A basic property of hydrated metal ions may offer a faster and more practical way to estimate how readily trace elements move from contaminated soils into plants, according to a new study published in New Contaminants.
"Soil and plant testing can require considerable time, equipment, and resources, especially when many different elements are involved," said lead author Hayley Jensen of the Bioeconomy Science Institute, Manaaki Whenua Landcare Research, New Zealand. "Our findings suggest that the distance between a metal ion and surrounding oxygen atoms in water could provide a simple chemical indicator of its likelihood of accumulating in plant tissues."
Trace element contamination is an increasing concern for agriculture and food safety. Elements released through mining, industry, electronic waste, fertilizers, and other human activities can enter soils and potentially be absorbed by crops or pasture plants. Once present in edible leaves, grains, fruits, or animal feed, these elements may move into the food chain.
However, predicting plant uptake remains difficult. The movement of an element through the soil and into a plant depends on soil acidity, organic matter, mineral composition, moisture, plant species, and many other factors. Researchers commonly use a bioaccumulation coefficient, which compares an element's concentration in plant tissue with its concentration in soil. Obtaining these values experimentally can be expensive, destructive, and time consuming.
The research team investigated whether several fundamental chemical properties could help explain plant uptake. Their main focus was the metal to oxygen bond distance, known as the Me to O distance, in hydrated cations. When positively charged metal ions are dissolved in water, they become surrounded by water molecules. The distance between the metal and the oxygen atoms of these water molecules reflects how strongly the ion interacts with its hydration shell.
The researchers compared Me to O distance, ionic potential, and hydrated radius with plant uptake data from three distinct systems: a perennial ryegrass pot experiment in Christchurch, pasture plants collected from 39 sites across New Zealand, and oil palm growing in Sumatra, Indonesia.
Across all three datasets, plants generally accumulated more of the elements whose hydrated ions had longer Me to O distances. The relationship was observed in very different plant groups and environmental settings, suggesting that the metric may capture a basic chemical influence on element mobility.
Me to O distance also performed more consistently than the other properties examined. Ionic potential was inversely related to plant uptake, but the relationship was not statistically significant in one dataset. Hydrated radius showed strong correlations in some cases, but published values were unavailable for several elements, including emerging contaminants such as gallium, indium, neodymium, and gadolinium.
Lanthanides, a group of rare earth elements, were an important exception. Their uptake decreased as Me to O distance increased, opposite to the pattern seen for most other elements. The authors attribute this difference partly to the unusually large atomic size and distinctive chemistry of lanthanides. Future models may therefore need to treat rare earth elements separately.
The proposed metric could be especially valuable when direct measurements are unavailable or impractical. It may help researchers estimate the behavior of poorly studied contaminants, extend existing datasets to additional elements, and reduce reliance on measurements of soil partitioning, root properties, water movement, and other complex variables.
The findings do not eliminate the need for soil and plant testing, but they provide a promising foundation for simpler screening tools and improved environmental models. The researchers recommend testing the relationship across more crops, soils, climates, and heavy elements before it is used in routine risk assessment.
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Journal reference: Jensen H, Lehto N, Almond P, Thompson-Morrison H, Gaw S, et al. 2026. Simple metrics for complex systems: the Me–O distance in hydrated cations is a potential new metric for predicting element uptake by plants. New Contaminants 2: e017 doi: 10.48130/newcontam-0026-0014
https://www.maxapress.com/article/doi/10.48130/newcontam-0026-0014
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About the Journal:
New Contaminants (e-ISSN 3069-7603) is an open-access journal focusing on research related to emerging pollutants and their remediation.
