Radiological impact of phosphogypsum applied to soils under bahiagrass pasture

Phosphogypsum (PG), a by-product in the manufacture of phosphoric acid, is primarily gypsum. The USEPA regulates the removal of PG from stacks because it contains 226Ra. Measures to quantify the transfer of radioactivity in PG to the agricultural environment are needed. The objective of the study was to collect data needed for assessment of the radiological impacts of PG applied to two Florida soils. Field experiments using 0,10, and 20 mg PG ha-1 were conducted for 2 yr at the University of Florida RCREC, Ona, FL. PG-attributable levels of 226Ra, 210Pb, and 210Po were observed in the top 5-cm layer of the soils. Surface 222Rn flux increased by 0.067 to 0.078 mBq m-2 s-1 per Mg PG ha-1. Radionuclide concentrations in regrowth forages increased at one site where the first post-treatment rainfall did not occur until 20 d after PG application. In mature forages, radionuclide levels generally increased with PG in both soils. No effects on radionuclide levels in subsurface water down to 90 cm and only slight effects on gamma radiation and on airborne 222Rn measured 1 m from the ground were noted. The linear regression slope for a radiological parameter normalized with respect to the pertinent radionuclide applied per m2 per Mg PG ha-1 is proposed as the transfer factor (TF) of that radionuclide in PG to the agricultural medium in terms of that parameter. The TF permits the calculation of the potential effect on certain radiological parameters of PGs containing different radionuclide concentrations from the one used in this study