© Dushlik stock.adobe.com
The US EPA has preliminarily determined that ethylene dibromide (EDB) presents an unreasonable risk to workers under ten of 12 evaluated conditions of use (COUs), according to a draft TSCA risk evaluation released on 18 August.
If the findings are upheld in a final evaluation, the agency would be required to initiate risk management actions under TSCA section 6(a).
Also known as 1,2-dibromoethane, EDB is used primarily as a lead scavenger in leaded aviation fuel (avgas) to prevent engine fouling. The chemical was designated as a TSCA high-priority substance in December 2019.
Updated 2024 Chemical Data Reporting (CDR) data indicate that current manufacture and import volumes are below 1 million Ibs per year, compared with EPA estimates of 1 million to 20 million Ibs based on 2016 submissions.
The draft risk evaluation found that unreasonable risks to workers are driven by inhalation and dermal exposures during activities including import, processing, industrial use, laboratory use, aircraft refuelling operations and disposal. Four of the ten COUs also present unreasonable inhalation risks to occupational non-users (ONUs), according to the draft.
Cancer was identified as the most sensitive health endpoint, with chronic inhalation or dermal cancer risks driving unreasonable risk findings across all ten affected COUs.
The agency did not identify unreasonable risks to consumers, the general population – including fenceline communities – or the environment.
The EPA’s draft derived a protective occupational exposure value (OEV) of 970ppt as an eight-hour time-weighted average (TWA), around 20,000-fold below the Occupational Safety and Health Administration (OSHA)’s existing permissible exposure limit (PEL), signalling the potential for significant risk management measures if the preliminary findings are upheld.
The draft evaluation comes as state governments and other entities continue their efforts to transition away from leaded aviation fuel, EDB’s primary current use.
However, the EPA noted that the draft risk evaluation addresses EDB alone and does not alter the agency’s 2023 endangerment finding for leaded avgas or the Federal Aviation Administration (FAA)’s ongoing work under the Eliminate Aviation Gasoline Lead Emissions (EAGLE) initiative to phase out leaded aircraft fuel by the end of 2030.
Uses posing unreasonable risk
The EPA preliminarily determined that ten of EDB’s 12 evaluated COUs contribute to unreasonable risk.
Most findings involved inhalation and dermal exposures for workers, with a smaller subset of four COUs affecting ONUs, which are workers who do not directly handle a chemical but may be indirectly exposed in the workplace.
The unreasonable risk findings were driven primarily by chronic inhalation and dermal cancer risks.
According to the draft risk evaluation, seven COUs present unreasonable cancer risk to workers through both inhalation and dermal exposure:
- import;
- processing into a formulation, mixture, or reaction product for fuels and fuel additives in petroleum refineries;
- processing into a formulation, mixture, or reaction product for fuels and fuel additives in all other petroleum and coal products manufacturing;
- processing as a reactant, including in pigment and dye manufacturing and plastic material and resin manufacturing;
- repackaging;
- processing as an unspecified aid in pigment and dye manufacturing; and
- commercial use as a laboratory chemical.
Two COUs present unreasonable risk to workers from inhalation exposure alone:
- industrial use in fuel agents in petroleum refineries; and
- commercial use in fuels and related products.
Disposal was found to present cancer risk to workers through dermal exposure.
In addition to EDB’s unreasonable risks to workers, four COUs presented unreasonable inhalation risk to ONUs:
- import;
- repackaging;
- industrial use as a fuel agent in petroleum refineries; and
- commercial use as a laboratory chemical.
The EPA also identified non-cancer risks for certain import and repackaging activities, including reproductive and developmental, liver and gastrointestinal toxicity concerns.
The EPA said many of the workplace risks could be addressed through the use of personal protective equipment (PPE) such as respirators and gloves, or other exposure controls.
Finally, two COUs were found not to significantly contribute to any unreasonable risk:
- distribution in commerce; and
- consumer use in fuels and related products.
Occupational exposure value
The EPA derived a draft OEV of 970ppt as an eight-hour time-weighted average (TWA), based on lifetime cancer risk from chronic inhalation exposure.
The agency said the value is intended to be protective against carcinogenicity and male reproductive effects and would also protect workers against non-cancer health effects.
The draft OEV is roughly 20,000 times lower than OSHA’s current PEL of 20ppm, which was adopted in 1971. It is also substantially lower than the National Institute for Occupational Safety and Health (NIOSH)’s recommended exposure limit of 0.045ppm, which was set in 1977.
The EPA also derived a draft 15-minute short-term exposure value (STEV) of 0.92ppm, which is higher than NIOSH’s 15-minute ceiling limit of 0.13ppm.
An OEV represents a risk-only figure that may be used to inform an existing chemical exposure limit (ECEL) during risk management. Any future ECEL established in a possible TSCA 6(a) risk management rule could differ after consideration of factors such as technological feasibility, the availability of alternatives and potential critical or essential uses.
Next steps
Before being finalised, the draft risk evaluation is subject to a 60-day public comment period and a peer review by the Science Advisory Committee on Chemicals (SACC).
The EPA said it is seeking information on topics including worker exposures, occupational monitoring data, PPE practices, engineering controls and aviation fuel refuelling activities. The agency is also seeking feedback on its draft OEV and STEV, as well as facility-specific information that could refine its exposure and release estimates.
Comments are due by 19 October.
If the EPA ultimately determines that EDB presents unreasonable risks, the agency would initiate risk-management rulemaking under TSCA section 6(a).
The EPA is due to finalise the risk evaluation by 12 February 2027 under a court-ordered consent decree.