SOILS PhD Student's Research Highlights Cadmium Contamination in Cacao Farms and Proposes Management Strategies

The two studies, focused on farms in the Piura region of northern Peru and the Sierra Nevada de Santa Marta (SNSM) region of northern Colombia, identify sources of cadmium contamination and explore strategies to mitigate its accumulation in cacao plants.

The Challenge of Cadmium in Cacao Farming

Cadmium, a toxic heavy metal, accumulates in cacao plants and poses significant health risks when consumed through chocolate, the primary product derived from cacao beans. Both studies revealed that cadmium concentrates primarily in the leaves of cacao trees, followed by the beans and soil, raising concerns for farmers in Latin America, where cacao is a vital crop.

The European Union's strict limits on cadmium in chocolate products exacerbate the economic challenges faced by cacao producers, potentially threatening their access to international markets. This is particularly concerning in Peru, where cacao production has expanded significantly, and in Colombia, where cacao farming serves as a key component of illegal crop replacement programs.

Key Findings: Sources of Cadmium

Guarin's studies investigated both natural and human-induced sources of cadmium contamination:

• Geogenic Sources: The Peruvian study found that alluvial soils and stable topographic positions had higher cadmium levels, likely due to sediment and water transport. In Colombia, the parent material, particularly sedimentary rocks, influenced soil cadmium concentrations.
• Anthropogenic Sources: Fertilizers, including bird guano, were identified as significant contributors to cadmium accumulation in Peru. In Colombia, geogenic sources and soil properties were the dominant factors, with fertilizer use playing a less pronounced role.

Management Strategies to Combat Cadmium Contamination

The research emphasizes the need for a multifaceted approach to reduce cadmium levels in cacao farms:

1. Soil Testing: The Mehlich 3 soil test offers a cost-effective method for initial cadmium screenings, as demonstrated in Peru.
2. Fertilizer Management: Using fertilizers with low cadmium content and limiting continuous application are critical to mitigating contamination.
3. Litter Management: Removing litter layers, although challenging, could reduce cadmium recycling in soils.
4. Soil Amendments: Techniques such as liming and biochar application can immobilize cadmium, reducing its mobility.
5. Phytoremediation: Employing plants to extract or immobilize cadmium offers a promising remediation strategy.
6. Cultivar Selection and Grafting: Selecting cacao varieties with lower cadmium uptake or grafting high-yield varieties onto low cadmium-accumulating rootstocks may lower contamination levels.
7. Cooperative Dilution: Farmer cooperatives can dilute high-cadmium beans with low-cadmium ones to meet regulatory limits.

Broader Implications for Cacao Farming

These studies shed light on the complex interplay of geological, biological, and anthropogenic factors contributing to cadmium contamination. They provide actionable insights for farmers, cooperatives, and policymakers to develop sustainable solutions that balance economic viability with environmental and health concerns.

Guarin's research, funded by the USDA USAID/Penn State Cacao for Peace project, and with collaboration from Universidad Nacional de Ingeniería (UNI), Lima, Perú, USDA-NRCS and CIAT in Colombia, underscores the importance of collaboration among stakeholders to address the challenges posed by cadmium contamination and ensure the long-term sustainability of cacao farming in Latin America.

Papers:

Guarín, D., Martín-López, J.M., Libohova, Z., Benavides-Bolaños, J., Maximova, S.N., Guiltinan, M.J., Spargo, J., Da Silva, M., Fernandez, A. and Drohan, P., 2024. Accumulation of cadmium in soils, litter and leaves in cacao farms in the North Sierra Nevada de Santa Marta, Colombia. Geoderma Regional, 36, p.e00762.

Guarín, D., Hamamura, N.R., Cortez, J.B., Benavides, J., Spargo, J., Guiltinan, M., Maximova, S., de la Cruz, O.A. and Drohan, P.J., 2023. Cadmium contamination in cacao farms of Piura, North Peru: A comprehensive assessment of geogenic and anthropogenic sources and implications for future production. Environmental Challenges, 13, p.100765.

For further details about the research, contact Dr. Patrick Drohan at pjd7@psu.edu