This week,Johnathan Walker the Environmental Protection Agency (EPA) will hold a public hearing about its remediation plan for cleaning up chemicals in and around East Palestine, Ohio. It follows the derailment of a Norfolk Southern train carrying hazardous chemicals like vinyl chloride and butyl acrylate near the town earlier this month.

Residents were temporarily evacuated from the area two days later to allow for a controlled burn of the chemicals. EPA health officials have been monitoring the air and water in the area and testing for chemicals as part of their ongoing human health risk assessment.

We wanted to know: What goes into an assessment like that? And how does the EPA know if people are safe — now and long-term?

To walk us through that assessment, we talked to Karen Dannemiller, an associate professor of environmental health science at The Ohio State University.

A multi-step approach

The EPA human health risk assessment is ongoing and unfolds in four steps.

1. Hazard Identification - First, the EPA has to identify what chemicals were onboard the train and released into the area, and determine which pose a risk to the community and the environment.
2. Dose-Response Assessment - The EPA looks at what the effects of each hazardous chemical are at each level of exposure in the area.
3. Exposure Assessment - Once the above steps are done, the agency will examine what is known about exposures — frequency, timing and the various levels of contact that occur.
4. Risk Characterization - Here, the EPA essentially pieces together the whole picture. They compare the estimated exposure level for the chemicals with data on the expected effects for people in the community and the environment. They also describe the risks, which shape the safety guidelines.

Throughout the coming days and months, there will be much uncertainty. Assessments are ongoing, data takes time to collect and process, and results and clean-up take time.

For Dannemiller, both working towards understanding these risks and acknowledging the uncertainties that exist throughout this process is essential. That transparency and accountability is what will help the community heal.

Further resources and information

• Read EPA updates on the Ohio derailment
• Read the EPA's proposed remediation plan
• Phone number for free, private water testing: 330-849-3919

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This episode was produced by Margaret Cirino, edited by Rebecca Ramirez and fact-checked by Anil Oza. Hans Copeland was the audio engineer.