Just one word: plastics. I mean microplastics. No, I mean BPA and PBDEs

icroplastics are small pieces of degraded plastic between 1 μm and 5 mm in diameter. Toxic compounds such as bisphenol A, phthalates, polybrominated diphenyl ethers (PBDEs), and per- and polyfluoroalkyl substances (PFASs) can leach out of them, which is bad; and they absorb toxic compounds from the environment, which is good. But only the bad features are being studied.

The UN is already trying to get involved, saying things like “51 trillion microplastics litter the seas.” That sounds like a lot, but a simple calculation shows it's not: if the average microplastic is a sphere 2.5 mm in diameter, and if we assume they're concentrated in the top ten meters of the ocean, 51 trillion of them would only be one part in 8.96 billion by volume. That's equivalent to 1 piece of microplastic in 346 Olympic-sized swimming pools.

The UN's website says:

According to UNEP [UN Environment Programme], actions to stem the growing tide of maritime litter could include reducing the use of single-use plastics at the individual level such as by using reusable shopping bags and water bottles, choosing products without microbeads and plastic packaging, and not using straws to drink.

So, in answer to the question of how dangerous they are, the answer is “very.” But what about microplastics?

Some bodies of water could contain more microplastics than others. Microplastics containing 164 micrograms of polycyclic aromatic hydrocarbons (PAHs) per gram were detected in the Forth Estuary in the UK. That sounds bad until you notice that the units are micrograms per gram of microplastic, not per gram of water. To get 164 μg of PAH from microplastics by drinking out of the Forth Estuary, you'd need to drink between 1,000,000 and 1,000,000,000 grams of contaminated water, or 1 to 1000 metric tonnes, which would kill you straight away.

Hazardous chemicals

Highly concentrated dihydrogen monoxide, a powerful solvent

On the other hand, PAHs are known carcinogens. Plasticizers are thought to cause endocrine problems and possibly obesity and cardiovascular disease. ^[1,2] The incidence of obesity in the USA varies dramatically with geography, with highest levels in every state along the Ohio and lower Mississippi Rivers, which suggests an environmental factor rather than diet as commonly assumed. (This could be one reason property values with a view of the Ohio are so low.) The question is whether a convincing link can be made with microplastics.

There is only one way to find out: a controlled clinical trial combined with well accepted principles of pharmacology: what is their bioavailability, what concentration is reached at the target, do the molecules engage the target, and what is the mechanism of action? Cell culture studies aren't good enough. Neither are animal studies. If we took all the resources and man-hours devoted to the speculation and did one decent trial, we would know the answer by now.

It won't happen. Why? Because a big study would only produce one publication, and scientific productivity is measured by the number of publications. So we get papers that say microplastics are too big, so they cause physical injury from their roughness. They are also too small, so no one can see them. Plastics contain forever chemicals, which can't be broken down, and they're readily digestible, so the chemicals are easily released.

It's a no-win for producers. Make indestructible plastics and the enviros complain. Make them oxo-degradable and they complain about that. The message is the same as for the dangers of 5G EM radiation, asthma from gas stoves, or flying saucers: the number of articles purporting to show that the effect is real is inversely proportional to the probability that it exists. If the finding were robust, we would only need one paper.

Speculation

Take this paragraph, from a recent review paper:

Bisphenol A (BPA) and phthalates are known endocrine-disrupting chemicals that affect development and reproduction in humans and other species. BPA and phthalates from MPs [microplastics] may also induce changes in the neuroendocrine system and signaling. BPA can pass through the blood-brain barrier, and exposure is linked with neuro­psychological dysfunction, neurobehavioral disorders, and neurodegenerative disease, as well as affecting DNA methylation.^[3]

The statements are all true, but the thing to notice is that every statement is qualified by “maybe” or “linked with.” Saying “maybe” makes any statement true. So far, the connection with microplastics is purely speculative. The author knows this and hopes to create a sense of urgency in order to attract funding. This is a standard tactic in science.

The vast majority of microplastics are microfibers released from clothing in washing machines. These fibers contain pigments, dyes, antimicrobial agents, and chemicals for wrinkle resistance (i.e., fabric softeners, which contain cationic surfactants). Other microplastics come from carpet, personal care products, and cigarette filters (made from cellulose acetate), car tires, and lost or abandoned fishing nets and ropes.

I've long advocated switching back to polyester, which not only produces fewer micro­plastics but, unlike cotton, never needs ironing and never shrinks. If these micro­plastics were as hazardous as the authors want us to think, wearing a piece of clothing, walking barefoot on a carpet, or putting a piece of clothing, carpet, or toothpaste in your mouth or drinking through a straw would be risking certain death.

Weak science

The authors also write:

Experimental studies of chemical toxicity can be performed by comparing virgin vs. weathered MPs, by using MPs ‘spiked’ with specific chemicals, or by using leachates. Such studies have demonstrated a variety of deleterious effects on development, reproduction, behavior, growth, etc., that appear to be related to the particular chemicals involved. For results to be meaningful and relevant, and the field to progress, researchers are encouraged to use environmentally relevant concentrations and types of MPs in exposure studies.^[3]

This is a polite way of saying that experiments are being done in such a way as to guarantee that a toxic effect is found. Instead of studying the problem, researchers give their mice artificial particles spiked with toxic chemicals or fluorescent dyes. The reason is either (a) real microplastics are rare, contrary to the pictures on the Internet purporting to show huge piles of them, or (b) they couldn't get any effect with real ones.

What is BPA?

BPA (bisphenol A, 2,2-bis(4-hydroxy­phenyl)­propane)

BPA is not a plasticizer, but a monomer that is covalently polymerized into the plastic. This is done by reacting the two OH groups on BPA with a reagent that joins the monomers together, creating a polyether, polyacetal, or similar compound. Thus, a properly manufactured plastic would contain no BPA. Its purpose is to raise the glass transition temperature so that the plastic doesn't melt in use. Without BPA, many elastomers would become rubbery and eventually melt even below room temperature.

BPA is a very weak xenoestrogen. Because of the panic about BPA, companies sometimes use other bisphenols such as bisphenol S and bisphenol F so they can be advertised as “BPA-free.” BPA could be thought of as an anti-plas­tic­izer; plastics would rarely contain both. Source:^[7]

The authors also deserve praise for spelling ‘leach’ correctly, which is rare in this field.

Zaheer et al.^[4] claimed that microplastics cause autism spectrum disorder in mice. They used manufactured polyethylene (PE) microplastics. The paper has many other flaws, including dissolving the PE in detergent but using saline for the controls; giving a high dosage; and using mouse behavior with questionable relevance to human ASD.

A big problem in measuring microplastics is lab contamination. Simply passing water through a filter to make it sterile causes strange microplastics and fibers to show up in your solutions, as I showed here. Bhat et al. found that even heating their filters at 450°C for 4 h only reduced the microplastic count by 50%.^[5]

Modern GC-MS/MS and LC-MS/MS methods can detect molecules in the attomole (10⁻¹⁸) range, which is on the order of a few thousand molecules. Given that these chemicals are in every bit of plastic, glass, and pipet tip in every lab, finding some in a biological sample is almost inevitable. Proving it's real is a challenge. Seeing an effect of a pure compound in an animal is easy; proving it's an environmental hazard is not.

One environmentalist group^[6] found 2400 “substances of potential concern” by looking up articles on Google Scholar. They discovered, to no one's surprise, there is such a thing as a potentially hazardous chemical. The reason for stating the obvious is to publicize their idea of a “transition to a sustainable circular plastic economy.” For the moment, that means recycling and reducing usage à la UNEP.

Skepticism

We can't have it both ways. If plastics are degradable, as they should be, we will have microplastics. Advocates of recycling want you to think it's easy, but there are hundreds of types of plastic. Mixing them together is not practical because it would result in an inferior product. The average person can't distinguish any type of plastic, even common ones like PVC, LDPE, HDPE, polypropylene, ABS, acetal, PMMA, polyethylene terephthalate, and polycarbonate, so sorting by the consumer is not an option. Thermoplastics can't be mixed with thermosetting plastics, as they are fundamentally different.

Thus, proposing recycling as a solution suggests either naivete about polymer chemistry or a cynical ploy to eliminate plastics altogether. This would force a return to the days of glass milk bottles, glass eyeglass lenses, glass medical supplies, all-metal pipe and appliances, and food wrapped in aluminum foil and paper like we had back in the 1950s.

Industry is not blameless either. Where are all the new biodegradable high-tech plastics? They've existed for decades—there are even books on the subject—but industry's belief that they're not financially viable until compelled by regulation makes them a sitting duck for people who want to eliminate plastics altogether.

Conclusion

There's certainly room for concern about polycyclic aromatic hydrocarbons from cigarette butts and cumulative hormonal effects from plasticizers. In general, burning things makes them more toxic. But until better quality research shows up, microplastics will continue to look like a minor problem and should be treated as such.

Microplastics are easy to measure; attomolar concentrations of BPA are not, so the risk is that regulators will use microplastics as a proxy for toxic chemicals, and use the pre­cau­tion­ary principle, which says we should ban it if there's any chance of a risk, as a shortcut.

We saw during Covid and with the ongoing bans on gas stoves how the fad of politicians banning things on the basis of weak science feeds the perception that science is too opportunistic and the adminis­trat­ive state is out of control. It will get worse if governments try to force regulatory action on plastics before convincing scientific results are available.

If you're worried about toxic substances in your water, you could put microplastics in the water to absorb them, then filter out the microplastics. Or better yet, buy a $34.98 Pur that slaps onto your faucet. Desalted, sorted, and done.

Anyway, forget plastics. I'd be happy if some of the writers in this field could just learn how to spell ‘leach’ correctly.

jan 21 2024, 4:47 am. updated and information boxes added jan 22 2024, 6:11 am