Cadmium mapping would aid Colombian cocoa producers

Cacao is one of Colombia’s most important crops. People in Colombia consume much of the crop, and it also generates more than $13 million in annual exports from the cacao beans, and cocoa, the processed form. Yet Colombia’s cacao beans often contain cadmium levels that surpass international limits, creating barriers for local producers.

To address this issue, a group of scientists mapped the distribution of cadmium concentrations in the soil and beans of the country’s main cacao-producing regions, including the areas where the beans showed high or low concentrations of the metal. The scientists published their findings in Science of the Total Environment (2024, DOI: 10.1016/j.scitotenv.2024.176398).

They found an average of 2.17–2.71 mg of cadmium per kilogram of cacao in the farms they studied, which means much of the crop exceeds the European Union’s limit of 0.8 mg of cadmium per kilogram. “Decision-makers in the government can use the map as a guide to determine where to improve strategies to correct or mitigate cadmium levels,” says Daniel Bravo, a geomicrobiologist at Agrosavia and lead author of the paper.

Two research groups used inductively coupled plasma mass spectrometry and atomic absorption spectrometry techniques to analyze cadmium levels in dry, peeled cacao beans from the most productive cacao-producing regions in Colombia.

Researchers also analyzed the soil’s chemical composition. They studied soil properties such as acidity, along with the levels of nutrients and minerals like calcium, potassium, and magnesium. In addition, they looked at the makeup of the soil based on age, rock types, and concentration of 57 elements, including cadmium, to see how the soil’s composition and origin might relate to its cadmium level. Cacao plants tend to absorb more cadmium from soil than other plants.

The metal is found all over the world, but its concentrations can be high in Latin American soils because of the region’s volcanic activity, mineral-rich soils, and metal deposits. But it wasn’t until 2019, when the European Union started regulating the limits of cadmium in cacao products, that the metal’s presence became an economic issue for Colombia and other Latin American countries.

“In all the previous research work that has been done in other countries, the number 1 cause [of cadmium] is the soil,” says Rachel Atkinson, an associate scientist at Bioversity International who wasn’t involved with the research but worked on a similar map in Peru.

Neither Bravo nor Atkinson consider the levels measured in the study to be hazardous to health. “Although cocoa as a plant accumulates a lot of cadmium, it is difficult to imagine that many people eat enough cocoa or drink enough chocolate to cause cadmium toxicity,” Atkinson says. But toxicological studies are needed in the region to know in detail the impacts of that cadmium, since much of Colombia’s cocoa is processed for domestic consumption.

Colombia has no official limits on cadmium, and many producers lack of awareness about both the metal’s presence in the crops and the international limits.

Bravo hopes that identifying hot and cold spots of cadmium in Colombian soils and crops can be used to create targeted interventions—for example, using bioremediation, which involves deploying cadmium-tolerating bacteria to help clean up the soil, or mixing cacao beans with lower levels of cadmium with those with higher concentrations to balance a batch’s average cadmium level. Bravo is currently working on other research that analyzes cadmium levels in fertilizer.

Ultimately, some amount will always be in the soil, Bravo says, but that doesn’t mean people should stop producing or consuming cacao from the region. “Cocoa production is of great economic relevance for the country, but it also has a social and cultural importance.”