EPA scientists assessed a dioxin cancer risks threshold in 2010, but a federal cleanup is only triggered at far higher levels

Newly released data shows soil in the Ohio town of East Palestine – scene of a recent catastrophic train crash and chemical spill – contains dioxin levels hundreds of times greater than the exposure threshold above which Environmental Protection Agency (EPA) scientists in 2010 found poses cancer risks.

The EPA at the time proposed lowering the cleanup threshold to reflect the science around the highly toxic chemical, but the Obama administration killed the rules, and the higher federal action threshold remains in place.

Though the dioxin levels in East Palestine are below the federal action threshold and an EPA administrator last week told Congress the levels were “very low”, chemical experts, including former EPA officials, who reviewed the data for the Guardian called them “concerning”.

The levels found in two soil samples are also up to 14 times higher than dioxin soil limits in some states, and the numbers point to wider contamination, said Linda Birnbaum, a former head of the US National Toxicology Program and EPA scientist.

“The levels are not screaming high, but we have confirmed that dioxins are in East Palestine’s soil,” she said. “The EPA must test the soil in the area more broadly.”

The data probably confirms fears that the controlled burn of vinyl chloride in the days after the train wreck in the town created dioxin and dispersed it throughout the area, experts say, though they stressed the new data is of limited value because only two soil samples were checked.

The train crash in East Palestine and its toxic aftermath has become a major issue in the US with locals and activists decrying a lack of action by both the government and the train operator, Norfolk Southern. The state of Ohio has now sued the rail giant over the derailment, calling it one of a “long string” of incidents involving the company.

Dioxins are a class of chemicals that are a byproduct produced when chlorine is burned, which is a common industrial process in making products like PVC.

The chemicals are highly persistent and can accumulate and stay for years in the environment or human bodies. Among other health issues, the compounds are linked to cancer, diabetes, heart disease, nervous system disorders and other serious health problems. Soil and food contamination are considered to be among the most common exposure routes.

After resisting calls for weeks to test for dioxins, the EPA on 3 March announced it would order Norfolk Southern to do so. Separately, Indiana last week commissioned testing of East Palestine soil because one of the state’s landfills is storing it. The testing was conducted by what Birnbaum characterized as a reputable laboratory.

The Indiana governor, Eric Holcomb, said the levels found in the soil “were not harmful”. Meanwhile, an EPA regional administrator, Debra Shore, during congressional testimony on 9 March characterized the dioxin levels found in Indiana as “very low” and “good news”.

But while the EPA can claim that the levels are “low” from a legal standpoint, the agency’s own science suggests they are not safe, and dioxin experts who spoke with the Guardian cast doubt on Shore’s and Holcomb’s assessments.

Regulators establish the toxicity of dioxins in a soil sample by calculating the “toxicity equivalence” of all dioxins in the soil compared with the most toxic dioxin compound, called 2,3,7,8 TCDD. East Palestine soil showed levels of “2,3,7,8 TCDD toxicity equivalence” of 700 parts per trillion (ppt). The level at which the EPA will initiate cleanup action in residential areas is 1,000 ppt.

However, the cleanup triggers are much lower in many states – 90 ppt in Michigan, and 50 ppt in California.

“So based on this, the concentrations are actually concerning,” said Carsten Prasse, an organic chemist at Johns Hopkins University and scientific adviser for SimpleLab. Federal cleanup standards of 1,000 ppt apply in Ohio.

Moreover, EPA scientists in 2010 put the cancer risk threshold for dioxins in residential soil at 3.7 ppt, and the agency recommended lowering the cleanup trigger to 72 ppt.

“When you run the numbers and do your best state-of-the-art risk calculations, that’s the number you get for the cancer risk,” said Stephen Lester, a toxicologist who has researched dioxins for 40 years and is science director for the Center for Health, Environment and Justice. “That’s why dioxins are described as one of the most toxic chemicals ever created.”

The rules were ultimately killed ”for political reasons”, Lester said. Exposure to that level of dioxin is probably widespread, and making the change would create fallout that would be extremely difficult for the government to manage, he added.

“Instead of making adjustments for the high risk of these chemicals, they dropped it, they just walked away from it, and that’s the crazy part of this story,” Lester said. Now the EPA can legally claim the levels in East Palestine are safe, even if agency science has suggested it is not.

The EPA did not respond to specific questions from the Guardian, but in a statement the agency doubled down on its assessment.

“The available data, analyzed and validated by an independent laboratory, shows the waste from East Palestine that went to Indiana does not contain harmful levels of dioxins,” a spokesperson wrote.

Experts also cautioned that the levels may be safe for Indiana’s purpose – storing toxic waste in a landfill – and unsafe in the context of public exposure to the chemicals around the crash site.

It is also unclear where and at what depth the samples were collected, Prasse noted, all of which has implications for potential health risks in East Palestine. The chemicals would especially present a risk in dust and gardens, or for children playing outside, he added. Many homes are a matter of feet from the wreck site.

“My main concern is: is this reflective of the level in the area in East Palestine … and of the levels individuals who live near the rail are exposed to?” Prasse said. “I certainly wouldn’t be comfortable living there.”

Moreover, if the soil that Indiana tested had been shipped to the state in a truck or train car, then it was mixed with other soil and probably diluted, which could make the soil appear safer than it is, and would conceal hotspots on the ground, Birnbaum said.

She noted the results revealed a wide range of dioxins, which suggests the chemicals were created in the vinyl chloride burn. Though dioxins are often present throughout the environment at low levels, especially in industrial areas like East Palestine, background profiles are usually limited to fewer types of dioxin, Birnbaum said.

In 1980, the EPA forced the evacuation of Times Beach, Missouri, when dioxin levels exceeding 1,000 ppt were found in the soil after the chemicals were sprayed on the town’s roads to prevent the spread of dust.

Experts who have begun reviewing Norfolk Southern’s plan for testing for dioxins are already raising concerns about its design, and say the EPA may fear a repeat of Times Beach.

“What you really need to know for the people in the area to be safe is where did the dioxins come from, where did the wind take it, where was it deposited and where is the area with heavy levels,” Birnbaum said.