Assessment of Pesticide-Related Water Pollution in the Ankara River Watershed: A Combined SWAT and Grey Water Footprint Approach

Agriculture poses severe impacts on water quality and health due to diffuse pollution via pesticide use. In this study, the impact of pesticide use on water quality in the Polatlı district—a region of intensive agriculture within the Ankara River Watershed—was assessed using the Grey Water Footprint (GWF) methodology. The study analyzed 34 active ingredients utilized in the 2023 production cycle of wheat, barley, onion, and sugar beet. District-level data on cultivated areas (ha) for each crop were obtained from the Turkish Statistical Institute (TURKSTAT) for 2023. For the GWF calculations, the natural background concentration was assumed to be zero, while the maximum allowable concentrations for each pesticide were retrieved from local regulations. A watershed-scale hydrological model, namely Soil and Water Assessment Tool (SWAT) were constructed for the study area and calibrated against observed streamflow data to ensure reliable simulation of pesticide transport. Pesticide applications were integrated into the model based on actual usage data. The pollutant loads transported from the Polatlı district to the Ankara River were calculated and subsequently utilized in the grey water footprint equation.

Our findings reveal that pesticide impacts vary significantly with respect to crop and active ingredient levels. For example, SWAT model simulation results for deltamethrin reveal a high environmental transport efficiency despite its low application rate (250 ml/ha) compared to other pesticides. This pesticide has an extremely high affinity for soil particles as clear from the organic carbon-water partition co-efficient value (K_oc = 1,000,000 L/kg); it binds strongly to soil rather than dissolve in water. The transport of deltamethrin is entirely driven by soil erosion, leading to its accumulation in riverine sediments. Due to its extreme K_oc value, the pesticide remains associated with suspended solids and bed sediments, posing a significant long-term threat to benthic organisms and aquatic biodiversity. This sediment-related pollution indicates that the GWF of the basin is not only a function of dissolved pollutants, but it can be heavily influenced by sediment quality. No leaching to groundwater or dissolved transport was observed, confirming its strong soil-binding behavior. This substantial variability in GWFs underscores the necessity for region-specific water quality standards to more accurately assess and manage the environmental impact of pesticide use. Our analysis addresses the complexities of mixed cropping systems typical of semi-arid regions, where water scarcity and intensive pesticide use converge to create critical water quality challenges. This study provides a framework for similar assessments in other agricultural regions, aiding in the development of more informed pesticide management strategies to enhance water resource sustainability. Our results highlight specific pesticides requiring priority attention: replacing or limiting high-GWF pesticides is essential for progress toward sustainable water management in the Ankara River basin.