Assessing and Predicting the Impact of Phosphogypsum Stockpiles on Regional Water Quality

Phosphogypsum (PG) stockpiles pose a persistent threat to regional water environments, yet their differential impacts on surface water and groundwater remain unclear. This study examined the pollution characteristics, sources, mechanisms, and model-predicted trends of PG-derived contaminants in both systems within a representative PG-affected region. Results showed that total phosphorus declined sharply from surface water to groundwater due to soil retention, whereas SO42− and F− remained comparable. Nitrogen species accumulated more in groundwater, indicating distinct transport and transformation processes. Arsenic was higher in surface water but rarely exceeded limits. In contrast, lead and manganese were significantly enriched in groundwater, exceeding standards by up to 27- and 11-fold, mainly due to reductive mobilization and subsurface geochemical processes. The Nemerow Index indicated heavy pollution in 35% of surface water and 43% of groundwater samples. Principal component analysis identified PG leachate as the dominant pollution source. Model predictions further suggested that increasing stockpile capacity would intensify contamination and pose long-term environmental risks. This study provided a scientific basis for understanding the distinct pollution mechanisms of PG stockpiles and offered guidance for targeted water environment management in PG-impacted areas. These findings have broader implications for regions globally facing similar challenges from industrial solid waste storage.