Phosphogypsum Amendment Effect on Radionuclide Content in Drainage Water and Marsh Soils from Southwestern Spain
2003
El-Mrabet, Rachid | Abril, José-María | Periáñez, Raúl | Manjón, Guillermo | García-Tenorío, R. (Rafael) | Delgado, A. (Antonio) | Andreu, Luis
Phosphogypsum (PG) is a residue of the phosphate fertilizer industry that has relatively high concentrations of ²²⁶Ra and other radionuclides. Thus, it is interesting to study the effect of PG applied as a Ca amendment on the levels and behavior of radionuclides in agricultural soils. A study involving treatments with 13 and 26 Mg ha⁻¹ of PG and 30 Mg ha⁻¹ of manure was performed, measuring ²²⁶Ra and U isotopes in drainage water, soil, and plant samples. The PG used in the treatment had 510 ± 40 Bq kg⁻¹ of ²²⁶Ra. The ²²⁶Ra concentrations in drainage waters from PG-amended plots were similar (between 2.6 and 7.2 mBq L⁻¹) to that reported for noncontaminated waters. Although no significant effect due to PG was observed, the U concentrations in drainage waters (200 mBq L⁻¹ for ²³⁸U) were one order of magnitude higher than those described in noncontaminated waters. This high content in U can be ascribed to desorption processes mainly related to the natural adsorbed pool in soil (25 Bq kg⁻¹ of ²³⁸U). This is supported by the ²³⁴U to ²³⁸U isotopic ratio of 1.16 in drainage waters versus secular equilibrium in PG and P fertilizers. The progressive enrichment in ²²⁶Ra concentration in soils due to PG treatment cannot be concluded from our present data. This PG treatment does not determine any significant difference in ²²⁶Ra concentration in drainage waters or in plant material [cotton (Gossipium hirsutum L.) leaves]. No significant levels of radionuclides except ⁴⁰K were found in the vegetal tissues.
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