Heavy Metal Contamination is Turning Green Leafy Vegetables Purple

Although not visible to the naked eye, leafy greens can be observed with sophisticated hyperspectral imaging turning purple (different than purple varieties of some vegetables).

This color shift was identified in cadmium-stressed kale and basil by Purdue researchers. Cadmium is a heavy metal that is hazardous to humans and animals.

(Photo : Bigstock)

Breakthrough

The breakthrough detection approach promotes efforts to develop a soil amendment that binds to the metal and keeps it away from plants, enhancing food safety in produce, baby food, and ready-to-eat meals.

"It's difficult to perceive heavy metal stress in plants," said Lori Hoagland, a Purdue University professor of horticulture and landscape architecture who conducted the study.

"We'll be able to develop soil amendments that sequester the harmful metals, as well as identify contamination before it reaches our plates if we can quickly see it and accurately measure it as the plants grow. Our goal is to be able to have drones that fly over fields and detect plant stress from cadmium, lead, and arsenic."

Chemical Analysis

(Photo : Pixabay.com)

Traditional chemical analysis procedures are substantially slower than hyperspectral detection. It also does not need the killing of the plant being studied, allowing for plants and soil amendments during various phases of development.

"We don't generally test for cadmium poisoning of plants because we can't see it," said Hoagland, who directs Purdue's Soil Microbial Ecology Lab

"When exposed to high amounts of cadmium, the plants suffer, but they don't shrink, wilt, or die; they seem fine till the cadmium levels are through the roof, and contaminated plants mature and are harvested."

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Cadmium

Cadmium is commonly linked to phosphate mined for fertilizers and is used in batteries. It and other heavy metals from garbage and pollution penetrate the soil worldwide and go to neighboring fields, which are absorbed by crops. Cadmium poisoning can cause renal illness, bone difficulties, cancer, and other health concerns.

"It's naturally found in modest amounts in many plants," she explained, "but high doses can be dangerous." "We must maintain these levels low in infant meals in particular, but it is an increasing problem across our food chain."

"I approached the study as a bit of a test, uncertain if it would work for my research," she explained. "I was shocked by how strong a tool it can be and how much data it creates in a short amount of time; these imaging techniques will help us understand and answer many scientific issues," says the researcher.

Plants are transported by conveyor belt to an imaging station at intervals determined by the researchers in the controlled-environment phenotyping facility. According to the findings of Hoagland's research, kale accumulated more cadmium than basil under the same soil conditions, but basil's cadmium stress symptoms were more severe. They also observed that cadmium stress only appeared in the early stages of plant growth.

Categorizing Data

To filter and categorize the data, the researchers used a machine-learning system.

The researchers first looked at the green light spectrum, thinking that the effect of cadmium toxicity stress on chlorophyll synthesis would be a good predictor. The color alteration that resulted was highly faint.

According to Hoagland, the team worked through additional stress-related alterations in the plant and other regions of the plant's reflectance spectra. They discovered that changes in metabolites resulting from the stress response provided a considerably sharper hyperspectral stress signal.

Hoagland and her colleagues looked at "vegetation indices," which are combinations of reflectance from various wavelengths that are the most effective for hyperspectral analysis of different plant attributes.

The Anthocyanin Reflective Index, or ARI, was discovered to be the most effective method for diagnosing cadmium stress, and a unique vegetation index ratio equation was established for it. They also created a soil additive to limit the amount of cadmium the plant absorbs. A study published in the journal Environmental Pollution describes the experiment in detail.

According to her, the tested formulation reduced cadmium levels in the plants by a bit. Farmers might use more of the modification as a remedy, but Hoagland intends to continue to tweak and perfect the recipe.

Utilizing Imaging

(Photo : Inigo dela Maza, Unsplash)

She also intends to utilize hyperspectral imaging to look for a definite lead and arsenic signature.

Purdue researchers Maria Zea, a graduate student in Hoagland's lab; Augusto Souza, a postdoctoral researcher for the phenotyping facilities; Linda Lee, professor of agronomy; and Krishna Nemali, controlled environment agriculture Extension specialist; worked on the project and are co-authors of the paper, in addition to Hoagland and Yang.

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