Soil, Site, and Management Factors Affecting Cadmium Concentrations in Cacao-Growing Soils

Overview

This study assessed cadmium concentrations in cacao-growing soils across four major agricultural regions of Peru (Madre de Dios, Ucayali, San Martin, and Amazonas) to identify the soil, site, and management factors that drive Cd accumulation in plantation soils. Forty sites with contrasting climates were sampled, with a broad range of potential factors evaluated at each site. Cadmium concentrations in soils ranged from 1.1 to 3.2 mg/kg, with all regional means below 2.7 mg/kg, the commonly used upper limit for non-polluted soils. Cadmium was significantly higher (p < 0.001) at higher elevations and in temperate, drier climates, and correlated positively with soil pH (r = 0.57; p < 0.05). Soil type was a strong predictor: alluvial sediments and Leptosols had significantly higher Cd. Management factors, including cacao variety, cultivation year, use of fertilizers, and agroecological practices, did not independently affect soil Cd concentrations.

Key numbers

Cd range across all 40 sites: 1.1–3.2 mg/kg (1,100–3,200 ppb). Regional means all below 2.7 mg/kg. Pearson correlation: Cd and pH r = 0.57 (p < 0.05); Cd and elevation r = 0.40 (p < 0.05). Year of cultivation showed r = 0.56 (p < 0.01) with pH (more recently planted fields more acidic), but management factors did not show direct Cd correlation. Soil type alluvial sediments and Leptosols significantly higher (p < 0.001). Regions: Madre de Dios (MD, n=12), Ucayali (UC, n=8), San Martin (SM, n=7), Amazonas (AM, n=13). Sampling period: November–December 2014. Analytical method: total Cd by EPA-3015A microwave extraction, AAS (EPA 700 B:2007), detection limit 0.2 mg/kg.

Methods (brief)

40 sites in four Peruvian regions, 8 subsamples per site from 100 m² area, surface layer 5–30 cm depth. Composite samples (n=40) sent to Mac-Minoprio analisi e Certificazioni s.r.l., Italy. Total Cd by EPA-3015A microwave extraction, AAS (Perkin Elmer). Soil pH in 1:2.5 water suspension. Agroecological function (AEF) scored per Norris (2006). Pearson correlations, statistical significance at p < 0.05 and p < 0.01.

Limitations

Soil Cd is reported; bean Cd is not measured in this study (a companion study covers that). Analytical detection limit of 0.2 mg/kg is high relative to the range of values — some samples near the lower bound may be imprecise. Single sampling window (November–December 2014) precludes seasonal variance assessment. Management factors are self-reported by farmers.

Implications

• Certification: Establishes that Peruvian cacao-growing soils span 1,100–3,200 ppb Cd, with elevation, pH, and soil type as the primary natural drivers rather than management practices. This is critical context for the HMT&C cacao source-region risk framework: Andean-region and higher-altitude Peruvian cacao will systematically carry higher soil Cd. EU Regulation 488/2014 thresholds (600 ppb in beans, 800 ppb in powder) were set partly in response to this geographic pattern.
• Courses: Demonstrates the geological and climatic origins of Cd elevation in cacao soil — contrasting with anthropogenic industrial sources — and why supply-chain provenance tracking is the primary mitigation tool rather than farm management.
• App: Geographic_breakdown for Cocoa Cd should include Peru regional soil Cd context. Alluvial/Leptosol soil types and higher elevation correlate with higher Cd; this informs the regional risk flag for Peruvian fine-flavor (single-origin) cacao.
• Microbiome: Not applicable.

Wiki pages updated on ingest

• Cocoa
• Cadmium
• soil-contamination

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