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Corridor serendipity battles toxic nasties in soil |
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A marriage of minds: Paul Milham and Tim Payne with silver beat - one of many food plants that absorb cadmium from soil
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Cadmium as a solid metal
(Photo courtesy of US Geological Survey)
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A serendipitous corridor chat, during a visit to the Australian Nuclear Science and Technology Organisation (ANSTO) in 2004, has lead to two Australian soil experts joining forces in the battle to keep toxic nasties out of our veggies and wheats.
The casual discussion between the two established a common goal to develop a better way to map the concentration in soil of a common heavy metal called cadmium and ultimately decrease absorption by agricultural produce, which could potentially damage human health if ingested at high levels.
Paul Milham from NSW Department of Primary Industries and Dr Tim Payne from ANSTO discovered they shared a love of soils when Paul came to ANSTO to meet physicists about a completely different project. Paul has studied cadmium in soil since the early 1990s, and Tim, radioactivity in soil via his work, which included advising uranium mining companies on how to manage their environmental impact.
The cadmium measurement tool they discussed, and which Tim recommended, was synchrotron x-ray technique where powerful x-rays beams are used to look at structural composition at the micro-scale. Following Paul's visit, he and Tim agreed that a research proposal be submitted to the Australian Synchrotron Research Program run by ANSTO. When the grant application proved successful, tests were scheduled at the Advanced Photon Source (APS) near Chicago in the United States. Now, four years later, the tests have been completed and the results have been reported in a scientific journal. They are encouraging.
According to Paul, conventional soil measurement processes cannot clearly indicate the cadmium levels because particles are so small but the synchrotron results clearly show it to be the most sensitive method to observe distribution.
"We are very pleased with the results in the sense that we can clearly see distribution. However, knowing the concentration is only one step towards better predictions about cadmium uptake in plants," said Paul.
"In many countries cadmium plant uptake is rising due to the use of phosphate fertilisers and intense farming, and in some places cadmium concentrations exceeds World Health Organisation recommended levels," he said.
"It's therefore very important that we find ways of predicting the levels at which plants start to absorb excess cadmium, which can cause osteoporosis and cancer when ingested at high levels."
Although cadmium is a naturally occurring heavy metal, the levels in agricultural soil are dramatically influenced by fertilisers, sometimes increasing levels up to 20 fold. In addition, the proximity of the soil to major roads and other industrial activities has a major impact and although the health risks at low levels are largely still unquantifiable, it is an area that is being closely watched by scientists and health experts.
Tim believes that even although the initial results were very informative, more synchrotron measurements are required to build a better predictive model.
"These initial tests have shown the synchrotron x-ray brilliance is the best way to see cadmium concentrations in both soil and fertiliser," he said. "However we need to conduct further tests with more powerful beams to get results in even more detail.
"We are therefore planning to spend more time at APS, especially now we have learned more about how to prepare and present the soil sample to the instrument."
The Chicago-based synchrotron consists of a one-kilometre ring where electrons circulate at faster than 99.9 per cent the speed of light and powerful magnets stimulate them to create x-ray beams which in turn analyse the sample to produce clear pictures of the structure.
"Ultimately what we want to produce is a three-dimensional map of cadmium in soils and study its chemical form. These measurements will allow us to have a unique understanding of the complex behaviour of this element in soil and this way we'll be able to better predict uptake by plants," said Tim.
"It is important that we produce the best model to accurately tell farmers what levels of cadmium uptake they will have in crops relative to the levels in the soil, although this is a little way off yet.
"All I can say though, we have come a long way in further understanding cadmium in soil, thanks to a chance meeting bringing Paul and I together, but that's science!" concluded Tim.
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With the chemical symbol Cd, cadmium is a heavy metal which is relatively abundant.
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It is a bluish-white, transition metal, is known to cause cancer and is found in zinc ores.
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The material is often used in batteries, pigments, coatings, plating and stablisers for plastics.
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Cd is used for shielding neutrons, produced during nuclear reactions.
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Tobacco smoking is the highest single source of cadmium exposure for people although primary exposure is the result of burning fossil fuels and industrial wastes.
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Cadmium is normally transported into the environment via air, water and soils.
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Plants absorb most of their cadmium from soil through their roots.
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Intake of cadmium through diet in Australia is low by world standards.
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