Chemical composition and Zn bioavailability of the soil solution extractedfrom Zn amended variable charge soils

A study on variable charge soils (volcanic Italian and podzolic Scottish soils) was performed to investigate the influence of soilproperties on the chemical composition of soil solution. Zinc speciation, bioavailability and toxicity in the soil solution were examined.The soils were spiked with increasing amounts of Zn (0, 100, 200, 400 and 1000 mg/kg) and the soil solutions were extracted usingrhizon soil moisture samplers. The pH, total organic carbon (TOC), base cations, anions, total Zn and free Zn2+ in soil solution wereanalysed. A rapid bioassay with the luminescent bacterium Escherichia coli HB101 pUCD607 was performed to assess Zn toxicity.The influence of soil type and Zn treatments on the chemical composition of soil solution and on Zn toxicity was considered anddiscussed. Di erent trends of total and free Zn concentrations, base cations desorption and luminescence of E. coli HB101 pUCD607were observed. The soil solution extracted from the volcanic soils had very low total and free Zn concentrations and showed specificZn2+/Ca2+ exchange. The soil solution from the podzolic soil had much higher total and free Zn concentrations and showed no evidenceof specific Zn2+/Ca2+ exchange. In comparison with the subalkaline volcanic soils, the acidic podzol showed enhanced levels of toxicfree Zn2+ and consequently stronger effects on E. coli viability.