Arsenic is a toxic and carcinogenic element, it is usually present in coals or the ores with various sulfur-containing minerals. Anthropogenic activities such as mining, smelting and coal combustion have resulted in the release of As into land surface environment, causing serious arsenic contamination. Approximate 70% of total arsenic deposits are distributed in China, however, an average of 70% of the exploited arsenic remain in tailings during the mineral processes under current technique level in China. The open pit dumping of arsenic containing tailings has released large amounts of hazardous matters into soils and surface waters through wind and hydraulic erosion. Several arsenic poisoning incidents that causing many people sick have been reported in Yunnan, Guangxi and Hunan provinces, these were usually related with the leaching of heavy metals in tailings that had entered into the surface water and groundwater systems. Arsenic can enter livestock and human bodies via food chain, rendering detrimental effects to human health. Endemic epidemics of arsenicosis have occurred in thirty-seven counties and eight provinces in China.

Currently, several techniques, e.g., chemical remediation and phytoremediation, have been employed to remediate arsenic contaminated soils and/or arsenic containing tailing dams in some nonferrous metal mines in south China. However, little efforts have been made on how to evaluate the effectiveness of the these techniques, given the fact that no remediation standards for the effectiveness assessment was established in China. Dr. WEI Chaoyang,Institute of Geographic Sciences and Natural Resources Research(IGSNRR) leading a group involved in several projects focusing on arsenic funded by the National Key Technologies R&D Program of China and the National Natural Science Foundation of China, initially tried to resolved such problems.

The study was conducted on a tailing dam in a arsenic mine, located in Shimen county, Hunan province．The mine has the biggest reserves of realgar in Asia, and has been exploited for more than 1500 years. The discharge of waste gases and solid wastes has led to arsenic contamination since 1958. Soils, waters in the rivers around the mine contained high arsenic, all far exceeding the values of the corresponding soil and water environmental quality standards in China. A tailing dam with 3.5 m in height and 6200 square meters in area was piled up during 1992-1994 at the mine. Arsenic concentration was as high as 5.24% in the tailings. The intensive wind and hydraulic erosion led to vegetation-less landscape on the tailing dam. Arsenic in the runoff waters of the tailing dam during a rainstorm was recorded as high as 5 mg L-1.

The phytoremediation project was put in practice in July 2003. Surface of the tailing dam was evened, followed with construction of drainage ditches and cement barriers across the dam. The tailing dam was then capped with a cover of 35cm of soils dug from the nearby hillsides. In order to assess the effectiveness of the project, quadrat survey method was employed to investigate and sample the dominant plant speciesgrowing on the rehabilitated tailing dam in April 2008, in addition, the fertilities of the soils were assessed, andconcentrations of arsenic and other heavy metals in the plant and soil samples were measured. Dr. WEI and his colleagues found that stable vegetation composed of planting Chinese Brake fern, natural colonizing Chinese silvergrass from soil seed banks and other local pioneer species of plants developed rapidly on the tailing dam. The authors stated that non-top soils had similar effect with top-soils for rehabilitation of plants on the tailing dams, therefore, non-top soils should be used for sake of economic reasons. Compared to farmland soils fertility standards, the capped soils had a relatively low level of fertilities, but they could maintain the normal growth of the plants on the tailing dam. Although concentrations of arsenic and cadmium in the capped soils exceeded the corresponding values of the National Standard for Soil Quality, they were still far lower than those in the tailings. Concentrations for mostof theheavy metals were in the normal range for terrestrial higher plants,but for arsenic in Chinese brake fern and cadmium in Chinese silvergrass, they were found to be exceeded. The authors concluded that phytoremediation project had greatly reduced the ecological and health risks caused by the tailing dam to the ambient environment, however, since the plants growing on the tailing dam contained high arsenic and cadmium, the rehabilitated tailing dam should not be used as farmland, and cattle should be kept away from the tailing dam．

Related research results have been published in Acta Ecologica Sinica (International Journal) 2010, 30(3) 178-183.