The arid regions in western China have single ecological structures with low stability, and are typical ecologically fragile areas. Frequent mining activities have brought about large environmental loads on the ecosystem functions and structures of the local ecologically fragile areas, which result in heavy metal pollution of soils,plants and water bodies, receiving extensive attention from all walks of life. Mining is the indispensable part of economy in western China. The investigation of soil, plant and water pollution and ecological risk assessment are the key to realize environmental protections and sustainable developments of resources, and can also provide a scientific basis for local government to carry out comprehensive management and planning.
The objective of this research was the soil, water body and plants around a gold mine in Xinjiang. The spatial distribution characteristics of total and available part of heavy metals in soils were analyzed by ArcGIS. At the same time, the vertical migration characteristics of total and available part of heavy metals in soils were
studied. The UNMIX model sources identification, factor analysis method and field investigation were used to analyze the sources of heavy metal pollution in soils. The bioavailability combined with the total risk assessment of heavy metals, constructed a regional ecosystem evaluation system and a human health risk assessment system based on the soil-water-plant system, which could provide scientific support for comprehensive risk assessment, risk management and pollution control in mining areas in China. The main findings were as follows:
(1) The spatial distribution patterns of total and available concentrations of Mn, Ni, Co, Cu and As were similar, while were different for Zn, Cd and Pb in the soil of study area. The available concentrations of soil heavy metals were low in the northern part of the gold mine. The total and available concentrations were similarly in the
longitudinal migration, but there was a tendency of inconsistent distribution in the east and south of the gold mine mainly because of the distinctive activity of heavy metals in different orientations. In addition, according to the UNMIX model sources identification, factor analysis and investigation results, it was found that the sources of
As, Cu, Ni and Co were the tailing dump and arsenic collection chamber, which contribute for 44.1%, 47.6%, 43.3% and 46.6% of total contamination for each metals.Mn element was mainly derived from the parent material and contribution rate was 46.6%, while Pb, Zn and Cd were derived from from mining and other sources, and the contribution rate were 47.1%, 40.7% and 34.6% for each metals.
(2) Soil is the main pollutant medium. The soils of Co, Cr, Ni, Cd, Zn and Pb in the study area were over-standard in a few samples, but the overall accumulation level was low. The soil Cu and As concentrations were high and the accumulation characteristics were significant. The maximum and average concentrations of Cu reached 1809 mg/kg and 108 mg/kg, which were 14 and 4 times of the background concentrations. The maximum and average concentrations of As were 1730 mg/kg and 206 mg/kg, which were 43 and 16 times the background in soils. However, the results of potential ecological risk assessment and risk assessment coding showed that most of the samples in the study area had low As and Cu pollution risks, and the risk of multi-media migration was small. The high-risk areas were mainly concentrated in the southwest and southeast parts of the field. The results of health risk assessment showed that the non-carcinogenic risk of soil Cu was very low, but the carcinogenic risk of soil As had a relatively high carcinogenic risk in some part of area. The non-carcinogenic and carcinogenic risks of Cu and As were also within the range prescribed by the state, and the overall health risk was at a controllable level. In addition, soil pH, Eh and heavy metal availability are three important factors affecting the potential ecological risk of heavy metals in mining areas. Therefore, in the evaluation of soil heavy metal pollution, not only the full amount should be paid attention, but also the available concentration of heavy metals should be paid attention.
(3) The concentrations of heavy metals in surface water and groundwater were all satisfied national safety standards in the study area. The concentration of As in pasture was slightly higher than that in other parts of Xinjiang. The concentration of Cu in pasture was consistent with that in other areas of Xinjiang, and the plant uptake factor (PUF) was less than 1. The soil-water-plant ecosystem in the study area was in good condition overall. The regional ecosystem health index H was 0.375, which belongs to a healthy state and was little affected by the stress of heavy metals As and Cu.
(4) According to the spatial distribution and vertical migration characteristics of heavy metal’s total and available concentration, and pollution risk assessment, regional ecosystem quality assessment, the risk management and control measures for soil heavy metal pollution around a gold mine in Xinjiang were taken as the source
control and cut off heavy metals. The migration and diffusion path would be used to repair the serious points of pollution and establish an early warning mechanism for pollution points.