After Los Angeles fires, the water, air and soil are still toxic (2025)

A spirit of optimism prevails in Los Angeles. Mobile excavators are currently clearing garage doors, burned-out cars, and debris from the ruins of houses. Specialized cleanup crews remove toxic waste from the rubble. And some residents are already filling out their applications for new building permits.

These are the first steps on a long journey to rebuild Pacific Palisades and Altadena – the districts of Los Angeles that were extensively destroyed by the severe fires in January. The fires claimed 29 lives, and 18,000 buildings were razed to the ground. Millions of tons of rubble and ash were left behind.

But the mood of optimism is overshadowed by serious concerns: How contaminated are the water, air and soil in the burned-out regions?

Lead, asbestos and chlorine in the rubble

From a health perspective, urban fires are significantly more dangerous than forest fires. It's not just trees and bushes that burn, but paints, batteries, cleaning agents, plastic – the whole spectrum of human-made materials. These include toxic building materials. In the Altadena district, 90% of the houses were more than 50 years old, meaning they dated back to a time when lead-based paint and asbestos were still used as a matter of course.

This toxic mix contaminated the air during the fires. According to studies by Caltech University, high levels of toxic substances were still detectable in the air 30 kilometers south of the Altadena fire. The concentration of lead in the air was a hundred times higher than usual in the region. Inhaling lead can cause serious damage to the brain and nervous system, especially in children.

The concentration of chlorine was also 40 times the usual measured values; chlorine in the air can damage the lungs and respiratory tract. Asbestos was also released by the fires. Even a single exposure to the chemical can cause cancer years later. «You can be hundreds of miles away and still have the effects of wildfire smoke on your health,» Kari Nadeau, a physician at Harvard University who has researched the health effects of fires in California, told the Wall Street Journal.

According to experts, even the N95 masks familiar from the coronavirus pandemic do not offer sufficient protection in this case because they do not filter out particularly fine dirt particles. Experts recommend masks with activated charcoal filters, but these were sold out in many places during the fires in Los Angeles.

Another concern: poisoned drinking water

The dangers do not disappear when the flames go out. If the fires have damaged drinking water pipes, smoke and toxic chemicals – such as benzene – can seep into them. In the short term, this can cause nausea and vomiting, and in the long term, cancer. Theoretically, such toxic substances can build up in the water pipes for years.

Large parts of Pacific Palisades and Altadena were therefore put under a drinking water ban in mid-January. Residents in the affected areas should only use bottled water to drink, brush their teeth and cook. The ban has since been lifted in most areas.

However, the danger from soot and ash is not yet over. Remnants of heavy metals and other toxic substances have settled on the rubble and are now stirred up every time people walk through the ruins. Health experts warn residents of this invisible danger and advise against poking around in the ruins to look for their belongings. Los Angeles County has also banned the use of leaf blowers in the burn areas.

Even the residents whose houses were spared from the flames are not safe from health hazards. On the contrary, the smoke has penetrated sofas, carpets and mattresses. «All of those materials tend to soak up a lot of the gases, and then over the next month they’re going to release it back,» Paul Wennberg, who teaches environmental engineering at Caltech University, told The New York Times. Whether to dispose of everything or try to clean it is something that everyone has to decide on a case-by-case basis. «If you’re one of those few standing houses in the middle of Armageddon, I don’t know what I would do.»

A study published in December on the consequences of a severe urban fire in Colorado in 2021 confirms this. Smoke and ash that were harmful to health could still be detected in intact houses months later.

Sanjay Mohanty, who teaches environmental engineering at the University of California Los Angeles, is very worried about heavy metals and toxic pollutants in the ash. «I’m very concerned about metals and toxic pollutants in that ash,» he said in an interview with a local television station. «It can cause many diseases people will develop over years.» Soot deposited as a fine layer on window sills and in the air ducts of houses is also dangerous.

Tidying up takes place in two phases

Accordingly, U.S. federal and state authorities are now trying to carry out thorough cleanup efforts. These are being carried out in two phases: In the first phase, cleaning teams from the Environmental Protection Agency (EPA) combed through the ruins in Los Angeles wearing special protective clothing. They walked through the rubble of the thousands of houses and removed lithium batteries, paint pots, pesticides and other highly toxic materials.

Lithium batteries, which are nowadays installed in countless household appliances such as laptops, smartphones and electric bicycles, are a particular cause for concern. This is because damaged batteries can spontaneously explode even weeks or months later and injure people or start new fires. According to experts, it was the biggest lithium battery cleanup operation ever.

This phase has now been completed. In a second phase, the U.S. Army Corps of Engineers has been deployed since mid-February. The Army Corps of Engineers is a special branch of the American military focused on civil engineering projects. They act on behalf of the disaster control authority, FEMA. Workers are removing cubic meters of ash and clearing charred trees, cars and other debris from properties.

If the concentration of heavy metals is high, says UCLA’s Mohanty, the first 15 centimeters of soil must be removed and replaced with new soil. This is the only way to prevent residents from being constantly exposed to heavy metals in the future. It is likely to take months before this process is completed for 18,000 properties.

Alternatively, homeowners can also hire private cleaners for the second step in order to meet the requirements for rebuilding a house more quickly.

Toxic substances can penetrate deep into the soil

For FEMA, the work is completed as soon as 15 centimeters of earth have been removed from the affected areas. However, toxic heavy metals can actually remain even deeper in the soil. This is shown by the example of the town of Paradise – a small town in Northern California with 27,000 inhabitants that was completely destroyed by a severe fire in 2018. A private consulting firm took soil samples from 12,500 plots of land there after FEMA had completed cleanup work.

The soil on a third of the plots still contained toxic substances such as lead and arsenic that exceeded the maximum levels recommended by the authorities. According to the Los Angeles Times, cleanup crews had to be deployed five times before the toxic substances were sufficiently reduced.

This does not bode well for the residents of Pacific Palisades and Altadena. The reconstruction may not be as quick as they hope.

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