HEAVY METAL MIGRATION CHARACTERISTICS AND POLLUTION RISK ASSESSMENT IN RECLAIMED LAND FILLED WITH FOREIGN SOIL AND COAL GANGUE

A positioning experiment of 5 years was conducted to explore the safety of heavy metal (HM) in reclaimed farmland filled with coal gangue in Chengcun mine area of Xinxiang City, China. The migration characteristics and ecological risk of soil HMs and health risk of crop were evaluated in reclaimed farmland. The results indicated that HMs in the reclaimed soil profile have a distribution pattern of high in surface and bottom soil layer but low in middle soil layer three years after reclamation. This suggests that HMs from the bottom coal gangue have migrated to the overlying soil layer and accumulated there. After five years of reclamation, the contents of HMs in reclaimed soil were higher than those in original foreign soil, especially the content of Cd that exceeded the risk screening value for soil pollution of agricultural land (SVSP). The contamination degree (CD) of all measured HMs in reclaimed soil reached moderate contamination level after five years of reclamation. However, the ecological risk assessment of soil HMs showed that the comprehensive ecological risk index (RI) of all measured elements in reclaimed soil was slight, only Cd showed a strong ecological risk. The HMs in wheat grains of reclaimed farmland did not exceed the grain limit standard, but were higher than those in regional normal soil. The analysis of crop risk indicated that the health risk index (HI) of adults and children exposed to multiple HMs was 1.98 and 2.70, respectively, which suggests that oral ingestion of wheat from reclaimed farmland poses a serious health risk, and the health risks to children are significantly higher than those to adults. Of all measured HMs, Cd and Zn in wheat are the main elements that cause health risks for local populations. Based on the above results, it can be concluded that it is not appropriate to grow crops on reclaimed farmland at present and may pose food safety risks.