Abstract: Whether Cd pollution in Xiaojiang River Valley of Dongchuan,Yunnan Province originates from copper mining or agricultural pollution was still unclear,which hinders the effective prevention and control of local heavy metal pollution.In this paper,the source of Cd pollution in Xiaojiang River Valley is diagnosed by associating the main pollutants of copper mining with the content of Cd of local chemical fertilizers on the basis of investigating the spatial distribution of Cd element in the river valley.Element characteristic analysis unveils that 1) the major pollutants produced from copper mining,namely,copper ore and tailing slag,are not capable of polluting the river valley as the average content of Cd in copper ore and tailing slag is only 0.30 mg/kg,far lower than that of Cd-polluted cultivated land (4.60 mg/kg) and floodplain (2.53 mg/kg);2) phosphorus fertilizer is more likely to be the main pollution source of Cd in the watershed because the average content of Cd in local phosphorus fertilizer is 83.45 mg/kg,18 times higher than that in Cd-polluted farmland;3) the spatial distribution of Cd content in floodplain shows no trend of continuous attenuation from the mining area to the downstream,which does not support the diffusion model of Cd pollution from copper mining;4) the content of Cd in cultivated land is generally higher than that in floodplain,indicating that cultivated land is closer to pollution source,which conforms to the pollutant diffusion mode of agricultural activities;5) the correlation between Cd content in cultivated land and floodplain and available phosphorus (AP) is much higher than that between Cd content and Cu content which represents copper mining,implying that Cd pollution is more closely related to phosphorus fertilizer application than copper mining.In conclusion,the contribution of phosphorus fertilizer in agricultural activities to Cd pollution is likely to be much greater than that of copper mining.

Key words: Cd pollution source, copper mining, element characteristic analysis, agricultural activity, Xiaojiang River Valley