Assessment of Herbicide Contamination of Surface Waters: Levels, Compliance and Risks in Cereal-Growing Areas of Western Burkina Faso

Abstract

Aims: This study aimed to assess the level of contamination of surface waters by herbicides used in cereal-growing areas of western Burkina Faso, and to evaluate the compliance of measured concentrations with international guideline values, as well as the associated environmental and potential health risks. Study Design: Cross-sectional field study combining spatially distributed sampling of surface waters with multi-residue chemical analysis of selected herbicides. Place and Duration of Study: The study was carried out in twelve localities located in four regions of western Burkina Faso (Hauts-Bassins, Boucle du Mouhoun, Sud-Ouest and Cascades). Two sampling campaigns were conducted in August and November 2020, and herbicide analyses were performed at the National Agency for Food, Environmental, Occupational and Health Product Safety (ANSSEAT), Ouagadougou, Burkina Faso. Methodology: In each locality, five cereal fields were selected. Surface water samples were collected inside fields or within approximately 100 m of the fields, in small water bodies directly influenced by agricultural practices. Water samples from each field were combined to obtain a composite sample, and, at the locality scale, field composites were again homogenised to produce a single composite sample per locality and per sampling phase. Thirteen herbicidal active ingredients were selected from a previously documented list of 25 molecules commonly used in cereal production. Residues were extracted using an adapted QuEChERS method, purified, concentrated and quantified by high-performance liquid chromatography with UV detection (HPLC–UV). Measured concentrations were compared with guideline values from the World Health Organization (WHO) and maximum admissible concentrations defined in the European Drinking Water Directive 2020/2184. Results: Herbicide residues were detected in most localities during both sampling periods, revealing widespread contamination of surface waters. In phase 1, corresponding to the peak period of herbicide use, almost all targeted substances were detected, with concentrations ranging from 0.013 µg/L for atrazine (Dano) to 1484.90 µg/L for nicosulfuron (Safané). In phase 2, conducted at the end of the rainy season, concentrations varied from 0.0103 µg/L for metolachlor (Douna) to 1531.68 µg/L for mesotrione (Kankalaba). Between phases, some molecules (such as atrazine, bensulfuron-methyl and haloxyfop-R-methyl) disappeared, while others, including terbuthylazine, showed marked increases, and metolachlor, absent in phase 1, appeared in several localities in phase 2. For more than 90% of the measurements, individual herbicide concentrations exceeded the European limit of 0.1 µg/L for a single pesticide in drinking water, and several concentrations also surpassed WHO guideline values, indicating a high ecotoxicological risk for aquatic organisms and raising concerns for rural populations using untreated surface waters. Conclusion: Surface waters in cereal-growing areas of western Burkina Faso are heavily and persistently contaminated by herbicides, with concentrations frequently exceeding international guideline values. These findings underline the urgent need to strengthen water quality monitoring, to promote integrated and more rational pesticide management, and to raise awareness among farmers and local communities about the risks associated with herbicide misuse in cereal-based agroecosystems.