Researchers have discovered that the presence of benzoxazinoids, which are produced in particularly large quantities by corn plants, reduces the arsenic toxicity of contaminated soil.
When crops grow in arsenic-contaminated soil, this toxic element accumulates in the food chain. A study involving the University of Basel has now discovered a mechanism used by corn plants to reduce arsenic uptake: the key factor is a special substance released into the soil by the roots.
Arsenic is a toxic metalloid of natural origin. Arsenic-contaminated soils and waters are found all over the world, especially in southeastern Asian countries like Bangladesh, Vietnam and China. Also, Switzerland has a few natural hot spots where arsenic is found in above-average concentrations. An example is soil at Liesberg in the canton of Baselland.
“The particular problem for plants is that arsenic behaves chemically similar to phosphorus,” said Professor Klaus Schlaeppi of the Department of Environmental Sciences at the University of Basel. Phosphorus is an important nutrient that plants take up through special transport channels in their roots. “The arsenic enters the plants through these channels,” Schlaeppi explained. As a result, more and more of the toxic substance accumulates in the biomass and gets into the food chain. In the long run, this negatively affects human health. High arsenic exposure can cause neurological damage and cancer, for example.
But as Schlaeppi’s team has now reported in the scientific journal PNAS, corn reduces arsenic toxicity through compounds known as benzoxazinoids. These substances are produced by most plants in the botanical group of grasses, which also includes corn and wheat. Corn produces particularly large quantities of benzoxazinoids, which are also released into soil through the root system. “There was already some evidence that corn takes up less arsenic than other plant species,” said Schlaeppi.
To test this hypothesis, the researchers grew corn plants in two types of soil: without arsenic and with high levels of arsenic. They performed the same experiment in parallel using corn plants that cannot produce benzoxazinoids because of a genetic defect. Schlaeppi performed these experiments in collaboration with the research groups of Professor Adrien Mestrot and Professor Matthias Erb at the University of Bern.
The result was unambiguous: benzoxazinoid-producing corn grew better in the arsenic-containing soil and accumulated significantly less arsenic in its biomass than the corn that did not exude benzoxazinoids. When the researchers mixed benzoxazinoids into the arsenic-containing soil, the mutant plants were also protected from arsenic toxicity. “This provided the proof that the presence of benzoxazinoids in soil reduced arsenic uptake into plants,” said Schlaeppi.
Next, the researchers wanted to find the underlying mechanism causing this effect. Analyses of the root microbiome indicated that bacteria and fungi were not involved. However, chemical soil analyses showed that a particularly toxic form of arsenic disappeared when benzoxazinoids are present. “This indicated that the benzoxazinoids transform arsenic in such a way that it can no longer be taken up through the root,” explained Schlaeppi. What chemical processes are involved is currently still unclear.
Further experiments showed that the positive effect of benzoxazinoids in soil persisted for a long time: even a second generation of corn still benefited from the benzoxazinoids discharge of the first generation.
“One application of these findings would be to cultivate at arsenic-contaminated locations plant varieties that release more benzoxazinoids,” says Schlaeppi. Hyper-emitting plants could be generated through classic breeding or targeted genetic modifications. “This way we could be more certain that less arsenic is entering the food chain,” he added.
FAQs
Corn plants offer solution to arsenic-contaminated soil challenges. Researchers have discovered that the presence of benzoxazinoids, which are produced in particularly large quantities by corn plants, reduces the arsenic toxicity of contaminated soil.
What plants remove arsenic from soil? ›
This plant accumulates large amounts of arsenic in its fronds, the portion of the fern that is above ground. This discovery led to the idea that brake fern could help clean up arsenic-contaminated soil. The use of plants to clean up contaminated soil and water is called phytoremediation.
How to remove arsenic from contaminated soil? ›
FERN PHYTOREMEDIATION OF ARSENIC-CONTAMINATED SOIL
Assume that ferns can remove 20 mg arsenic per kg soil in 20 weeks. At the end of 20 weeks, ferns are harvested and replanted until the desired soil arsenic concentration is reached.
What happens when crops are grown in soils contaminated with substances like arsenic? ›
Higher concentrations of As in crop soil and groundwater may result in increased crop loss and catastrophic health effects in humans. Rice grains have been shown to accumulate 2.24 mg kg−1 As compared to other main food crops [40].
What absorbs arsenic from soil? ›
Some plants, such as rice, asparagus, and beets, are more likely to absorb arsenic than others. This is because these plants have a high affinity for arsenic and can take it up from the soil even at low concentrations.
What cancels out arsenic? ›
Chelating agents administered within hours of arsenic absorption may successfully prevent the full effects of arsenic toxicity. Dimercaprol (2, 3 dimercaptopropanol, also known as British anti Lewisite or BAL), was previously the most frequently recommended chelating agent for arsenic.
What plants clean toxic soil? ›
Small plants like ferns and grasses have been used where contamination is shallow. Because tree roots grow deeper, trees such as poplars and willows are used for hydraulic control or to clean up deeper soil contamination and contaminated groundwater.
How long does arsenic stay in soil? ›
(3) One estimate of the residence time for arsenic in soil is 9000 years. (2) Since arsenic is expected to remain in soil for centuries or longer, contaminated soil left at the site must be considered a potential source of exposure throughout this time frame.
How do you remediate arsenic contamination? ›
Several techniques have been proposed to remove arsenic from groundwater including precipitation, coagulation/filtration, adsorption, ion exchange, lime treatment, oxidation, and membrane filtration.
What causes arsenic in soil? ›
Arsenic in soil results from human activities including pesticide use, mining and ore processing operations, operating coal burning power plants, and waste disposal. Sites of former tanneries, which make leather from animal hides, have large amounts of arsenic in the soil.
Unless your soil has exceptionally high levels of lead or cadmium (which you can find out by testing—see below), it's probably safe to eat vegetables after washing them thoroughly. Wash with cold running water just before eating, cutting or cooking.
Where is soil contamination the worst? ›
Land pollution such as this is normally found in cities, old factory sites, around roadways, illegal dumps and sewage treatment stations.
Can arsenic in soil get into vegetables? ›
Arsenic is readily taken up by leafy green crops, whereas Pb generally has a low tendency for uptake into above-ground tissues because of its very low solubility in soils that are not strongly acidic [10, 17]. However, the UC for As in leafy vegetables is strongly dependent on plant species [17].
How do you remove arsenic from contaminated soil? ›
Soil washing enhanced the dissolution of arsenic-bound iron oxides. The arsenic removal efficiency was linked to the extraction of iron. The synergistic effect effectively enhanced the extraction of arsenic from soils. The composite washing agent had a limited effect on soil physicochemical properties.
Do plants take up arsenic from the soil? ›
Most edible plants absorb some small amounts of arsenic, but usually do not contain enough arsenic to be of health concern. The amount of arsenic absorbed by plants can depend on many factors. Some of the most important factors are soil acidity, nutrient content, iron, organic matter, and plant type.
How do you identify arsenic in soil? ›
Various analytical techniques commonly used are based on hydride generation coupled with atomic absorption spectroscopy (AAS) or inductive coupled plasma-atomic emission spectroscopy (ICP-AES). However, these methods were often complex, lengthy, and/or expensive.
What is a natural way to get rid of arsenic? ›
Vitamin C: Vitamin C can actually act as a chelating agent and help remove arsenic directly from the bloodstream. Vitamin B and C deficiencies have been linked to poor tolerance of heavy metals, making it easier for a person to have higher levels of toxicity.
What herbs are good for arsenic removal? ›
Curcumin has been used historically in Ayurvedic medicine against various human diseases. Anti-hepatoxic effects of curcumin are well-documented and according to the literature, curcumin reduces liver toxicity caused by environmental toxicants such as arsenic, cadmium, chromium, lead and mercury.
What dissolves arsenic? ›
The cubic form is slightly soluble in water. The solubility of arsenic trioxide in 100 g of water is 1.2 g at 0° C, 2.1 g at 25° C, and 5.6 g at 75° C. It is claimed that the aqueous solutions have a sweet, metallic taste. The rate of dissolution is very low, and several weeks are required to achieve equilibrium.
