Pyrethroids in sediments and wastewater treatment plant-derived biosolids from Ireland

Pyrethroids are widely used synthetic insecticides. This study reports the occurrence, distribution, and ecotoxicological risks of eight pyrethroids in sediments and biosolids from wastewater treatment plants (WWTPs) across Ireland. A total of 120 sediment samples were collected along with 3 biosolids samples from each of seven WWTPs (n = 21). The relative abundance of individual pyrethroids differed between sediment and biosolids samples. Permethrin, cyfluthrin, and cypermethrin were predominant in sediments, with cyfluthrin, permethrin and deltamethrin predominant in biosolids. Such disparities may reflect the anaerobic conditions and shorter residence times of biosolids within WWTPs compared to sediments, which may influence the extent of degradation of our target pyrethroids and drive differences in their relative abundance between biosolids and sediments. Pyrethroid concentrations in Irish sediments were generally within the global range. Among the four pyrethroids currently registered in Ireland (cypermethrin, esfenvalerate, deltamethrin, and λ-cyhalothrin), cypermethrin showed the highest concentrations in sediments, likely reflecting both agricultural, aquacultural, and indoor uses. Meanwhile, permethrin and cyfluthrin, although not registered for plant protection in Ireland, were also prevalent—permissible biocidal uses may explain the presence of permethrin, while cyfluthrin warrants further scrutiny. Risk quotient assessment of pyrethroid concentrations in Irish sediments, revealed that while bifenthrin and resmethrin posed low ecotoxicological risks, other pyrethroids such as permethrin, cyfluthrin, and cypermethrin presented moderate to high risk in many sediment samples. These findings highlight the widespread distribution and ecotoxicological risks associated with pyrethroid contamination in Ireland's aquatic environments, emphasising the need for continued monitoring and risk management strategies to mitigate their environmental impacts.