New research shows that the extreme weather and fires of recent years, similar to the flooding that has struck Louisiana and the Midwest, may be making Americans sick in ways researchers are only beginning to understand.

By knocking chemicals loose from soil, homes, industrial-waste sites or other sources, and spreading them into the air, water and ground, disasters like these — often intensified by climate change — appear to be exposing people to an array of physical ailments including respiratory disease and cancer.

“We are sitting on a pile of toxic poison,” said Naresh Kumar, a professor of environmental health at the University of Miami, referring to the decades’ worth of chemicals present in the environment. “Whenever we have these natural disasters, they are stirred. And through this stirring process, we get more exposure to these chemicals.”

Kumar’s research has focused on the spread of PCBs, a suspected carcinogen, in Puerto Rico after Hurricane Maria in 2017. He led a team of researchers in Guánica, and found that PCB levels had tripled since Maria, to 450 parts per million. Worse, it was not just the soil showing elevated PCBs. It was the people, too.

The researchers tested 50 residents and found levels two to three times greater than the national average.

Other research examined Hurricane Harvey in Houston, and the wildfires in California, looking at the contaminants dislodged and the resulting health effects. “Typically with these situations you have a mixture, a toxic stew,” said Aubrey K. Miller, senior medical adviser to the National Institute of Environmental Health Sciences. “We’ve been able to demonstrate human health effects in some of these, but that information is not adequately captured.”

That is beginning to change. Until recently, researchers had been hamstrung by the difficulty of tracking long-term health changes after a disaster. One of the first cases in which good data was available, Miller said, was the collapse of the World Trade Center in the terrorist attacks of Sept. 11, 2001. Researchers have been following a group of more than 71,000 people since 2003.

That research showed the severity of health effects linked to exposure to dust from the towers, which included heavy metals, silica, wood dust, asbestos fibers and other contaminants. Ten % of enrollees developed asthma within six years, and firefighters saw drops in lung function. A 2013 paper reported greater-than-expected rates of thyroid and prostate cancer among rescue workers; a paper published in March showed higher rates of pulmonary fibrosis.

What that data could not reveal was whether that event was unique. So in 2010, the NIH’s environmental health sciences institute began awarding research grants quickly after an event to gather human health data after a disaster.

The researchers said their work has shown health effects that they say have surprised them.

After the California wildfires in 2017, epidemiologist Irva Hertz-Picciottoused an online survey to get health information from thousands of people exposed to the smoke.

“There’s been a conventional wisdom that when people have symptoms from fires, they are transient and there’s not persistence,” she said. But her research showed that months after the initial exposure, about 15% respondents who had never had asthma reported asthmalike symptoms.

Other researchers are examining the health effects of contaminants shifted by hurricanes.

In September 2017, after Hurricane Harvey dropped 4 feet of rain on Houston, dislodging chemicals from the soil, ship channels and chemical facilities, a team from the Baylor College of Medicine distributed questionnaires; took nasal swabs, spit and saliva tests and fecal samples, and distributed silicon wristbands that measure what chemicals the residents were exposed to.

The early results show a range of reactions, including sinus problems, skin irritation and respiratory ailments, Walker said. Now researchers are using geospatial analysis to determine which participants were close to which chemical sites, as well as what contaminants are present in their bodies and homes, to try to link specific toxins to specific health effects.