CNN's Toxic Take on the Danger of Methylene Chloride in Decaf Coffee

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As long as we don't run out of chemicals, we will never run out of chemical scares. Most are unfounded, especially the current one – that the use of methylene chloride to decaffeinate coffee will somehow harm you. The numbers say otherwise. There is nothing to worry about here.

If you've already read this recent story on the CNN news site, perhaps it's not too late to get back the deposit on the casket you may have put down in sheer terror after reading the article:

"Is decaf coffee safe to drink? Experts weigh in on claims by health advocacy groups."

It's as fine an example of non-fine science as a bunch of non-experts could imagine: grotesquely phony scare tactics, omission of dose, and the distortion of the predictive value of animal models. It's worthy of, let's say, The Environmental Defense Fund (EDF), which is an astounding coincidence since the EDF is one of the groups pushing the FDA to ban the use of the solvent methylene chloride (dichloromethane or DCM) in the decaffeination of coffee (1,2)

This is hardly the first time the EDF has been in the news saying stupid s### about chemicals. I've taken them to task for pushing a ridiculous policy for testing 10,000 chemicals in food and a super-scary report on lead. I've yet to discover a chemical that the group actually likes (although they are strangely silent about the 2,600 chemicals in cannabis, including 100 of which have been deemed toxic. Perhaps this is why...

Methylene chloride – a personal memoir

Having spent 30 years in a lab as an organic chemist, I'm guessing that I used methylene chloride thousands (probably more like tens of thousands) of times. It's a very commonly used, excellent solvent – this is why it's used to extract caffeine from coffee – that (ironically) has mostly replaced chloroform (a solvent with similar properties) because it's less carcinogenic. Chloroform, which is now rarely used, scares me. Methylene chloride does not. That said:

  • With a boiling point of 103oF, it evaporates very quickly.
  • Even so, it's unpleasant to get on your skin. The stuff stings.
  • You really don't want to get it into your eyes. Bad news.
  • It's impossible to avoid breathing some of it, even under the most stringent lab conditions. 
  • It has a unique, sickeningly sweet odor that can be detected at low concentrations.
  • All I can say is that after using it for a long career, there is nothing noticeable is wrong with me.



Let's get serious - unlike the decaf scare

The CNN article can be used as a template for any cancer or toxicity scare for any chemical. Let's look at a few examples of the"scare" and then take it apart.

"For people avoiding caffeine, decaf coffee seems like a harmless option."

That's because it is.


"But some health advocacy groups that argue otherwise are petitioning the US Food and Drug Administration to ban a key chemical involved in the decaffeination process due to cancer concerns."

We shall see.


"[The] chemical is methylene chloride, a colorless liquid that’s used in certain industrial processes, including paint stripping, pharmaceutical manufacturing, paint remover manufacturing, and metal cleaning and degreasing... "

This is irrelevant. Aside from the fear factor, how are other uses of the chemical relevant to the risks of using it in decaffeination? Water is also used for waterboarding. 

CNN uses a quote from Dr. Maria Doa, senior director of chemical policy for EDF:

“In addition to being carcinogenic, methylene chloride can cause other health harms, such as liver toxicity and at higher exposures neurological effects, and in some cases death.

Dr. Doa has a Ph.D. in chemistry and had a long career at the EPA. She clearly knows her stuff, which makes the second half of her quote disingenuous. As you will see, there is so little methylene chloride left in decaf coffee that I wonder why she would even mention what the chemical may do at (very) high doses. But this is standard practice for environmental groups looking to get something banned, harmful or not. More on this later.

"The Environmental Defense Fund and its co-petitioners argue that by allowing methylene chloride in food, the FDA “has been disregarding” a 66-year-old addition to the federal act called the Delaney Clause, which requires the FDA to ban food additives proven to cause or induce cancer when ingested by humans or animals."

If we strictly interpreted the spirit of the Delaney Clause (which dates back to 1958), we'd be living on distilled water bean sprouts. This is because the Delaney Clause is unscientific; it addresses only potentially carcinogenic chemicals added to food while ignoring the same chemicals naturally present in the food, when, in fact, they are indistinguishable. How a given chemical gets into a food is irrelevant; only its presence and dose matter. (3)

The always popular ACSH Thanksgiving menu demonstrates in living color that we're eating carcinogens in just about every meal.

Once again, Dr. Doa:

"Thus, these chemicals [according to the Delany Clause] categorically cannot and should not be deemed as safe."

This is nonsense for a variety of reasons. First, it is impossible to categorically prove a negative, including whether chemicals covered in the Delaney Clause (or any others) are safe. Second, the clause does not take into account the amount/dose of the chemical in question or its degree of carcinogenicity or toxicity.

Even the safest chemicals in the world are toxic at high enough levels, and the most wicked poisons around are harmless at low enough levels. 

"These days, many people consume portions of beverages or food larger than the smaller standard sizes of decades ago, said Monique Richard, a registered dietitian nutritionist..."

Seriously?? Can consuming larger cups of coffee make any difference in the potential harm of methylene chloride/DCM? No. This is where the scare falls apart. The amount of the solvent present is so small that doubling it makes no difference. We need to do some math to show this.

Math defuses the scare (4)

The maximum amount of methylene chloride  (DCM) residue in decaf permitted by the FDA is 10 ppm (0.001%), but the actual amount of the solvent present, which varies significantly by brand, is usually much lower than that. The numbers in the quote below don't come only from the coffee lobby; they originate from a study by the Clean Label Project, an ethically challenged anti-chemical extremist group.

EDF’s petition admits that in 17 coffee samples tested by CLP (the test results have not been independently verified), methylene chloride traces remained from 10% to 99.5% or more below FDA’s safe level.

National Coffee Association

The average number for all samples of DCM decaffeinated on earth is unknowable, but to be on the "safe side," let's pick 2 ppm (0.0002%). It should become obvious that CNN and EDF are worrying about nothing, 

It takes about two tablespoons (21g) of coffee to make a 12-ounce cup. Let's assume that all the DCM is transferred from the dry coffee to the cup during brewing. Doing the math, this comes to 0.042 mg of DCM per cup, an absurdly low amount. How low? A lethal dose of ricin, one of the deadliest poisons known, is estimated to be 1 mg in humans. And the lethal dose of fentanyl – something we really ought to be concerned about – is about 1-2 mg. Are we really supposed to believe that methylene chloride, something I slopped all over myself for 30 years, is 25-50 times more toxic than ricin or fentanyl? No, 0.042 mg of methylene chloride (or anything else) isn't going to harm anyone. 

It gets worse: animal studies and cancer

I don't want to go into an extensive discussion about the reliability of animal models used in determining human carcinogenicity. However, some conclusions from a comprehensive review in the journal Regulatory Toxicology and Pharmacology should put the DCM/coffee/cancer argument to rest. 

  • DCM inhalation resulted in lung and liver tumors in mice but not in rats and hamsters. (5)
  • The order of DCM-related [carcinogenicity] is: mice ≫ rats/hamsters ≫ humans. 
  • "Epidemiology data do not convincingly support a conclusion of the cancer hazard of DCM."

And here are a few quotes to back this up: [my emphasis]

In laboratory animals, DCM is moderately toxic after ingestion. Longer term exposures have resulted in liver and lung effects depending on the animal species and exposure conditions

[In a drinking water experiment], oral exposure of rats to DCM did not induce an increased incidence of tumors up to and including doses of 250 mg/kg bw/day.

Let's pause for a moment to discuss what that number means. 250 mg/kg bw/day means that the rats drank 250 mg of DCM per kilo of body weight – about 500 grams for a rat. The rats, therefore, consumed about 125 mg of DCM every day for 104 weeks – their entire life span. Although rat-to-human comparisons of toxicity or carcinogenicity are, at best, rough approximations and not quantitative measurements, the rat doses used represent approximately 17 grams per day in humans. That is about 4,000,000 times the amount of DCM in a cup of decaf coffee. And the freaking rats still didn't develop cancer! It should now be obvious why the size of the cup is irrelevant, just like the scare.

Humans can be harmed by DCM at higher doses

As I said earlier, it is wise for chemists to limit their exposure to DCM, but under normal circumstances, none of us will ever be exposed like this:

The principal effects of human exposure to high DCM-concentrations (in excess of 1000 ppm) are incoordination, drowsiness and dizziness, and at very high concentrations, unconsciousness and coma which can be fatal.

All quotes and data are from Dekant et al., "Evaluation of the carcinogenicity of dichloromethane in rats, mice, hamsters, and humans," Regulatory Toxicology and Pharmacology Volume 120, March 2021, 104858

Bottom line

There are scares, and there are scares. This one is ridiculous. Forget all the nonsense about paint stripping; that's completely irrelevant and part of the phony scare. Ignore the ignorant (?) busybodies who are screaming to ban DCM from decaffeination. But do not forget that these groups are using the classic phony scare technique: ignoring dose. Yes, DCM can be detected in decaf coffee, but this says nothing about its potential risk. 

I could not care less whether DCM or one of the other "safer" methods are used to decaffeinate coffee. None of them are harmful. An environmental argument (lower production of a potential pollutant) may or may not be valid but if the EDF and other groups want the chemical banned they should, at the very least, state their agenda rather than dress it up as a nonsensical health scare.

DCM in coffee is a non-event. Given the minuscule exposure, the chances that it affects human health are slim to none (and closer to none than slim, IMO).

Drink up and stop worrying.


(1) For details on the decaffeination process, see my 2018 article

(2) There are other methods to get the caffeine out of coffee, including extraction with ethyl acetate (a safer solvent), water, and carbon dioxide. These won't hurt you either. The use of methylene chloride for decaffeination is called the European Method.

(3) There is a common fallacy that chemicals added to food are somehow different from the same chemicals already in the food. This is nonsense. 

(4) My math is so bad that I used to make errors in ~100% of the articles that included it. Now I use ChatGPT. If it's wrong blame Elon Musk.

(5) The exposure in these experiments was generally in the 500-5000 ppm range. Compare this to a few ppm in coffee.