Spring 2024

Evolving Chemical Risk Evaluation and Management Under the Toxic Substances Control Act: Trichloroethylene as an Example

By Lisa Bailey, Ph.D., and Satori Marchitti, Ph.D., DABT

In 2016, the US Congress signed into law the Lautenberg Chemical Safety for the 21^st Century Act, which amended and modernized the Toxic Substances Control Act (TSCA).  Since then, the US Environmental Protection Agency (US EPA) has designated 33 chemicals for high-priority risk evaluations, and has completed final evaluations for the first ten chemicals, including asbestos, trichloroethylene (TCE), perchloroethylene (PCE), carbon tetrachloride, methylene chloride, 1-bromopropane, and 1,4-dioxane (US EPA, 2024).  For five of these chemicals, namely asbestos, TCE, PCE, carbon tetrachloride, and methylene chloride, the agency released proposed risk management rules for public comment in 2023.  Of the 23 additional designated chemicals, US EPA has released draft risk evaluations for tris(2-chloroethyl)phosphate (2023) and formaldehyde (March 2024), and the remaining chemicals are in the scoping/drafting stage of the evaluation process.

Within the proposed rule for TCE, US EPA acknowledged that the ECELs are neither feasible nor achievable long term…[and] has proposed to ban many TCE uses.”

In 2022-2023, subsequent to the release of the final risk evaluations for the first ten chemicals, US EPA determined that a “whole chemical approach” for risk evaluation was more appropriate than evaluating risks for individual chemical uses (US EPA, 2021).  Based on this approach, US EPA released final revised risk determinations for these chemicals, concluding that when a “majority” of conditions of use throughout the lifecycle of a chemical present an unreasonable risk to human health, the chemical as a whole presents an unreasonable risk.  Ultimately, the agency reached this conclusion for each of the first ten chemicals.  Further, in contrast to the final risk evaluations released in 2020, which estimated risks for workers with and without consideration of personal protective equipment (PPE), the revised risk determinations do not consider whether workers wear PPE appropriately.  Instead, US EPA stated that use of PPE will be considered as part of the risk management process.  In addition, in response to public comments, US EPA released a draft screening level approach for assessing ambient air and water exposures to fenceline communities in 2022 (US EPA, 2022).  Accordingly, chemical-specific screening levels for the first ten chemicals were available for public comment in the proposed rules.

Items Exempted from the Trichloroethylene (TCE) Ban

Prior to the release of the first five proposed risk management rules, including for TCE, US EPA derived existing chemical exposure limits (ECELs) for workers based on a 40-year worker lifetime exposure and toxicity criteria described in the risk evaluations.  However, since the ECELs were not part of the risk evaluations, an opportunity for public comment on these exposure limits was not possible until the proposed rules became available in late 2023.

In the proposed rule and risk management for TCE, US EPA proposed an ECEL based on fetal cardiac defects (0.0011 ppm) and another Primary Alternative ECEL based on autoimmune effects (0.004 ppm) (US EPA, 2023a,b).  These ECELs for TCE are very low and highly uncertain due to a number of critical issues, including lack of reproducibility across studies and major flaws in study design and data analysis.  These issues and others have been acknowledged by US EPA and/or identified by various expert panels, including the Science Advisory Committee on Chemicals (SACC).  Overall, the proposed ECELs for TCE are not based on the best available science for TCE toxicity as mandated by TSCA.

Within the proposed rule for TCE, US EPA acknowledged that the ECELs are neither feasible nor achievable long term as part of a workplace chemical protection program (WCPP); consequently, the agency has proposed to ban many TCE uses.  In addition, US EPA has proposed the inclusion of several ten-year exemptions from the TCE ban under TSCA section 6(g) for uses US EPA considers “critical to national security and the national economy and critical infrastructure” (US EPA, 2023a).  These exemptions include US Dept. of Defense (US DOD) vessel production and maintenance, rocket production, and battery separator manufacturing (e.g., used in electric vehicles and energy storage systems).  US EPA’s ECEL requirements within the proposed rule are somewhat contradictory and, essentially, equivalent to an outright ban on all TCE uses because, on one hand, US EPA acknowledges that the ECELs for TCE are not feasible or achievable long term; yet, on the other hand, the agency states that critical exempted uses “must comply with the WCPP requirements…including meeting the ECEL to the extent possible” (US EPA, 2023a).

Depending on the final rule for TCE, exempted critical use industries will likely have to work with US EPA to propose alternative ECELs based on feasibility, analytical methodologies, application of the best available science, and consideration of engineering controls and worker use of PPE.  Notably, and in contrast to risk evaluations for the first ten chemicals, the recent draft risk evaluation for formaldehyde includes an evaluation of risks to fenceline communities and a draft ECEL for worker exposures.  Therefore, interested parties will have an opportunity to comment on these portions of the formaldehyde risk evaluation earlier in the process than was possible for the first ten chemicals.