Abstract:
The soil heavy metal content in grassland open-pit coalmine area is related to the policies making on coal mining and ecological restoration. It can provide an important reference for analyzing the impact range of coal mining. The content of heavy metals in the soil around the pit in the mining area was analyzed to define the impact types and boundaries of coal mining from the perspective of heavy metal pollution. The sampling lines were centered on the Baorixile No. 1 open-pit coalmine,set radially from edge of the pit outward to west,northwest,north,northeast,east and south. After the collection and processing of soil samples,Nemero comprehensive pollution index,Geo-accumulation in- dex and Potential ecological risk index were used to evaluate the pollution level of the heavy metals in the soil sur- rounding the pit. The one-way analysis of variance was used to analyze the change characteristics of soil heavy metal content with distance to the pit in different directions. It helped to assess whether the mining activities had an obvious influence on soil heavy metal content outside the pit and whether there was a certain influence range. Through correla- tion analysis,it could find out whether different heavy metal elements in the soil had the same source of soil pollution. The study shows that ① according to the content of heavy metals in the soil around the pit,Pb,Zn and Cr does not ex- ceed the first level specified in National Standard of Soil Environment Quality (GB 15618—1995) in the study area, except that the content of Cu has an over-standard rate of 28% . However,none of them exceed the second level of na- tional standards,which means that the heavy metal content in the soil around the pit has no serious effect on the human health. ② The content of Pb and Cu in partial soil samples has exceeded the background values of heavy metal ele- ments in the soil of Inner Mongolia,while the content of Zn and Cr in all soil samples are within the background val- ues. The comprehensive pollution level has reached the level of “warning line”,which should be a cause for concern. Because the potential ecological risk index is less than 150,the degree of soil pollution around the pit is relatively slight. ③ The content of Pb is universally high in the west and northwest of the pit,where road S201 is located nearby. ④ There are close correlations between Zn and Cu in the eastern pit,as well as between Pb and Cu in the northern pit. However,the other heavy metals are not significantly correlated with each other in all directions. Besides,the con- tent of Pb,Cr,Zn and Cu has no significant correlation with the distance from the edge of the pit,which means that the content of heavy metal does not show a significant downtrend with the increasing distance from the stope. ⑤ According to soil environmental quality risk control standard for soil contamination of agricultural land ( GB 15618—2018),the content of various soil heavy metals is far lower than the specified risk value,and the risk of soil pollution is very low. The study concludes that the content of soil heavy metals within 4 km away from the pit in Baorixile mining area is generally in the state of non-pollution. The soil samples with comparatively high heavy metal content are distributed near to residential areas,power plants and transportation routes. The content of Pb,Cr,Zn and Cu does not show a sig- nificant downtrend with the increasing distance from the pit.