Ecological Risk Evaluation and Characterisation of Pesticide Residues in the Sediments of the Lavononkaha Dam, Karakoro, Northern Côte d’Ivoire

Abstract

Background: The use of pesticides in agricultural areas surrounding dams can lead to their transfer into bottom sediments, where they may become persistent sources of aquatic pollution. This study evaluated pesticide residues in sediment samples from the Lavononkaha dam and assessed the associated non-carcinogenic health risks through common exposure routes. Methods: Ten sediment samples were collected from the dam bank near cultivated soils in July 2025. The samples were homogenised, frozen, transported to the Central Laboratory of Agrochemistry and Ecotoxicology of LANADA in Abidjan, and analysed for pesticide residues after liquid-liquid extraction. Detection and quantification were performed using absorption spectrophotometry and high-performance liquid chromatography (HPLC) equipped with a programmable UV/Visible wavelength detector. Results: A total of 17 pesticides were analysed in the sediments. The concentrations ranged from 0.012 to 0.14 µg/kg. The detected pesticides belonged mainly to herbicides (82%) and insecticides (18%). Most detected compounds were mixtures, with three to six pesticide residues observed in the sediment samples. The majority of the detected pesticides (47.1%) were very persistent (DT50 > 365 days), while simazine, monuron and metamitron were among the most frequently detected compounds. The exposure-pathway assessment indicated that ingestion contributed more to risk than dermal contact and inhalation. Non-carcinogenic risks were higher in children than in adults, mainly because of ingestion-related exposure. Conclusion: The hazard index values remained below the threshold value of 1.0 for both children and adults, indicating no non-carcinogenic risk under the assessed conditions. Nevertheless, the presence of persistent pesticide residues in sediments suggests that regular monitoring and pollution-control measures are needed to limit long-term ecological effects.