Occurrence and risk assessment of pesticides in a Mediterranean Basin with strong agricultural pressure (Guadiana Basin: Southern of Portugal)

The study aimed to assess the occurrence and environmental risk of a group 51 selected pesticides in Guadiana Basin (a biodiversity hotspot, Mediterranean). most abundant were bentazone 2,4-D, while terbuthylazine together with terbutryn constituted ubiquitous pesticides. Eighteen out 38 detected are no longer approved Europe, 5 them included list priority substances. assessment showed that azinphos ethyl, diflufenican, irganol, imidacloprid, oxadiazon occurred occasionally, but always concentrations above their respective ecotoxicological threshold value. Contrary, bentazone, terbuthylazine, presented high sampled locations periods. site-specific spatial temporal pattern, higher occurring mainly intermittent streams, drought period. presence banned from EU market since 2009 importance improving monitoring process, identify main sources pollution fate these emerging compounds. results need implementing actions improve sustainable use agricultural areas, working farmers management entities reduce contamination aquatic ecosystems. Transboundary water governance is also required solve potential transboundary problems.