Heavy Metal and Chocolate: Not the Best Pairing  



  • Next Generation Crops

Almost every living organism on earth requires the element iron to carry out fundamental processes. For humans, iron binds to hemoglobin proteins found in our blood and is critical for transporting oxygen throughout our bodies, giving blood that characteristic bright red color. For plants, iron is crucial for photosynthesis–the process of converting sunlight into food for plants and for people.

I study Theobroma cacao, the plant that produces a seed that, when fermented, becomes cocoa, the raw ingredient for one of the most popular treats in the world: chocolate. Unfortunately for cacao and chocolate lovers around the world, a rogue element is “passing” as iron and entering the plants’ root system, damaging its health and accumulating in the seeds. The culprit is cadmium, a non-essential heavy metal and an environmental toxin. In a sense, cadmium is like an evil twin to biologically important metals, appearing just enough like them to slip past transport proteins that are meant to be selective, only allowing in what is needed. Once inside the plant, cadmium disrupts cacao’s

fine-tuned biological processes, causing cellular damage.

Cadmium is as equally destructive to humans as it is for plants and has a bad habit of sticking around in our bodies for decades. Over time, cadmium can accumulate in the kidneys and liver to toxic levels and can cause bone demineralization, kidney failure and in extreme cases, death. Because the most common source of cadmium exposure is through the consumption of cadmium-contaminated foods, the European Union (EU) recently enacted maximum allowable limits for cadmium in food, specifically products made with cacao. With the EU representing half of global chocolate consumption, the negative impacts of the regulation are threatening the livelihoods of numerous producers, many of whom are smallholder farmers in Latin American and Caribbean countries.

2018 FFAR Fellow, Zachary Dashner

Research is actively underway to create immediate and long-term solutions to reduce cadmium accumulation in cacao beans to meet the EU standards. Under the direction of my advisor Dr. Erin Connolly and in collaboration with the Guiltinan-Maximova Lab at Pennsylvania State University, our research group is seeking to identify iron and zinc transport proteins involved in the root uptake of cadmium. Thinking of the transport proteins as near-sighted bouncers at an exclusive club, we want to improve the “vision” of these proteins so that they can better distinguish “good iron” from its evil twin, “bad cadmium”. To do this, we are testing how modifications to the recognition region of the transporter affect selectivity, a process which would be like an ophthalmologist having their patient try on different prescription glasses until they obtain 20-20 vision. Once these proteins can properly see, they can continue letting iron enter and keep cadmium outside on the curb.

We hope our work will support plant breeders who are actively trying to develop low cadmium-accumulating varieties of cacao.  The development of these varieties has important implications for the livelihood of producers and the wellbeing of consumers.

I am thrilled to work with my FFAR Fellows industry sponsor, Mars Wrigley Confectionery. Through the mentorship of Dr. David MacKill, Senior Director of Genetics and Breeding, I am learning the importance of a work-life balance. As an FFAR Fellow, I have acquired essential skills that prepare me for the scientific workforce and have made lasting interpersonal relationships with colleagues. I look forward to graduating soon and pursuing a plant breeding position where I can make a difference to the sustainability of the food system and to food security.

Diagram of cacao cadmium uptake

More about Zachary Dashner

2018-2021 FFAR Fellow

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