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Abstract
This study reports the efficiency of low pressure UV photolysis for the degradation
of pesticides identified as priority pollutants by the European Water Framework Directive
2000/60/EC. Direct low pressure UV photolysis and advanced oxidation processes (using
hydrogen peroxide and titanium dioxide) experiments were conducted in laboratory grade
water, surface water, and groundwater. LP direct photolysis using a high UV fluence
(1500 mJ/cm(2)) was found to be extremely efficient to accomplish the degradation
of all pesticides except isoproturon, whereas photolysis using hydrogen peroxide and
titanium dioxide did not significantly enhance their removal. In all matrices tested
the experimental photolysis of the pesticides followed the same trend: isoproturon
degradation was negligible, alachlor, pentachlorophenol, and atrazine showed similar
degradation rate constants, whereas diuron and chlorfenvinphos were highly removed.
The degradation trend observed for the selected compounds followed the decadic molar
absorption coefficients order with exception of isoproturon probably due to its extremely
low quantum yield. Similar direct photolysis rate constants were obtained for each
pesticide in the different matrices tested, showing that the water components did
not significantly impact degradation. Extremely similar photolysis rate constants
were also obtained in surface water for individual compounds when compared to mixtures.
The model fluence and time-based rate constants reported were very similar to the
direct photolysis experimental results obtained, while overestimating the advanced
oxidation results. This model was used to predict how degradation of isoproturon,
the most resilient compound, could be improved.