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

Abstract

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 CaCO 3, 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. The amendments led to significant increases in pH and decreases in NH 4NO 3-extractable Pb. A 99% decrease in extractable Pb was only observed in the treatments containing CaCO 3. The addition of the synthetic zeolite 4A gave a 69% and that of compost a 10% reduction. The addition of zeolite and CaCO 3 mobilised soil organic matter as indicated by increased contents of CaCl 2 extractable C and increased CO 2 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+CaCO 3 was added. The addition of compost, especially when combined with CaCO 3, 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 14CO 2, so that the ∑CO 2- 14C-to-biomass 14C ratio remained unaffected.