Main Participants: GAO Bo, WU Wenqiang, GAO Jijun, XU Dongyu, WAN Xiaohong, GAO Li, LI Yanyan, LIU Xiaoru, ZHANG Panwei, LI Kun, ZHAO Xiaohui and LI Ang

Heavy metals are one of the main pollutants in the environment. At present, 16.1% of soil (21% of cultivated land) and 46.4% of sediment of China are suffering from excessive heavy metal pollution. Thus heavy metal pollution constitutes a major ecological and environmental problem in China, posing potential threats to water environment and human health. In the basic monitoring indicators of Environmental Quality Standards for Surface Water (GB 3838-2002) of China, eight among the 24 indicators are related to heavy metals. The toxicity, migration and bio-availability of heavy metals in the environment mainly depend on their chemical form/valence state and transformation process rather than the total concentration. However, the absence of evaluation systems and standards for the liable concentration of heavy metals and the lack of relevant theoretical studies have caused great difficulties in identifying the potential ecological risks of heavy metal pollutants in environment. This project focuses on the research of "environmental process and effect of liable concentration of heavy metals", and the results can provide theoretical and technical support for assessing, preventing and controlling the risks of heavy metals posed to environmental and ecology in China.

·   Study on the spatial distribution mode, transfer and transformation and influence factors of heavy metals in the sediment profile solid phase — pore water — overlying water and soil solid phase — pore water systems.

·   Exploration of the release and resupply kinetics of heavy metals in the soil/sediment solid-liquid phase system and the driving mechanisms, and quantification research on the transport of heavy metals in the basin-scale “land-reservoir-river-sea” system.

·   Construction of in situ valence method framework and chromium form analysis techniques targeting multi-valent trace toxic elements (Cr, As, Sb, etc.).

·   The occurrence characteristics of labile concentration of heavy metals in multimedia environments (soil, water and sediment profiles) have been clarified. The ecological risk assessment system of labile heavy metals in multimedia environments has been constructed by combining the heavy metal quality criteria and the labile heavy metal quantification model, thus achieving an accurate assessment of ecological and environmental risks posed by labile concentration of heavy metals.

·   The influence of the flooding process on the transport fluxes and the fate of the labile heavy metals at the "soil-water in water-level-fluctuation zone" interface have been clarified. The total amount of heavy metals in the soil of the water-level-fluctuation zone in the Three Gorges Reservoir Region has remained unchanged after the flooding, but the labile concentration of heavy metals transporting into the reservoir after the flooding has increased by nearly five times (from 213 to 1,278 tons), while the labile heavy metals only accounted for 10% of the total heavy metals entering into the Three Gorges Reservoir.

·   The concept of "in-situ metal speciation" has been proposed for the first time, the method framework of in-situ metal speciation analysis and monitoring has been constructed based on in-situ DGT accumulation and HPLC-ICP-MS high-precision measurement, and the methods of in-situ metal speciation analysis of chromium (Cr) in different water environments have been established, simultaneous acquirement the information on the in-situ Cr(III) and Cr(VI).

The theoretical results above have been published in 28 high-quality papers at international mainstream SCI journals specialized in water environment and water ecology, hydrology and water resources, soil science, etc. In addition, two monographs have been composed. One of them, "Characteristics and Effects of Water Environment Evolution of Heavy Metal Pollutants in Three Gorges Reservoir", published by Science Press in 2021, was funded by the National Publication Fund Project in 2021.

Figure 1. Transmission flux and fate of heavy metals under different hydrological regimes

Figure 2. Kinetic processes of labile heavy metals in soil/sediment solid-liquid- DGT systems.

Figure 3. Simultaneous measurement of Cr(III) and Cr(VI) by combining DGT and HPLC-ICP-MS