Method on site-specific source apportionment of domestic soil pollution across China through public data mining: A case study on cadmium from non-ferrous industries.

The lack of emission data of major Cd-emitting enterprises has long limited the source apportionment of soil cadmium (Cd). Non-ferrous metal enterprises (NMEs) contribute the most Cd emissions in China in recent years. We estimated the cumulative Cd emission of 8750 NMEs across China through public data collection and material balance methods for the first time. The results showed that the total Cd emissions were estimated at 133,177 tons, of which 78.68% contributed by zinc primary smelting and mining. The emission hotspots are mainly concentrated in the south of the Yangtze River, such as Nanling Mountain areas, Nanpan River Basin, and Jincheng River Basin, as well as a few parts of the North and Northwest China. Then a significant positive spatial correlation was furtherly detected between NMEs and soil Cd, except for secondary smelting enterprises. Moreover, the hotspots of soil Cd pollution caused by NMEs were identified across China. By promoting the accounting calibrator from annual emission intensity of regional (mainly provincial) scale to the cumulative emission of site-specific enterprise in its entire life cycle, this study realized the finer description of the spatial heterogeneity of Cd emission from non-ferrous industry on a large scale and make it possible to refine the reliability of follow-up site-specific source apportionment, by introducing the emission intensity instead of the enterprise sites density. Finally, a modified approach for the regional source apportionment of soil pollution was proposed to obtain a more realistic and precise drawing. The results pointed out key NMEs subcategories and the affected hotspots which require continuous strengthening of Cd-related rectification. This methodological framework is expected to contribute to the precise management and differential sources control of Cd pollution and can be further extended to other pollutants for the precise targeting of key industries and hotspots during source pollution control in the future.