Formerly, OSHA had no limit for atrazine; an 8-hour TWA of 5mg/m3 was proposed. The final rule establishes this limit, which isconsistent with that of the ACGIH. NIOSH (Ex. 8-47, Table N1) concurs withthis limit for atrazine. Atrazine is a stable, white, crystalline compound.
Animal studies indicate that the oral toxicity of thes-triazine herbicides, of which atrazine is the best known, is relatively low. However, the ingestion of high doses can cause ataxia, dyspnea and convulsions in animals (ACGIH 1986/Ex. 1-3, p. 44). Rats, dogs,horses, or cattle fed dietary levels of more than 25 ppm of atrazine for extended periods did not exhibit adverse effects. The s-triazine herbicides are apparently excreted in urine and feces within relatively short periods of time (Bakke, Larson, and Price 1972/Ex. 1-950). The s-triazines appear to interfere with carbohydrate metabolism by blocking the production of sugars (Gysin 1962/Ex. 1-740; Gast 1958, as cited in ACGIH 1986/Ex.1-3, p. 44).
There have not been reports of atrazine poisoning in exposed people (ACGIH 1986/Ex. 1-3, p. 44). Because there are no reports of human reactions to atrazine that can be correlated with airborne concentrations, the 5 mg/m3 limit was set on the basis of animal studies. Long-term feeding studies in dogs have established 3.75 mg/kg as the highest no-adverse-effect level (PEA 1979, as cited in ACGIH 1986/Ex. 1-3,p. 44).Assuming that lung absorption is less than 50 percent and applying a safety factor would yield an 8-hour TWA limit for humans of 5mg/m3 (Zielhuis and van der Kreek 1979/Ex. 1-613).
Wayne Bellinger, Corporate Safety Director of ConAgra, Inc.,objected to the establishment of permissible exposure limits on the basis of a no-adverse-effect level (Ex. 3-635). In support of this position, ConAgra referred to the proposed limit for atrazine; according to ConAgra, PELs should not be set "where there are no reports of human reactions that can be attributed to air concentrations" (Ex. 3-635, p. 2).
OSHA believes that ConAgra has misunderstood the phrase "no-observed-adverse-effect level" as it is used in toxicology. As discussed in the Description of the Health Effects section, above, this term simply means a level below which overt toxic effects have not been observed and above which they have. The use of a no-observed-adverse-effect level to establish "acceptable" exposure levels, intake values, etc. is common, both in the health effects literature and in public health agencies; this approach is widely used with substances that have threshold effects. In addition, it is standard toxicological practice to rely on animal data when human data aresparse or nonexistent, as is the case for atrazine. OSHA has reviewed the health effects evidence for this substance and finds the proposed rule's limit both appropriate and necessary to protect against significant workplace risk.
In the final rule, OSHA is establishing an 8-hour TWA PEL of5 mg/m3 for atrazine. The Agency concludes that this limit will protect employees from the significant risk of neuropathic and metabolic effects, which constitute material health impairments that are likely to occur at levels above the new PEL.