A solid phase extraction (XAD-2) preconcentration procedure has been developed specifically for bioassays of pesticide contaminated water. Adsorption and elution efficiencies of XAD-2 columns were examined using solutions of the 14C-labelled pesticides 2,4 dichlorophenoxy acetic acid (2,4 D), pirimicarb, atrazine and phenmedipham in concentrations 0.4-5.4 μg/l. The adsorption was strongly dependent on pH. Serial preconcentration at two different pH's (pH 2.0 and pH 7.0) implied approximately 85% pesticide recovery in the final extracts. Using spiked surface water, the efficiencies decreased significantly, but efficiencies of about 70% could be accomplished with two consecutive extractions at pH 7.0 and pH 2.0. The toxicity of an atrazine extract (1000 times concentrated from originally 15 μg/l) was similar to that of the pure compound as assessed using a test battery with 3 different species - Selenastrum capricornutum, Daphnia magna, andLemna minor . This result indicates that no modification of toxicity occurs during the preconcentration step. Two water samples with a different degree of pesticide contamination were collected from a small rural, lowland stream, the Højvads Rende (Lolland, Denmark) and subjected to preconcentration and toxicity testing. The technique proved sensitive enough to detect the presence of toxicity. It is concluded that bioassays on water concentrates obtained by means of XAD solid phase extraction have a considerable potential as a new monitoring tool for pesticides and their metabolites in water.

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