Lopez et al. 2022 - biochar mitigation of cadmium uptake in cacao
Lopez and colleagues tested whether biochars made from coffee husk, quinoa straw, and oil palm residues could reduce bioavailable Cd in cacao-growing soils and Cd uptake into cacao plants. This is crop-mitigation evidence for cacao supply chains, not finished chocolate or cocoa-powder occurrence evidence.
Key numbers
The study used two cacao-farm soils where elevated cacao-bean Cd had previously been reported. The slightly alkaline soil had pH 7.30 and came from Manabi province; the moderately acidic soil had pH 5.52 and came from Azuay province. The authors state that cacao beans at both farms exceeded the 0.60 mg/kg Cd trading threshold used for EU chocolate-market access. Baseline pseudo-total soil Cd was 0.57 +/- 0.06 mg/kg in the slightly alkaline soil and 0.61 +/- 0.12 mg/kg in the moderately acidic soil; after Cd spiking, the corresponding averages were 1.38 +/- 0.44 mg/kg and 1.64 +/- 0.14 mg/kg.
The abstract reports that quinoa biochar at 2% reduced bioavailable Cd by about 71% across moderately acidic and slightly alkaline soils and lowered leaf Cd by about 48%. The highlights describe up to 80% reduction in bioavailable Cd and up to 48% reduction in cacao-plant Cd.
Table 2 reports 130-day greenhouse values. In non-spiked moderately acidic soil, the control had CaCl2-Cd 80.1 +/- 1.9 ug/kg, NH4OAc-Cd 185 +/- 3 ug/kg, HCl-Cd 529 +/- 28 ug/kg, and leaf Cd 4.6 +/- 1.0 mg/kg. Quinoa biochar at 2% lowered those to CaCl2-Cd 22.9 +/- 1.3 ug/kg, NH4OAc-Cd 92.7 +/- 10.9 ug/kg, HCl-Cd 519 +/- 30 ug/kg, and leaf Cd 2.6 +/- 0.1 mg/kg.
In Cd-spiked moderately acidic soil, the control had CaCl2-Cd 246 +/- 38 ug/kg, NH4OAc-Cd 568 +/- 12 ug/kg, HCl-Cd 1454 +/- 19 ug/kg, and leaf Cd 13.9 +/- 1.1 mg/kg. Quinoa biochar at 2% lowered those to CaCl2-Cd 54.3 +/- 14 ug/kg, NH4OAc-Cd 298 +/- 8 ug/kg, HCl-Cd 857 +/- 10 ug/kg, and leaf Cd 6.4 +/- 0.6 mg/kg.
In Cd-spiked slightly alkaline soil, the control had CaCl2-Cd 19.7 +/- 1.3 ug/kg, NH4OAc-Cd 200 +/- 5 ug/kg, HCl-Cd 828 +/- 19 ug/kg, and leaf Cd 4.6 +/- 0.3 mg/kg. Quinoa biochar at 2% lowered those to CaCl2-Cd 4.9 +/- 0.6 ug/kg, NH4OAc-Cd 137 +/- 3.3 ug/kg, HCl-Cd 801 +/- 12 ug/kg, and leaf Cd 3.9 +/- 0.0 mg/kg.
Table 3 reports reduction factors for soil Cd pools. Quinoa biochar at 2% had CaCl2-Cd reduction factors of 4.1 +/- 0.5 in spiked slightly alkaline soil, 3.5 +/- 0.2 in non-spiked moderately acidic soil, and 3.7 +/- 0.3 in spiked moderately acidic soil. For NH4OAc-Cd, the corresponding reduction factors were 1.5 +/- 0.0, 2.1 +/- 0.3, and 1.9 +/- 0.1.
Methods (brief)
Biochars were produced in Ecuador by Bioenergia de los Andes using a modular auger reactor. Coffee husk biochar and quinoa straw biochar were produced at 550 C; oil-palm-residue biochars were produced at 600 C, including one commercial inoculated palm-residue biochar. Each biochar was incorporated into soils at 1% or 2% dry weight, with unamended controls.
The soils were equilibrated, split into natural-Cd and Cd-spiked treatments, and then planted with CCN-51 cacao under greenhouse conditions. Bioavailable Cd was assessed with CaCl2, NH4OAc, and HCl extractions; pseudo-total Cd and nutrients were measured by ICP-OES after aqua regia digestion. The greenhouse endpoint was 130 days.
Implications
Certification: Use as mitigation and supply-chain-control evidence for cacao/cocoa sourcing. Do not admit the greenhouse leaf-Cd or spiked-soil values into cocoa, chocolate, coffee, quinoa, or palm-oil occurrence pools.
Courses: Strong example of a pre-harvest intervention where amendment choice matters: quinoa biochar at 2% consistently outperformed coffee, palm, and inoculated palm biochars for lowering bioavailable Cd.
App: Context only. The paper does not measure finished consumer foods or ingredients as sold.
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Verification notes
The DOI, title, author list, journal, and year were taken from the Heliyon PDF. The auto-fetched filename is a coffee/cadmium gap hit because coffee-husk biochar is one tested amendment, but the target matrix is cacao-growing soil and cacao leaves. Products are intentionally empty; the routeable value is mitigation performance, not finished chocolate or cocoa occurrence.
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.
| Commit | Date | Description |
|---|---|---|
| 4039d20 | 2026-06-10 | scope: broaden ingest to the full upstream+downstream literature (marine, atmospheric, attribution, exposure, toxicology) — inclusion is the default |