A team led by Martin Wagner at the Norwegian University of Science and Technology compiled every chemical known or likely to be used in plastics, then screened each one against hazard criteria.
They identified 16,325 chemicals used or present in plastics. More than 4,200 (about 26%) are of concern because they last a long time in the environment, build up in living things, spread easily through water and soil, or are toxic. Around 400 chemicals of concern were found in every major type of plastic. Fewer than 6% are regulated by international agreements, and more than 10,000 have no hazard data at all.
The report matters because it is the most complete inventory of plastic chemicals, it superseded the UN's earlier count of 13,000, and it underpins calls for the plastics treaty to regulate chemicals of concern as a group rather than one at a time.
The counts reflect chemicals that could be present, not what is in any particular product; hazard screening is based on existing data, which is missing for most chemicals.