Differences between total amount of heavy metals and their occurrence form contents in the wastelands of a molybdenum mine area

Abstract

In a single sample plot, the total amount of heavy metals in the soil could not necessarily reflect the contents of their effective states. This must be considered when attempting to determine the degree of soil heavy-metal pollution in an area. In the present study, the soil around the molybdenum mining area in Huludao, China, was surveyed and sampled to evaluate soil heavy-metal pollution using the Nemerow multifactor pollution index method. The Tessier continuous extraction method was used to analyze the distribution of heavy-metal forms’ and their content changes in the soil of this area. Thus, the bioactivity of heavy metals in the soil, the absorption of heavy metals by plants, and the distribution of heavy metals in plants were explored to provide data supporting the use of phytoremediation technology to treat the heavy-metal pollution in the molybdenum mining area and develop ecological restoration strategies for the area’s wastelands. The pollution index results indicate that heavy-metal pollution in the soil around the tailings pond is severe, mainly due to Pb and Zn heavy metals. Heavy-metal pollution in the surrounding land is mainly due to Cd and Zn. Content analysis of the heavy-metal forms/states in soils shows that exchangeable forms, which are most effective and toxic to plants, of the following metals are highest in the following areas: Cd, Cu, and Zn in the mountains around the stope; Zn, Mo, and Cu in the cultivated land around the dump; and Cd, Zn, and Mo in the cultivated land around the tailings pond. The pollution index analysis provides a basic overview of soil heavy-metal pollution across the entire mining area. However, content analysis of heavy-metal forms/states better reflects the relationship between the availability of heavy metals in the soil and the effectiveness of plants. Thus, the latter analysis can help ensure that phytoremediation strategies are adequately targeted, science-based, and effective.