The potential negative health impacts of plastics are making headlines once again
111045799 © Alexandr Kornienko |


The potential negative health impacts of plastics are making headlines once again

Public health experts' concerns over the use of plastics is likely overblown.

Between Halloween and the New Year, the holiday season can be the trigger for a vast number of phobias. Arachnophobia (spiders), ophidiophobia (snakes), and wiccaphobia (witches) are common examples. Curcubitophobia (fear of pumpkins) is especially pronounced in the Autumn, driving many people, well, out of their gourds. As we move into Thanksgiving, triptophanophobia (fear of post-Turkey coma) will emerge, and of course, Christmas will bring Santaphobia, elfophobia, Rudolphobia, eggnogophobia, and especially mistletoephobia (yes, I made some of those up). The New Year will undoubtedly trigger those with neoannophobia. Lately, a new phobia seems to be re-emerging at the end of 2021, which I call plastiphobia – the irrational fear of plastics, as the next great evil that will destroy the Earth.

I first started studying the plastiphobia phenomenon with the Reason Foundation back in the year 2000, when the plastiphobes launched a war on a class of chemicals that virtually nobody could pronounce, much less pick out of a two-person police lineup. That class of chemicals was called “phthalates,” and is usually pronounced “thall-eights.” I wrote a policy study about phthalates, and, well, never really lived it down among my colleagues. Some thought it was a rather esoteric concern at the time, and that explaining the fear of phthalates would be a quixotic endeavor, given that most people couldn’t pronounce them. Most of them just thought I was a nerd.

But lo and behold, 21 years later, phthalates are back in the news, as a new crusade has been launched against them. (Prescience Badge Unlocked!) So once again, let’s take a look at pthalatophobia and see if this is a bogeyman in the closet or just a misinterpretation of a wrinkled overcoat seen through a gap in the closet door.

To get the unpleasant chemistry stuff out of the way, let’s recall what phthalates are from our high-school chemistry studies (we had those, right? Right?). Phthalates are a class of chemicals that make plastics, well, plastic-like: they make what would otherwise be a rigid material made with plastic monomers (like PVC pipes, or Lucite cubes for example) into flexible materials, which is a prized characteristic in a lot of plastic objects like intravenous bags and tubing, dialysis tubing, plastic drinking bottles, plastic car tires, plastic food packaging, vinyl and spandex clothing, toys, cars, medical examination gloves, medical implants, and, well, you name it.

So what’s the basis of the renewed war on phthalates? Well, some 20 years later, it’s pretty much the same as it was the first time I wrote about it. A new study is in the news, ostensibly showing that exposure to phthalates will cause the usual panoply of health risks, particularly, “endocrine disruption,” in humans and animals, heart disease, and assorted relatively obscure cancers. The latest study is “Phthalates and attributable mortaility: a population-based longitudinal cohort study and cost analysis,” published last month in the Journal Environmental Pollution was released just in time for the Holiday media cycle. And it has been a hit on media from left and right.

CNN proclaimed in a headline, “Synthetic chemical in consumer products linked to early death, study finds.” Meanwhile, the New York Post tells us that “Synthetic “everywhere chemicals” linked to deaths among older Americans, study says.”

The verbiage surrounding this new study read like a bad crime show. The New York Post said:

“These chemicals have a rap sheet and the fact of the matter is that when you look at the entire body of evidence, it provides a haunting pattern of concern,” said Trasande, who also directs NYU Langone’s Center for the Investigation of Environmental Hazards.”

Of course, we must be cautious. “I’m never going to tell you this is a definitive study. It is a snapshot in time and can only show an association,” [Dr. Leonardo] Trasande told the network, adding that finding out exactly how the chemicals may affect the body requires a double-blind randomized clinical trial,” which alas, can’t be done because human experimental ethics precludes it.

But despite that inability to ever really know how phthalates actually affect the human body,  Dr. Trasande goes on, stating, “…we already know phthalates mess with the male sex hormone, testosterone, which is a predictor of adult cardiovascular disease. And we already know that these exposures can contribute to multiple conditions associated with mortality, such as obesity and diabetes.”

“This study,” Trasande tells us, “adds to the growing database on the impact of plastics on the human body and bolsters public health and business cases for reducing or eliminating the use of plastics.”

So, what’s inside the new phthalate scare study of 2021? Not much. Trasande study data “…included 5303 adults aged 20 years or older who participated in the US National Health and Nutrition Examination Survey 2001–2010 and provided urine samples for phthalate metabolite measurements. Participants were linked to mortality data from survey date through December 31, 2015.” The data was processed in 2020.

The results were presented in the abstract, thus:

“Multivariable models identified increased mortality in relation to high-molecular weight (HMW) phthalate metabolites, especially those of di-2-ethylhexylphthalate (DEHP). Hazard ratios (HR) for continuous HMW and DEHP metabolites were 1.14 (95% CI 1.06–1.23) and 1.10 (95% CI 1.03–1.19), respectively, with consistently higher mortality in the third tertile (1.48, 95% CI 1.19–1.86; and 1.42, 95% CI 1.13–1.78). Cardiovascular mortality was significantly increased in relation to a prominent DEHP metabolite, mono-(2-ethyl-5oxohexyl)phthalate. Extrapolating to the population of 55–64 year old Americans, we identified 90,761–107,283 attributable deaths and $39.9–47.1 billion in lost economic productivity.”

Sounds bad, doesn’t it? But if you dig down a bit and unpack the math to see what all that means, you find some surprising problems with the study. First, for those who are fond of that whole idea of empiricism, understand that Trasande is purely correlative: no mechanistic relationship connecting phthalate exposure at various levels to the negative health outcomes is documented or discussed in the study. Worrying about such things as mechanistic linkages may be considered quaint these days, though some diehards might consider that absence troubling.

Despite the lack of all that empirical mechanistic stuff, Trasande takes old health survey responses (a notoriously dubious data-collection method to begin with), correlates them with old urine test results from a sample of respondents, and then mines the data to see if they can relate those correlations with changes in mortality as recorded in the National Health and Nutrition Examination Study, or NHANES.

For example, while the study population was consistent with the racial demographics of the United States ­­— 76.0% non-Hispanic White, 9.1% Hispanic and 10.2% non-Hispanic Black ­­—  they were not so representative otherwise:

  • Nearly three-fifths of the sample were college-educated or higher,
  • 52.6% (SE 0.9) were female and almost one tenth met the federal poverty definition. One-third were obese, while another third were overweight.
  • Nearly half were past or current smokers,
  • Nearly one-fifth reported moderate or heavy drinking.

And, “levels of low-molecular weight phthalates were higher in younger participants, men, non-Hispanic Blacks and Hispanics as well as lower education subpopulations. DEHP metabolites were higher in males, more highly educated and moderately drinking populations.” In other words, something of a risk-taking sub-population where any number of other unmeasured risks could outweigh risks from their uses of plastics.

Another problem with the study is that for an epidemiology study, the Hazard Ratios (akin to odds ratios) found in the study are unimpressive. As the CDC itself explains: An odds ratio (a type of metric similar to the hazard ratio) of

• 1.0 (or close to 1.0) indicates that the odds of exposure among case-patients are the same as, or similar to, the odds of exposure among controls. The exposure is not associated with the disease.

• Greater than 1.0 indicates that the odds of exposure among case-patients are greater than the odds of exposure among controls. The exposure might be a risk factor for the disease.

• Less than 1.0 indicates that the odds of exposure among case-patients are lower than the odds of exposure among controls. The exposure might be a protective factor against the disease.

The Trasande hazard ratios were, as a reminder, barely above 1.0. As CDC elaborates, “The magnitude of the odds ratio [again, a similar metric to the hazard ratio] is called the ‘strength of the association.” The further away an odds ratio is from 1.0, the more likely it is that the relationship between the exposure and the disease is causal. For example, an odds ratio of 1.2 is above 1.0, but is not a strong association. An odds ratio of 10 suggests a stronger association.” Yes, you read that right. Above 10. And Trasande is talking about 1.1 to 1.2.

In 1995, Science writer Gary Taubes interviewed several high-ranking experts in human health risk management who talked about the relevance of risk ratios in epidemiology studies. “As a general rule of thumb,” says Angell of the New England Journal, “we are looking for a relative risk of three or more (before accept publication), particularly if it is biologically implausible or if it’s a brand-new finding.” Robert Temple, director of drug evaluation at the Food and Drug Administration, puts it bluntly: “My basic rule is if the relative risk isn’t at least three or four, forget it.” But as John Bailar, an epidemiologist at McGill University and consultant for the NEJM, points out, there is no reliable way of identifying the dividing line. “If you see a 10-fold relative risk and it’s replicated and it’s a good study with biological backup like we have with cigarettes and lung cancer, you can draw a strong inference,” he says. “If it’s a 1.5 relative risk, and it’s only one study, and even a very good one, you scratch your chin and say maybe.”

So, the grave threats that Dr. Trasande talked about in his interviews with CNN and the New York Post could be rather less than meets the eye. As for the proclaimed economic losses, debunking that bit of silliness would take another thousand words I don’t have here, but in a nutshell, Trasande takes the correlation game one step further, and multiplies estimates of elevated mortality against estimates of lifetime earnings for people in the same age cohort, and defines these as “lost economic productivity” for the US, as if, in some odd way, anyone whose productivity is made lower than average is somehow causing a “loss” of social-economic productivity.

This is, to say the least, a highly ideological concept, but one much beloved by the public health community, which has long associated things like this with social “lost revenues.” As I observed in another Reason Foundation study on the war on automobility (regrettably lost in the mists of digitization), if someone is deterred in walking to a store to shop because of fear of crossing a road, then to a public health analyst that “economic loss,” is somehow attributable to the fact that society uses automobiles as a primary means of transportation. Even more, if someone dies “prematurely,” because they are in an automobile accident, the taxes that they don’t pay as a result of early mortality are considered a loss of economic productivity to society. Why, it’s almost as if the public health people think that society owns people, and their fullest measure of economic productivity rather than the idea that people might own themselves, and make choices that affect that economic productivity as they deem appropriate for their lives.

The crusade against phthalates, one of the newest seasonal entries in the war on plastics, is much like the crusade from 20 years ago: findings from an epidemiology study that are seen in detail to be massively overblown, combined with the presumption that somehow, by using plastics, people are both dying early, and denying society of part of their lifetime economic potential are spun to justify another regulatory attack against plastics. Don’t believe the hype: enjoy your holiday foods and presents. Just be careful how you unwrap them. Paper cuts can be brutal during the holidays.