The study also mentioned that polypropylene and polyethylene are polymers that are often used to make plastic bottle caps. Also, 4% of retrieved plastic particles were found to have signatures of industrial lubricants coating the polymer.[17] The research was reviewed by Andrew Mayes of the University of East Anglia (UEA) School of Chemistry[18] The European Food Safety Authority suggested most microplastics are excreted by the body, however the UN Food and Agriculture Organization warned that it is possible that the smallest particles (< 1.5 μm) could enter the bloodstream and organs, via the intestinal wall.[19][20]