Soil is a source of food contamination

A new study from the American Society of Agronomy has investigated sources of food contamination in the soil. According to Professor Angelia Seyfferth, it all comes down to the soil’s chemistry. 

For her latest research, Professor Seyfferth has been studying rice. She reports that the elements arsenic and cadmium are often present in the paddies where rice is grown. 

“Contaminants being taken up by crop plants is a route of dietary exposure to contaminants that is understudied,” said Professor Seyfferth. “We can help decrease human exposure to toxins by applying our knowledge of soil chemistry.”

Small amounts of arsenic and cadmium are present in many food products. In fruits and vegetables, the elements can pose a threat to human health depending on their levels of concentration and how much of the contaminated food an individual eats. 

Arsenic and cadmium are harmful to the body in high concentrations, and can even cause cancer over time. These elements are found in different chemical forms depending on their environment. If a contaminant in the soil resembles a nutrient, it is likely to be taken up by plants growing in the soil. 

“How food is grown affects not only the concentration of contaminants, but also where the contaminants are stored within the food,” explained Professor Seyfferth. “If we understand the chemical forms of contaminants in soil, we can design solutions to decrease plant uptake of them.”

When it comes to rice, arsenic can be taken up when the field is flooded, while cadmium is more likely to be taken up when the field is not flooded. 

Professor Seyfferth has been searching for a way to prevent plants from taking up arsenic and cadmium. One method that can be used is adding materials to the soil, called amendments. By using these materials, researchers can help control the chemical forms and plant uptake of contaminants in the soil.

In the current study, Professor Seyfferth found that adding rice husk residue to rice paddy soils can help lower the amount of arsenic and cadmium absorbed by plants. 

Rice husk residue is high in the element silicon, which is an important nutrient for rice. The chemical form of silicon is similar to the form of arsenic taken up by rice plants when fields are flooded. Rice husk residue also makes the soil less acidic, which can help lock up cadmium so that it is not readily available.

“Not all sources of silicon behave the same way though,” said Professor Seyfferth. “In order for it to be effective, the silicon source must provide silicon in a high enough concentration during the time the rice plant is filling grain. Rice husk residue is a successful source because it breaks down slowly and releases silicon throughout the growing season.”

The study showed that adding rice husk residues can also help prevent yield loss. Considering that half of the world depends on rice as a staple food, the research has great potential.

For most American adults, the amount of arsenic and cadmium they consume from rice is not enough to cause concern. However, there are other populations that eat these products more frequently.

“People need to be aware of their daily load of contaminants, which depends on their body weight, the concentration and chemical form of the contaminant in the food, and the amount consumed,” said Professor Seyfferth.

“The daily load is highest for people who consume rice multiple times a day and who may also have arsenic in their drinking water. Some examples include populations in South and Southeast Asia.”

The study was supported by the National Science Foundation, the National Institute of Food and Agriculture, and the University of Delaware. 

The research was presented at the 2020 ASA-CSSA-SSSA Annual Meeting.

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By Chrissy Sexton, Earth.com Staff Writer