Soil-to-crop transfer of natural radionuclides in farm soil of South Africa

The activity concentration of natural radionuclides in farm soil and most common indigenous food crops (maize, potato, cowpea) in oil-producing (Philippi, Uitenhage, and Hertenbos farms) and non-oil-producing (Ukulinga farm) areas of South Africa was measured using a Hyper Pure Germanium detector. Consequently, the transfer of these radionuclides from soil-to-crops was estimated. The mean activity concentration of 226 Ra, 232 Th, and 40 K for farm soil samples are 30.71 ± 11.77, 31.97 ± 8.90, 345.97 ± 98.62 Bq.kg −1 for Philippi; 18.67 ± 6.70, 31.55 ± 11.48, 191.93 ± 33.39 Bq.kg −1 for Uitenhage; 38.03 ± 17.44, 41.18 ± 31.54, 381.89 ± 163.40 Bq.kg −1 for Hartenbos; and 8.47 ± 2.87, 8.65 ± 3.52, 94.22 ± 25.97 ± 25.97 Bq.kg −1 for Ukulinga. The mean activity concentration of 226 Ra, 232 Th, and 40 K for crop samples are 4.54 ± 1.47, 4.87 ± 1.69, 140.18 ± 35.38 Bq.kg −1 for Philippi; 9.17 ± 4.79, 3.85 ± 1.87, 136.75 ± 22.04 Bq.kg −1 for Uitenhage; 7.97 ± 2.91, 4.62 ± 2.40, 105.97 ± 48.65 Bq.kg −1 for Hartenbos; and 4.23 ± 1.63, 2.72 ± 1.19, 48.36 ± 15.55 Bq.kg −1 for Ukulinga. The activity concentration and soil-to-crop transfer factors for 40 K were found to be much higher, possibly because this element is critical in crop growth. The results showed that the crop samples’ transfer factor is in the order cowpea>potato>maize. This study showed that activity concentrations of 226 Ra, 232 Th, and 40 K in crops and the corresponding transfer factors depend on activity concentrations of the same radionuclides in soil.