Evaluation of the radioactive impact of the phosphogypsum wastes used as amendment in agriculture soils

Abstract

Some 3×109 kg of phosphogypsum (PG) wastes are annually generated by two fertiliser-production factories in Huelva (south-western Spain). PG has relatively high concentrations of 226 Ra and other radionuclides, with an special concern due to the 222 Rn emissions. These wastes could be used to improve the fertility of agriculture soils in a large former marsh area of the Guadalquivir river. Thus, it is interesting to study the levels and behaviour of natural radionuclides within this system to evaluate the radioactive impact of this amendment. An agronomical test is being conducted by one of the authors in an experimental farm in Lebrija (Seville). The soils are treated with 13 and 26 t ha-1 of PG, 30 t ha-1 of manure. Each treatment was repeated twice and continued for two years with beetroot and cotton plant production. We are measuring 226 Ra (by alpha counting and gamma spectrometry) and U isotopes (by alpha spectrometry and ICP-MS analysis) in drainage waters, soils and vegetal-tissues samples. The PG used in the treatment has 620 ± 70 Bq kg-1 of 226 Ra. The drainage waters have 226 Ra contents similar to those from non-contaminated natural waters, but the uranium concentrations are one order of magnitude higher. Our results are suggesting that the major uranium input comes from the application of phosphate-fertiliser. No significant levels of radionuclides were found in the vegetal tissues.