The present study evaluated the capacity of a semi-closed, tubular horizontal photobioreactor (PBR) to remove pesticides from agricultural run-off. The study was carried out in July to study its efficiency under the best conditions (highest solar irradiation). A total of 51 pesticides, including 10 transformation products, were selected and investigated based on their consumption rate and environmental relevance. Sixteen of them were detected in the agricultural run-off, and the estimated removal efficiencies ranged from negative values, obtained for 3 compounds, namely terbutryn, diuron, and imidacloprid, to 100%, achieved for 10 compounds. The acidic herbicide MCPA was removed by 88% on average, and the insecticides 2,4-D and diazinon showed variable removals, between 100% and negative values. The environmental risk associated with the compounds still present in the effluent of the PBR was evaluated using hazard quotients (HQs), calculated using the average and highest measured concentrations of the compounds. HQ values > 10 (meaning high risk) were obtained for imidacloprid (21), between 1 and 10 (meaning moderate risk) for 2,4-D (2.8), diazinon (4.6) and terbutryn (1.5), and < 1 (meaning low risk) for the remaining compounds diuron, linuron, and MCPA. The PBR treatment yielded variable removals depending on the compound, similar to conventional wastewater treatment plants. This study provides new data on the capacity of icroalgae-based treatment systems to eliminate a wide range of priority pesticides under real/environmental conditions.
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