  Water is an essential resource for all living organisms. The continuous and
increasing use of pesticides in agricultural and urban activities results in
the pollution of water resources and represents an environmental risk. To
control and reduce pesticide pollution, reliable multi-residue methods for the
detection of these compounds in water are needed. In this context, the present
work aimed at providing an analytical method for the simultaneous determination
of trace levels of 51 target pesticides in water and applying it to the
investigation of target pesticides in two agriculture-impacted areas of
interest. The method developed, based on an isotopic dilution approach and
on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry,
is fast, simple, and to a large extent automated, and allows the analysis of
most of the target compounds in compliance with European regulations. Further
application of the method to the analysis of selected water samples collected
at the lowest stretches of the two largest river basins of Catalonia (NE
Spain), Llobregat and Ter, revealed the presence of a wide suite of pesticides,
and some of them at concentrations above the water quality standards (irgarol
and dichlorvos) or the acceptable method detection limits (methiocarb,
imidacloprid, and thiacloprid), in the Llobregat, and much cleaner waters in
the Ter River basin. Risk assessment of the pesticide concentrations measured
in the Llobregat indicated high risk due to the presence of irgarol,
dichlorvos, methiocarb, azinphos ethyl, imidacloprid, and diflufenican (hazard
quotient (HQ) values>10), and an only moderate potential risk in the Ter River
associated to the occurrence of bentazone and irgarol (HQ>1).
