“A credit card a week”? Estimates of how much microplastic we eat
An estimate of 5 g a week and one about a millionth of that: why the estimates differ so much
The answer
“5 g a week (a credit card)” is the upper end of the range (0.1 to 5 g a week) estimated in a 2021 paper, and WWF spread it as the “average.”
Another study from the same year estimated the adult median at about 4.1 μg a week (about a millionth of 5 g) and wrote that “5 g is above the 99th percentile of our distribution and does not represent the average person.”
The main estimates
| Estimate | Unit | Value | Based on |
|---|---|---|---|
| Cox et al. (2019) | Count | 39,000 to 52,000 particles a year (74,000 to 121,000 including breathing) | From reported values for foods that make up about 15% of Americans’ calories. Drinking only bottled water adds 90,000 particles a year; only tap water, 4,000. The authors say this is an underestimate. |
| Mohamed Nor et al. (2021) | Weight | Adult median of 583 ng a day (about 4.1 μg a week), or 883 particles a day | Particles of 0.001 to 5 mm, from 8 kinds of food and from air. The upper end of the distribution is also calculated. |
| Senathirajah et al. (2021) | Weight | 0.1 to 5 g a week | Counts from 59 papers converted to weight (assuming an average weight for particles of 0 to 1 mm). |
| WWF (2019) | Weight | About 5 g a week on average, “the weight of a credit card” | An announcement based on the study above (commissioned by WWF from the University of Newcastle). |
Pletz (2022) points out that the Senathirajah et al. estimate is “an overestimate by several orders of magnitude” because of how the data were combined and which particle sizes were chosen.
Why do they differ so much?
- Count or weight: A particle’s weight grows with the cube of its diameter. One 1 mm particle weighs as much as a million 0.01 mm particles. Whether a few large particles are included can change the total weight by many orders of magnitude.
- How large a size range is included: The lower and upper limits of the range counted differ between studies.
- Mean, median or upper end: Calling a mean (pulled up by some people’s high values) or the upper end of a range the “average” changes the impression a great deal.
- Quality of the underlying data: Reports counted by eye alone tend to be high because they also count particles that are not plastic. For table salt, the identification method alone made a 10- to 600-fold difference (Lee et al. 2021).
Where does most of the intake come from?
- In the estimate by Cox et al. (2019), people who drink only bottled water take in 90,000 more particles a year, and people who drink only tap water 4,000 (but studies of bottled water have been criticized for how they measured → Bottled water).
- One study estimates that fibers falling onto the plate from household dust during a meal come to 13,731 to 68,415 particles per person per year, orders of magnitude more than the amount from mussels (123 a year in the UK) (→ Household dust that falls onto food during meals).
- EFSA (2016) estimated that even a serving (225 g) of the most contaminated mussels comes to about 7 μg.
Sources
- Cox KD, et al. Environ Sci Technol 2019;53:7068 (correction issued 2020)
- Mohamed Nor NH, et al. Environ Sci Technol 2021;55:5084
- Senathirajah K, et al. J Hazard Mater 2021;404:124004
- Pletz M. J Hazard Mater Lett 2022;3:100071
- University of Newcastle (Australia), announcement of June 2019
- EFSA CONTAM Panel. EFSA J 2016;14(6):4501
- Catarino AI, et al. Environ Pollut 2018;237:675
- Lee HJ, et al. J Hazard Mater 2021;402:123743
Last checked 2026-10-01. Research and regulations change over time. This page is a translation of our Japanese page; if they differ, the Japanese page is the reference.