the 5-mg/m3 TWA limit for the respirable fraction is retained. NIOSH (Ex. 8-47, Table N4) concurs with the selection of these limits. Malathion is a noncombustible, yellow to deep brown liquid with a skunk-like odor.
Malathion is a widely used organophosphorus insecticide having a relatively low level of toxicity; some authors have determined that malathion is approximately 1/100th as toxic as parathion (Johnson, Fletcher, Nolan, and Cassaday 1952/ Ex. 1-149). Rats fed malathion at a concentration of 100 ppm for two years exhibited no toxic effects (Hazleton and Holland 1953/Ex. 1-126). Several occupational and research exposures involving scientists or human volunteers produced no changes in blood cholinesterase or other effects (Rider, Mueller, Swader et al. 1959/Ex. 1-189; Hayes, Mattson, Short, and Witter 1960/Ex. 1-90; Culver, Caplan, and Batchelor 1956/Ex. 1-177). Fatalities have been reported in the Japanese and Indian literature, but these deaths have always involved extremely high doses of malathion (Chabra 1970/Ex. 1-151; Horiguchi 1973/Ex. 1-221). The symptoms of malathion overexposure include headache, lacrimation, vomiting, tremors, and convulsions.
The Agency received, in addition to NIOSH's comment, two record comments on malathion. ConAgra, Inc. (Ex. 3-635) questioned the classification of this substance as a nuisance dust "since most malathion-containing pesticides are liquids and are available over the counter for public use in retail stores" (Ex. 3-635, p. 2). OSHA points out that this health effects category includes all particulates (i.e., can include aerosols and mists generated by the handling of liquid materials).
Another commenter, Lawrence H. Hecker, Director of Corporate Industrial Hygiene and Toxicology for Abbott Laboratories, questioned the need for a skin notation for a substance with a dermal LD(50) of 200 mg/kg or less in animal tests when there was no evidence of systemic effects in humans as a result of skin contact (Ex. 3-678, p. 3). Dr. Hecker stated that this 200-mg/kg cutoff would be consistent with OSHA's Hazard Communication Standard (29 CFR 1910.1200). OSHA agrees with Dr. Hecker that a consistent policy in regard to skin notations is appropriate but does not agree that the 200-mg/kg level is an appropriate cutoff point. The Agency finds that a dermal LD(50) in rabbits of 1000 mg/kg is a better indicator of dermal toxicity; this is the Hazard Communication Standard's upper cutoff for a toxic, rather than highly toxic, substance administered by the dermal route (see Section VI.C.18 of this preamble for a discussion of OSHA's reasoning on this issue). In addition, OSHA believes that evidence that a substance has caused systemic toxicity in humans exposed via the dermal route is sufficient reason to retain a skin notation; in the case of malathion, OSHA has received reports of exposed workers whose blood cholinesterase levels were reduced after dermal exposure to this substance. OSHA is therefore retaining the skin notation for malathion in the final rule.
In the final rule, OSHA is establishing PELs of 10 mg/m3 TWA (total particulate) and 5 mg/m3 TWA (respirable particulate) with a skin notation. The Agency finds that exposure to malathion poses a significant risk of material health impairment in the form of cholinesterase inhibition.