Beyond agriculture: Land use thresholds governing pesticide mixture risks in megacity surface waters

Growing concerns have emerged regarding the risks of pesticide mixtures in surface water ecosystems, yet the mechanisms through which human activities, especially land use patterns, affect these risks remain inadequately studied. This research presents an innovative approach, combining multi-scale land use analysis with pesticide risk assessment, quantifying relationships between mixed pesticide ecological risks and land use patterns. Findings indicate that the impacts of urban land use on pesticide ecological risks surpass the traditionally recognized agricultural effects, demonstrating significant spatial scale-dependent effects. Generalized additive model analysis reveals that 1-3 km and 2-3 km buffer zones represent the critical ranges where urban land use and cropland, respectively, have significant impacts on pesticide risks. Non-parametric change point analysis determined critical land use thresholds triggering significant ecological risk increases: 10-25 % for cropland and 10-30 % for urban areas. These discoveries provide crucial quantitative foundations for landscape planning and pesticide risk management. The results not only challenge traditional views of agricultural activities as primary pesticide sources but also provide new perspectives for pesticide pollution control and water quality management in large cities.