LAUSR

River water-column and bottom-sediments samples were screened for 160 pesticide compounds to compare the types of pesticides present in the water-column versus bottom-sediments, and between segments of rivers flowing through intensively-managed versus semi-natural habitats. Of the 35 pesticide compounds detected, current-use pesticides accounted for 96% (water) and 76% (bottom sediments). Pesticide mixtures were present in 72% (water) and 51% (sediment) of the total samples. Only the river flowing through the most intensively managed habitat showed a wide range of pesticides in sediments, and many of these pesticides were also present in the water-column of that river. Current-use fungicides were detected in both the water-column and bottom-sediments but not in samples taken from rivers flowing predominantly through semi-natural habitats. The study period (May to August) corresponds to the peak time of regional pesticide applications and hence the time period that is most likely to show elevated concentrations of current-use pesticides in the water-column. The environmental concentrations of pesticide mixtures detected in the water-column were used to calculate Pesticide Toxicity Index (PTI) values as it applies to non-vascular or vascular plants, invertebrates, and fish. The PTI values were largest for non-vascular and vascular plants, reflecting that the pesticide mixtures in water-column were dominated by herbicides.