In Defense of Methylene Chloride

If you’re familiar with methylene chloride (which I’m sure you are since it’s one of the most widely used laboratory solvents), you know that it’s developed a reputation for being one of the “bad boys” of the solvent world. The bad press has certainly been earned. It’s been attributed to over 60 deaths in the last 4 decades. It’s also pretty aggressive – exposure to just a few ounces for a few minutes can be enough to cause severe damage or death. And since it’s a colorless liquid, an innocent-looking spill could be a severely harmful hazard.

Though it’s a solvent with a bad reputation, I feel as though I need to come to its defense, because it’s a necessary solvent for a lot of laboratories doing sample preparation and extractions of volatile and semi-volatile organic compounds. EPA Methods 8270 and 625.1 (just to name a couple of examples) require the use of methylene chloride during the extraction process. This solvent is critical for accurately and reliably extracting the hundreds of compounds that are outlined in those methods. Methods like 8270 and 625 are just 2 out of dozens and dozens of methods that are designed to guide labs in extracting compounds that are contaminating our air, soil and water. So, if you ask me, methylene chloride is one of my heroes. The key is to handle it with caution and respect.

Treat Methylene Chloride with Respect

Almost all laboratories use dangerous reagents and chemicals in their day-to-day or month-to-month operations. Anyone who has used a blast shield when using perchloric acid or suffered skin burns from an aqua regia spill knows just how dangerous some of these chemicals can be. But we can’t always avoid using them. If we could, alternative laboratory procedures would have been developed a long time ago! Since we find ourselves in contact with these chemicals from time to time, it’s important to respect them. It’s also important not to fear them. That may seem like a strange thing to say since the effects of these chemicals are kind of scary. But fear can cause us to react physically (to become paralyzed or to shake violently). Fear can cause us to do something quickly, without pausing to think through all the possible consequences.

Imagine yourself using hydrofluoric acid in the lab. (For anyone who’s unfamiliar, it’s a great solvent for dissolving silica-based compounds, but it’s also a calcium-loving chemical that will eat through your bones if it comes into contact with your skin – not cool!) Now imagine yourself working with that acid and you spill a small amount as you’re pouring it from the solvent bottle to a graduated cylinder. If fear takes over, you’d see the acid splash onto your skin and you’d probably react by panicking, hyperventilating and crying. If you’d been trained to treat the acid with the respect it deserves, you’d see the acid splash onto your skin and you’d probably react by grabbing the nearest tube of calcium gluconate, applying it generously to your skin, then make your way quickly to the nearest hospital.

Now let’s go back to methylene chloride and review what you need to know to handle it with the respect it deserves.

Know Your Exposure Routes

If you’re using a chemical in the lab, the best way to learn its potential to harm you is through its safety data sheet (SDS). Here’s an example SDS for methylene chloride.

It’s never a bad idea to skim through the SDS periodically to refresh your memory on how to handle the chemical properly and how to react if you become overexposed to it in some way. But if this is your first time working with a particular chemical, you should definitely review the SDS and ask questions if there’s anything in it that doesn’t make sense or doesn’t seem clear to you.

Here are a few general tips to help make sure you handle methylene chloride with caution and react properly if an accident occurs:

Ingestion

Presumably, this is the least likely way for you to be exposed to methylene chloride, but accidents are unpredictable – hence why they’re called accidents. If methylene chloride splashes anywhere near your face and mouth, make sure you wash your face really well with soap and water and rinse out your mouth. Then drink lots and lots of water. And when you think you’ve had enough water, drink some more. Methylene chloride is one of the solvents that’s harmful if you try to throw it up. It’s safer to let your body handle the solvent the way it would handle all the liquids you drink during a normal day – as long as there isn’t too much solvent for your body to handle. That’s where the water comes into play. Drinking a lot of water dilutes the amount of solvent that’s in your body and helps to flush it out of your system.

Absorption

We always work diligently to avoid spills in the laboratory, but accidents happen – flasks tip over, beakers crack and leak, splashes occur as you’re pouring from a large stock bottle to a small graduated cylinder. If a spill or splash occurs and any part of you comes into contact with methylene chloride, wash it off immediately with soap and water. If any of your clothing gets splashed, get it off your body as quickly as possible and wash it thoroughly before you put it back on.

Inhalation

This route of exposure is the most dangerous and the exposure route responsible for almost all the deaths that have been attributed to methylene chloride. Methylene chloride has a noticeable smell, but if you work with organic solvents in the lab, you’re used to being around solvents with noticeable smells and you may not necessarily distinguish those coming specifically from methylene chloride.

Methylene chloride vapors act quickly and attack via 2 different mechanisms. When we inhale methylene chloride vapors, our body converts it to formaldehyde and carbon monoxide to metabolize it. The carbon monoxide displaces oxygen in our body and eventually causes us to suffocate. It doesn’t take much carbon monoxide to develop before you’ll start to feel dizzy and eventually pass out. Once you’re unconscious, suffocation and death isn’t far behind. At the same time, the methylene chloride vapors can overwhelm your nervous system and cause sensory problems or cognitive impairment.

Given the inhalation hazard, methylene chloride should always be handled in well-ventilated locations, but if you become exposed to the vapors in some way (accidentally, of course!), find some fresh air fast. Once you’re breathing the safe air you’re used to breathing, your body will slowly replace all that carbon monoxide with oxygen and get rid of the carbon monoxide that was building up.

Know the After-Effects

Knowing what to watch for after an exposure is just as important as knowing what to watch for at the time of exposure. It’s not always easy to figure out how much methylene chloride you came into contact with during an accident. How many milliliters of solvent splashed onto your arm? How concentrated were the vapors in the air when you started feeling dizzy?

And even if you did know the answers to those questions, each person’s reaction to the solvent could be a little bit different. So even if you’ve reacted to an accident exactly as you should have, it’s important to know what to watch for in the following days. Did a rash develop on your skin the next day? Did you develop a sudden headache or are you feeling more tired than usual? Many SDS sheets have a section that includes notes for a physician to help them treat someone who has been exposed – methylene chloride is no different. Make sure you’re familiar with the symptoms and effects that are described for physicians and watch for those in the days following an accident.

Know How to Be Safe

The key to working safely with methylene chloride – or any solvent, for that matter – is knowing how to be safe around it. Knowing how to react to an accident is certainly part of that. But knowing how to be around it, in general, is part of being safe. How should it be stored? How should it be transported? How should it be disposed of?

When you’re actively working with it, how should it be handled? Are there certain materials that should be avoided (should you avoid using plastic labware, for example)? Are there solvents that will react violently with methylene chloride? Will it react to moisture or oxygen in the air? Will it react if it’s exposed to light?

It’s important to know this information before you even step foot into the lab. The safety data sheet will help answer all these questions, so keep a copy handy, and proceed with caution – not with fear.

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