Overview
This field experiment tested three biological and organic mitigation strategies for reducing Cd uptake in cocoa beans in Huánuco, Peru — a region where soil Cd is elevated (0.78 mg/kg total) and baseline bean Cd (1.07 mg/kg) substantially exceeds the EU maximum permissible level (0.8 mg/kg for chocolate with ≥50% cocoa solids). Arbuscular mycorrhizal fungi (AMF) applied alone reduced bean Cd concentration by 40.43%; Callisia repens (a herbaceous competitor plant) applied alone reduced bean Cd by 30.85%; their combination achieved a 24.47% reduction; biochar at 1% and 2% w/w did not produce statistically significant effects. Critically, Cd concentrations still exceeded EU limits under all treatment conditions after six months, indicating that these strategies alone cannot bring a highly contaminated site into compliance within a single growing season.
Key numbers
Site soil Cd: 0.78 mg/kg total (Huánuco region, 671 m elevation, 9°12’25” S, 75°56’17” W) Baseline bean Cd: 1.07 mg/kg (control, genotype CCN51)
Bean Cd under each treatment (mg/kg, six months post-establishment):
- Control: 1.07 (baseline)
- AMF alone: 0.56 (40.43% reduction, p < 0.01)
- C. repens alone: 0.74 (30.85% reduction, p < 0.01)
- AMF + C. repens: 0.81 (24.47% reduction, p < 0.01)
- Biochar 1%: not significantly different from control
- Biochar 2%: not significantly different from control
Soil available Cd (EDTA extraction, 0.19–0.21 mg/kg): AMF, C. repens, combination, and 2% biochar all reduced available Cd relative to control; total soil Cd unchanged across all treatments (p = 0.19).
EU limit reference: 0.8 mg/kg Cd for chocolate products containing ≥50% cocoa solids (European Commission Regulation No 488/2014)
Methods (brief)
Randomised complete block design, 3 blocks, 30 trees per block, 90 trees total (CCN51 genotype, 8 years old). Cd extracted from beans using HNO₃/HClO₄ digestion; quantified by ICP-OES. Available soil Cd by 0.05M EDTA extraction at pH 7.0; measured by AES. Lab accredited by INACAL, Peru. Statistical analysis in R Studio 4.0.2; ANOVA + LSD test (α = 0.05).
Limitations
Single site, single growing season (6 months), single genotype (CCN51). No baseline soil or bean Cd values were available for individual plots before treatment establishment; initial Cd content differences among plots cannot be ruled out. The study is conducted on soil with pre-existing high Cd; applicability to lower-Cd sites is not assessed. Biochar results (non-significant) may reflect insufficient exposure time or quantity.
Implications
- Certification: Confirms that even 40% Cd reduction from AMF does not bring a contaminated Peruvian site within EU regulatory limits. This is evidence that supply-chain screening (excluding high-Cd-soil origins) is more reliable than field mitigation alone for achieving ≤0.8 mg/kg Cd thresholds.
- Courses: Useful case study for the “mitigation options” module on cocoa Cd — demonstrates what biological strategies can and cannot achieve in a single season. Biochar result is notable: widely recommended but here not significant.
- App: Does not change baseline contamination_profile values for cocoa; this is a mitigation study. Flag for cocoa-cadmium page.
Related evidence
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