Overview
Boostani and colleagues tested whether bentonite combined with pristine or phosphoric-acid-modified biochars could immobilize cadmium in contaminated calcareous soil. The study is mitigation evidence: it uses Cd-spiked soil and amendment treatments, so its values should not be routed into coffee, food, or ingredient occurrence pools.
Key numbers
The source soil was a loam from Darab, Fars province, southern Iran, with pH 7.40, EC 1.40 dS/m, 43.7% calcium carbonate equivalent, 1.50% organic matter, and total Cd below AAS detection before spiking. The experimental soil was spiked to 50 mg Cd/kg soil using cadmium chloride.
The 90-day incubation used three bentonite levels: B0 0% wt., B1 1% wt., and B2 2% wt. Biochar treatments were no biochar control, coffee grounds biochar (G), phosphoric-acid-modified coffee grounds biochar (GH), municipal solid waste biochar (M), and phosphoric-acid-modified municipal solid waste biochar (MH), each at 2% wt. The full factorial design had three replications.
Table 3 reports water-soluble plus exchangeable Cd (WsEx). The unamended C + B0 control had 8.66 mg/kg. Coffee grounds biochar without bentonite (G + B0) lowered WsEx to 4.79 mg/kg, but adding bentonite to G raised WsEx to 5.41 mg/kg at B1 and 7.68 mg/kg at B2. The abstract summarizes those bentonite additions as increasing WsEx by 12.9% and 60.3% compared with G alone.
Table 3 reports Cd mobility factor. The C + B0 control was 50.5%. G + B0 was 37.5%, a 25.7% reduction. M + B2 was 39.9%, a 21% reduction. The text states that bentonite alone lowered mobility factor by 15.6% from B0 to B2, while municipal-solid-waste biochar plus bentonite showed a synergistic immobilization effect.
Table 3 also shows fraction shifts. M + B2 had WsEx 5.95 mg/kg, carbonate-bound Cd 14.0 mg/kg, Fe-Mn-oxide-bound Cd 4.51 mg/kg, residual Cd 25.5 mg/kg, and mobility factor 39.9%. G + B0 had WsEx 4.79 mg/kg, carbonate-bound Cd 14.0 mg/kg, Fe-Mn-oxide-bound Cd 4.26 mg/kg, residual Cd 27.0 mg/kg, and mobility factor 37.5%.
Figure 3 and the desorption text report that M + B2 had the lowest 24-hour EDTA-extracted Cd release at 22.4 mg Cd/kg soil, an 18.7% reduction compared with C + B0. Table 4 reports that M + B2 produced the greatest decrease in the power-function e constant (-29.8%) and the highest increase in f (+40.0%); the initial desorption-rate parameter ef was 1.14 for M + B2 versus 1.29 for C + B0.
Methods (brief)
Soils were air-dried, sieved, spiked with CdCl2 solution to 50 mg Cd/kg, and repeatedly wetted and dried to equilibrate Cd with the soil. Biochars were prepared from coffee grounds and municipal solid waste by slow pyrolysis at 400 C for 2 hours under limited oxygen; modified biochars were treated with 5 N phosphoric acid.
After 90 days of incubation at near field capacity, soil Cd was separated into water-soluble/exchangeable, carbonate-bound, Fe-Mn-oxide-bound, organic-matter-bound, and residual fractions. EDTA desorption used 0.01 M EDTA at pH 7.0 over 5 to 1440 minutes, with Cd measured by atomic absorption spectroscopy.
Implications
Certification: This source supports mitigation and supply-chain soil-management evidence only. It does not measure coffee, food, beverage, or finished-product occurrence.
Courses: Strong example that amendment combinations can be matrix-specific: bentonite improved municipal-solid-waste biochar Cd immobilization but worsened the water-soluble/exchangeable fraction when combined with coffee-grounds biochar.
App: Context only; the spiked-soil values are not consumer-product concentrations.
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Verification notes
The DOI, title, author list, journal, and year were taken from the Scientific Reports PDF. The auto-fetched filename is a coffee/cadmium hit because coffee-grounds biochar is one tested amendment, but the target matrix is experimentally Cd-spiked soil. Products and ingredients are intentionally empty so spiked-soil and amendment-performance values do not enter occurrence-threshold calculations.
The matrices: slugs (calcareous-soil, coffee-grounds-biochar, municipal-solid-waste-biochar, bentonite, soil-remediation) are descriptive free-text outside the controlled food/personal-care matrices vocabulary, which is appropriate for a Cd-spiked soil-remediation study; with empty products: and ingredients: arrays, the routing layer correctly treats this source as remediation evidence only.
GPT audit (2026-06-09 autonomous) flagged “M + B2 carbonate-bound Cd 14.0 mg/kg” as a transposition of the 14.9 mean; verified against Table 3 (M+B2 cell = 14.0) and the page 6 source text (“the combined treatments of G + B0 (14.0 mg Cd kg-1) and M + B2 (14.0 mg Cd kg-1)”) — finding was a false positive because the auditor confused the M-column mean (14.9) with the M+B2 cell value (14.0).
Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and 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.