A new study linking microplastic pollution to low reproductive rates in Pacific oysters underscores the need to overhaul the use of petroleum-based plastics, according to a leading American ecotoxicologist.

“The reason why we study these species is because we know they’re indicators for what is happening to us,” said environmental chemist Sherri Mason of the State University of New York at Fredonia, whose work has documented widespread microplastic contamination in aquatic ecosystems. “People are ingesting microplastics when they eat shellfish and other seafood.”

In the new study, researchers in France exposed Pacific oysters for two months to water contaminated with microplastics smaller than a fifth of an inch across, at a concentration that equalled the amount found in the Great Pacific Garbage Patch.

They found that compared with oysters grown in plastic-free water, the exposed oysters produced fewer and smaller egg cells, slower-moving sperm, and fewer, slower-growing offspring.

“We know that filter-feeder animals, animals that filter water to catch plankton, they are particularly vulnerable to this kind of pollution,” said the study’s lead author, marine biologist Rossana Sussarellu of the French Research Institute for Exploitation of the Sea in Nantes, France. “So we can assume that other shellfish, like clams and scallops, are also at risk.”

The study adds to growing evidence that microplastic pollution can harm animals at the bottom of the marine food chain and has entered the human food supply.

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“We have a lot of data indicating that while the microplastics don’t immediately kill organisms, they can pass them on to other animals,” Mason said. “As they get ingested by other organisms, say a fish, it’s not able to move as quickly, and it’s going to be more easily captured by a predator, and then it’s passing on all the plastics and the toxins that are associated with those plastics to the predator.”

In 2013, researchers reported that lugworms, a burrowing animal sometimes called the earthworm of the ocean, consumed less food and were less energetic when they lived in sediment highly contaminated with microplastics.

Scientists found in a 2014 study that when a tiny, freshwater crustacean called daphnia ate microplastics, 68 percent of its offspring were malformed.

In another 2014 study, Belgian scientists reported finding microplastics in mussels and oysters cultivated for human consumption—enough to expose European consumers to up to 11,000 pieces of microplastic a year.

Researchers last year reported finding microplastics in sea salt on the shelves of supermarkets across China.

The risks to human health go well beyond the potential gross-out factor. That’s because microplastics in the environment absorb persistent organic pollutants that can cause cancer and harm reproductive health, including PCBs—polychlorinated biphenyls, once widely used in electrical equipment—and PAHs, or polyaromatic hydrocarbons, which are byproducts from burning fossil fuels.

In 2015, researchers reported finding microplastics contaminated with phthalates, brominated flame-retardants, and other persistent pollutants in more than 18 percent of Mediterranean bluefin, albacore, and swordfish sampled.

“The plastics become like little poison pills,” Mason said. “As they are ingested, all those chemicals are ingested,” and once in the moist, warm confines of an animal’s digestive system, “those chemicals will tend to de-sorb from the plastic and get stored in their fatty tissues.”

Last year, environmental experts at the United Nations recommended a global ban on microbeads in personal care and cosmetic products, citing the harm microplastic pollution is causing to marine life.

Several European nations have called for a EU-wide ban on microbeads, including the Netherlands, which enacted a ban in 2014.

The Canadian government announced plans to ban microbeads in July.

Mason’s own work, which has revealed that the Great Lakes are highly contaminated with microplastics, helped spur Congress in 2015 to pass a federal ban on plastic microbeads in toothpaste, face wash, and other consumer products. Researchers have estimated that 8 trillion microbeads enter aquatic ecosystems every day in the United States alone.

President Obama signed the measure into law, giving companies nearly two years to fully phase out microbeads.

Mason called it “an incredible first step” but noted that microbeads are not the major source of microplastic pollution.

Microplastics also form as larger pieces of plastic break down in the environment. “A plastic bag is in use, on average, for 12 minutes, and will be alive in the environment for 100 years,” Mason said.

A 2011 study showed that the polyester fleece and other plastic fabrics shed microscopic plastic fibers when washed. The researchers behind that study found plastic microfiber contamination on 18 shoreline sites across six continents.

Mason believes solving the microplastics crisis means replacing most petroleum-based plastics with safe materials. “I think the big movement is in finding plastics that can come from renewable resources,” she said, and “truly biodegrade when they’re released in the environment, regardless of where they’re released.”

“Microplastics are just so incredibly small, and so enmeshed in the life of the ecosystems where they exist, that you can’t clean up the plastic without destroying the ecosystem you’re trying to save,” she said. “You’re mostly talking about letting Mother Nature do what Mother Nature does” by breaking down contaminants in ecosystems over time.

The Earth “has been here for 4.5 billion years,” she added. “It’s quite robust in its own way and good at taking care of itself, if we give it the opportunity. What we have to do is lessen our impact.”