The Environmental Protection Agency says an unknown amount of a dangerous chemical linked to birth defects and cancer may have washed downriver from a Houston-area Superfund site during the flooding from Hurricane Harvey.

EPA announced Thursday night it has ordered the companies responsible for the San Jacinto River Waste Pits site to take immediate action to address damage to a protective cap of fabric and rock intended to keep sediments highly contaminated with dioxins from spreading. International Paper and McGinnis Industrial Maintenance Corp. have made initial repairs to the section where the protective rock was missing.

EPA said a sample collected by an agency dive team from the exposed area showed dioxins levels at 70,000 nanograms per kilogram — more than 2,300 times the level set to trigger a cleanup.