Red soil mineral captures trace metals over time

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Trace metals, though tiny in amount, play a crucial role in the health of both plants and animals. These metals, like zinc, are essential nutrients that organisms need to function properly.

Animals obtain these metals through their diet or environment, while plants absorb them from the soil. However, the balance is delicate: too little of a trace metal can lead to a deficiency, but too much can be toxic.

Scientists have uncovered that a significant portion of trace metals in soils and urban areas—possibly up to half—might be clinging to mineral grains.

This means they’re not readily available for organisms to use. Researchers at Washington University in St. Louis have delved into this phenomenon, particularly interested in what keeps these metals bound to minerals.

Jeffrey G. Catalano, a professor with a focus on Earth, environmental, and planetary sciences, and his Ph.D. student Greg Ledingham, have discovered that a common soil mineral known as goethite plays a significant role in this process.

Goethite, rich in iron and widespread in soils worldwide, has a knack for incorporating trace metals into its structure as time passes. This process essentially locks these metals away, making them inaccessible for consumption or exposure.

Their research showed that the likelihood of a trace metal being bound to goethite depends on the size of the metal’s ions.

For instance, nickel, with relatively small ionic radii, was found to be nearly 70% non-recoverable once bound to goethite, whereas only 8% of cadmium was permanently attached.

This study, published in the journal Environmental Science & Technology, stands out because of the methodology used.

Traditionally, studies on how trace metals bind to minerals required altering chemical conditions in unrealistic ways.

But Ledingham used a novel approach called isotope exchange, which tracks metal binding and detachment in real-time and under realistic conditions, like those found in actual soils and river systems.

The findings indicate that minerals like goethite might be even more effective at trapping trace metals than previously believed. This has significant implications.

On one hand, trapping harmful metals could help clean up contaminated soils and water. On the other, it means that trace metals used as nutrients in agriculture might become less available over time, potentially affecting crop growth.

This research not only sheds light on the complex interactions between trace metals and soil minerals but also highlights the need for a balanced approach in managing trace metals in the environment.

Understanding how goethite and similar minerals bind with trace metals can help scientists predict the movement of contaminants and design better strategies for both environmental protection and agricultural productivity.

The research findings can be found in Environmental Science & Technology.

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