Irrigation of soil with synthetic landfill leachate — speciation and distribution of selected pollutants

The fates and toxicities of selected landfill leachate pollutants in a soil with a low attenuation potential were investigated. Soil columns consisting of a loamy sand which had been irrigated with synthetic landfill leachates were dissected and analysed for pH, electrical conductivity, copper and zinc species, iron and phenol concentrations and microbial activity. Copper was found to be least mobile and accumulated in the top 4 cm of the soil columns. Sequential extraction of the soil revealed that at least two-thirds of the total copper was in the EDTA-, NaOH-extractable and residual fractions. Approximately 2% of the copper was water soluble and between 1 and 22% was in the MgCl2-extractable fraction. Zinc and phenol were relatively mobile and were detected throughout the soil-column profile as well as in the column effluents. The greatest zinc fraction (55–71%) was MgCl2-extractable. Zinc solubility in water was again low (1–4%). Phenol was partially adsorbed by the soil but its main attenuation occurred by biodegradation. Microbial activity was affected by the availability of the carbon source as well as the presence of copper and zinc. Copper was more inhibitory to microbial activity than zinc. In the presence of phenol, the simultaneous application of zinc and copper distinctly reduced microbial activity. No inhibitory effect of copper and zinc was observed in the absence of phenol when the microorganisms were severely carbon limited.