Risk assessment of individual pesticides and their mixtures in surface waters

This study aims to evaluate the risk of pesticides and their mixtures in surface waters of agricultural areas of the Golegã council. From 12 pesticides analysed by SPME/ GC-MS, the priority substances alachlor, atrazine, chlorfenvinphos, chlorpyrifos and other pollutants (3,4-DCA, ethofumesate, metolachlor and terbuthylazine) were detected. Alachlor and chlorpyrifos were determined with concentrations higher than their respective environmental quality standards for surface waters. According to the toxic unit summation method, only in two samples collected at Alverca do Campo were expected elicit effects larger than 50% on Daphnia and algae, due mainly to chlorfenvinphos and alachlor, respectively. The application of this method enables to use the existing information on risk assessment of individual pesticides, requiring only more demanding research and evaluation of the need of risk mitigation measures for those pesticides with greater aquatic risk in the mixture