Ramtahal et al. 2016 — Cd in cacao tissues and soils across 45 plantations in Trinidad and Tobago
Ramtahal et al. measured cadmium in leaves, pod husks, shells, and nibs (beans) of cacao plants, and in corresponding soils, from 45 plantations spanning all seven major soil types (I–VII) across Trinidad and Tobago. The study evaluated whether Cd levels in readily accessible tissues (leaves, pods) could predict Cd in beans (nibs), which would allow screening without waiting for harvest. A wide range of cultivars was sampled, giving the correlations broad applicability.
Cd levels in cacao tissues varied in the order: leaves (0.54–5.21 µg/g) > pods (0.53–4.49 µg/g) > shells (0.44–4.41 µg/g) > nibs (0.35–3.82 µg/g). Soil total extractable Cd ranged 0.3–1.7 µg/g. All inter-tissue correlations were statistically significant (p < 0.05) and strongly positive: nib/shell r = 0.86, nib/leaf r = 0.79, nib/pod r = 0.76, shell/leaf r = 0.83, shell/pod r = 0.68, leaf/pod r = 0.80. Nib-to-soil correlations were weaker but significant: nib/soil r = 0.35, shell/soil r = 0.43. This suggests that leaf and pod Cd can serve as practical predictors of bean Cd, enabling pre-harvest screening of farms and cultivars for Cd compliance before beans are harvested and sold.
Key numbers
- 45 plantations, 7 soil types, Trinidad and Tobago
- Cacao nib (bean) Cd: 0.35–3.82 µg/g dry weight (mean not given in text; values across soil types)
- Cacao leaf Cd: 0.54–5.21 µg/g dry weight
- Soil total HNO₃-extractable Cd: 0.3–1.7 µg/g
- Nib-shell correlation: r = 0.86 (p < 0.05)
- Nib-leaf correlation: r = 0.79 (p < 0.05)
- Nib-soil correlation: r = 0.35 (p < 0.05)
- Method: FAAS; HNO₃ digestion for tissues and soils; QC with NIST SRM 1570a (Spinach Leaves, 95.5% recovery) and SRM 2710 (Montana Soil, 99.0% recovery)
Implications
Certification: Trinidad and Tobago cacao nib Cd up to 3.82 µg/g exceeds the EU maximum level for cocoa beans (0.30 mg/kg as of Regulation 488/2014 amendment period). The leaf/pod pre-harvest screening approach could be a cost-effective audit tool for supply chain Cd risk assessment. Courses: Illustrates the soil-plant Cd pathway in cacao; the weak soil-nib correlation (r = 0.35) suggests that total soil Cd is a poor predictor — bioavailable Cd matters more — consistent with findings from Ecuador studies. App: Trinidad and Tobago is a secondary high-Cd cacao origin (lower volume than Ecuador/Peru but with documented exceedances).