Sunlight-activated spray could protect crops and mitigate food shortages

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Scientists have formulated a sunlight-activated spray that could protect crops with minimal risk to humans. (AP Photo/Matias Delacroix)

European researchers are repurposing a material typically used in electronics to form a spray that prevents plant pathogens from ruining crops, a technique that could block humans from ingesting toxins and lessen the severity of food shortages worldwide.

Described in a paper published May 5 in the Journal of Photochemistry and Photobiology B: Biology, the method turns nano-sized, light-activated particles of zinc oxide — often used in semiconductors — into a spray with which farmers can layer crops. The researchers say the chemical poses minimal risk to humans while still killing bacteria and fungi that threaten the plants. 

"This technology is very universal," study author Zivile Luksiene, a professor at Vilnius University in Lithuania, told The Academic Times. "We successfully applied it on strawberries for preservation and protection from spoilage. We also used it on grains to protect them from microfungi. But this is far from everything it can be used for."

Luksiene noted that each year, approximately 15% of all cereal crops around the world are lost due to fungal contamination and deterioration — up to 50% in tropical regions. In developing countries, she stressed, over half of fresh produce becomes spoiled because of fungi. 

This all adds up to approximately $45 billion in crop losses annually, and as plants account for over 80% of human food consumption, losing crops to plant disease can heavily contribute to food shortages. In the 1940s, for instance, rice production in the region of Bengal in West India was reduced by up to 60% due to a fungal disease called Cochliobolus miyabeanus, or colloquially, brown spot. An estimated 3 million people died of starvation. 

In response, along with her team, the researcher has been working to find ways to prevent the pathogens from proliferating. Not only do they strain countries' food production, but also humans' health. Mycotoxins, natural toxins produced by fungi on many types of crops, can cause immunosuppression, neurological deficiencies and developmental issues for unborn babies, among other severe outcomes.

"More than 4.5 billion people are exposed to high levels of mycotoxins on a daily basis from food," Luksiene said. "There are more than 100 fungal species that can infect plants and produce mycotoxins."

She added that Fusarium spp, the most common and harmful species in Europe, has also been reported in the U.S. to contaminate wheat flour, the main wheat product.

The hazardous species of fungi, one that the U.S. Department of Agriculture is working to control, was inactivated on wheat crops by 51.7% when exposed to the novel spray and visible light. This prevention of fungi proliferation indicates that if farmers were to use the chemical on a bright and sunny day, crop production could be greatly enhanced. 

"I had a feeling that photocatalytic treatment has potential to protect us from harmful mycotoxins [and] fungicides and save the crops — and my research confirmed it," Luksiene said.

Further, because the chemical is sustainable and nontoxic to humans, Luksiene notes that it is a terrific alternative to current harmful plant protectants. According to the U.S. Environmental Protection Agency, some common pesticides can affect the nervous system, irritate the eyes or even cause cancer. 

A recent study also found that pesticide levels in U.S. waterways are toxic enough to endanger aquatic life, and a separate report found that the harmful chemicals are threatening pollinators, as well.

"In several studies, it was found that zinc oxide nanoparticles have high antimicrobial specificity, and only minimal effects have been observed on human cells," the researcher highlighted.

When the spray's active ingredient, zinc oxide, was first approved by the U.S. Food and Drug Administration to use in medicine, cosmetics and agriculture, it introduced the possibility of using zinc oxide for purposes beyond electronics. For instance, it's now widely used as a preservative in the linings of packaged food.

"Every physicist knows zinc oxide as an n-type semiconductor," Luksiene said. "But the secret of nature is that it gives several faces to most molecules."

The benefit of the team's spray stems from two features: It is based on nanoparticles, or very tiny particles, of zinc oxide, and the chemical is activated by ultraviolet and visible light, or sunlight. 

"Small particles have a larger surface area for interactions, [and] thus greater binding capacity to the microbial cell wall," Luksiene explained. "In sunlight, zinc oxide nanoparticles can produce a plethora of reactive oxygen species that kill pathogenic microorganisms."

While too little sunlight may not activate the particles, too much sunlight doesn't pose an issue, according to the research.

"The technology is really easy to maintain," she said. "The farmer just has to spray the zinc oxide nanoparticles on their harvest on a sunny morning."

Because the nanoparticles are able to offer a larger surface area with less resources, Luksiene said, the invention is cost-effective, too.

"Also," she continued, "zinc oxide has secondary benefits on soil fertility and plant growth, which is extremely important from an ecological point of view."

The study, "Visible light-activated ZnO nanoparticles for microbial control of wheat crop," was published May 5 in the Journal of Photochemistry and Photobiology B: Biology, was authored by Bernadeta Zudyte and Zivile Luksiene, Vilnius University.

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