Can the conclusion of ‘no risk’ be supported by ‘no data’? One of the common pitfalls in critical thinking is to neglect the logic that the absence of evidence is not evidence of absence. The ‘having plastic particles in your body is safe’ conclusion conjures up a classic error known as the ‘appeal to ignorance’ fallacy Locke (1690), which is, ‘there is no evidence against x. Therefore x is true.’ This type of statement has no place in rational thinking. Note that to propagate claims of this type is to unduly shift the burden of proof onto those seeking conclusive evidence.

...

The European Environment Agency’s two Late Lessons from Early Warnings reports (European Environment Agency, 2013, European Environment Agency, 1896-2000) highlighted the danger. The reports analyze the impact of past inaction (or action) on environmental damage caused by, for example, polychlorinated biphenyls (PCBs), and public health issues generated by exposure to asbestos or diethylstilbestrol (DES). Each case is deconstructed to identify patterns leading to delays in appropriate decision making. The insights led to recommendations regarding how to respond to new warnings with the precautionary principle, i.e. to act to reduce potential harm as the preliminary signs of harm are still arising. It is interesting to note that the EEA had difficulty in identifying any cases of overregulation of a pollutant that had turned out to be benign when all the science was in. Most early warnings turn out to be legitimate. The costs of inaction are often drastically underestimated (European Environment Agency, 2013).

"Where is the evidence that human exposure to microplastics is safe?", HA Leslie, MH Depledge, Environ Int. 2020 Jun 26;142:105807.

<https://pmc.ncbi.nlm.nih.gov/articles/PMC7319653/>

We are aware of harms from materials leaching from plastics, as well as direct harms from PFAS (<https://www.epa.gov/pfas/our-current-understanding-human-hea...>) and BPA (<https://pubmed.ncbi.nlm.nih.gov/25813067/>), to name only two of the myriad compounds and constituents of plastics.

Absence of evidence is not evidence of absence.