Zakrzewska et al. 2023 — MICP treatment reduces Cd uptake by crop plants
Supplementing Cd-contaminated agricultural soil with metabolites containing carbonates (MCC) produced by the ureolytic bacterium Ochrobactrum sp. POC9 reduced the bioavailability of cadmium in soil by 27–65% (depending on MCC volume applied) and reduced Cd uptake by root parsley (Petroselinum crispum) by approximately 86% in shoots and 74% in roots relative to untreated controls. The study demonstrates that microbially-induced carbonate precipitation (MICP) can be applied at trace but legally permissible Cd concentrations characteristic of agricultural soils, where conventional remediation methods are often unsuitable because they disrupt soil function. Additional benefits observed included improvement of soil microbiological activity and plant condition due to nitrogen-containing co-metabolites produced during urea hydrolysis.
Key numbers
Cd bioavailability reduction in soil: 27–65% across MCC volume treatments (specific volumes and absolute concentrations not reported in Marker-converted text; see original for dose-response data).
Cd uptake reduction in parsley shoots: approximately 86% in MCC-treated vs. control pots; roots: approximately 74% reduction.
Experimental system: pot experiments using agricultural soil from Poland with low to moderate Cd contamination (trace concentration, legally permissible range per UNECE guideline of 0.9 mg/kg); crop species Petroselinum crispum (root parsley). MCC added as pre-produced bacterial metabolite mixture to avoid the variability of live-inoculation.
Cd speciation in soil measured by sequential extraction to track immobilisation into carbonate-bound fractions. Presence of cadmium carbonate (CdCO3) confirmed by X-ray diffraction in MCC-supplemented soils.
Soil microbiological properties (quantity and activity of microorganisms) improved in MCC-treated soils, attributed to ammonia and secondary metabolites co-produced during urea degradation.
Methods (brief)
Ureolytic bacterium Ochrobactrum sp. POC9 (isolated from sewage sludge) was cultured under optimised conditions to produce MCC. Agricultural soil was spiked with trace Cd concentrations and supplemented with varying MCC volumes. Petroselinum crispum was grown in supplemented and unsupplemented pots. Cd uptake in shoots and roots measured by unspecified ICP method. Sequential extraction characterised soil metal fractionation. MICP process confirmed by XRD identification of CdCO3 mineral phase. Analytical specifics and sample sizes not recoverable from Marker conversion; consult original manuscript for dose-response detail.
Implications
Certification: Relevant to HMT&C supply-chain and mitigation guidance for agricultural soil Cd management. Demonstrates a biologically feasible intervention that reduces food-crop Cd uptake at sub-regulatory soil concentrations where hard remediation is not triggered.
Courses: Illustrates MICP as an agronomic lever for Cd mitigation; connects to broader discussion of soil amendments that reduce heavy metal bioavailability without destroying soil function.
Supply-chain: Supports the case for soil-level interventions as a supply-chain Cd control point upstream of agrochemical and processing interventions.