Background
Methylene chloride, also known as dichloromethane (DCM), is a common solvent used in a variety of consumer/commercial applications and is found in many academic research labs. The EPA determined that methylene chloride poses an “unreasonable risk to human health or the environment” following review under Toxic Substance Control Act (TSCA) regulations. The final rule was published in April 2024, which prohibits most consumer and commercial uses. An exemption for laboratory use is granted, provided that a workplace chemical protection program (WCPP) is developed.
What are the health risks?
Methylene chloride poses both non-cancer and cancer health risks from acute and chronic inhalation and dermal exposures. University staff exposure can increase the risk of developing cancer based on some animal studies, neurotoxicity effects (headaches, dizziness, etc.), heart and Liver damage, and skin or eye irritation.
New Exposure Limits
The new EPA regulation severely reduced the exposure threshold relative to the OSHA standard (See Table 1). To put this in perspective, the odor threshold for methylene chloride is 250 parts per million (ppm), which is 125 times the new eight-hour time weighted average (TWA, 2 ppm).
| Table 1: Comparison of the OSHA methylene chloride exposure limits to the new EPA rule. | ||
|---|---|---|
| Rule | OSHA | New EPA |
| 8-Hour Time Weighted average (TWA) | 25 ppm | 2 ppm |
| 15-Minute Short Term Exposure Limit (STEL) | 125 ppm | 16 ppm |
| Action Level | 12.5 ppm | 1 ppm |
First Steps
Health, Safety, and Risk Management (HSRM) is asking all departments to complete the methylene chloride use survey. Please review your areas for commercial products that contain methylene chloride (paint stripers, adhesives, metal cleaners, lubricants, etc.) and dispose of them. Research laboratories that have methylene chloride solvent should dispose of it if it is not used or consider switching to safer alternatives (Table 2). Please note that other chlorinated solvents such as 1,2-dichloroethane are under EPA review and are likely to be placed under similar restrictions. Therefore, they should not be considered as alternatives.
| Table 2: Alternative solvents to methylene chloride | ||
|---|---|---|
| Application | Alternative Solvents | Additional Resources |
| Chromatography | Ethyl Acetate Heptanes Methyl tert-butyl ether (MTBE) | A convenient guide to help select replacement solvents for dichloromethane in chromatography. |
| Extractions and Purifications | Ethyl Acetate MTBE Toluene 2-Methyltetrahydrofuran (2-MeTHF ) | Chlorinated solvents: their advantages, disadvantages, and alternatives in organic and medicinal chemistry. |
| Biphasic reactions such as alkylation, amidation, nucleophilic substitution | 2-MeTHF | Greener solvent alternatives. |
Workplace Chemical Protection Program
All researchers unable to eliminate methylene chloride from their processes must develop a WCPP to limit employee exposure. HSRM staff will assist in WCPP implementation and provide resources where possible. The program will include:
- Initial monitoring - All employees or a single individual in an area representing the worst-case scenario will be monitored by HSRM for methylene chloride exposure.
- Establishment of a regulated area - Areas where airborne concentrations of methylene chloride exceed exposure limits will be marked as a designated area with restricted access.
- Exposure control plan - All users must identify and implement exposure controls to reduce inhalation exposure to a level at or below the 8-hour TWA (2 ppm) or STEL (16 ppm). This may include a description of the regulated area, engineering controls, restricted access to regulated areas, and reporting procedure for any changes that may increase employee exposure.
- Respiratory Protection and Personal Protective Equipment (PPE) - Respiratory protection (supplied air) will be required in areas when inhalation exposure exceed acceptable limits. Chemical resistant gloves such as polyvinyl alcohol (PVA) or Silver Shield are required to prevent dermal exposure.
- Training - Staff will undergo training prior to working in methylene chloride restricted areas.
- Periodic Monitoring - Restricted areas will be monitored periodically by HSRM staff for inhalation exposure depending on risk or if there are procedural changes. Exposure levels below the action limit (1 ppm) for the 8-hour TWA and at or below the STEL (16 ppm) will be monitored every 5 years. All other concentrations will require monitoring every 3 or 6 months depending on severity.