A wave of research has linked microplastics—tiny plastic particles capable of infiltrating human tissues—to health issues in recent years, including increased risk of heart attack, certain cancers, and reproductive problems. Researchers are still working to understand exactly how microplastics affect our health, but newly discovered documents suggest industry scientists have been aware of the potential risks for decades.

An investigation by the Los Angeles Times obtained internal memos among chemical company scientists and executives revealing that the plastics industry has been aware of and concerned about the possibility of microplastics contamination in the human body for at least 50 years.…