Contamination of surface waters by pesticides continues to be the focus of concern for water authorities
due to the growing evidence of their deleterious effects on aquatic life. In this context, the present work
investigates the occurrence of 16 selected pesticides belonging to the classes of triazines, phenylureas,
organophosphates, chloroacetanilides and thiocarbamates in surface waters from the Llobregat River
(NE Spain) and some of its tributaries (Anoia and Rubí) and assesses their potential impact on the aquatic
organisms by applying a recently developed index, the Short-term Pesticide Risk Index for the Surface
Water System (PRISW-1), which takes into account the pesticides concentrations and their overall toxicity
against three aquatic organisms (algae, Daphnia, and fish). Chemical analysis, performed by means of a fully
automated method based on isotope dilution on-line solid phase extraction–liquid chromatography–
electrospray–tandem mass spectrometry (on-line SPE–LC–ESI–MS/MS), revealed diuron and diazinon as
the most ubiquitous and abundant compounds with levels up to 818 and 132 ng L 1, respectively. Total
pesticide concentrations, which in only 1 out of 66 samples surpassed 500 ng L 1, were higher in the tributaries
than in the river but their contribution in terms of mass-loads to the overall pesticide pollution of
the Llobregat River was relatively small. Contamination increased downstream of the river and was clearly
influenced by rainfall and hence river flow. Application of the PRISW-1 index indicated that, although pesticides
levels fulfilled the European Union Environmental Quality Standards (EQS) for surface waters, the
existing pesticide contamination poses a low to high ecotoxicological risk for aquatic organisms, that algae
and macro-invertebrates are at higher risk than fish, and that the organophosphates diazinon and
malathion and the phenylurea diuron are the major contributors to the overall toxicity and therefore
the most problematic compounds.
