Seven workers from the U.S. Centers for Disease Control and Prevention got sick while investigating the derailment of a Norfolk Southern train in Ohio earlier this year.

A team of investigators from the CDC and the Agency for Toxic Substances and Disease Registry were investigating potential chemical exposure and health effects related to the Feb. 3 derailment of the freight train in East Palestine. Several of the cars caught fire and different chemicals were released into the surrounding area.

The chemicals included vinyl chloride, butyl acrylate and ethylhexyl acrylate, according to the Environmental Protection Agency.

Vinyl chloride, which was burned off as part of a controlled release to avoid an explosion, is considered a carcinogen that has been linked to liver, brain and lung cancers with high enough exposure.

The workers fell ill on March 6 while investigating. They experienced sore throat, headache, coughing and nausea, according to the CDC and the agency.

Residents have reported similar symptoms since the derailment occurred. The government workers’ illnesses came after officials from government as well as Norfolk Southern said the air and water in the area was safe.

The workers who reported feeling sick said their symptoms cleared up the same day they first noticed them and have not reported any ongoing conditions.

The CDC’s assessment of potential chemical exposure caused by the derailment, which consisted partly of conducting surveys with residents and first responders, was scheduled to end Monday.