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The Phosphate Knowledge Center
News Record
Queen's research inspires national guidelines for phosphite 'fertilizers'
April 21, 2010

2009-09-23

A crisis may be looming if the difference between phosphates and phosphites doesn't receive public attention says Queen's University Biology professor William Plaxton.

"It may be one little vowel – reflecting a chemical change at the molecular level – yet the difference between phosphite and phosphate could be dangerous to the environment and your health," says Dr. Plaxton, who teaches biology at Queen's University.

Phosphite is an important agricultural commodity that has raised considerable controversy since it is being widely marketed as either a crop fungicide or as a superior source of crop phosphorus nutrition.
Phosphite products are used extensively in agricultural and turf grass industries in Canada and around the world, including the fruit belt of the Okanagan Valley of B.C., as well as the grape crop in the Niagara Wine Region of Ontario.

Dr. Plaxton has been tracking phosphite use and its effects for almost two decades. His federally-funded research provided the Fertilizer Section of the Canadian Food Inspection Agency (CFIA) with the basic research information required for establishing strict standards that phosphite products must meet in order to be legally sold as fertilizers in Canada – possibly the first time a national government has imposed guidelines on the sale of phosphites as fertilizers.

Researchers have conclusively established that phosphite application effectively suppresses fungal pathogens responsible for a host of important crop diseases.

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"However, evidence that plants can use phosphite as a source of phosphorus nutrition is lacking," says Dr. Plaxton. "In fact, phosphite, which is also known as phosphonate, actually functions as an 'anti-fertilizer' as it specifically and rapidly kills plants growing in phosphate deficient soils – as witnessed by the wide-scale destruction of bean crops by so-called phosphite 'fertilizers' in the U.S. state of Georgia in 2004."

Nevertheless, farmers in many countries have been applying large quantities of phosphite formulations labeled as a phosphorus fertilizer, rather than as a fungicide.

Farmers, agronomists and consumers should be aware that one of the features that makes phosphite an effective fungicide is that it is retained in crop tissues for a long time and moves in the same way as phosphate does, often ending up in fruits and seeds. As phosphite is extremely toxic to plants or yeast receiving inadequate phosphate nutrition, there is an obvious need for a critical assessment of the long-term consequences of the significant input of phosphite into crops and the environment.

"In particular, what levels of phosphite occur in foods derived from phosphite-treated crops, and does chronic consumption of these products pose any threat to people who consume them?" asks Dr. Plaxton.

Farmers and gardeners are encouraged to check the products they use for phosphites masquerading as phosphates.

"What we don't know about phosphites may be more alarming than what we do – and that is disturbing enough," says Dr. Plaxton.

Dr. Plaxton's research involves plant biochemistry, plant carbohydrate metabolism, biochemical adaptations of phosphate starved plants, enzymology, protein purification, enzyme kinetics, metabolic control and proteomics. Original source

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