Large-scale pesticide monitoring across Great Barrier Reef catchments - Paddock to Reef Integrated Monitoring, Modelling and Reporting Program

► Pesticides were detected at all sampling sites. ► Atrazine, hexazinone and tebuthiuron were the most frequently detected pesticides. ► Passive samplers and grab sampling demonstrated differences in the type and number of pesticides that were detected. ► Atrazine, diuron and metolachlor exceeded Australian and New Zealand water quality trigger values for ecosystem protection. ► Mixtures of PSII herbicides were found which far exceeded the toxicities of the PSII herbicides individually.