Matthew Campen's laboratory at the University of New Mexico used pyrolysis gas chromatography mass spectrometry, which burns tissue and identifies the chemical signatures of different polymers, to measure plastic in 62 donated placentas.
Every placenta contained measurable plastic, at concentrations ranging from 6.5 to 790 micrograms per gram of tissue. Polyethylene, the most common packaging plastic, made up about 54% of the plastic mass, followed by PVC and nylon.
The study matters because it moved beyond counting a few particles to measuring total plastic mass, and found it in all samples.
The same pyrolysis method used in this lab's later brain study has been criticised for possibly misreading body fats as polyethylene. The placenta findings have not been challenged in the same way, but the method caveat applies.