Perhaps one of the clearest indications of the Anthropocene may be the presence of plastic. Starting with the commercialization of Bakelite in 1907 by Leo Baekeland, plastics have taken the world by storm. Courtesy of being easy to mold into any imaginable shape along with a wide range of properties that depend on the exact polymer used, it’s hard to imagine modern-day society without plastics.

Yet as the saying goes, there never is a free lunch. In the case of plastics it would appear that the exact same properties that make them so desirable also risk them becoming a hazard to not just our environment, but also to ourselves. With plastics degrading mostly into ever smaller pieces once released into the environment, they eventually become small enough to hitch a ride from our food into our bloodstream and from there into our organs, including our brain as evidenced by a recent study.

Multiple studies have indicated that this bioaccumulation of plastics might be harmful, raising the question about how to mitigate and prevent both the ingestion of microplastics as well as producing them in the first place.

Polymer Trouble

Plastics are effectively synthetic or semi-synthetic polymers. This means that the final shape, whether it’s an enclosure, a bag, rope or something else entirely consists of many monomers that polymerized in a specific shape. This offers many benefits over traditional materials like wood, glass and metals, all of which cannot be used for the same wide range of applications, including food packaging and modern electronics.

Unlike a composite organic polymer like wood, however, plastics do not noticeably biodegrade. When exposed to wear and tear, they mostly break down into polymer fragments that remain in the environment and are likely to fragment further. When these fragments are less than 5 mm in length, they are called ‘microplastics’, which are further subdivided into a nanoplastics group once they reach a length of less than 1 micrometer. Collectively these are called MNPs.

The process of polymer degradation can have many causes. In the case of e.g. wood fibers, various microorganisms as well as chemicals will readily degrade these. For plastics the primary processes are oxidation and chain scission, which in the environment occurs through UV-radiation, oxygen, water, etc. Some plastics (e.g. with a carbon backbone) are susceptible to hydrolysis, while others degrade mostly through the interaction of UV-radiation with oxygen (photo-oxidation). The purpose of stabilizers added to plastics is to retard the effect of these processes, with antioxidants, UV absorbers, etc. added. These only slow down the polymer degradation, naturally.

In short, although plastics that end up in the environment seem to vanish, they mostly break down in ever smaller polymer fragments that end up basically everywhere.

Body-Plastic Ratio

In a recent review article, Dr. Eric Topol covers contemporary studies on the topic of MNPs, with a particular focus on the new findings about MNPs found in the (human) brain, but also from a cardiovascular perspective. The latter references a March 2024 study by Raffaele Marfella et al. as published in The New England Journal of Medicine. In this study the excised plaque from carotid arteries in patients undergoing endarterectomy (arterial blockage removal) was examined for the presence of MNPs prior to the patients being followed to see whether the presence of MNPs affected their health.

What they found was that of the 257 patients who completed the full study duration 58.4% had polyethylene (PE) in these plaques, while 12.1% also had polyvinyl chloride (PVC) in them. The PE and PVC MNPs were concentrated in macrophages, alongside active inflammation markers. During the follow-up period during the study, of the patients without MNPs 8 of 107 (7.5%) suffered either a nonfatal myocardial infarction, a nonfatal stroke or death. This contrasted with 30 of 150 (20%) in the group with MNP detected, suggesting that the presence of MNP in one’s cardiovascular system puts one at significantly higher risk of these adverse events.

The presence of MNPs has not only been confirmed in arteries, but effectively in every other organ and tissue of the body as well. Recently the impact on the human brain has been investigated as well, with a study in Nature Medicine by Alexander J. Nihart et al. investigating MNP levels in decedent human brains as well the liver and kidneys. They found mostly PE, but also other plastic polymers, with the brain tissue having the highest PE proportion.

Interestingly, the more recently deceased had more MNP in their organs, and the brains of those with known dementia diagnosis had higher MNP levels than those without. This raises the question of whether the presence of MNPs in the brain can affect or even induce dementia and other disorders of the brain.

Using mouse models, Haipeng Huang et al. investigated the effects of MNPs on the brain, demonstrating that nanoplastics can pass through the blood-brain barrier, after which phagocytes consume these particles. These then go on to form blockages within the capillaries of the brain’s cortex, providing a mechanism through which MNPs are neurotoxic.

Prevention

Clearly the presence of MNPs in our bodies does not appear to be a good thing, and the only thing that we can realistically do about it at this point is to prevent ingesting (and inhaling) it, while preventing more plastics from ending up in the environment where it’ll inevitably start its gradual degradation into MNPs. To accomplish this, there are things that can be done, ranging from a personal level to national and international projects.

On a personal level, wearing a respirator while being in dusty environments, while working with plastics, etc. is helpful, while avoiding e.g. bottled water. According to a recent study by Naixin Qian et al. from the University of California they found on average 240,000 particles of MNPs in a liter of bottled water, with 90% of these being nanoplastics. As noted in a related article, bottled water can be fairly safe, but has to be stored correctly (i.e. not exposed to the sun). Certain water filters (e.g. Brita) filter particles o.5 – 1 micrometer in size and should filter out most MNPs as well from tap water.

Another source of MNPs are plastic containers, with old and damaged plastic containers more likely to contaminate food stored in them. If a container begins to look degraded (i.e. faded colors), it’s probably a good time to stop using it for food.

That said, as some exposure to MNPs is hard to avoid, the best one can do here is to limited said exposure.

Environmental Pollution

Bluntly put, if there wasn’t environmental contamination with plastic fragments such personal precautions would not be necessary. This leads us to the three Rs:

• Reduce
• Reuse
• Recycle

Simply put, the less plastic we use, the less plastic pollution there will be. If we reuse plastic items more often (with advanced stabilizers to reduce degradation), fewer plastic items would need to be produced, and once plastic items have no more use, they should be recycled. This is basically where all the problems begin.

Using less plastic is extremely hard for today’s societies, as these synthetic polymers are basically everywhere, and some economical sectors essentially exist because of single-use plastic packaging. Just try to imagine a supermarket or food takeout (including fast food) without plastics. A potential option is to replace plastics with an alternative (glass, etc.), but the viability here remains low, beyond replacing effectively single use plastic shopping bags with multi-use non-plastic bags.

Some sources of microplastics like from make-up and beauty products have been (partially) addressed already, but it’d be best if plastic could be easily recycled, and if microorganisms developed a taste for these polymers.

Dismal Recycling

Currently only about 10-15% of the plastic we produce is recycled, with the remainder incinerated, buried in landfills or discarded as litter into the environment as noted in this recent article by Mark Peplow. A big issue is that the waste stream features every imaginable type of plastic mixed along with other (organic) contaminants, making it extremely hard to even begin to sort the plastic types.

The solution suggested in the article is to reduce the waste stream back to its original (oil-derived) components as much as possible using high temperatures and pressures. If this new hydrothermal liquefaction approach which is currently being trialed by Mura Technology works well enough, it could replace mechanical recycling and the compromises which this entails, especially inferior quality compared to virgin plastic, and an inability to deal with mixed plastics.

If a method like this can increase the recycling rate of plastics, it could significantly reduce the amount of landfill and litter plastic, and thus with it the production of MNPs.

Microorganism Solutions

As mentioned earlier, a nice thing about natural polymers like those in wood is that there are many organisms who specialize in breaking these down. This is the reason why plant matter and even entire trees will decay and effectively vanish, with its fundamental elements being repurposed by other organisms and those that prey on these. Wouldn’t it be amazing if plastics could vanish in a similar manner rather than hang around for a few hundred years?

As it turns out, life does indeed find a way, and researchers have discovered multiple species of bacteria, fungi and microalgae which are reported to biodegrade PET (polyethylene terephthalate), which accounts for 6.2% of plastics produced. Perhaps it’s not so surprising that microorganisms would adapt to thrive on plastics, since we are absolutely swamping the oceans with it, giving the rapid evolutionary cycle of bacteria and similar a strong nudge to prefer breaking down plastics over driftwood and other detritus in the oceans.

Naturally, PET is just one of many types of plastics, and generally plastics are not an attractive target for microbes, as Zeming Cai et al. note in a 2023 review article in Microorganisms. Also noted is that there are some fungal strains that degrade HDPE and LDPE, two of the most common types of plastics. These organisms are however not quite at the level where they can cope with the massive influx of new plastic waste, even before taking into account additives to plastics that are toxic to organisms.

Ultimately it would seem that evolution will probably fix the plastic waste issue if given a few thousand years, but before that, we smart human monkeys would do best to not create a problem where it doesn’t need to exist. At least if we don’t want to all become part of a mass-experiment on the effects of high-dose MNP exposure.