Wei et al. 2021 - eggshell and ureolytic bacteria for Pb/Cd remediation
Wei and colleagues tested microbially induced carbonate precipitation as a remediation strategy for Pb- and Cd-contaminated water and soil. The source is mitigation evidence, not mineral-water occurrence evidence: all Pb and Cd values are spiked-solution or spiked-soil treatment endpoints.
Key numbers
The source soil for the incubation experiment was collected from uncontaminated farmland in the suburbs of Xi’an, Shaanxi province, China, then spiked with Pb(NO3)2 and Cd(NO3)2 to final concentrations of about 106 mg kg-1 Pb and 10 mg kg-1 Cd. Table 1 describes the starting soil as pH 7.8, cation exchange capacity 17.2 cmol kg-1, electrical conductivity 375 us cm-1, total nitrogen 0.07%, available phosphorus 16.1 ppm, and available potassium 172 ppm.
Four urease-producing isolates were selected. Table 2 reports minimum inhibitory concentrations: UR1 tolerated 1100 mg L-1 Pb and 500 mg L-1 Cd; UR16 tolerated 1200 mg L-1 Pb and 400 mg L-1 Cd; UR20 tolerated 1400 mg L-1 Pb and 500 mg L-1 Cd; and UR21 tolerated 1300 mg L-1 Pb and 400 mg L-1 Cd.
In solution tests with 2 mM Pb or Cd and 0.7 M urea, the highest Pb removal rate after 72 h was 81.9% for UR21, followed by 77.1% for UR20. For Cd, UR21 had the highest removal rate at 65.0%. The text states that Pb and Cd removal became stable from 60 to 72 h.
In the soil fractionation experiment, the control soil’s Pb was dominated by exchangeable Pb at 64.64%, followed by carbonate-bound Pb at 16.7%, Fe-Mn-oxide-bound Pb at 10.6%, organic-matter-bound Pb at 4.12%, and residual Pb at 3.91%. Across treated groups, soluble-exchangeable Pb declined to 19.5%-43.8% and carbonate-bound Pb increased to 18.5%-35.9%.
The control soil’s Cd was dominated by exchangeable Cd at 70.68%, followed by carbonate-bound Cd at 11.01%, Fe-Mn-oxide-bound Cd at 8.37%, organic-matter-bound Cd at 4.17%, and residual Cd at 5.78%. Across treated groups, exchangeable Cd was reduced to 20.22%-37.78% and carbonate-bound Cd increased to 17.61%-36.71%.
For DTPA-extractable metals after 40 days, the UR21 + urea + eggshell-waste treatment reduced extractable Pb by 29.2% and Cd by 25.2% compared with the control. The UR21 + eggshell-waste treatment reduced DTPA-extractable Pb by 27.1% and Cd by 20.6%.
The soil pH increase after 40 days was 0.41 units for UR21 + urea + eggshell waste, 0.36 units for UR21 + eggshell waste, 0.07 units for UR21 + urea, and 0.06 units for UR21 alone. The soil CEC after 40 days was 35.41 cmol kg-1 in the UR21 + eggshell-waste group and 33.91 cmol kg-1 in the UR21 + urea + eggshell-waste group. Soil urease activity increased by 120% in the UR21 + urea group and 82% in the UR21 + urea + eggshell-waste group; catalase activity increased by 71% in the UR21 + urea + eggshell-waste group and 50% in the UR21 + urea group.
Methods (brief)
The authors isolated ureolytic bacteria from Pb mine tailing soil in Huayin, Shaanxi province, screened isolates on PbCl2 and CdCl2 media, and identified strains by 16S rRNA sequencing. Solution tests used YA broth, 0.7 M urea, 2 mM Pb from PbCl2, and 2 mM Cd from CdCl2. Pb and Cd in supernatant and soil extracts were measured by atomic absorption spectrometry. Precipitates were characterized by SEM-EDS and XRD; the text identifies PbCO3 and CdCO3 crystals. Soil fractions were measured by Tessier sequential extraction, and available Cd/Pb were extracted using DTPA-TEA.
Implications
Certification: Do not use the Pb/Cd removal rates, spiked-soil concentrations, fraction percentages, or DTPA reductions as food, drinking-water, mineral-water, or product occurrence data. They are remediation-performance endpoints.
Courses: Useful for remediation training because it ties a waste-derived calcium source, eggshell waste, to MICP-driven conversion of soluble Pb/Cd into carbonate-bound or precipitated forms.
App: Context only. The source does not estimate consumer-product contamination probability.
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Verification notes
Recovered from skip:not-food-occurrence under the 2026-06-10 inclusion-by-default rule. The old skip treated “not bottled/mineral-water occurrence” as exclusionary, but the paper is in-scope a2 mitigation/remediation evidence.
All numbers above were re-checked against the extracted PDF text, including the abstract, Materials and Methods, Tables 1 and 2, and the Results sections on removal efficiency, Pb/Cd fractionation, DTPA-extractable metals, pH/CEC, and enzyme activity. Units are preserved as reported. The source is a Research Square preprint; the title page states that a version of record was published in Environmental Science and Pollution Research with DOI 10.1007/s11356-021-15138-0.
Page history
The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.