The US Environmental Protection Agency’s internal watchdog division is opening an investigation into the handling of the East Palestine train wreck which caused a toxic disaster in the small Ohio town.

An agency spokesperson declined to comment on why it is launching the investigation, but a public memo from the EPA office of inspector general states that it will “conduct interviews, gather data, and analyze a variety of issues, including hazardous waste disposal, air and water monitoring, soil and sediment sampling, and risk communication”.

The agency’s response to the train crash has drawn intense criticism from the town’s residents and public health advocates who say it has failed to fully protect East Palestine from toxic chemicals released from train cars and a controlled burn of vinyl chloride in the days after the wreck.

Critics say the Joe Biden administration has not been cautious enough in its approach, or taken strong enough action against Norfolk Southern, the rail company behind the disaster. Much of the ire over the management of the toxic wreck’s aftermath was directed at the EPA, and rightwing pundits and politicians have politicized and racialized the controversy.

Public health advocates praised the announcement of the inspector general’s involvement, and the investigation is “warranted”, said Kyla Bennett, a former EPA scientist now with the Public Employees for Environmental Responsibility non-profit.

“There are too many unanswered questions and conflicting information,” she said. “The IG can get to the bottom of how decisions were made to conduct testing the way they were and whether that was sufficient.”

The EPA’s inspector general has issued reports critical of the agency over what it has found to be a mishandling of controversies in recent years.

Chemical pollution experts and residents have consistently questioned whether the EPA took a robust enough approach to testing water, soil and air in the days and weeks after the wreck and controlled burn.

Residents said they were concerned the EPA told them it was safe to return home too soon just days after the burn. Many had questions about air quality, especially indoors, and received conflicting messaging from state and federal officials about how to protect themselves.

Meanwhile, the contractor hired by Norfolk Southern to test indoor air quality has links to the industry and residents told the Guardian they did not trust the results because the testing was not conducted by an independent entity.

“Putting the fox in charge of the henhouse is never a good idea,” Bennett said.

The controlled burn likely created dangerous compounds such as dioxins and chlorinated PAHs that could pose a long-term health threat in the East Palestine area and downwind. The EPA for weeks resisted a chorus of calls from chemical pollution experts and residents to test for the dangerous compounds.

After the EPA agreed to require Norfolk Southern to test for dioxins, an initial round of sampling found East Palestine soil to contain levels hundreds of times greater than the exposure threshold above which EPA scientists in 2010 found poses cancer risks.

Still, EPA leadership has told Congress the dioxin levels are “very low” and the agency has not taken any additional steps. It remains unclear if environmental officials ever tested for chlorinated PAHs, or PFAS, another toxic substance likely in the ground and water around the site.

The EPA did not immediately respond to a request for comment.

Residents in East Palestine still say they are getting rashes and their lungs are irritated, said Amanda Kiger, director of Ohio River Valley Organizing, which has been advocating for residents on the ground. Frustration is also aimed at Ohio governor Mike DeWine’s administration’s environmental agency, she added.

Residents have said financial assistance offered by Norfolk Southern is not enough, and the federal government should be providing more relief, or forcing the rail company to put more towards assistance.

“They’re not doing their job and everyone knows it,” Kiger said. “For lack of a better term, it’s all a clusterfuck, but I’m hoping it’s a good investigation, and thorough.”