Decomposition of 14C labelled glucose in a Pb-contaminated soil remediated with synthetic zeolite and other amendments

In an incubation experiment, we assessed the effects of a synthetic zeolite (type 4A) on biomass and community structure of soil microorganisms in a highly Pb-contaminated soil. The effects of zeolite were compared with other amendments that increase soil pH, such as CaCO3, or improve microbial properties, such as compost. In a separate experiment, the effect of the different amendments on the efficiency of microbial substrate use was determined using 14C labelled glucose. endments led to significant increases in pH and decreases in NH4NO3-extractable Pb. A 99% decrease in extractable Pb was only observed in the treatments containing CaCO3. The addition of the synthetic zeolite 4A gave a 69% and that of compost a 10% reduction. The addition of zeolite and CaCO3 mobilised soil organic matter as indicated by increased contents of CaCl2 extractable C and increased CO2 production rates. Microbial biomass C was increased by all amendments, but in most cases it was not significant. Maximum biomass C was measured where the combined amendment zeolite+compost+CaCO3 was added. The addition of compost, especially when combined with CaCO3, resulted in an increased ergosterol content. In contrast, the sole addition of synthetic zeolite had a significant depressive effect on the ergosterol content and, thus, on the ergosterol-to-biomass C ratio. The most striking feature of the treatments containing synthetic zeolite was the effect on glucose decomposition. Zeolite increased both incorporation of 14C into microbial biomass and mineralisation to 14CO2, so that the ∑CO2-14C-to-biomass 14C ratio remained unaffected.