Development of an inhalation unit risk factor for ethylene dibromide

Area of Science:

• Environmental Toxicology
• Chemical Risk Assessment
• Public Health Science

Background:

• The Texas Commission on Environmental Quality (TCEQ) establishes toxicity factors for airborne chemicals.
• Ethylene dibromide (EDB) is a chemical emitted in Texas requiring updated toxicity assessments.

Purpose of the Study:

• To develop an inhalation unit risk factor (URF) for ethylene dibromide (EDB).
• To establish a health-protective air concentration for chronic EDB exposure.

Main Methods:

• Utilized data from a National Toxicology Program (NTP) 2-year inhalation cancer bioassay on EDB.
• Applied benchmark concentration (BMC) modeling and animal-to-human dosimetric adjustments.
• Identified nasal cavity adenocarcinomas in female rats as the critical carcinogenic endpoint.

Main Results:

• The URF for EDB was calculated as 3.4E-04 per ppb (4.4E-05 per µg/m³).
• The 95% lower confidence limit of the BMC at the 10% excess risk level (BMCL10) was 292.8 ppb.
• A lifetime air concentration of 0.029 ppb (0.22 µg/m³) corresponds to a one in 100,000 excess cancer risk.

Conclusions:

• The developed URF is based on the most sensitive tumorigenic effect in the most sensitive species and sex.
• The established air concentration is considered sufficiently health-protective for the general public.
• This URF will aid in managing potential carcinogenic risks from chronic EDB exposure in ambient air.