Can we find the study this refers to? And do we think it's accurate?
So we do a quick search and find a lot of hits. They look like they are mostly about the same study. We could go two directions here. We could trace it to the original study, or look for additional reporting on the claim that goes beyond parroting this one study.
In this case we look for a fact-check first by typing [[fact-check]] after [[swallowing a credit card a week]]. When we do that we find that there is a fact-check by reputable outlet Truth or Fiction.
As usual, the Truth or Fiction article has a wealth of information, but its final conclusion is that the figure is decontextualized in a deceptive way.
The meme claimed that the average person ingests 2,000 ocean plastic particles per week, thus essentially “eating one credit card” per person per week. But even shallow reporting on the research indicated that those estimates were at the high end, and the WWF’s report noted variables such as drinking water quality and habits as well as shellfish consumption affected even those estimated figures. A study published in an environmental journal’s range of figures differed slightly from the WWF numbers, which were — again — still under review when the reporting first started. All reports noted that the actual effects of microplastic consumption on human health is still unknown. Nevertheless, the World Wide Fund for Nature never suggested that every human or even most humans on Earth ate “a credit card a week,” despite using the comparison as a benchmark.
High-end estimates said it was possible that some individuals could be ingesting (not just eating, but inhaling) up to five grams of microplastics a week. But as the claim travelled the web, that nuance got stripped. Additionally, while scientists are working to understand the effects of such ingestion, we currently don't know if this amount of microplastic is harmful or not.