Ecological and radiological risk assessment of natural radioactivity from phosphate industry by-products used in construction: a case study from Crotone, Italy

Abstract

Phosphogypsum (PG), a by-product of phosphate fertilizer production, has been widely considered for reuse in construction materials in line with the principles of the circular economy. However, PG and associated secondary compounds such as metasilicate phosphate often contain naturally occurring radionuclides, including ²²⁶Ra, ²³⁸U and ²³²Th, which may pose radiological hazards. This study assesses terrestrial and marine radiological exposure scenarios associated with phosphate industry residues used in road construction and stored at a former coastal industrial deposit in Crotone (Calabria, Italy). Sixteen road-pavement composite cores and 28 deposit-site samples were investigated by high-resolution gamma-ray spectrometry. Maximum activity concentrations in the road-pavement samples reached 1235 Bq kg⁻¹ for ²³⁸U, 1212 Bq kg⁻¹ for ²²⁶Ra and 317 Bq kg⁻¹ for ⁴⁰K. The ERICA Tool was applied using a screening dose rate of 10 µGy h⁻¹. For several terrestrial and marine reference organisms, risk quotients exceeded unity, triggering Tier 2 and Tier 3 assessments. These screening exceedances indicate that the scenarios could not be screened out as being of low radiological concern. Tier 2 identified lichens and bryophytes as the most exposed terrestrial reference organism and phytoplankton as an important marine reference organism. Tier 3 sensitivity analysis showed that uncertainty in ²²⁶Ra transfer parameters strongly controlled variability in predicted dose rates. The marine calculations represent a conservative nearshore sediment deposition scenario because radionuclide concentrations were not measured directly in seawater, marine sediment or biota. The results support improved control, monitoring and site-specific characterization of exposed NORM-containing residues in coastal environments.

Graphical abstract