(KRON) -- Contra Costa County firefighters were on the scene of a hazardous materials incident in Concord on Monday afternoon. Con Fire said the incident occurred at Bisso Lane and was due to an accidental spill of organo phosporus. ICE arrests mother and daughter at SFO Sunday night Two patients wi th moderate exposure, as well as two firefighters, were transported to a hospital. Photo: Confire Organo phosporus compounds are extensively used in pesticides and can cause great hazards to human health, according to the National Library of Medicine. Fire officials wrote at 3 p.m., "The chemical has been isolated. Crews will remain on scene for an extended time." ...read more read less