Speaker
Description
Phosphate fertilizers are widely used in Uruguay due to the natural phosphorus deficiency of most agricultural soils. These fertilizers contain naturally occurring radionuclides which may represent a potential source of radiological exposure for the population. This study aims to evaluate the impact of phosphate fertilization on the distribution of natural radionuclides in horticultural systems and to estimate the associated radiation doses under different exposure scenarios.
Pot experiments were conducted using soil from two regions with contrasting characteristics: Canelones, an intensively cultivated agricultural area, and Rocha, a coastal zone without previous farming activity. Three phosphate fertilizers (phosphate rock, NPK, and triple superphosphate), an organic fertilizer, and an unfertilized control were applied. Spinach (Spinacia oleracea) was cultivated for three months under controlled irrigation conditions. After harvesting, soil, leachate water, and plant biomass samples were collected for analysis.
Activity concentrations of radionuclides (²²⁶Ra, ²³²Th, ⁴⁰K, ²¹⁰Po, ²³⁸U, and ²³⁴U) were determined by high-resolution gamma spectrometry and alpha spectrometry using standardized procedures and certified reference materials. Soil-to-plant transfer factors and concentration ratios between solid and aqueous phases were calculated to assess radionuclide mobility.
Experimental results indicated that, under the tested conditions, differences in radionuclide concentrations between fertilized and control soils were not statistically significant. Consequently, an indirect approach was adopted for dose assessment, estimating soil activity concentrations from fertilizer radionuclide contents and application rates, assuming homogeneous mixing within the topsoil layer.
Radiological risk assessment was performed using the RESRAD-ONSITE and RESRAD-OFFSITE codes for representative rural and urban exposure scenarios. For phosphate rock fertilization, the maximum total effective dose from all radionuclides and all exposure pathways in rural scenarios was estimated at 2.32 × 10⁻³ mSv·year⁻¹, occurring at 1000 years, with external gamma exposure as the dominant pathway and ²²⁶Ra providing the largest contribution to external dose. For triple superphosphate fertilization, the maximum total effective dose was estimated at 2.057 × 10⁻³ mSv·year⁻¹, also occurring at 1000 years, with ²²⁶Ra again being the main contributor to external exposure. In contrast, for NPK fertilization, the maximum total dose was 7.8 × 10⁻⁵ mSv·year⁻¹, occurring at time zero, with ⁴⁰K representing the largest contribution to the total dose.
In all cases, the estimated doses remained well below recommended radiological protection limits, indicating a low radiological impact associated with routine phosphate fertilizer use in Uruguay. This study represents the first comprehensive radiological assessment of phosphate fertilization in the country and establishes a baseline for future investigations, contributing to regional knowledge on natural radionuclide behavior in agricultural systems.