Researchers at the University of Victoria in Canada reviewed 26 studies measuring microplastics in common foods, drinks and air, and combined them with US dietary guidelines to estimate how many particles an average person takes in.
They estimated that people ingest 39,000 to 52,000 microplastic particles a year through food and drink, depending on age and sex, rising to 74,000 to 121,000 when inhalation is included. People who drink only bottled water take in about 90,000 extra particles a year, compared with 4,000 for tap water.
This is the source for the recommended alternative to the discredited 'credit card a week' claim: people ingest tens of thousands of particles a year, and the particles turn up throughout the body.
The foods studied covered only about 15% of calorie intake, so the particle count is probably an underestimate. The study says nothing about mass, and particle counts do not translate into a known health risk.