It was that last point, the degree of risk to people, that drew a lot of attention from Merkley and witnesses from industry and public health groups testifying.
Matt Seaholm, president and CEO of the Washington-based Plastics Industry Association, said his group welcomed the studies called for in Merkley's legislation, suggesting there's not enough evidence to draw conclusions.
"Has there been significant scientific evidence ... for the vast majority of the discussion on chemicals? No," Seaholm said. "In Sen. Merkley's recently introduced bill, there are studies that would be funded for it, and we would welcome studies to be done looking at things like microplastics because there isn't scientific evidence to report the claims."
But another witness, scientist John Peterson Myers, told the committee there is "extensive" evidence that chemicals in plastic waste contribute to lowering sperm counts in men, among other health impacts.
Myers, who is board chair and chief scientist at the group Environmental Health Sciences, was asked about his conclusions by Sen. Roger Wicker, R-Miss., who called Myers' testimony on sperm count, autism and changes in brain wiring from chemical exposure "very startling."
Myers' written testimony noted a 2022 study that identified a 50 percent decline worldwide in human male sperm counts between 1973 and 2018 and said the decline is "linked by strong evidence from other research to exposure to chemicals common in plastics, including phthalates, bisphenols and perfluorinated compounds."
"There is extensive scientific documentation," Myers told Wicker.
Myers called for much more extensive testing of chemical compounds in plastics, saying that most chemicals have been grandfathered in to existing commerce rules and have not been tested with 21st century tools.
He said plastics are not inert materials and can be biologically active based on which monomers and additives are used and by impurities in manufacturing processes.
"Most of the chemicals in plastics have not been tested for safety," Myers said. "None have been tested thoroughly."
Merkley picked up on that point and at one point asked Seaholm if he would support "full transparency" for chemicals used in plastics. Seaholm said the industry relies on the Food and Drug Administration review for safety of plastics used in food-contact materials.
"We have full faith in the FDA's approval and decision-making process," Seaholm said. "When it comes to food contact, in particular, we never cut corners when it comes to safety. … I think the FDA approval process is certainly sufficient, and we participate and fully support it."
Merkley replied that he appreciated Seaholm's point about review of food-contact materials but said "one of the challenges we have" is from plastics in nonfood uses that degrade in the environment, become microplastics and release chemicals over time.
At another point in the hearing, the Oregon senator asked Seaholm if he was concerned about the impact of plastics on human health. Merkley mentioned studies finding plastics in human breast milk and concerns about endocrine-disrupting chemicals.
"Absolutely. Like I said earlier, the most important thing that our members, especially those manufacturing anything that's going to come in contact with the human body, care about is safety," Seaholm said. "If they don't have a safe product, they don't have a sustainable business. Safety is at the forefront of everything they do."