In the early 1960’s, plastics were hot. Advances in plastic chemistry and technology created the ubiquitous plastic bag. Young designers started using plastic in furniture, dishes, ceiling tiles, clothing … but by the end of the decade, plastic had already come to signify cheap and artificial.
In the 1967 film The Graduate, Walter Brooke tries to persuade a young Dustin Hoffman that plastics are the (bleak) future; that same year, Jaques Tati’s masterpiece Playtime made the same dystopian point.
Plastics today are increasingly looking like the past, and a past that won’t fade away. They are persistent and so universal that they serve as indicators of the late Anthropocene. Sedimented into the landscape, these techno-fossils signal the human ingenuity and myopia of the Plasticene and are increasingly being used by contemporary archeologists for fine time resolution (1-3).
These techno-fossils are as durable as more traditional fossils, and far more prevalent. Microplastics, nanoplastics and plasticisers have permeated the food webs, our environment, our bodies and our brains.
Marine filter feeders (shellfish) are full of microplastic particles, as you would expect (4, 5). They provide a key point of entry into the marine food webs, so that microplastics are also in fish (6-10). They are in the water vapour that rises from the oceans and recycles as rain, so fruits, vegetables and cereals also carry a plastic payload (11); as do mineral water (12), tap water and beer (13), honey and sugar (14). Table salt is another predictable source (13).
It is becoming impossible to find any foodstuff that is not contaminated (15). But does it matter?
There is persuasive evidence that microplastics are deleterious to marine species (7, 8), and to plants where they trigger changes in plant biomass, tissue elemental composition, root traits and the mycorrhizal populations which are symbiotic for many commercially important plants (16, 17). Disruption of food production by microplastics is a new field of study, but is beginning to look like a real issue (ie 18, 19).
We not only consume microplastics in our food and beverages, we also inhale them (20-22); and when you add all these sources, it has been estimated that we may be ingesting as much as 8000 particles weighing 21 grams / month (22).
Other scientists have come to similar conclusions (ie 23). The mass media have pointed out that this is the equivalent of 4 credit cards – and our credit may be running out.
As the apex of the food chain (at least while we are alive), we perforcedly also contain microplastics. They are in everyone’s bowels (24), and as they have been previously shown to adversely impact on the microbiome and gut health in other species (ie (25-32), it seems unlikely that they are doing any good there. But they do not stop there.
Once ingested, particles smaller than 2.5 μm enter the gastrointestinal tract through endocytosis by M cells, specialized MALT cells located in Peyer’s patches in the wall of the small intestine. The function of these cells is to sample the contents of the gut, and they play a central role in innate immunity and the differentiation of self and non-self. They ingest nanoparticles of CaPo4 carrying adsorbed dietary antigens, and yeast cells containing 1-3, 1-6 beta glucans, which are recognized, metabolized and utilized.
They also ingest micro- and nanoparticles of plastic, TiO2 and other synthetic compounds that have entered our diet (33, 34). These cannot be broken down, and there is a growing suspicion that they may accumulate in M cells and contribute to the rising tide of allergy and autoimmune disease. Micro- and nanoparticles in the gut can also enter the body via persorption, the mechanical kneading of particles through epithelial gaps at villus tips.
We do not absorb all the microplastics we eat, but enough are absorbed to ensure that they are found in every tissue including the placenta (35) and, probably, the brain (36). Others enter the body through the enormous surface are of the lungs (20, 22, 37, 38), where they exert genotoxic, cytotoxic and pro-inflammatory effects (39, 40).
The idea that they may be altering brain function is an interesting one. There is no human data at all, but we do know something about the ability of microplastics to induce behavioural changes in other life forms. In zebra fish, exposure to nanoplastics reduces swimming, exploration, predator avoidance, aggression and shoaling (8, 9).
This might sound innocuous but speed, exploration, aggressiveness and shoaling, whereby fish swim close together to reduce the risk of being captured by predators, are all linked to evolutionary fitness. In short, the affected fish become less likely to survive. Could this possibly be relevant to humans?
Microplastics have one last trick up their sleeve. They contain and/or adsorb endocrine-disrupting chemicals such as Bisphenol A, PAH’s, PCB’s, OCP’s, PBDE’s and phthalates (41-45), and carry these into the body. Could nanoparticles, with their larger surface area, have the potential to bind and thereby expose us to greater amounts of these toxins?
Once these compounds enter the body they remain and accumulate. They are linked to falling sperm counts (46), early menopause (47-49) and reduced intelligence (50). They are also linked to altered sexual differentiation and increasing adiposity (50-54), not only in humans but also in the domestic and feral animal species (52) that share our polluted planet. Is their growing association with multiple health problems, from cancer to heart disease (50, 51, 53), contributing to our failing public health?
These forever compounds, which recent studies found in 100% of pregnant women, their babies (54) and their breast milk (55), have built up in the human population to the point where they can be measured in the output from sewage processing plants (56). They are accumulating in the food chain, and in us. Could ingested and inhaled microplastics be contributing to this?
There is reason to believe that many and perhaps all the synthetic polyaromatic compounds hit mitochondrial trip wires and precipitate the primeval chronic cell defense response (57-59). Many of them trigger epigenetic changes (59, 60). Could these mechanisms be causing neurodevelopmental damage (61) in neonates, and degenerative disease in adults?
When you do a literature search on microplastics and plasticisers, many papers have titles which, like the preceding paragraphs, end with a question mark. A lot of the research is preliminary, and some will eventually be found to be wrong or just immaterial. It is not yet possible to accurately quantify the overall risk they pose to human health (62), but it may be considerable (63).
After a few weeks digging in the databases, however, it is hard not to conclude that there is something bad lurking there; another insult to add to those caused by our modern diet and lifestyle, and which is contributing to our declining public health.
Bio-degradable plastics are a part of the solution, and ocean clean-up / river interception is another. Reducing exposure is a third strategy; cutting down on bottled water and cutting out plastic tea-bags is a good first step. Better nutrition will likely help, as at least some of the putative adverse effects of the microplastics likely involve inflammatory mechanisms (64, 65) and dysbiosis (24-32).
Next, bring on the Friesians.
Cows may be part of the solution to the plastic problem. Their rumen contains an unruly and immensely transformative microbial community that breaks down cellulose and other plant polymers into sugars and fatty acids that the cow can utilize. It also breaks down synthetic polymers, including the ubiquitous PET (66). Cattle could turn plastic into porterhouse on an industrial scale, were it not for those pesky plasticisers.
Reducing exposure to the endocrine disruptors, which is particularly important during pregnancy and childhood (47-51, 53, 67), requires different strategies.
- Replace plastic food containers with glass, stainless steel or waxed paper (67).
- Check your canned foods. Steel cans are often lined with plastic.
- Choose basic produce over ultra-processed foods. Organic is preferrable, if genuine.
- Wash hands before eating – nano-plastics and plasticisers occur widely in dust.
- Avoid fragranced soaps, cosmetics, cleaning and other products. Essential oils are a safer alternative.
- Dust and vacuum regularly, using a HEPA filter if possible.
Finally, for anyone interested in an evolutionary view of cellular function, the modern diet and health, I cannot recommend the work of Robert Naviaux (ie 58, 68) highly enough. He may not see all of the moon – no one person can – but he sees far more of it than the waning crescent I peer at.
‘Plastics. Think about it.’ (69).
PAH – polycyclic aromatic hydrocarbons
PCB -polychlorinated biphenyls
OCP – organochlorine pesticides
PBDE – polybrominated diphenyl ethers
Next week: How to care for your liver. Take the fava beans, hold the chianti!
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