Dichloromethane, a solvent widely used in organic chemistry and manufacturing, is what chemistry Prof. Bryan Hunter calls a “Goldilocks of the solvents.” 

DCM is particularly useful as a reaction solvent because it doesn’t mix with water, can dissolve many compounds and has a low boiling point, which makes it easy to evaporate away once it has completed its role in a reaction, said Northwestern Director of Research Safety and Chemical Hygiene Officer Justin O’Neill.

Despite its advantageous properties, DCM is classified as a known carcinogen by the Environmental Protection Agency. While most uses of the solvent are completely banned under the Toxic Substances Control Act, research labs are still able to use a regulated quantity of DCM.

The EPA ban, issued April 2024, impacts the use of DCM in manufacturing more so than in research, Hunter said, since labs require a much smaller quantity than industries. However, researchers in his inorganic chemistry lab will be required to transition completely to using DCM in fume hoods, he said. 

“The real issue is that it’s kind of irreplaceable for a lot of things,” Hunter said. “The literature that we go off of has often established protocols for using dichloromethane in reactions. So it’s kind of like going back to the lab with a blindfold on, because if you’re going to replace it with something else, you’re going to need to develop whole new procedures.” 

DCM has a number of features that make it an exceptional solvent, O’Neill said. Rather than avoid the use of DCM completely, the goal is for researchers to handle the solvent safely or find a less harmful alternative with similar properties.

The new action values, which are maximum thresholds for substances set by the Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health, are significantly lower for DCM than before the EPA released its rule, O’Neill said.

“This is an example of how science evolves with safety,” O’Neill said. “It’s walking that line of allowing the scientists to do what they need to do and use it where it’s necessary but also be safe while using it.”

In terms of what safety in the lab looks like, chemistry has evolved significantly even over the past few decades, said chemistry Prof. Carine Nemr. Protocols considered standard nowadays — like wearing gloves and pipetting with equipment rather than by mouth — were uncommon even 60 years ago.

After learning about the ban, Nemr said she reflected on how much DCM exposure she may have accumulated throughout her lifetime. Besides DCM, there are other substances with harmful effects that we may still be unaware of without long-term data, Nemr said. 

“As chemists, I think this is not something we should be really surprised about,” Nemr said. “As we get more long-term data about specific chemicals, I don’t think it’s going to be surprising that we start seeing changes in regulations, not only for DCM, but other things.”

Nemr said general chemistry labs have pushed to make labs more sustainable or “greener,” which includes using less hazardous materials such as DCM as well as reducing waste generated from experiments.As long as labs can demonstrate exposure to DCM is small, Hunter said, researchers can continue using the chemical without harm. 

“We’re not being forced not to use it — we’re being asked to be responsible,” Hunter said. “My students’ safety is obviously the most important thing to me, so if that’s something we need to be aware of, we’ll be aware of it.”

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