Cacao Yes - Cadmium No

Introduction

The cacao plant (Theobroma cacao L.) is a cadmium accumulator and can accumulate cadmium from the soil - especially in the cacao beans. Through regular consumption of cacao products, consumers can ingest considerable amounts of cadmium over the years and thereby damage their health due to the chronic toxicity of cadmium.

As a preventive health protection, maximum levels for cadmium were specified in the EU by Regulation (EC) No. 1881/2006 for cacao products, which became valid from 01.01.2019. The amount depends on the type of cacao product. For example, cacao powder may contain a maximum of 0.6 milligrams of cadmium per kilo of cacao powder.

Cacao beans from Latin America are particularly contaminated. In most cases, an increased cadmium content is geogenic and goes back to the naturally cadmium-rich volcanic soils of South America.

For the smallholders who grow cacao, cadmium levels in their cacao beans can be an economic problem. They earn less income with contaminated cacao.

Starting position

Acanchia cooperates with small cacao farmers in Peru in the Junin province in the VRAEM region on the Rio Ene. The cadmium content of cacao beans was determined by around 40 small farmers. The cadmium values fluctuated between 0.15 and 0.87 mg Cd/kg cacao beans. About 1/3 of the samples had a Cd content of less than 0.38 mg Cd/kg cacao beans and are therefore particularly suitable for the production of low-cadmium cacao powder (Cd values less than 0.6 mg Cd/kg). On the basis of the cadmium values found in the investigation area, it can be determined that the cacao beans are indeed contaminated with cadmium and are for the most part not suitable for the production of low-cadmium cacao powder, but that the cacao beans here are not heavily contaminated with cadmium. Cacao beans with cadmium levels above 1 mg Cd/kg are common in Northern Peru and Ecuador.

Experiment

In order to check suitable measures to reduce cadmium, 8 small farmers were selected, each of whom set up a test field measuring 20 x 20 m

Trial fields for cadmium reduction in cocoa beans

These test fields were divided into 4 small fields (10 x 10 m). Samples of fermented and dried cacao beans were obtained from these small fields at the beginning of the experiment after 6 months and one year. The sample size was 500 g of cacao beans in each case. Various possible measures were tested on these small fields, which are potentially able to reduce the cadmium content in the cacao beans. These measures include removing the cacao leaves that have fallen from the cacao trees from the ground and disposing them in a separate depot. The background to this measure is that cadmium is also accumulated in cacao leaves. By removing these cacao leaves, cadmium should be removed from the cycle. The phytoremediation or phytomediation process aims into the same direction. Here, the soils contaminated with cadmium are rehabilitated with the help of plants that accumulate the cadmium and thus remove it from the soil. Spinach was selected as the model plant for phytoremediation. The third method used was the liming of the soil around the cacao trees. Liming increases the acidity of the soil. The uptake of cadmium by plants depends on the pH of the soil. As a rule, the higher the pH value of the soil, the lower the cadmium uptake by the plants.

Liming of a small trial field to reduce cadmium in cocoa beans

Based on these considerations, the small-scale test fields were divided as follows:

•     blind test (leave cacao leaves lying)
•     remove leaves + phytomediation (spinach)
•     leave the cacao leaves lying around + liming
•     remove leaves + liming + phytomediation (spinach)

In addition, soil samples were taken from the test fields from different depths (0 - 50 cm). The degree of acidity and the Cd content were determined in these soil samples.

Result of the experiments to reduce cadmium in cocoa beans

Sample preparation on a small-scale test field for the determination of cadmium in cacao beans

Liming increases the acidity of the soil around the cacao trees. The assumption that the cadmium uptake in the cacao beans decreases as a result of the increase in the pH value was confirmed in experiments with liming on the soil. Within 6 to 12 months, the cadmium level in cacao beans was reduced significantly by an average of 0.2 mg cadmium/kilogram cacao beans.

As a result, approx. 47% of the cacao beans are now suitable for the production of low-cadmium cacao powder.

In the attempts to reduce cadmium by removing the cacao leaves, a slight trend towards cadmium reduction emerged after 1 year, but this is not significant. This method needs further investigation. If so, the removal of the cacao leaves leads to a long-term reduction in cadmium in the cacao beans for a period of more than a year.

The attempt of phytomediation with the help of spinach plants was a failure. The spinach plants were not viable under the tropical conditions. They germinated, but were then destroyed by fungus and other microorganisms. Phytomediation experiments must be carried out with other potential vegetable accumulators.

The examination of the cadmium content of the soil samples did not reveal any useful correlation between the cadmium content in the soil and the cadmium content in the cacao beans. This will be due to the fact that the cadmium uptake by the plant depends on many factors. The factors are e.g. the cadmium content in the soil, the content of freely available and bound cadmium, the content of antagonists of cadmium such as zinc and the acid content.

Pilot test

With the improved cultivation to reduce cadmium and together with an intensive cadmium mapping of the cacao farmers, it is possible to improve the sourcing in particular of cacao beans with a low cadmium content and in sufficient quantities for cacao powder production. With the developed and established methodology, cacao powder that is low in cadmium can be produced on a large scale.

Summary

By liming the soil around the cacao trees, the cadmium content of cacao beans can be reduced by approx. 0.2 mg Cd/kg cacao beans within one year. This means that a significantly larger proportion of the cacao grown can be used for the production of low-cadmium cacao powder. The increase in usable cacao beans by approx. 50%. It is essential to closely monitor the cadmium levels of the individual growers in order to sort out the suitable cacao beans.

Acknowledgments: We would like to thank the DEG for the financial support, our cooperation partner in Peru for the on-site support and the smallholders for the disciplined execution of the cultivation trials and the conscientious application of the improved cultivation methodology.