Microplastics: how toxic and what exactly are they?
Microplastics is a growing concern for our planet. It is very widely found and has very diverse sources of pollution. How concerned should we be based on existing research?
Summary and TLDR
The smaller the molecule or particle, the higher the risk for health impact.
There is limited research on direct microplastics particle impact on human health. The likely first line of impact would be through toxic plastic additives, such as BPA, phthaltes, carried within microplastics.
More research is needed on the impact of microplastics particle accumulation in human body.
We should strive for elimination of harmful plastics additives as a first step.
This is part 1 of a 2 piece post. The second part will go into the detail on the amount we consume and sources of it, as well as what are the main products creating microplastics.
Headline review
Microplastics get featured a lot in our media and there is a growing concern around its impact on human health and the broader planet.
So let’s dig into these aspects:
Size of microplastics and what other similar particles are there?
Research on direct human health impact from microplastics
Sources of microplastics intake
Size of microplastics and what other similar particles are there?
Source: Visual Capitalist
Size definition
There appears to be no strict definition of microplastics in size, but more or less it ranges from 1 micron (µm) to 1 milimeter (mm).
So as we can see in the image above, in that size range it covers everything from bacteria to sand to human hair.
Technically microplastic is a mechanically separated piece of plastic from a bigger item. Everything around us decomposes naturally through wear and tear and plastics are not immune to it.
What’s smaller than microplastics?
One thing I always wondered myself is how are microplastics different from contaminant molecules.
Let’s take benzene for one (more on it here), which has 6 carbons and 6 hydrogen. A quick internet search suggests it’s diameter is 6 nanometers (source), which is hundreds of times smaller than the lower end of microplastic size range. So does this size matter when it comes to causing damage and risk to our bodies? We know for a fact that benzene is toxic, increases cancer risk and can be instantly deadly at very high concentrations. Is it so toxic because it is so small or is it more about the chemical properties of it?
Smaller particles → higher risk of impact across the whole body
Citing research, particles 150 µm in size or smaller have the potential to cross the intestinal barrier of mammals, whereas particles 20 µm in size or smaller may have the potential to penetrate deeply into tissues.
There then exists a size range when it is small enough to enter our body, but big enough to manage to evade being engulfed and dispatched through the standard immune response, creating an inflammatory response. Asbestos fibrils (3–20 µm) and carbon nanotubes (10–20 µm) have been cited (source: section 4) to lead this impact and microplastics are certainly also a candidate based on their size .
Sand
Referencing the image above, sand is roughly 90 µm. Research shows it causes a number of negative health impacts, mainly through microbes which inhabit it. In particular it has been found that the presence of fecal indicator bacteria (FIB) corresponds to gastrointestinal and skin illnesses of beachgoers (source and source). However, no research exists on the impact of pure 90 µm sand particles to the human body.
PM2.5
PM2.5 are air floating microparticles and are a result of combustion processes, in particular related to industrial factories, plants and road traffic. As the name suggests these are under 2.5 µm diameter, so at the smaller range of microplastics. The big risk of these particulates is that they are freely present in the air and can then travel into our breathing system and lungs. In fact they appear to migrate further into the whole body from the lungs due to their small size (source).
While the exact functional principle of PM2.5 impact on human body does not seem to be clear, research mentions impacts on airway inflammation, decline in lung function, incidence and exacerbation of asthma and chronic obstructive pulmonary disease and impacts on birth outcomes among others (source and source).
The PM2.5 chemical composition appears to include smaller molecules such as NH4+, EC, OCM, NO3−, Si, Na+, and SO42− (source).
Research on direct human health impact from microplastics
Microplastics appear to primarily accumulate in the gut, leading to first impacts there. Microplastics can also carry the FIB found on sand, can carry remains of other chemicals such as heavy metals or additives used in production. And then there are molecules which are subcomponents of plastics and are considered endocrin disrupting such as PFAS, phthalates, BPA (source).
No human studies
However, purely for microplastics as a group few good human studies exist. In fact I could not find a single one. There are papers which look into heavy metals typically found in plastics and study the impact of metals. There are mentions of Bisphenol A (toxic and partially banned in the EU). There are phthalates and PFAS and other additives which are toxic, but as these are added as functional additives, plastics can exist without them.
Mixed findings of mice studies
There are also not a great deal of mice studies (source) and those show a somewhat mixed picture. One study reported very limited changes to health even at daily intake of a set amount of microplastics for 30 days. Another showed more impact, mainly in terms of altered composition of the gut microbiota and modified metabolism, liver inflamation, but there are questions of dosage and methodology. I saw in some papers mention of cancer but not a study directly attributing the two.
Human body clears a great deal
Let’s not forget that the human body is highly adaptable. When I did research on PFAS (see the CDC chart towards the end) I was actually surprised that even those tiny PFOS molecules (<1 nm) which take hundreds of years to break down got cleared from human blood, arguably over a super long time of 10+ years. Crucially to note, that depending on the dosage, waiting for such a long duration can be too late.
For microplastics, research shows that up to 90% of microplastics get cycled through and removed from the body (source).
Particle accumulation or plastic additive toxicity?
It seems that the pathway for microplastics to damage human health is then twofold:
through overtime particle accummulation and
through carrying additional contaminants which then get absorbed into the critical systems.
On the former no studies yet exist. However, if it is anything like Asbestos, the risk can be high.
On the latter we know quite a lot, and additives such as phthalate, PFAS, BPA, heavy metals are highly dangerous to human health. However, it is not clear how much of BPA, phthalate and heavy metals we get from our daily dose of microplastics.
All the additives which are found in microplastics are especially dangerous to children. Exposure to plastic related additive chemicals is mentioned to increase the risk of prematurity, stillbirth, low birth weight, birth defects of the reproductive organs, neurodevelopmental impairment, impaired lung growth, and childhood cancer (The Minderoo-Monaco Commission on Plastics and Human Health).
Can there be plastic which is safe?
But if the major risk relates to plastic additives, perhaps there can be a future with plastics but without the additives and the health risks? We would have to accept the presence of microparticles from plastics as a given in that case though.
Better research yet is needed on the clean plastic microparticle accumulation in our bodies.
Best sources
For those interested: the best 2 sources I found on this topic: