The United States Environmental Protection Agency has moved to place a ban on methylene chloride (dichloromethane, DCM) citing associations to a higher risk of cancer and neurological and liver problems. This was proposed in 2014 and under the Lautenberg Chemical Safety for the 21st Century Act, which amended the Toxic Substances Control Act (TSCA), EPA was required to perform risk evaluations on the uses of ten specific chemicals, including methylene chloride.
With a new administration and concern about "secret science" and "sue and settle" efforts at EPA in the past, it was unclear if EPA would want to revisit the risk assessments of this volatile organic compound. They have accepted the findings from 2017 and will prohibit consumer and commercial paint stripping uses of it.
Why it is a concern.
DCM is the paint stripper of choice and that is why it's so popular. It works very well. But it is volatile (has a low boiling point) so fumes are inevitable. Inhaling the fumes can be harmful and it is also absorbed through the skin. It can be detected at very low concentrations by its sweet smell but smelling it doesn't speak to whether a dangerous exposure has taken place. As with all chemicals, it's the exposure that determines the harm, even though OSHA maintains that once you can smell it you are already overexposed (2).In high concentrations, it can be deadly. In a high-profile 2012 case, a worker using a methylene chloride product to refinish a bathtub died in an unventilated bathroom.
In industrial settings, there is much less risk because workers wear full-face respirators like in the image, and that is why the ban will only be for commercial and residential paint stripping products.
1. Why not create a new standard instead of banning it?
There is no way to significantly reduce exposure to methylene chloride if it is being used to strip paint, especially in a non-industrial setting, such as homes. It takes a lot to do the job completely, and it is so volatile that it is impossible not to inhale some unless you are using a commercial full-face respirator, something that do-it-your-selfers are unlikely to do.
When a chemical is banned finding an alternative can be challenging. The Halogenated Solvents Industry Alliance (HSIA) argues that current replacements are less effective, may be as toxic, and some are flammable (1).
2. Is the ban an example of EPA overreach?
"Methylene chloride is arguably the most dangerous of all the solvents sold at Home Depot," said Dr. Josh Bloom, Senior Director of Chemical and Pharmaceutical Sciences at the American Council on Science and Health. "Chemists use it all of the time, but we do so in fume hoods. Some argue it's not necessary to ban it, but this is not a knee-jerk chemophobic response by EPA. There is real risk here." (3)
It is used in for other applications, like adhesives, pharmaceuticals, and aerosols, but only paint strippers have any risk.
Given the assessments done, this is an instance where EPA concern is warranted.
(1) Halogenated hydrocarbons, such as methylene chloride and chloroform are not flammable. Another, carbon tetrachloride is actually used in fire extinguishers.
(2) The OSHA position is more regulatory than scientific. One drop of DCM in a room will probably be detected by smell but will cause no harm to anyone. A comparison of this to workers exposed to high concentrations of the chemical, especially in poorly ventilated areas, is meaningless.
(3) Methylene chloride may be toxic to humans, but it is even more so to paint, which comes sloughing off as soon as the solvent is applied. Nothing works better. The question is what will be used to replace it. Dr. Bloom says "There is nothing strips paint better than methylene chloride. Since all halogenated solvents (like chloroform) are just as toxic, or worse, it will be interesting to see what the substitute will be. My best guess a mixture of toluene and acetone, but it won't work as well and toluene has its own toxicity issues."