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TENTH INTERIM REPORT OF THE SUBCOMMITTEE ON ACUTE EXPOSURE GUIDELINE LEVELS 15 trichloride is one-third of the HCl AEGL-1, based on the proposed mechanism. The subcommittee agreed that information was not sufficient to derive an AEGL-1. AEGL-2: Summary: It was suggested that AEGL-2 could be derived by dividing the AEGL-3 value by 3, as outlined in the SOPs, should the NAC revise the TSD. Using the same approach as for AEGL-1, the boron trichloride AEGL-2 is derived by a surrogate approach based upon AEGL-2 values for HCl, as there are no relevant data for the boron trichloride. The committee suggested that the SOPs be followed and the AEGL-2 derived from the AEGL-3 by dividing by 3. AEGL-3: Summary: While concerned about the paucity of data, the subcommittee agreed with the proposed approach. The proposed AEGL-3 values are based on a one-third value of the 1-hr male rat LC50 data of Vernot et al. (1977) with a total uncertainty factor of 30 applied. While the reviewers had concerns about the lack of reporting of details in Vernot et al., they agreed with the derivation of the AEGL-3, as there are no relevant human data and these are the only relevant animal data. Specific Comments Page viii and page 11. Some concluding statement about the confidence the reader can place in the AEGL values should be included here, given the fact that only two publications could be located in the literature. Page vii-viii. The AEGL derivations for BCl3 follow the identical logic utilized by the TLV committee in derivation of the values for boron trifluoride and boron tribromide. All of these derivations by analogy make the assumption that the parent materials possess no inherent toxicity independent from their degradation to corresponding halides. At pages viiâviii and pages 8â10, all of the AEGL values for all time points are based on the HCl arising from the decomposition of BCl3. The problem here is that the boron entity is neglected in these discussions. It is appropriate to discuss the observations made on page 2311 by Spiegel that âinhaled elemental boron itself was judged ârelatively nontoxicâ in that âexposure to >70 mg/m3 over 30 days produced no deaths or other signs of toxicity in miceâ. This observation is reflected in the TLV for boron oxide (10 mg/m3); however, the occupational experience with boric acid (J. Occup. Med. 26(8):584â 586, 1984)âas one decomposition product (page 6, line 28; page 7, line 3)âand the TLVs for the borate salts (1â5 mg/m3) reflect the irritation associated with exposure to the acid. An explanation of the contribution of the boron entity and boric acid to the overall disposition and toxicity of inhaled boron trichloride should be included in Section 4.2. Page 1. Discussion of the production and use of boron trichloride should be expanded: âThere is only one company in the United States which produces commercial quantities of BCl 3, and it has an annual capacity of ~275 metric tons. Industrial grade BCl3 contains 0.01â 0.09% phosgene and Cl2. Over 95% of the BCl 3 produced is consumed in the manufacture
TENTH INTERIM REPORT OF THE SUBCOMMITTEE ON ACUTE EXPOSURE GUIDELINE LEVELS 16 of boron continuous filament fibers (whisker crystals) that are produced during thermal decomposition of boron trichloride. Boron filaments are stronger than carbon fibers and are incorporated into polymer and metal matrices used in both the aerospace and sporting goods industries. Boron trichloride is also used as a catalyst in polymerization of styrene and cyclopentadiene in aluminum refining, and it is used along with TiCl4 in zinc vapor to form a titanium-boron alloy applied to the carbon fiber surface to promote carbon diffusion and to promote fiber âwettingâ. âCommercial BCl3 is shipped in steel cylinders (0.9â817 kg). The material can explode upon contact with water and at elevated temperature; it decomposes to produce chlorine gas.â Page 1, 1st paragraph. It would be helpful if the NAC would contact the sole production company (Kerr-McGee Chemical) and obtain details about how this substance is handled (e.g., exclusively closed-systems?), transported, and where and how many facilities use this material in production of aerospace/sporting goods. Additional information on the range of quantities commonly stored on-site or on whether the substance is used immediately upon receipt would be helpful. Page 1, Table 1: The dissociation constant should be added to the table. Page 2, lines 19â24: It should be noted in the study description of Vernot et al. (1977) that the lethality data are not shown in the report (only the LC50 and confidence limits are presented). The methods for exposure generation and measurement should be described. Page 2, line 26: The highest concentration for the two 7-hr daily periods in Stockinger and Spiegel (1953) is 85 ppm (not 80 ppm). It should also be noted that a âwet, sticky layer appeared on the cage floors and animal fur.â Page 3, line 5. The statements as written do not make sense. If all of the rats died after exposure to 20 ppm for 7 hr, then it does not follow that 30% mortality was found after similar exposure to 85 ppm for the same exposure duration (see also in Table 2). Page 3, line 8: Apparently only the rats showed swelling; double check as to whether mice also showed swelling. Pages 4: Why is it necessary to repeat the information presented in Sections 3.2.1, 3.2.2 and 3.2.3 that was already given in Sections 3.1.1, 3.1.2, and 3.1.3, respectively? These studies are not utilized to derive AEGLs. The presentation would be improved substantially by presenting all of the data (given the fact only two studies are available) in one section and then explain the mode of action and rationale for establishment of the AEGLs by analogy. Page 5, lines 2â3. Have other borates been considered by either IARC, NTP, or EPA? Page 5, line 21. Rephrase sentence to show it is compared with other guinea-pig study. Page 7, Section 4.2. This section and table need to provide more explanation. It should be clearly acknowledged that the mechanism of toxicity for BCl3 is not known. Further, what