Key takeaways

New research shows that microplastics can harm birds in much the same way they harm humans, possibly threatening these species’ survival and their ecosystems. In a new study published in the journal Environmental Pollution , researchers from UC Santa Cruz and the San Diego Zoo Wildlife Alliance ( SDZWA ) found that plastic swallowed by northern fulmars— seabirds found in the North Atlantic and North Pacific Oceans—can leach chemicals inside the birds’ stomachs that interfere with their hormones.

This is the second study from a collaboration between UC Santa Cruz and SDZWA to reveal how plastic exposure may cause endocrine disruption in wild seabirds. This disruption can impair the birds’ fertility, development, and behavior with consequences that ripple through ecosystems. While researchers have long suspected plastics might trigger such effects, by using fulmar endocrine receptors, this study provides the first evidence in a wild seabird.

According to the study, an estimated 8 million tons of plastic enter the ocean annually, posing significant risks to wildlife through ingestion of the inescapable material.

“We’ve long known that plastic ingestion can cause physical harm to seabirds, but this study shows it may also have hidden biological effects,” said lead author Liesbeth Van Hassel, who completed her Ph.D. in 2024 and helped lead this study while conducting research at UC Santa Cruz. “What’s especially concerning is that these chemicals don’t just pass through—they interact with key hormone receptors in the body.”

In lab tests, the researchers soaked pieces of plastic retrieved from the stomachs of deceased birds in solvents to draw out their chemicals. The team then tested those chemicals on hormone receptors cloned from northern fulmars to see if they disrupted hormonal activity. Nearly half the birds’ stomachs—13 of the 27—contained plastic that activated or blocked these hormone receptors.

Bad for birds and humans

The hormonal response seen in the fulmar receptors was similar to the response seen in human hormonal receptors when exposed to the same chemicals, raising red flags for species across the food web. Notably, this response was unrelated to the type of plastic found in the birds’ stomachs. Instead, the researchers suggest the chemical additives in these plastics—like BPA and phthalates, known hormone disruptors in humans and other animals—were to blame.

In humans, the variety of microplastics and the difficulty of estimating accumulation in our body make it hard to pin down risks. But findings in models show inflammation, cell death, lung and liver effects, changes in the gut microbiome, and altered lipid and hormone metabolism, according to a 2023 piece in Harvard Medicine .

In February, a study led by researchers at the University of New Mexico heightened concerns about the unavoidability of plastics in everything from our food to medical implants. The study found microplastics in human brains at much higher concentrations than in other organs, accumulating to amounts roughly equivalent to an entire plastic spoon.

The plastic-leaching experiments on fulmars were carried out at UC Santa Cruz, in the laboratory of Myra Finkelstein, an adjunct professor of microbiology and environmental toxicology and co-author on the study. The researchers found that nine of the birds had ingested plastic that in their stomachs that kept leaching chemicals over multiple days after collection.

“Some of these plastics kept leaching active chemicals for two weeks,” Christopher Tubbs, co-author and associate director of reproductive sciences at the zoo alliance. “This suggests seabirds are not only swallowing harmful materials—they may be getting a continuous dose of hormone-altering chemicals.”

Finkelstein said this research highlights the dangers plastics pose to humans and wildlife. However, she acknowledges that living without plastic, which is in everything from computers to produce bags, isn’t a realistic goal for most people.

“You’re not going to get plastic out of your life, it’s just too hard,” she said. “But you can try to make choices on a day-to-day basis. Do you really need to buy that pre-packaged, 100-calorie pack of almonds, or can you buy by bulk in a bag that you bring to the store? There are choices you can make that are not that difficult, that you can do every day.”

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