Effects of organic matter on natural-remediation process of typical copper-zinc polluted soils

In order to clarify the effect of soil organic matter (SOM) on natural-remediation of the polluted soils, the remediation processes of copper (Cu) and zinc (Zn) in three kinds of contaminated typical soil of China were studied by incubation under controlled condition. The soils were red soil, fluvo-aquic soil and black soil, taken from 3 long-term fertilization experiments, with different SOM contents. 400 mg/kg Cu, 500 mg/kg Zn were added in soil samples and the incubation time were 90 d. Results showed that, in all soil samples, concentrations of soil available Cu or Zn decreased rapidly within the first 10-20 d, then the rate of decrease slowed down in short time, and dynamic balance were achieved after 30-60 d. The remediation process of Cu or Zn contaminated soils could be simulated by the second-order equation. After 90 days incubation, equilibrium concentrations of Cu in the low SOM content treatments in red soil and fluvo-aquic soil were 24.2%-57.1%, which were higher than those in high SOM content treatments. However, in black soil and fluvo-aquic soil, the equilibrium concentration of Zn in high SOM content treatment was 3.44-6.33 times of those in low SOM content treatment. This result implied different effects of increased SOM in the three kinds of soil. In red soil, the increased SOM repressed the availability of Cu; In fluvo-aquic soil, the increased SOM repressed the available Cu and promoted available Zn; And in black soil, the increase of SOM promoted the availability of both Cu and Zn. In fluvo-aquic soil, the remediation velocity was the largest, dynamic balance time was the shortest, and the equilibrium concentration of Cu and Zn in fluvo-aquic soil was lowest in the three kinds of soil, while such parameters in red soil were opposite. In conclusion, increasing SOM can be one of effective ways to decrease the availability of Cu in red soil and fluvo-aquic soil, whereas might increase the risk of environmental Zn pollution in black soil and fluvo-aquic soil.