Environmental Safety Assessment of Natural Radioactive Contaminants in Fertilizers and Phosphogypsum.

This study presents results of a safety assessment of natural radionuclides often present in Brazilian fertilizers and phosphogypsum.  Phosphate fertilizers are typically obtained by wet reaction of igneous phosphate rock with concentrated sulfuric acid to produce phosphoric acid as the starting material for the phosphate fertilizer, and dehydrated calcium sulfate (phosphogypsum) as a byproduct. Phosphate rocks used as raw material often contain small amounts of radionuclides (notably the U and Th natural series). We present results of measured ²³⁸U and ²³⁴U contents of Brazilian fertilizers, and of the ²²⁶Ra and ²¹⁰Pb contents of the phosphogypsum byproducts.  The radiological implications of using these products as either a fertilizer or a soil conditioner (phosphogypsum) are discussed.  We used the HYDRUS-1D software package to compare possible soil and groundwater pollution scenarios following their long term (300 year) use in agricultural operations.