How much cadmium is contained in cocoa beans?

Cocoa beans can absorb toxic heavy metals such as cadmium from the soil. Some cultivation areas, especially in South America, are polluted with these heavy metals, in some cases considerably. In combining different X-ray fluorescence techniques, a team at BESSY II has now been able to non-invasively measure for the first time where cadmium accumulates exactly in cocoa beans: Mainly in the shell. Further investigations show that the processing of the cocoa beans can have a great influence on the concentration of heavy metals.

People have been harvesting the beans of the cocoa bush for at least 5000 years. They have learned to ferment, roast, grind and process the beans with sugar and fat to make delicious chocolates. Today, around five million tonnes of beans are on the market every year, coming from only a few growing areas in tropical regions.

Soul food chocolate

Chocolate is considered a soul food: amino acids such as tryptophan brighten the mood. Cocoa beans also contain anti-inflammatory compounds and valuable trace elements. However, cocoa plants also absorb toxic heavy metals if the soils are polluted, for example by mining, which can gradually poison groundwater and soils.

Where do the toxic elements accumulate?

An important question is,  where exactly the heavy metals accumulate in the bean, whether rather in the shell or rather in the endosperm inside the bean. From the harvest to the raw material for chocolate, the beans undergo many steps of different treatments, which could possibly reduce the contamination. And ideally the treatment could be optimised in order to make sure that the heavy metals are reduced but the desirable trace elements are retained.

Mapping the beans at BESSY II

A team led by Dr. Ioanna Mantouvalou (HZB) and Dr. Claudia Keil (TU Berlin/Toxicology) has now combined various imaging methods at the BAMline of BESSY II to precisely map the heavy metal concentrations in cocoa beans. They examined cocoa samples from a cultivation region in Colombia, which were contaminated with an average of 4.2 mg/kg cadmium. This is well above the European limits of 0.1-0.8 mg cadmium/kg in cocoa products.

Read more on the HZB website

Image: Cocoa beans are the main ingredients of chocolate, a famous “soul food”. However, cocoa plants also absorb toxic heavy metals if the soils are polluted. At BESSY II, a team has now mapped the local distribution of heavy metals inside the beans.

Credit: © AdobeStock

Metal pollutants cause metabolic alterations in algae

Contamination by metals like cadmium or mercury is considered a serious threat to the environment and human health. Several human activities such as mining, metallurgy industry, and extensive use of mineral fertilizers are the main sources of ongoing metal pollution in numerous ecosystems. This environmental risk is potentiated by bioaccumulation and trophic chain biomagnification phenomena, which are associated with the long persistence of toxic metals in the polluted ecosystems. Aquatic and soil ecosystems affected by runoffs loaded with toxic metals are particularly vulnerable, where primary producers photosynthetic organisms (phytoplankton and soil microalgae) represent the first stage of pollution build-up. Knowledge about mechanisms of toxicity in these organisms is essential for appropriate assessment of environmental risks.

Researchers from the Plant Physiology Laboratory of the Department of Biology, also affiliated with the Research Centre for Biodiversity and Global Change, at the Autonomous University of Madrid (UAM), have discovered the major changes of biomolecules caused by cadmium and mercury in the model green microalga Chlamydomonas reinhardtii.

The use of synchrotron technology at MIRAS beamline was a valuable tool and has made it possible to analyze in detail variations in the biomolecular pattern caused by heavy metals at levels of resolution rarely described before. “Among the cellular components that readily changed upon metal treatments, we detected alterations in the lipid composition by synchrotron light infrared spectroscopy at ALBA, which corresponded to accumulation of neutral lipids and increased fatty unsaturation” specifies Ángel Barón, scientist at UAM.

Read more on the ALBA website

Image: Electron transmission microscopy of Chlamydomonas reinhardtii cells to show alterations caused by cadmium and mercury. The pyrenoid (p) looks aberrant, with proliferation of lipid vesicles (green arrowhead) and starch grains (s). Metals also triggered the appearance of autophagy vesicles (red arrowhead). Right: image of Chlamydomonas reinhardtii 

Credit: image of Chlamydomonas reinhardtii  Wikimedia Commons.