On April 30, 2024, the EPA banned many uses of methylene chloride, a chemical widely used as a paint stripper and in industrial applications, based on an “unreasonable risk to human health.” This presents a total reversal of their earlier conclusions that methylene chloride did not pose an unreasonable risk. How did EPA use the same data to reach two opposing conclusions?
Methylene chloride is used in adhesives, paint and coating products, metal cleaning, aerosols, and in the manufacture of other chemicals. It is also used as a paint stripper and as a laboratory solvent. Between 2016 and 2019, the total production volume ranged from 100 to 500 million pounds.
EPA Administrator Michael Regan said that the new rule,
“brings an end to unsafe methylene chloride practices and implements the strongest worker protection possible for the few remaining industrial uses, ensuring no one in this country is put in harm's way by this dangerous chemical” [emphasis added]
However, there are significant exceptions (carve-outs) to the rule, which raise the question of how impactful the ban is.
Toxic Substances Control Act Risk (TSCA)
This begins with the Toxic Substances Control Act (TSCA), where the EPA uses risk assessments to determine whether a chemical presents an unreasonable risk of injury to health under the conditions of use.
In 2020, the EPA’s risk assessment concluded that it did not present an unreasonable risk to human health. The EPA’s revised assessment, the basis for the new rule, used the same data as in the 2020 assessment; however, the EPA revised several aspects of the risk assessment process:
- In 2020, EPA made individual risk determinations based on individual conditions of use. [1] In 2022, the EPA aggregated these numbers as a “whole chemical approach, consisting of one overall risk determination for methylene chloride because it ‘better aligns with the statute and Congress’ intent,’ and enables the Agency’s risk determinations to better reflect the potential for combined exposures across multiple conditions of use”.
- In 2020, the EPA assumed that personal protective equipment (PPE) was always provided and used in occupational settings; now, they assume no use of PPE. This was based on the recognition that some workers may not be covered under Occupational Safety and Health Administration (OSHA) standards or because many of OSHA’s standards are “outdated and inadequate for ensuring protection of worker health.”
With these changed assumptions, the EPA risk “flipped,” finding methylene chloride presents an unreasonable risk of injury to health.
Health Effects
The EPA notes the adverse impact of methylene chloride on the central nervous system, liver, and the development of cancers.
Central nervous system effects: Exposure to very high levels of methylene chloride results in dizziness, incoordination, drowsiness, respiratory depression, and coma. In the U.S., from 1980 to 2018, there were 85 methylene-chloride-related fatalities, the majority (87%) in occupational settings, most in small, unventilated rooms. From 1985 to 2017, there were 37,201 non-fatal cases of methylene chloride poisoning, with a decrease in the annual number of cases beginning in the late 1990s. [2]
Liver effects: Very high exposure can cause liver injury. Additionally, methylene chloride is partially metabolized (broken down) in the liver to carbon monoxide, which can decrease blood’s ability to carry oxygen.
Cancer: Methylene chloride has caused lung and liver tumors in mice but not in rats. The data from human studies are mixed, with most studies not demonstrating cancer after long-term exposure. Using the linear exposure model, which overestimates risk, the EPA considers methylene chloride to be “likely to be carcinogenic to humans” based on studies in mice. [3]
The real risks from methylene chloride exposure are to unprotected individuals who are exposed to very high levels of the chemical in unventilated rooms, resulting in central nervous system effects. Effects on the liver are rare, and cancer is not a concern, as cancer has only been observed in mice, not in humans.
Exceptions to the Rule
With this ruling, the EPA banned many uses of methylene chloride, including the manufacturing, processing, and distribution of methylene chloride for all consumer uses and most industrial and commercial uses, including paint and coating removers. However, the EPA carved out exceptions to the ban for methylene chloride used:
- in the production of other chemicals that are important to reduce global warming
- in the production of battery separators for electric vehicles
- as a processing aid in a closed system
- as a laboratory chemical
- in plastic and rubber manufacturing, including polycarbonate production
- in solvent welding
Additionally, EPA allowed specific uses of methylene chloride required by the National Aeronautics and Space Administration (NASA), the Department of Defense (DOD), and the Federal Aviation Administration (FAA) to continue with strict workplace controls, stating that “sufficient reductions in exposure are possible in these highly sophisticated environments, thereby minimizing risks to workers.”
Let’s look at these exceptions. While it is difficult to obtain numbers for total methylene chloride use, its use as a processing aid in plastic and rubber manufacturing and solvent welding is significant. Its continued allowable use as a laboratory chemical will make organic chemists everywhere, including ACSH’s Dr. Bloom, very happy. The carve-out for chemicals used to reduce global warnings and battery separators for electric vehicles is a nod to politically correct rulemaking.
The EPA’s assertion that select government agencies are given a carve-out because they can reduce exposures due to their “highly sophisticated environments” is nonsensical; private companies contract with the government to do this work, and they are no more sophisticated in their workplace controls than private companies not working for the government.
Looking at the carve-outs in total, it is questionable whether this is actually an “almost total ban,” as the administration has touted, and whether the rule's significance is anywhere near the hype behind it.
[1] Conditions of use include manufacturing, processing, industrial, 33 commercial, and 12 consumer applications.
[2] The EPA calculates margins of exposure (MOE) for the central nervous system and liver effects, consisting of benchmark dose levels for each effect divided by the exposure concentration for the specific scenario being evaluated.
[3] The EPA used cancer risk estimates, calculated from studies in mice, that estimate the probability of an individual in an exposed population developing cancer over a lifetime.
