6. **Biological degradation**

The CCl4 was transformed into chloroform by biological degradation in the soil. It was manifested by the fact that CCl4 and chloroform both existed in the soil samples around the pesticide plant and only CCl4 was founded in the pore water (Zhu et al., 2006). Chloroform was not detected in the wastewater discharged from the pesticide and the karst groundwater. This suggests that the CCl4 bio-degradation for its attenuation in the karst aquifer can be ignored.
