The application of phosphogypsum in agriculture and the radiological impact

Radium-226 in phosphogypsum produced in a phosphate industry, SICNG operating at Thessaloniki, Northern Greece since May 1966, varied from 261 to 688 Bq kg−1 (mean value 508 Bq kg−1). This radionuclide in soil tilled with phosphogypsum used for agricultural purposes varied from 50 to 479 Bq kg−1 (average 205 Bq kg−1), while in the regular soil of cultivated fields it varied from 37 to 54 Bq kg−1 (average 48 Bq kg−1). Radium-226 in rice originated from cultivated fields tilled with phosphogypsum or not varied from 0.36 to 1.98 Bq kg−1 (average 1.53 Bq kg−1) with the higher values observed in samples originated from cultivated fields tilled with phosphogypsum. Radium-226 transfer factors, TF, from soil tilled with phosphogypsum to plants for the case of rice varied from 6.5 × 10−3 to 2.0 × 10−2 (geometric mean: 1.1 × 10−2). A mean 226Ra content in rice 1.53 Bq kg−1 results in a daily intake of 226Ra by humans in Greece 0.0084 Bq day−1 leading to an annual effective dose for adults 0.86 μSv y−1 which is much less in contributing to the average exposure to natural radiation sources (2.4 mSv y−1) and particularly to the part due to ingestion (0.29 mSv y−1). It is necessary to continuously control (monitoring) 226Ra in phosphogypsum before any use for agricultural purposes.