OSHA's existing limit for dichlorodiphenyltrichloroethane (DDT) is 1 mg/m3 TWA as an 8-hour TWA, with a skin notation. The ACGIH has the same 8-hour TWA limit for DDT, without a skin notation. NIOSH has a REL of 0.5 mg/m3 for DDT. The Agency proposed to retain both the skin notation for DDT and the existing 8-hour TWA limit. The final rule retains the skin notation and the Agency's 8-hour TWA PEL. DDT is a noncombustible, colorless to white powder with a slightly aromatic odor.
The U.S. Public Health Service (Neal, von Oettingen, Smith et al. 1944, as cited in ACGIH 1986, p. 168) reports that six daily exposures of one hour each to 423 mg/m3 DDT was without effect in human volunteers. Barnes (1953, as cited in ACGIH 1986, p. 168/Ex. 1-3) reported that a review of the world literature revealed no illness among workers from many countries who applied DDT as an insecticide. At chronic exposure levels of 35 mg/person/day, no adverse health effects are observed in humans, but DDT does accumulate in the fatty tissues of the body and it is possible that delayed effects might occur after many years (ACGIH 1986, p. 168/Ex. 1-3). OSHA received no comments on DDT except those from NIOSH (Ex. 8-47, Table N6B), which urged regulation of DDT as a potential occupational carcinogen. The dermal LD(50) in rabbits is 400 mg/kg (Dangerous Properties of Industrial Materials, 7th ed., Sax and Lewis 1989), indicating a significant degree of percutaneous absorption that justifies the skin notation.
Based on a review of the evidence of the health effects of exposure to DDT, OSHA concludes that the existing PEL of 1.0 mg/m3 is adequate to protect workers from the significant risk of bioaccumulation of DDT in adipose tissue, which may have the potential to produce delayed ill effects in later years. The Agency finds that the existing limit, with its skin notation, provides appropriate protection against DDT's systemic effects.