Assessment of the radiological environmental impact of using phosphogypsum as soil amendment: soil availability modification and radiological impact evaluation

Phosphogypsum is a by-product of the phosphate industry, which presents enhanced concentrations of heavy metals and naturally occurring radionuclides, mainly ²²⁶Ra, ²¹⁰Po and ²¹⁰Pb. Taking into account sustainability goal and green chemistry, it is also considered a resource with numerous commercial applications, being its use as soil conditioner and/or amendment one of them. This application can also cause a potential hazard because it may introduce these contaminants into the human foodchain. Plant uptake depends on the association of these radionuclides to soil particles. In this study, we considered a typical Mediterranean soil which was amended with phosphogypsum, and two different sequential extraction schemes were applied to the original soil, phosphogypsum and amended soil. Phosphogypsum application did modify the pattern in which radionuclides were associated to soil particles. From the results of these extractions, it was observed that in amended soil uranium association to diluted-acid and moderately reducible fraction increased; while a reduction of ²²⁶Ra exchangeable fraction and an increase of reducible fractions, also for ²¹⁰Po, was observed. Distribution of ²²⁶Ra and ²¹⁰Po, most important radionuclides in phosphogypsum, cannot be derived from the individual distribution from original soil and phosphogypsum. Finally, the dose rates to non-human biota were below international benchmarks, and therefore no deleterious effects were to be expected.