EPA Adopts New Risk Assessment Approach for Surfactants
The Environmental Protection Agency (EPA) refined its inhalation risk assessment approach for surfactants using a new approach method (NAM). NAMs refer to any non-animal technology, methodology, approach or combination thereof that can be used to derive chemical hazard and risk profiles. Surfactants act as key functional additives in lubricant formulations to manage cleanliness, dispersion, emulsification and surface interactions, as well as provide lubrication itself, depending on the formulation.
The new approach uses a predictive in vitro tissue model of the human upper airway to evaluate respiratory irritation impacts from exposure to two well-known surfactants. This development is part of the EPA’s broader commitment to eliminate animal testing by 2035 and is expected to inform new chemical reviews under Section 5 of the Toxic Substances Control Act (TSCA).
Two Reference Surfactants Anchor the Framework
In an implementation memorandum, the EPA explained that, as an interim approach, the agency will rely on the MucilAir™ 3D human airway epithelial model — a peer-reviewed in vitro platform — to derive human equivalent concentrations (HECs) for portal-of-entry respiratory irritation. Simply put, instead of animal testing, the EPA will use lab-grown human airway tissue to measure how surfactants affect the respiratory tract.
The mechanics are straightforward: The tissue is exposed to the chemical, and the results are used to calculate safe exposure levels for workers and consumers. The EPA has also published a guide for classifying which substances qualify as surfactants under this framework.
The method currently covers most common surfactant types (nonionic, anionic and zwitterionic). Cationic surfactants are not yet included. The EPA derived HECs from two benchmark chemicals:
- Triton X-100 (nonionic) — occupational HEC: 0.06 mg/m³
Oleoyl sarcosine (anionic) — occupational HEC: 0.20 mg/m³
Premanufacture notification (PMN) submitters whose substance-specific data are insufficient may expect the EPA to apply read-across from one of these reference HECs — a conservative default that could significantly constrain the risk characterization for a new surfactant ingredient.
Regulatory Implications for Lubricant Manufacturers
Surfactants appear as emulsifiers, dispersants, lubricants and wetting agents across nearly all metalworking fluid (MWF) formulations (soluble oils, semisynthetics, synthetics) and in passenger car motor oils (PCMOs). Any PMN submission for a new surfactant ingredient in these product lines will now be evaluated against this framework. The practical consequences include:
- Lower points of departure, more regulation. The Triton X-100 HEC of 0.06 mg/m³ is a low benchmark. If the EPA applies it via read-across, risk characterization results will be conservative, and standard industrial hygiene controls may not be sufficient to avoid a Section 5(e) order or significant new use designation.
A structural concern with the reference chemical. Triton X-100 is a branched alkylphenol ethoxylate built on an isooctylphenol chain derived from isobutylene oligomers — a branched architecture. Many surfactants used in MWF and PCMO formulations rely on straight-chain alkyl groups. Branched and straight-chain analogues can exhibit meaningfully different toxicological profiles; reproductive effects sometimes observed with branched structures are not reliably predictive of effects from their straight-chain counterparts. If Triton X-100’s NAM data ultimately reflect toxicity attributable to its branched structure, using those results as the universal nonionic surfactant benchmark could overstate inhalation risk for straight-chain alkyl surfactants used in lubricant formulations.
Need for more surfactant references. In the memo, the EPA acknowledges that Triton X-100 “may not represent all subclasses” and that additional surfactant analogues will be added as data become available. PMN submitters should consider whether the structural classification guide supports distinguishing their substance from the Triton X-100 reference.
Learn more about EPA’s announcement here.
