The US Court of Appeals for the Ninth Circuit [official website] reinstated the ban [opinion, PDF] on the pesticide chlorpyrifos on Thursday, overturning the Environmental Protection Agency (EPA) [official website] order [text, PDF] that allowed continued use of the pesticide.

Environmental and farm-worker advocacy groups took charge in the petition [Earthjustice Report] for review by the court of the EPA order, citing studies [Columbia University study] showing links to the pesticide, which was developed as a nerve gas during World War II, and harm to the developing brains of children. The petitioners had filed objections in the EPA’s review process contemporaneously with the petition for review before the court.

The EPA argued that the court did not have jurisdiction until the EPA responds to the objections that the petitioners filed through the EPA process, but the court rejected this argument.

Having established that jurisdiction to review the order was proper, the court reviewed the merits. The EPA did not present any arguments defending its decision in the order. The court found that the EPA’s own risk assessment from 2016 showed that the pesticide did not meet the standard of a “reasonable certainty of no harm” which is in conflict with the language of the order describing “significant uncertainty” of health effects of the pesticide. Therefore, the court granted the petition as the EPA was acting against its own research. The court vacated the EPA order and remanded the case to the EPA “with directions to revoke all tolerances and cancel all registrations for chlorpyrifos within 60 days.”