One of the big challenges of the energy transition is to wean humanity off of planet-warming fossil fuels swiftly but sustainably. Many environmentalists worry that in our desperation to solve global warming, we’ll reach for novel technologies without fully understanding their potential downsides. And evidence is mounting that this may be the case with the batteries powering millions of electric vehicles. A new study published in the journal Nature Communications finds that lithium-ion batteries contain “forever chemicals,” or PFAS, that are polluting the air and water.

PFAS (per- and polyfluoroalkyl substances) are man-made chemicals typically used to make products resistant to things like grease and water. Exposure to PFAS through contaminated food, water, and air has been linked to a number of health problems in humans, including kidney and testicular cancer, low birth weight, and high cholesterol, which is why the Environmental Protection Agency has started cracking down on their use. But lithium-ion batteries may be overlooked as a source of these nasty pollutants as we rush to scale up EV adoption and clean energy storage.

In lithium-ion batteries, a type of forever chemical called bis-perfluoroalkyl sulfonimides, or bis-FASIs, are often used as electrolytes, which allow an electrical charge to travel between the battery’s cathode and anode. For this study, researchers wanted to measure how bis-FASIs make their way into the environment at the beginning and end of a battery’s life.

They tested the air, water, soil, and sediment near lithium-ion manufacturing plants and found elevated concentrations of bis-FASIs compounds, which they believe can travel long distances in the air, “meaning that areas far from manufacturing sites may be affected as well,” according to a news release. They also found bis-FASIs in landfills, suggesting these chemicals are leaching into the ground after lithium-ion batteries are thrown away, a disturbing thought considering that just 5% of these batteries get recycled. With demand for lithium-ion batteries projected to surge in the coming years, some 8 million tons of them are expected to be sitting in landfills by 2040.

Worryingly little is known about how bis-FASIs affect human health. But this study suggests that when fish are exposed to even low levels of these kinds of chemicals, their behaviors change, and so does their metabolism. Given what we know about other PFAS, it’s not unreasonable to assume these might be dangerous for humans, too.

“Our results reveal a dilemma associated with manufacturing, disposal, and recycling of clean energy infrastructure,” said Jennifer Guelfo, an associate professor of environmental engineering at Texas Tech University and one of the study’s authors. “Slashing CO2 emissions with innovations like electric cars is critical, but it shouldn’t come with the side effect of increasing PFAS pollution. We need to facilitate technologies, manufacturing controls, and recycling solutions that can fight the climate crisis without releasing highly recalcitrant pollutants.”

PFAS aren’t the only environmental downside to lithium-ion batteries. They require huge amounts of energy and water to produce, and lithium mining wreaks havoc on surrounding communities and habitats. The good news is that there are some promising alternatives, such as sodium-ion batteries and solid-state batteries. And the researchers say the methods currently being used to remove PFAS from water could also work on bis-FASIs, though of course this is extremely expensive, and won’t address other sources of exposure, like air.

The study’s authors hope their findings serve as a reminder to think carefully and critically about new clean energy technologies. They write: “We should use the momentum behind current energy initiatives to ensure that new energy technologies are truly clean.”