At its meeting held on January 17-19, 2007, the committee reviewed the revised AEGL technical support document (TSD) on boron trifluoride. The presentation was made by Claudia Troxel of Oak Ridge National Laboratory, and James Dennison of Century Environmental Hygiene, LLC.
A revised draft TSD can be finalized if the recommended revisions are made appropriately. The primary difference between this version of the boron trifluoride TSD and the version the committee reviewed in 2002 is the addition of the 2005 report by A.M. Bowden (of the Huntingdon Laboratories), which was sponsored by Honeywell International (Bowden 2005). Although the Bowden report addresses the 4-hour (h) inhalation toxicity of boron trifluoride dihydrate rather than the dimethyl ether, the report is clearly relevant, and the authors have used its data to revise the AEGL-1. As discussed in the TSD, upon contact with even low levels of moisture in the air, boron trifluoride reacts to form the dihydrate. Boron trifluoride dihydrate is strongly corrosive to the eyes and skin of rabbits. The Bowden report was not included with a copy of the revised boron trifluoride document, but the document described the data in detail on pages 11 through 13. The Bowden report appears to be a well-conducted acute inhalation study from an established laboratory recognized for the quality of its toxicology studies.
The previous TSD on boron trifluoride raised a major concern for the committee because it used delayed irritancy (seen at 2 weeks after starting exposure) as the criterion upon which to base the AEGL-1. The Bowden data provide a better basis for the AEGL-1 and resolved the concern about using delayed irritancy. Additionally, the committee pointed out that in 1960 the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) committee set the TLV for boron trifluoride at 1 part per million (ppm) (2.8 mg/m3) based partly on work that Bowden conducted on the Manhattan project at Rochester. Although these studies were not published, Stockinger and Spiegl (1953) discussed them. This is important for two reasons: (1) the only human data available for boron trichloride consist of one accidental exposure, and (2) the current AEGL-1 (2.5 mg/m3) is much closer to Stokinger’s and Spiegl’s recommendation (2.8 mg/m3) than the previous value (0.6 mg/m3). The current AEGL-1 is also a better match for the Torkelson data where the NOAEL was 1.5 ppm (Torkelson et al, 1961).
The revised basis for establishing the AEGL-3 for boron trifluoride presented on page 27, uses the same data (Rusch et al. 1986) as the 2002 TSD but uses a different method (log-probit analysis with EPA benchmark dose software version 1.3.2) for interpretation of these data. Looking at the data presentation in Figure 1 (category plot on page 30) and in the probit plot on page 46, use of the different method seems reasonable and appropriate. The revised TSD provides more scientific and defensible AEGL values for boron trifluoride at all three levels.
The revised TSD corrects the typos found in the previous version and improves the wording in a few places.
The document is not consistent in its use of NOEL and NOAEL. For example, the summary on page vii says, “The AEGL-1 is based on a NOEL for irritation.” In contrast, page 23 says, “The AEGL-1 is based on a NOAEL for irritation.”
It would be helpful to the reader to add an explanation to the probit plot on page 46 (which has no log scale) to indicate how it relates to the log-probit analysis.