When fire broke out at battery energy storage facility in January 2025, its thick smoke blanketed surrounding wetlands, farms and nearby communities on the central California coast.

Highways closed, residents evacuated and firefighters could do little but watch as debris and ash rained down. People living in the area reported headaches and , and some pets and livestock fell ill.

Two days later, officials announced . But the initial all-clear decision missed something important – heavy metal fallout on the ground.

A chunk of charred battery debris found near bird tracks in the mud, with a putty knife to show the size. The surrounding marshes are popular stopovers for migrating seabirds. Scientists found a thin layer of much smaller debris across the wetlands.

When , the makeup of the chemical fallout can be a mystery for surrounding communities. Yet, these batteries often contain to humans and wildlife.

The smoke plume from the fire in at Moss Landing released not just hazardous gases such as hydrogen fluoride but also soot and charred fragments of burned batteries that landed for miles around.

I am a who has been in marshes adjacent to the Vistra facility for over a decade as part of a wetland-restoration project. In a new study published in the journal Scientific Reports, my colleagues and I were able to show through detailed before-and-after samples from the marshes and what happened to the heavy metals.

The batteries’ metal fragments, often too tiny to see with the naked eye, didn’t disappear. They continue to be remobilized in the environment today.

The Vistra battery energy storage facility – the large gray building in the lower left, near Monterey Bay – is surrounded by farmland and marshes. The smoke plume from the fire rained ash on the area and reached four counties. ,

What’s inside the batteries

Moss Landing, at the edge of Monterey Bay, has long been shaped by industry – a mix of power generation and intensive agriculture on the edge of a delicate coastal ecosystem.

The Vistra battery storage facility rose on the site of an , which was once filled with turbines and oil tanks. When Vistra announced it was converting the site into the world’s largest lithium-ion battery facility, the plan was hailed as a . Phase 1 alone housed batteries with 300 megawatts of capacity, enough to power about 225,000 homes for four hours.

The energy in rechargeable batteries comes from the flow of electrons released by lithium atoms in the anode moving toward the cathode.

In the type of batteries at the Moss Landing facility, the cathode was rich in three metals: nickel, manganese and cobalt. These batteries are prized for their high energy density and relatively low cost, but they are also prone to .

Lab experiments have shown that like confetti.

Metals found in wetlands matched batteries

When my team and I returned to the marsh three days after the fire, ash and burned debris covered the ground. Weeks afterward, .

Our measurements with portable X-ray fluorescence compared with data from before the fire. As soon as we saw the numbers, we alerted officials in four counties about the risk.

Marine geologist Ivano Aiello measures marsh soils immediately after the fire using a portable X-ray fluorescence detector. The smokestacks of the old Moss Landing power plant, where the battery energy storage facility was located, are in the background. John Haskins

We estimate that about (55,000 pounds) of heavy metals were deposited across roughly half a square mile (1.2 square kilometers) of wetland around , and that was only part of the area that saw fallout.

To put this in perspective, the part of the Vistra battery facility that burned was hosting 300 megawatts of batteries, which equates to roughly 1,900 metric tons of cathode material. Estimates of the amount of batteries that burned range to . Based on those estimates, roughly 1,000 to 1,400 metric tons of cathode material could have been carried into the smoke plume. What we found in the marsh represents about 2% of what may have been released.

These contour maps show how metals from the Moss Landing battery fire settled across nearby wetlands. Each color represents how much of a metal – nickel, manganese or cobalt – was found in surface soils. Darker colors mean higher concentrations. The highest levels were measured about two weeks after the fire, then declined as rain and tides dispersed the deposits.

We took samples at and examined millimeter-thin soil slices with a scanning electron microscope. Those slices revealed metallic particles smaller than one-tenth the width of a human hair – small enough to travel long distances and lodge deep in the lungs.

The in these particles matched that of nickel, manganese and cobalt battery cathodes, clearly linking the contamination to the fire.

Over the following months, we found that surface concentrations of the metals dropped sharply after major rain and tidal events, but . They were remobilized. Some migrated to the main channel of the estuary and may have been flushed out into the ocean. Some of the metals that settled in the estuary could enter the food chain in this wildlife hot spot, often populated with sea otters, harbor seals, pelicans and herons.

A high-magnification image of a leaf of bristly oxtongue, seen under a scanning electron microscope, shows a tiny metal particle typically used in cathode material in lithium-ion batteries, a stark reminder that much of the fallout from the fire landed on vegetation and croplands. The image’s scale is in microns: 1 micron is 0.001 millimeters. Ivano Aiello

Making battery storage safer as it expands

The fire at Moss Landing and its fallout hold lessons for other communities, first responders and the design of future lithium-ion battery systems, as utilities seek to balance renewable power and demand peaks.

When fires break out, emergency responders need to know what they’re dealing with. A California law passed after the fire helps address this by requiring at large battery installations and meetings with local fire officials before new facilities open.

How lithium-ion batteries work, and why they can be prone to thermal runaway.

Newer lithium-ion batteries that use iron phosphate cathodes are also . These are becoming more common for utility-scale energy storage than batteries with nickel, manganese and cobalt, though they store less energy.

How soil is tested is also important. At Moss Landing, some of the government’s sampling of the metals, likely because the samples came from broad, mixed layers that diluted the concentration of metals rather than the thin surface deposits where contaminants settled.

Continuing risks to marine life

Metals from the Moss Landing battery fire still linger in the region’s sediments and food webs.

These metals bioaccumulate, building up through the food chain: The metals in marsh soils can be taken up by worms and small invertebrates, which are eaten by fish, crabs or shorebirds, and eventually by top predators such as sea otters or harbor seals.

Our research group is now in Elkhorn Slough’s shellfish, crabs and fish. Because uptake varies among species and seasons, the effect of the metals on ecosystems will take months or years to emerge.

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