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Tenth Interim Report of the Subcommittee on Acute Exposure Guideline Levels
COMMENTS ON HYDRAZINE
At its July 21–23, 2003 meeting, the subcommittee reviewed the AEGL document on hydrazine. The presentation was made by Robert Young of Oak Ridge National Laboratory. The subcommittee recommends a number of revisions. A revised draft should be reviewed by the subcommittee at its next meeting.
The uncertainty factors (UFs) are not applied consistently. For irritants and direct acting chemicals (and the case is made for irritation as the primary effect for AEGL-1 and AEGL-2 values), interspecies and intraspecies UFs generally applied were 3 each. This was done for the hydrazine AEGL-1. However, for AEGL-2 values, the statement is made, “An uncertainty factor of 10 for interspecies variability was applied to account for the high degree of variability in the data due to the extreme reactivity of hydrazine that compromised exposure concentration measurements.” There is no explanation of how the deposition of hydrazine on chamber surfaces and difficulties in concentration measurements relate to interspecies variability, especially when hydrazine appears to be direct acting agent. The study by Latendresse et al. (1995) does not appear to suffer from compromised exposure concentration measurements. If the NAC believes the overall uncertainty factor of 30 is appropriate, the subcommittee recommends using inter- and intraspecies UFs of 3 and 3, with a possible modifying factor of 10 for the compromised exposure concentration measurements, which will make the magnitude of all factors to be 100. However, that adjustment cannot apply to the Latendresse study. The subcommittee recommends using a smaller UF based upon the quality of the study and a possible modifying factor to account for the small database and numbers of animals.
The section on level of distinct odor awareness (LOA) is misplaced in the Executive Summary after AEGL-1 and before the AEGL-2 values. The 10-min AEGL-3 is proposed by the NAC to be 63 ppm. How does the NAC explain this level compared with the odor threshold level of 3–4 ppm cited on page 30? From an emergency response perspective, the odor threshold is very important because this is the level at which people will start detecting exposure to hydrazine.
A general statement regarding exposure concentrations should be included. In addition to being highly reactive, the subcommittee understands that hydrazine also adsorbs to most materials, including Teflon. Therefore, the subcommittee recommends that the NAC focus on the more recent studies that have presumably solved the technical problems with concentration measurements and use other studies as supporting information.
In Section 2.2.2, the Morgenstern and Ritz study (it is only one) seems to have been added without considering what influence those data have on the rest of this section. For example, in the first paragraph, reference is made to a more recent study (1987) when the Morgenstern study was reported in 2001. Does the Morgenstern study follow up or include individuals from the previous studies? How are these studies linked, if at all? Delete the last paragraph. With the Morgenstern (2001) study, the information presented in the last paragraph does not seem to apply.