Distribution of thorium in soils surrounding the rare-earth tailings reservoir in Baotou,China

Thorium distribution was investigated in the soils surrounding the rare-earth (RE) tailings reservoir near the Baotou grassland of Inner Mongolia, northern China. Totally 77 soil samples were collected from 8 different directions in the periphery of the RE tailings reservoir, and then were determined for ²³²Th. The ²³²Th activity degree ranges from 9.1 to 307.1 Bq kg^?1 with an average value of 42.4 Bq kg^?1. In some samples, the degree is higher than that of global average, showing that these soils were polluted by thorium. There is a high linear correlation coefficient between the thorium diffusion coefficient parameter and the wind intensity parameter which indicates that the distribution of ²³²Th is mainly correlated with wind speed and direction. The geo-accumulation index method was used to evaluate the level of thorium pollution, and the Kriging method was applied to estimate the land area at each level. By calculation, result shows that the area at each pollution level is 2.10 km² with medium-strong pollution, 38.29 km² with medium pollution, and 47.19 km² with slight pollution. The remaining 738.63 km² of land investigated is clear from thorium pollution.