Distribution characteristics of heavy metal(loid)s in aggregates of different size fractions along contaminated paddy soil profile
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Soil aggregates exert a significant influence on the retention and availability of heavy metal(loid)s in soil. In this study, the concentration distribution and chemical forms of heavy metals (Cu, Zn, Cd, Pb, and Hg) and a metalloid (As) in different aggregate-sized fractions (2–0.25, 0.25–0.05, 0.05–0.002, and < 0.002 mm) along the profile (0–1, 1–5, 5–15, and 15–25 cm) of a contaminated paddy field were investigated. The results showed that the values of pH, free Fe oxides (Fed), bulk density, and catalase activity gradually increased, whereas the soil organic matter (SOM), cation exchange capacity (CEC), electrical conductivity (EC), microbial biomass carbon (MBC), and urease activity decreased with depth. Long-term heavy metal pollution might impact the catalase activity but showed no obvious influence on the urease activity. Additionally, there was a notable difference in physicochemical properties among the soil aggregates of various particle sizes. The 2–0.25-mm fraction aggregates contained more organic matter, whereas the highest values of CEC and Fed were observed in the < 0.002-mm fraction. The concentrations of all six heavy metals/metalloid decreased with depth. In different layers, Cu and Cd showed the highest concentrations in the 2–0.25 mm-fraction, followed by the < 0.002-mm fraction, whereas the highest concentrations of Zn, Pb, and As appeared in the < 0.002-mm fraction. No obvious distribution regularity was observed for Hg among the aggregates. All of the metal(loid)s had lower activity in the deeper soil layers, except for Hg. Furthermore, Cu and Cd displayed more stable forms in the < 0.002-mm fraction aggregates.
KeywordsPaddy soil profile Heavy metal(loid)s Aggregates BCR method Soil enzyme Smelting plant
This work was supported by the GDAS’ Special Project of Science and Technology Development (2017GDASCX-0830), the Natural Science Foundation of China (Nos. 41701320, 41501298 and 51521006), the High-level Leading Talent Introduction Program (2060599), the SPICC Program (The Scientific Platform and Innovation Capability Construction Program of GDAS, 2016GDASPT-0105 and 0304), the Construction of Innovative Talents for Pollution Control and Management of Heavy Metals in Farmland (2016B070701015), and Key Research Items in Science and Technology Program from China Hunan Provincial Science and Technology Department (No. 2015SK2004). We would like to thank Ninglin Luo, Qiu Zhang, Mei Huang, and Xiuqing Zhai of Hunan University for the sampling and laboratory analysis.
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