Harnessing hyperaccumulative plants to remediate agricultural soils contaminated by metals mine discharge

Intensive mining activities in China to support double-digit economic growth have contributed to massive land and water contamination of as much as one-fifth of the entire agricultural lands of the country. This poses a major challenge for ecological risk and food security in China. In northern Guangdong province, where a few hundred mines are located, indiscriminate discharges of toxic mining wastes to adjacent lands have contaminated canals and rivers. Farmers using the polluted water for irrigation have "unknowingly" created a major soil contamination problem. According to unpublished data from the Guangdong Department of Environmental Protection, about 30% of the soils exceeded the limits of the Chinese national soil quality standards for cadmium and lead. Numerous studies of soil contamination and human health risks associated with the mining areas of Dabaoshan have shown alarmingly elevated cadmium levels in the soils, crops, and humans. To remediate the agricultural soils that are impacted with heavy metals, we are harnessing the natural ability of plants to uptake metals. Using a selection of hyperaccumulative plants (e.g. Sedum alfredii), we have conducted both pot experiments and field trials to evaluate the phytoremediation of the contaminated soils. An intercropping phytoremediation system (e.g. Sedum and maize) and chelator addition were also studied to accelerate the uptake of metals. After 5 years of intercropping phytoremediation, initial cadmium levels of 1mg/kg in soils were reduced to <0.3 mg/kg, which is below the national soil quality standard. This paper will present results of successful case studies utilising Sedum alfredii to phytoremediate contaminated agricultural soils. (author)