Microplastics: Much Less Than You Wanted To Know

post by jenn (pixx), kaleb (geomaturge), Brent · 2025-02-15T19:08:14.561Z · LW · GW · 5 comments

Contents

  What are the current recommended limits for microplastic intake?
    Canada
    EU
    USA
    World Health Organization
    Recommended Limits For Specific Chemicals Exist
    A Good Paper on Microplastic Regulation Meta
  Health Effects of Microplastics
  Quantities Ingested and Main Exposure Pathways
    Food contamination
        Lower estimate
        (grams/person/year)
        Upper estimate
        (grams/person/year)
        The presence of microplastics in commercial salts from different countries
    Household dust
      How to reduce the amount of microplastics you have
      Misc links
        Total Intake assessments
  Appendix: Research Agenda and Format
None
5 comments

Microplastics have been in the news and the local rationalist discord with increasing frequency over the past few months. Of note are Nat Friedman's PlasticList, and this 2024 preprint demonstrating that some human brains are now 0.5% plastic by weight. There was also an article on black plastic cookware that was quickly retracted^[1]. The volume of discussion made it clear that few people seem to have a clear understanding of what we actually know about microplastics, so we had a meetup about it. 

Here are the notes from Kitchener-Waterloo Rationality's in-person meetup [? · GW]^[2] researching the current understanding of microplastics in a time-boxed format. Sort of like partitioned book club [LW · GW], the goal of the meetup was to power of friendship teamwork our way into a better understanding of a complex topic with relatively little individual effort.

tl;dr: The field is so new that there's a striking lack of scientific consensus, standardized measurements, or regulatory frameworks:

• Health effects of microplastics are severely understudied, and research into this topic really only began a year or two ago.
• Current testing methods can't reliably detect particles smaller than 20 micrometers, but microplastics smaller than 10 micrometers in length have an increased likelihood of causing adverse health effects in mammals.
• No official safety limits exist for microplastic consumption basically anywhere.

This write-up represents about 90 minutes of focused research per section. Attendees aimed to quickly build a broad understanding of each sub-topic rather than produce a comprehensive review. We welcome specific corrections and links to additional key papers we missed. However, critiques about comprehensiveness or depth should keep in mind that this is very much a product of a "what can five people learn in an evening?" approach.

What are the current recommended limits for microplastic intake?

tl;dr we don't have any.

Canada

There are no rules or standards for allowable limits for microplastics in bottled water in Canada. We couldn't find any rules or standards for microplastics in food, in general.

As of July 2018, we have a ban on “microbeads” (plastic microbeads that are ≤ 5 mm in size) from toiletries like soaps and shampoos, due to concern that they’ll get into our waterways and cause pollution there. Not much in terms of concern for human health; this makes sense, it was before the recent hubbub about human health concerns.

EU

Basically the same situation as Canada; some limits on microplastics in toiletries, nothing related to human consumption.

USA

FDA, July 2024 does not think that it makes sense to regulate microplastics yet due to the lack of good quality studies on its health impact:

The presence of environmentally derived microplastics and nanoplastics in food alone does not indicate a risk and does not violate FDA regulations unless it creates a health concern. While many studies have reported the presence of microplastics in several foods, including salt, seafood, sugar, beer, bottled water, honey, milk, and tea, current scientific evidence does not demonstrate that the levels of microplastics or nanoplastics detected in foods pose a risk to human health. Additionally, because there are no standardized methods for how to detect, quantify, or characterize microplastics and nanoplastics, many of the scientific studies have used methods of variable, questionable, and/or limited accuracy and specificity.

The EPA does not currently monitor microplastic levels in drinking water. It is doing some preliminary research into doing so, and recognizes that testing methods ASTM D8332-20 and ASTM D8333-20 are available for microplastics. But these are ways to test for microplastic content, not standards on what the limits should be. 

100+ environmental nonprofits submitted a report to the EPA in November 2024 requesting that they start a microplastic monitoring program for drinking water nation-wide. According to the nonprofits, the EPA has the standing and funding to do this via provisions in the Safe Drinking Water Act.

In 2022, the California Water Board settled on a two-step approach to test drinking water over a period of four years, with time in between to review results and adjust. Under the Board’s two-step approach, Phase I (2023-2025) of the program focuses on source water monitoring, whereas Phase II (2026-2028) focuses on treated drinking water monitoring. Again, they’re just monitoring the contents; as for recommended limits, “numerical guidance could not be developed”. Two interesting points that are concerning when combined:

1. Microplastics smaller than 10 micrometers in length have an increased likelihood of causing adverse health effects in mammals and should be prioritized for monitoring when possible.
2. Available analytical methods can only reliably quantify microplastics as small as 20 micrometers in length. Concentrations of smaller particles will need to be estimated through “application of well-conserved size distributions”.

World Health Organization

2019 report: Routine monitoring of microplastics in drinking-water is not recommended at this time, as there is no evidence to indicate a human health concern. Concerns over microplastics in drinking-water should not divert resources of water suppliers and regulators from removing microbial pathogens, which remains the most significant risk to human health from drinking-water along with other chemical priorities. Honestly yeah that seems pretty legit.

Section 3.4.1: ingestion of larger microplastics aren’t a concern because they just pass through the digestive system, but smaller particles are more concerning.

Recommended Limits For Specific Chemicals Exist

PlasticList links to the PlastChem project, which maintains a list of over 20,000 plastic-related chemicals with varying levels of human exposure and health hazards.

PlasticList chose 18 to test for their project to test a bunch of food items sourced in the Bay Area. If you scroll down a page or two on this page, there is a list of the 18 that they chose, and if you click them they expand to show more details. Presumably someone smart went through the PlastChem project and some other resources and narrowed down the study to the chemicals that they found the most relevant for human health. (But see here for a reasonable critique of the project.)

A few different entities give recommendations for daily limits, including the EFSA in the EU, and the CDC, FDA, and EPA in the US. The reports they link tend to be pretty scant (example of EFSA (EU) and FDA (US) document). But I think these are just the summary docs for manufacturers and probably there are more in-depth documents out there somewhere.

A Good Paper on Microplastic Regulation Meta

Regulatory Science Perspective on the Analysis of Microplastics and Nanoplastics in Human Food, March 2024. Authors argue:

• Current microplastic regulations focus heavily on primary microplastics (deliberately manufactured small plastic particles, like Canada’s microbeads ban), which are actually a relatively minor source of environmental microplastic pollution compared to secondary microplastics from degradation of larger plastic waste.
• Regulations need more precise and enforceable definitions, people mean a bunch of different things when they currently say “microplastics”
• Current (human or eco) toxicity data have not defined which polymer or plastic properties (size, shape, chemical composition, additives, etc.) are responsible for inducing harm which is specific to microplastics
  • Different plastics have vastly different profiles vis-à-vis harm to human health, and lumping them together is maybe counterproductive
• Plastics genuinely do a lot of things other materials can’t, banning them or reducing their use will come with tradeoffs that we need to think carefully about
  • Many years of research have gone into the materials we currently use, and thus their physical/chemical properties and costs are optimized from the point of view of manufacturers.
  • Environmentalists want to push for more biodegradable materials, but some intended uses for polymers specifically care about longevity (e.g. paints or adhesives), so biodegradability is a bit of a nonstarter for at least some plastic products.

Health Effects of Microplastics

THE EFFECTS OF MICROPLASTICS ON HUMAN HEALTH HAVE NOT BEEN STUDIED MUCH. However, we could conjecture some effects based on their effects in marine organisms, and some limited studies on mammals like mice. Most of the information below is from this paper, which has sources for various specific claims.

Various bad effects of microplastics have been observed in marine organisms, such as plankton and fish.

• Oxidative stress is an imbalance between free radicals and antioxidants in the body, which could lead to cell damage. Microplastics could cause oxidative stress due to either oxidizing species being adsorbed to their surface (due to their high surface area) or due to causing an inflammatory response, leading to reactive oxygen being released. Oxidative stress after exposure to microplastics has been reported in zebrafish and mice.
• Microplastics may reduce energy intake due to decreased feeding activity, which has been observed in marine worms, crabs, clams, or due to changing digestive enzyme activity, which has been observed in fish.

There has been some research studying the effects of microplastics in vitro. A study exposing mice cells to microplastic solutions for several days (0.1 mu-m to 2 mu-m) reported decreased cell viability (percentage of living and healthy cells in a sample).

In general, plastics have various chemicals that are known to be endocrine disruptors. Endocrine disruptors basically mess with the natural functioning of the hormonal system, which has various bad effects. Due to their high surface area, microplastics may be better vectors for some chemicals??? But we are exposed to endocrine disruptors from various other sources anyway.

Rough Notes Dump

• • https://forum.longevitybase.org/t/how-to-reduce-microplastics/126 - long comment on things to avoid, but unsure of source reliability
    • General point is that human effects are somewhat understudied; animal studies could serve as proxy
    • thread offers no distinction between ~quick wins (e.g. "don't buy bottled water") and more elaborate and less useful tips (e.g. "avoid having to have blood transfusions", "fund silk clothing"); end result is that the thread feels comprehensive but vaguely unserious
  • Academic reviews I’ve found seem to focus on more categorizing by e.g. particle sizes, sources, etc, rather than by “chemical type” so to speak (polymer type may count)
  • Metabolic effects (including obesity), immune system (lungs, IBD, …), neurotoxicity, reproductive/developmental toxicity https://pubs.acs.org/doi/full/10.1021/envhealth.3c00052
  • Different particle sizes have effects at different levels, as one would expect https://doi.org/10.1016/j.scitotenv.2021.145758
  • (aquatic organisms) Claims that out of various factors, particle size is the main one that affects the possible effects on the body (more in the sense that different sizes cause different effects rather than strictly better or worse), though for some of the other factors it’s more of a lack-of-data issue https://link.springer.com/article/10.1186/s43591-022-00040-4
    • In that line: total mass vs total particle number may be relevant to different health effects; it is encouraged to report both

  Considerations regarding additives https://pmc.ncbi.nlm.nih.gov/articles/PMC7068600/

Quantities Ingested and Main Exposure Pathways

The main pathways for microplastic exposure are via eating, drinking, and breathing. In principle, exposure through the skin is also possible, but research suggests this is negligible compared to other pathways. Getting a consistent absolute quantitative estimate of average microplastic intake is hard, but estimates of the relative exposure from various pathways are fairly consistent. 

The extant literature primarily measures microplastic consumption in two ways. Firstly, estimating the amount of plastic entering the body such as preparing food or drinks, then washing the plastics off the food and measuring the number of particles with spectroscopy (A,B). Secondly, estimating the amount of plastic exiting the body via fecal matter analysis (C). There is a dearth of studies that measure the accumulation of plastics in humans directly.

A recurring issue in the literature is that measuring the number of microplastic particles ingested is fairly feasible, but measuring the mass and size distribution of those particles is more difficult (D). As smaller particles are suspected to be worse than larger particles, simple quantity-of-particles estimates are insufficient. Moreover, as the size distribution of particles varies across sources, it is difficult to compare numbers across studies; one such comparison led to the claim that we eat one credit card per week (which is likely largely overestimated.)

One consistent finding we found surprising was how respiratory microplastic intake is comparable or potentially even worse than dietary intake (E,F). One researcher claims "If I keep a piece of fish on the table for an hour, it has probably gathered more microplastics from the ambient air than it has from the ocean." Indoor air was consistently shown to be worse than outdoor air, in another win for touching grass.

In summary:

1. Mass intake estimates are difficult as the distribution of particles over size is not well-understood .
2. Estimating the quantity of particles ingested is easier, but less useful for toxicology.
3. We do not understand the proportion of ingested plastics that stay in the body, and where or how they accumulate.
4. Exposure quantities from respiration and diet appear to be comparable. In particular, synthetic textiles in households are a major contributor to microplastic intake.
5. We suggest these low-hanging actions one can take to reduce their quantity exposure:
   1. Stop using plastic bottles and plastic food storage containers,
   2. Stop using plastic cutting boards,
   3. Install a microplastics filter on your washing machine and buy less plastic clothes, linens, and towels,
   4. Air your house frequently and vacuum often (you should be doing these anyway).

(Health benefits of said actions are unknown, but you can be smug about being less plastic-by-weight than your friends)

Outstanding questions:

• Do we expect the distribution of particle sizes to be approximately consistent across intake sources? If so, quantity is a decent proxy for danger.
• What are the outstanding challenges to measure plastic mass in human bodies directly, instead of measuring intake?
• What proportion of plastic intake is systemic? That is, even if you personally do not purchase, consume or interact with any plastic products, how much plastic do you still ingest

Rough Notes Dump - Person A

Ingestion (Dietary Exposure)

Food Contamination: Microplastics have been detected in seafood, salt, sugar, honey, fruits, vegetables, and processed foods. Marine organisms, particularly shellfish and fish, can accumulate microplastics from their environment.

Water and Beverages: Microplastics are found in bottled and tap water, tea, coffee, and other drinks.

Food Packaging and Processing: Plastic packaging and storage can introduce microplastics into food, especially through degradation and friction.

Inhalation (Airborne Exposure)

 

Indoor and Outdoor Air: Microplastics are present in both indoor and outdoor air, originating from textiles, synthetic fibers, and industrial emissions.

Household Dust: Indoor sources, such as carpets, upholstery, and clothing, release microplastic fibers that can be inhaled and even ingested indirectly.

Workplace Exposure: Individuals in certain industries (e.g., textile, plastic manufacturing) may experience higher levels of airborne microplastics.

Dermal Absorption (Skin Contact)

 

Cosmetics and Personal Care Products: Some skincare products, soaps, and exfoliants contain microplastics (e.g., microbeads).

Clothing and Textiles: Synthetic fabrics (e.g., polyester, nylon) release microplastics during wear and washing.

Water Contact: Bathing or swimming in microplastic-contaminated water (e.g., oceans, lakes) may result in skin exposure, though dermal absorption is considered a minor pathway compared to ingestion and inhalation.

Among these, ingestion and inhalation are considered the most significant pathways of human exposure to microplastics.

Food contamination

https://www.ewg.org/research/invisible-threat-ewg-analysis-shows-you-could-be-eating-many-12-plastic-bags-year

Mentions cutting boards as a main pathway

drinking from plastic water bottles is up there

PVC water pipes, but less of a source than water bottles

0.06 and 0.10 grams of plastic from drinking water.

10.87 and 20.88 grams of plastic from food.

7.40 and 50.71 grams of plastic from cups, boards and containers.

 

Category	Exposure route	Literature reference	Reported type of plastic exposure	Lower estimate (grams/person/year)	Upper estimate (grams/person/year)	Notes
Water	Drinking water	Senathirajah et al. (2021)	Direct mass	0.06	0.10	Predominantly nanoplastics (mass is very small) Predominantly bottled water
Food	Dietary: Beverages, honey, meat, seafood, vegetables	Bai et al. (2022)	Microplastic total	0.070	0.076	Predominantly nanoplastics (mass is very small) Predominantly bottled water Diameter = 100 µm
	Salt	Senathirajah et al. (2021)	Direct mass	10.8	20.8
Plasticware	Cutting boards	Yadav et al. (2023)	Direct mass	7.4	50.7	Assuming polyethylene (vast majority)
	Plastic cups	Zhou et al. (2022)	Microplastic total	0.0023	0.0055	Predominantly nanoplastics (mass is very very small) Diameter = 50 µm
	Takeout containers	Du et al. (2020)	Microplastic total	0.0003	0.0052	Predominantly nanoplastics (mass is very very small) Diameter = 100 µm
Total				18.33	71.69

 

Very surprised how high salt is on this list

Digging into salt a little more

The presence of microplastics in commercial salts from different countries

https://www.nature.com/articles/srep46173

“ According to our results, the low level of anthropogenic particles intake from the salts (maximum 37 particles per individual per annum) warrants negligible health impacts. However, to better understand the health risks associated with salt consumption, further development in extraction protocols are needed to isolate anthropogenic particles smaller than 149 μm.”

Seems to be a theme that smaller particles are harder to detect in many experiments

Contrary to the above chart, seeing claims that salt is very low, and water is very high from this infographic (though this chart is per gram/litre of the product, so may need to be divided by consumption to match the above chart). It is also number of particles per thing, rather than mass of particles per thing. The above chart is based on mass (e.g. many smaller plastics could have the same mass as one large microplastic)

https://www.statista.com/chart/18299/how-we-eat-drink-and-breathe-microplastics/

 

https://www.ucsf.edu/news/2024/02/427161/how-to-limit-microplastics-dangers

 

Some small studies showing babies had higher concentration than adults (n=16)

https://www.sciencenews.org/article/microplastics-human-bodies-health-risks

Babies might face particularly high exposures. A small study of six infants and 10 adults found that the infants had more microplastic particles in their feces than the adults did. Research suggests microplastics can enter the fetus via the placenta, and babies could also ingest the particles via breast milk. The use of plastic feeding bottles and teething toys adds to children’s microplastics exposure.

 

Microplastic ingestion increasing with time, at different rates in different parts of the world

https://healthpolicy-watch.news/humans-now-ingest-six-times-more-microplastics-since-1990/

Household dust

https://www.sciencedirect.com/science/article/abs/pii/S0269749116312325

“The results show that human exposure to natural and synthetic fibers may occur in indoor environments. Because of their size, these fibers are not likely to be inhaled but as there is still no evidence, further work is needed to better understand this risk.”

Potentially could be ingested from settled dust

"smaller inhalable fibers (down to the nanofiber scale) may be present in indoor an outdoor air but could not be counted with the method used."

Higher concentration of fibres in indoor air vs outdoor air

-> I wonder if people spending more time inside is having an effect

“fibers settled on indoor surfaces are most likely released in wastewater, e.g., when cleaning floors. Previous studies pointed out to washing machine effluents as a source of fibers in aquatic environments (Browne et al., 2011).”

https://www.sciencenews.org/article/microplastics-human-bodies-health-risks

Airborne particles may turn out to be more of a concern than those in food. One study reported in 2018 compared the amount of microplastics present within mussels harvested off Scotland’s coasts with the amount of microplastics present in indoor air. Exposure to microplastic fibers from the air during the meal was far higher than the risk of ingesting microplastics from the mussels themselves.

https://pubmed.ncbi.nlm.nih.gov/29604577/

Extrapolating from this research, immunologist Nienke Vrisekoop of the University Medical Center Utrecht says, “If I keep a piece of fish on the table for an hour, it has probably gathered more microplastics from the ambient air than it has from the ocean.”

This seems very important, would be nice to have a good comparison chart

Perhaps good news: Microplastics seem unable to penetrate the skin. “The epidermis holds off quite a lot of stuff from the outside world, including [nano]particles,” Leslie says. “Particles can go deep into your skin, but so far we haven’t observed them passing the barrier, unless the skin is damaged.”

There are many studies that look at how many microplastics are in an environment (e.g. collecting them from a textile company)

https://openaccess.cms-conferences.org/publications/book/978-1-958651-88-9/article/978-1-958651-88-9_25

But this doesn’t necessarily translate to them entering the body

How to reduce the amount of microplastics you have

Some mention of blood donation reducing PFAS (“forever chemicals”), but not necessarily microplastics

https://www.reddit.com/r/nutrition/comments/1g2utgb/removing_microplastics_from_the_body/?rdt=62429

https://www.reddit.com/r/biology/comments/198dybp/blood_plasma_donation_as_a_means_of_removing/

Misc links

https://polyrisk.science/

https://cusp-research.eu/

We are 75 organisations from 21 countries working within five large-scale research projects united in CUSP – the European research cluster to understand the health impacts of micro- and nanoplastics (MNPs).

Rough Notes Dump - Person B

• • Papers from McGill investigating food sources

    Cutting Boards: An Overlooked Source of Microplastics in Human Food? | Environmental Science & Technology - Yadav et al

    Plastic Teabags Release Billions of Microparticles and Nanoparticles into Tea | Environmental Science & Technology - Hernandez et al

    • Plastic (polyethelene, polystyrene) cutting boards may account for 70% of the particles (by mass?)
    • Brewing plastic tea bags could release millions of >1ug and billions of <1ug particles

    Total Intake assessments

    Early work: ​​Human Consumption of Microplastics - PubMed - Cox et al

    • Estimates 39000-52000 particles under 5mm from food intake, 74000-121000 with respiratory
    • Suggests bottled water as a primary consumption vector

    Lifetime Accumulation of Microplastic in Children and Adults | Environmental Science & Technology - Mohamed Nor et al.

    • Microplastic (1–5000 μm) median intake rates are 553 particles/capita/day (184 ng/capita/day) and 883 particles/capita/day (583 ng/capita/day) for children and adults, respectively.
    • Accumulation effects are poorly understood since we do not know absorption rate & how much is filtered out from the body over time 

    A Review of Human Exposure to Microplastics and Insights Into Microplastics as Obesogens - PMC - K&V

    • Indoor air exposure is worse than outdoor, likely due to synthetic textiles
    • Air exposure is comparable or even greater than dietary exposure

    Low levels of microplastics (MP) in wild mussels indicate that MP ingestion by humans is minimal compared to exposure via household fibres fallout during a meal - PubMed

    • Researcher stated in an interview that “If I keep a piece of fish on the table for an hour, it has probably gathered more microplastics from the ambient air than it has from the ocean.” 

    https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.777865/full

  Parry sound pilot project found microplastic filters in washing machines are effective at reducing the amount of plastic entering bodies of water

Appendix: Research Agenda and Format

The meetup description is here [? · GW]. Before the meetup, the organizer (Jenn) came up with a draft research agenda, which is basically a list of relatively independent questions around microplastics. These were discussed, refined, and assigned to the attendees in the first 30 minutes of the meetup, and then we had two pomodoro sessions that were around 40 minutes each. Attendees were encouraged to spend the last 20 minutes or so of work time refining their write-up instead of doing further research. Then we shared our results!

The agenda:

Contribute all the questions you have to this list. At the meetup, we’ll ask people to signal which questions we think are the most important to answer, and then portion out our research time based on that.^[3]

Approximate format: Top level questions are questions that can go to an atomic researcher or research team. Sub-questions are questions that make sense to be answered by the researcher or research team answering the top-level question.

• What are the current scientific estimates for how many microplastics the average person ingests per week/year? How reliable are these estimates?
  • How much microplastics are in the average human body?
• What are the current recommended limits for microplastic intake? Where did the recommendations come from?
• What are the main pathways of human exposure to microplastics?
  • Are there ways to reduce the amount of microplastics you have in your body?
• What is the current scientific consensus on health effects of microplastic exposure?
  • What are the known mechanisms of harm?
  • What are the key unknowns and uncertainties?
• Are there specific types of microplastics that are more concerning than others?
  • What are the most useful things to avoid?

1. ^{^}

   But not before Jenn threw out all her black plastic stuff and replaced it with silicone. Perhaps this is for the best.

2. ^{^}

   Kitchener-Waterloo Rationality is experimenting with group rationality and having more visible outputs. If you're in the area, come check us out!

   Those who either did not have LW accounts and/or didn't want this product associated with them are not listed in the list of co-authors.

3. ^{^}

   this ended up not being done because we had 5 lines of inquiry and 5 people showed up, so we decided to do the easier thing. Responses to some top levels questions were consolidated in this write-up for clarity and to reduce redundancy.

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