On toxic couches and carcinogens: Chemophobia, deconstructed.

Last week I attended a great session on chemophobia at ScienceOnline 2013 headed by Carmen Drahl and Dr. Rubidium. The session emphasized how "trigger words" - alarmist phrases judiciously placed in the middle of otherwise well-intentioned paragraphs - can make people believe that something is more serious than it is. The session also reinforced the all-important point that context makes all the difference when it comes to chemistry.

Sadly I could not read a recent post about flame retardants in couches on the Scientific American Guest Blog without remembering some of these caveats. The post unfortunately seems to me to present a first-rate example of how well-intentioned opinion and advice can nonetheless be couched in alarmism and assertions drawn out of context. It evidences lapses that are common in chemophobic reporting. Let me state upfront that my argument is as much about the tone and message of the post as it is with the pros and cons of the scientific evidence (although there's some highly questionable scientific conclusions in there). Some of my analysis might look like nitpicking, but the devil is often in the details.

The article is written by Sarah Janssen, an M.D. Ph.D. who is worried about supposedly "toxic chemicals" in her couch. In this case the chemical turns out to be something called Chlorinated Tris. Dr. Janssen is apparently so worried that she has already decided that her family should sit on the floor/carpet or eat at the table than be exposed to the couch. At the end of the post she says that she will look forward to the time when she can buy a "toxic-free couch".

The trigger words start coming at you pretty much right away:

"A nationwide study of 102 couches revealed that my couch, among others tested, contains OVER A POUND of chlorinated Tris, a cancer-causing chemical removed from children’s pajamas in the 1970s and now listed on California’s Proposition 65 list of carcinogens"

Observe how ONE POUND is capitalized, as if the capitalization makes any additional arguments in favor of the compound's toxicity superfluous. But we all know that the dose depends on the context; there's more than one pound of lots of chemical substances in almost every piece of furniture that I use, but the weight by itself hardly makes the material harmful. In fact since the weight of a typical couch is at least 20 pounds, I wouldn't expect to find any less than one pound of a flame-retardant substance in it. The point is that simple manipulations like capitalization enhance the public's perception of impact, and doing this without a good reason sends the wrong message.

Now let's look at the chemical itself, Chlorinated Tris, or TRIS(1,3-DICHLORO-2-PROPYL) PHOSPHATE (TDCPP) in chemical parlance (there, did the capitalization make it sound more sinister?). Googling this chemical turns up a bunch of newspaper articles without primary references. How about a more formal source, in this case a June 2011 report by the California EPA? Scientifically inclined readers will find lots of interesting data in there and it's clear that chlorinated tris has a variety of observable and potentially concerning effects on cells. But for me the most important part of the report talked about a study on the effects of TDCPP on cancer risk in a group of 289 workers at a TDCPP plant between 1956 to 1980. The operative line in that paragraph is the following:

"The authors concluded that although the SMR (standard mortality rate) from lung cancer was higher than expected, overall there was no evidence linking the lung cancers to TDCPP exposure because all three cases with lung cancer were heavy to moderate cigarette smokers. Small sample size and the inability to account for confounding factors make it difficult to draw conclusions from this study."

In addition the paragraph states that p-values (a measure of statistical significance) could not be calculated because of small sample size. Now this study was done with people who have literally lived and breathed in a TDCPP-rich environment for almost thirty years. If anyone should suffer the ill-effects of TDCPP it should probably be this group. And still the conclusions were dubious at best, so one wonders if merely sitting on a couch would do anything at all.

As is usually the case, the report has much more information about the effects of TDCPP in mice and here you do see evidence of tumor formation. But the sample sizes are again small. More importantly, what's the dosage of TDCPP that causes statistically significant cancers to appear in mice? It's 80 mg per kilogram per day. This would translate to 5.6 grams per day for a 70-kg human being. And although I haven't read all the original studies with mice, I am assuming that this amount would have to be ingested, inhaled or injected. So no, unless you are out of supplies in a nuclear holocaust and are forced to survive by actually eating the foam from your couch, you would most likely not get cancer from simply sitting on a couch with TDCPP in it. And even this tenuous conclusion comes from studies with mice; as indicated above, the data is far from clear for humans. In fact I would guess that the probability of suffering an obesity-induced heart attack from sitting for long periods on a couch exceeds the probability of getting cancer from TDCPP.

Now that doesn't mean that I am claiming that TDCPP has no harmful effects in humans. But it's clear that at the very least we need to get much more rigorous data to establish a causal relationship with any kind of confidence. For now the evidence just doesn't seem to be there. Claiming that simply sitting on a TDCPP-filled couch could cause cancer, with any kind of probability, is really no more than a theory disconnected from data.

It gets worse. The post later talks about the smoke from fire retardant-containing furniture "putting firefighters' health at greater risk of cancer". When you click on that link it takes you to an article in the San Francisco Chronicle documenting the story of a firefighter named Stefani who is a cancer survivor. The firefighter had expressed concerns about his cancer being linked to smoke inhalation from household items like furniture. But here's what the article itself says at one point:

"The relationship between Stefani's job and transitional cell carcinoma is less clear...there's no hard evidence yet that chemicals contribute to this condition, said Dr. Kirsten Greene, a UCSF assistant urology professor who helped run the study."

When an expert who ran the study questions the link between cancer and flame retardants, it should give you pause for thought (on a related note, kudos to the SFC for reporting the skepticism).

Finally, there's no better way to drive home the pernicious influence of "chemicals" than to demonstrate their existence in the bodies of every species on the planet:

"But flame retardants aren’t just polluting our homes—they are polluting the world, literally. During manufacturing, use and disposal, these chemicals are released into the environment where they can be found in air, water, and wildlife. Birds, fish, mammals including whales and dolphins and animals living far from sources of exposure, such as polar bears in the Arctic, have been found to have flame retardants in their bodies."

But take a look at the polar bears paper. Notice that we have now switched from TDCPP to brominated flame retardants, a different category of compound. If there's anything chemists know, it's the fact that function follows structure; no chemist would assume that TDCPP and brominated ethers would have the same effects without explicit evidence. The subsequent paragraph describing a variety of other non-carcinogenic effects also talks about brominated compounds. The continuity in the article would have you believe that we are still talking about TDCPP and couches. More importantly though, chemical substances are not all toxic just because they show up in multiple species, and bioaccumulation does not automatically translate into carcinogenicity (as is clear from the polar bear study). Since the advent of human civilization there have been thousands of synthetic molecules that have been dispersed in the environment, and the vast majority of them co-exist in peace with other species. But the most important point here is that it's extremely hard to extrapolate these studies to the conclusion that sitting on your couch may expose you to a carcinogen; that kind of extrapolation pretty much ignores dose, context, statistical significance and species-specific differences and lumps all "flame retardants" into the same category without allowing for compound-specific effects.

Trigger words proliferate the rest of the post: "dangerous chemicals", "harmful chemical substances", "toxic-free couch"...the list goes on. I don't want it to sound like I am picking on this particular post or author; sadly this kind of context-free alarmism is all too common in our chemophobic culture. But articles like this keep on making one thing clear: the details matter. You really cannot write a report like this without looking into details like statistics, nature of test organisms, dosage, method of administration, controls, sample size and species-specific differences. Lack of attention to these details is often a common hallmark of articles propagating chemophobia. If you ignore these details you are not really reporting science, you are simply reporting a gut feeling. And gut feelings are not exactly good metrics for making policy decisions.