Divergent behavior of leachate pollutants in China: Insights from a national database and long-term monitoring

Despite the significant spatial heterogeneity of leachate quality across municipal solid waste (MSW) landfills in China, the underlying mechanisms and potential divergent behavior among different pollutants remain poorly understood. To address this gap, a national leachate quality database encompassing 130 landfills across three major climatic zones (the northwestern semi-arid, northern semi-humid, and southern humid zones) was compiled. Furthermore, the temporal evolution of pollutant concentrations was analyzed using seven- and ten-year continuous monitoring datasets from two typical landfills located in northern and southern China, respectively. National-scale analysis revealed that the concentration of organics (represented by COD Cr ) exhibited a systematic spatial decrease from semi-arid to humid zones, attributable to the dilution effect of precipitation ( R 2 = 0.058, p = 0.009). Conversely, total nitrogen (TN) concentration showed no apparent spatial variations ( R 2 = 0.002, p = 0.269), indicating an insensitivity to hydrological drivers. Long-term monitoring data further demonstrated that COD Cr is governed by the coupled effects of short-term hydrological dilution and long-term source attenuation. In contrast, TN follows an independent evolutionary pattern dictated by slow internal biochemical processes. A biogeochemical conceptual framework based on the contrasting pathways of efficient carbon removal and internal nitrogen locking was proposed to account for the observed divergent behavior. These findings offer guidance for optimizing regional leachate treatment strategies and conducting long-term environmental risk assessment.