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[2] researching the current understanding of microplastics in a time-boxed format. Sort of like partitioned book club, 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