In 2019 World Wide Fund for Nature (WWF) publicised a University of Newcastle (Australia) analysis estimating that people ingest about 5 grams of plastic a week, roughly the weight of a credit card. The figure went viral and still appears in campaigns, news articles and classroom materials.
In 2021 Mohamed Nor and colleagues published an independent re-analysis in Environmental Science & Technology that estimated median adult intake at about 4.1 micrograms a week, around a million times lower. A further 2022 critique documented additional methodological flaws in the original, including how particle sizes and masses were combined.
The episode matters because it shows how a striking but unreliable number can crowd out better evidence and damage the credibility of the wider issue.
Site guidance: do not use the credit-card figure. Say instead that people ingest tens of thousands of microplastic particles a year (Cox 2019), that the total mass is tiny, but that the particles are found throughout the body.