The way the Environmental Protection Agency has reported its test results since a Norfolk Southern train derailed and officials released and burned chemicals that spewed a toxic cloud over East Palestine, Ohio, makes it hard for residents to know the full extent of contamination and potential risks to their health.

Data analyzed by The Associated Press show the EPA doesn’t provide a specific measurement for chemicals that fall below a reporting limit, making it harder to know how much is there.

The EPA has said that residents shouldn’t worry about contamination from chemicals that are below the human health screening level that indicates danger and is usually higher than that reporting limit. But some health experts say that when mixed together, as they are in East Palestine, even levels of chemicals below that standard could raise the risk for cancer or other serious health problems. Extended exposure to low levels of chemicals might also cause problems.

The agency’s lack of transparency, combined with independent tests that appear to show lingering problem areas from the February 2023 derailment, are making it hard for some residents to trust the EPA’s assurances that they will be safe.