A study on the impact of phosphate fertilizers on the radioactivity profile of cultivated soils in Srirangam (Tamil Nadu, India)

Phosphate fertilizers are enriched with 238U during its production from phosphate rocks. Since, application of phosphate fertilizers in modern agriculture is ever on the increase, the present study investigated the impact of phosphate fertilizers on the radioactivity profile of cultivated (fertilized) soils as against virgin soils. Thirty soil samples each from cultivated fields and virgin fields were collected from Srirangam taluk and analyzed for the activity concentrations of 238U, 232Th and 40K employing gamma ray spectrometry. Similar analysis was also undertaken in commonly used phosphate fertilizers. Among the phosphate fertilizers analyzed single super phosphate (396.3 Bq/kg) and triple super phosphate (284.2 Bq/kg) registered higher level of 238U. The mean activity level of 238U in cultivated soil (8.4 Bq/kg) was 25% higher than that of virgin soil (6.8 Bq/kg), while the mean 232Th and 40K activities in cultivated soil (98.4 Bq/kg & 436 Bq/kg) were elevated by 12.4% and 4% respectively as compared to virgin soil (87.5 Bq/kg & 419 Bq/kg). The mean radium equivalent (Raeq) value for virgin and cultivated soil samples was found to be 164.5 Bq/kg and 181.7 Bq/kg respectively. It is evident that the application of phosphate fertilizers elevated 238U level of the soil. However, the mean Raeq value for soil samples is well below the permissible limit of 370 Bq/kg and hence cultivated soils do not pose any radiological risk.