Spreading phosphate fertilisers contaminates fields with Uranium

Phosphorus (P) is a vital mineral for all crops. Farmland has to be supplied with phosphorus regularly by applying fertiliser, in order to provide crops with sufficient phosphorus. P fertilisers are produced out of rock phosphates by means of different processes from sedimentary (fossil) or magmatic deposits. Rock phosphates from sedimentary deposits are characterised by a high content of elements which can also be detected in standard fertilisers.

Scientists at the Institute of Plant Nutrition and Soil Science of the Federal Agricultural Research Center in Braunschweig, Germany have found that commercial P-fertilisers also contain the toxic radionuclide uranium (U). From their own analyses and extensive literary enquiries they have discovered that because of the high affinity of U to phosphorus, the U content originally contained in the rock phosphates of 13- 75 mg/kg, during the reprocessing to super- or triple-superphosphorus raises to 85-191 mg/kg. Fertilizers with two-nutrients (NP or PK) contain 89-96 mg/kg U, NPK-fertilisers 14 mg/kg U. Sewage-sludges reaches a content of 4-32 mg/kg U. Fertilisers without any P components (N-, K-, NK-, Mg-, S- and lime fertiliser) have contents of more than 1 mg/kg U. But, remarkably, in spite of their significant P content, farmyard manures and slurries are only slightly contaminated with U (seldom above 2 mg/kg U).

U is the heaviest naturally occurring chemical element and as a radioactive alpha-emitter and toxic heavy metal is recognised as a risk for human health and the environment. The German scientists say that this doubly increased threat has been unrecognised until now.

As a natural element U occurs in all areas of life and in very different concentrations and therefore it represents one of the basic dangers in life. U mainly accumulates in bones and can cause several diseases ranging from functional disturbances of the kidneys, lungs and liver, to cancer and mutations. The probability of such fatal effects on health is a function of the amount of U taken up by the organism i.e. the risk increases with the duration and amount of intake. That is one reason why there are no definite limits in respect to health consequences of U pollution.

For the last 50 years the amounts of U released into the environment by human activities, have been increasing and with them the danger of raised pollution in the food chain. The main cause of U discharge to agricultural soils is fertilisation with mineral P sources. The scientists of FAL calculated that a typical P-fertiliser application of 22kg/ha P with mineral P-fertilisers (an amount in accordance with international Codes of Good Agricultural Practice) would spread 10-22 g/ha U on to treated fields each year. But hardly more than 1 g/ha Uranium is removed by crop products, leaching and erosion.

So, when applying mineral P-fertiliser, the accumulation of U in the soil is inevitable. With increasing amounts of U in the soil, there is the increased absorption of Uranium by plants in the food chain and a consequent deterioration in food quality.

By contrast, where P is applied by farmyard manures and slurry, the amounts of U applied to the soil are nearly equal to those removed by natural processes. Against this background P-fertilising with a farms own fertilisers is preferable to a supply of P with mineral fertilisers.

Further information can be found in Uran- Umwelt- Unbehagen” in the FAL from 25th November 2004 under “workshops”
in: http://www.pb.fal.de/index.htm?page=/home.htm

Or contact: Prof. Dr. Dr. Ewald Schnug, Federal Agricultural Research Center (FAL), Institute of Plant Nutrition and Soil Science (FAL), Bundesallee 50, 38116 Braunschweig, E-mail: pb@fal.de