Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
REVIEW OF ACUTE HUMAN-TOXICITY ESTIMATES FOR HD 61 of eight men (clothed, wearing protective gas masks, and not exercising) in which exposures of 500 mg-min/m3 for over 1 hr produced severe scrotal effects in four of the eight men (Heinen et al. 1945). The estimate is supported by the results of exposure to lower concentrations of HD in the same study. The subcommittee concludes that the proposed estimates for hot and moderate temperatures are scientifically valid. ECt50 for Threshold Effects CDEPAT's proposed ECt50 estimates for threshold (minimal) effects from percutaneous exposure to HD vapor are 50 mg-min/m3 for moderate temperatures and 25 mg-min/m3 for hot temperatures, assuming exposure durations of 30 to 50 min. There are no existing estimates for the threshold effects of HD (CDEPAT 1994). Human data used to support the proposed estimate, which apparently came from the Project Coordination Staff (PCS) report of 1946, were not given in sufficient detail in the CDEPAT report to allow for full evaluation. The PCS report concluded that the maximum safe exposure to HD for percutaneous exposure is 50 mg-min/m3. At that exposure, HD was associated with no important injury. More data on the effects of low vapor doses would have to be available to evaluate these estimates fully. The subcommittee recommends that these ECt50 estimates (for hot and moderate temperatures) serve as interim values until further research is conducted to establish the estimates with a greater degree of confidence. INHALATION VAPOR EXPOSURE Lethal Effects (LCt50) CDEPAT's proposed estimate for the LCt50 effects from inhalation exposures to HD vapor, assuming exposure durations of 2 to 10 min and minute volumes of 15 liters, was reduced from the existing value of 1,500 mg-min/m3 to the value of 900 mg-min/m3 (CDEPAT 1994). Because of the nature of the end point (lethality), the LCt50 estimates were based on animal data. CDEPAT averaged the LCt50 from all the 10-min LCt50 data in different animal species to arrive at its estimate. No animal LCt50 studies on HD are adequate for use in estimating the human