Assessment of chemical footprints of hydrophobic pesticide/biocide contamination in western Kenya using polydimethylsiloxane silicone passive samplers

In a previous study based on LC-HRMS screening of pesticides and other organic micropollutants, it was shown that pesticide pollution of water resources in western Kenya poses a significant risk to aquatic and human health. In the current study, this assessment was completed with the investigation of more hydrophobic organochlorine, organophosphate and pyrethroid pesticides in surface waters and wastewater treatment plant (WWTP) influents and effluents using polydimethylsiloxane silicone passive samplers and Gas Chromatography-Tandem Mass Spectrometry (GC-MS/MS). Chemical footprints were assessed based on the mixture risks of the detected pesticides on algae, fish and crustaceans determined using the Toxic Unit approach. In total, 19 additional pesticides could be detected. The highest concentrations were found for chlorpyrifos with 263 ng/L in rivers, 717 ng/L in WWTP influents and 143 ng/L in WWTP effluents. Organochlorine and pyrethroid pesticide concentrations were detectable in concentrations up to 1 respective 2 ng/L. Driven mainly by chlorpyrifos, 93 % of river samples and 88 % of WWTP effluent samples posed acute risks to crustaceans, while 64 % and 63 % of river and WWTP effluent samples, respectively, exceeded chronic risk thresholds for fish. Risks to algae were low. Chlorpyrifos was the main driver of the chemical footprint of pesticide application on crustaceans and fish. In comparison to the previously screened LC-HRMS compounds, none of the hydrophobic compounds analyzed here contributed significantly to the footprint on algae, which is dominated by more hydrophilic herbicides.