Summary
The present study is to determine the activity concentration of radioactive nuclide in plant fertilizers used in agriculture in the Iraqi Kurdistan Region and to estimate their radiological impact of long-term exposure due to their application. The high- purity germanium detector (HPGe) gamma spectrometer was used to determine the activity concentrations of 226Ra, 232Th, 40K and 137Cs in fifty different types of plant fertilizers that were commonly used in agriculture in Iraqi Kurdistan Region. The results showed that the mean value and a range of activity concentrations of 226Ra, 232Th, 40K and 137Cs in these fertilizers are 6.69 ± 0.91 Bq/kg (0.05 – 133.38) Bq/kg, 4.07 ± 0.87 Bq/kg (0.02 – 73.88) Bq/kg, 2480 ± 92 Bq/kg (0.4 – 11540) Bq/kg, and 0.04 ± 0.01 Bq/kg (ND – 1.17) Bq/kg, respectively. The highest value of activity concentrations of 226Ra and 232Th are found in NPK (nitrogen (N), phosphorus (P) and potassium (K)) chemical fertilizers, while the lowest values were found in Urea and Calcium fertilizers. This variation of radionuclide activities in studying fertilizers may be due to the different origins of raw material and the chemical processes during manufacturing of the fertilizer.
The highest value of activity concentration of 40K was found in potassium sulfate fertilizers, while the lowest value was found in urea and calcium fertilizers. This is due to the high concentration of K2O in potassium sulfate fertilizer. On the other hand, when comparing chemical and organic fertilizers in terms of their containment of radioactive nuclides, we noted that chemical fertilizers are more likely to be radioactive.
Concentrations of elements 226Ra, 232Th and 40K in plant fertilizer sample were calculated. The results showed that the mean value and a range of concentrations of 226Ra, 232Th and 40K in fertilizer samples are 0.56 ± 0.03 ppm (0.004 – 10.800) ppm, 1.18 ± 0.07 ppm (0.005 – 18.197) ppm, and 7.924 ± 0.41% (0.001 – 36.869) %, respectively.
The effect of the usage of chemical fertilizers on the natural radioactivity levels in agricultural soil was investigated. The results showed that the range of activity concentrations for 226Ra, 232Th, 40K, and 137Cs in virgin soils are (10.59 – 16.18) Bq/kg, (8.79 – 10.75) Bq/kg, (241.8 – 340.9) Bq/kg, and (3.76 – 8.18) Bq/kg, respectively. While the range of activity concentrations for 226Ra, 232Th, 40K, and 137Cs in agricultural soils are (11.94 – 18.24) Bq/kg, (8.8 – 12.36) Bq/kg, (247.7 – 338.3) Bq/kg, and (3.29 – 12.08) Bq/kg, respectively. The variations in the activity concentrations of naturally occurring radioactivity nuclides 226Ra, 232Th and 40K in the soil of various locations depends on the geological and geographical conditions of the area and the extent of fertilizer applied to the agricultural lands. The variations in the activity concentration of 137Cs in the soil samples are due to the fact that it is not necessary for the fall out to be uniformly distributed on the earth’s surface.
The activity concentrations of 226Ra, 232Th, 40K, and 137Cs in plant crop samples were measured by using gamma-ray spectrometry system to investigate the effect of the usage of chemical fertilizers on the radioactivity levels in the plant crops, including grain, vegetables, fruits, tubers and roots, collected from greenhouses and agricultural fields in Erbil city in Iraqi Kurdistan Region, in addition to determine the soil to plant crop transfer factor. The results showed that the range of activity concentrations for 226Ra, 232Th, 40K, and 137Cs in plant crops are (0.2 – 1.45) Bq/kg, (0.11 – 0.48) Bq/kg, (68 – 1355) Bq/kg, and (ND – 0.43) Bq/kg, respectively. The variations in the activity concentrations of naturally occurring radioactivity nuclides in plant crops are essential as a result of different plant and soil types and environmental conditions. The highest value of activity concentrations of 226Ra, 232Th, 40K, and 137Cs were found in Radishes (root crop). The lowest value of activity concentration of 226Ra was found in Courgettes, while the lowest value of activity concentrations of 232Th and 40K was found in rice grains. Except for Radish (Root crop), no activity concentration of 137Cs was detected in the other plant crops.
The calculated average and the range value of soil to plant transfer factor of 226Ra, 232Th, 40K and 137Cs are 0.04 ± 0.01(0.011 – 0.087) Bq/kg, 0.02±0.01 (0.011 – 0.046) Bq/kg, 2.03 ± 0.30 (0.201 – 5.13) Bq/kg, and (ND – 0.075) Bq/kg, respectively. A wide range in value of soil to plant crop transfer factor has been observed, mostly as a result of different soil and plant crop types and ecological conditions. Interactions between radioactive nuclides in soil and root of the plant are very complicated and depend on soil characteristics, type of plants and climatic conditions.
The highest value of soil to plant crop transfer factor for 226Ra, 232Th, 40K and 137Cs were observed in radish (root crop). The lowest value of soil to plant crop transfer factor for 226Ra was observed in Courgette, and for 232Th and 40K the lowest value of soil to plant crop transfer factor was found in rice. This may be due to the concentration of radioactive nuclide in the plant crops, which depends on the metabolic characteristics of the plant species.
To estimate the radiological hazard due to the exposure of the farmers and workers in the plant fertilizer factory and stores, as well as to estimate the radiological hazards to farmers’ health resulting from exposure to gamma-rays emitted from radionuclides exist in soils from agricultural fields, the radium equivalent activity (Raeq), the external absorbed dose rate (DR), annual effective dose (AED), external hazard index (Hex) and excess lifetime cancer risk (ELCR) for different types of fertilizer samples, virgin and agricultural soils were calculated. From the obtained data about these radiological hazard parameters, we conclude that the use of plant fertilizers to enhance crop yield enhances the exposure of workers working in a fertilizer factory and stores of fertilizer materials and farmers in agricultural fields.
The annual effective dose from the consumption of plant crops by adults represented by ingestion annual effective dose (IAED) and the internal hazard index (Hin) were calculated. The total and the range value of the ingestion annual effective dose due to the intake of 226Ra, 232Th, and 40K from consumption of plant crops are 30.50 ± 8.88 (0.01 – 33.50) µSv/y, 9.27 ± 3.04 (0.004 – 8.14) µSv/y and 230 ± 16.65 (0.44 – 168.45) µSv/y, respectively. The highest value of the ingestion annual effective dose was found in the consumption of wheat grain, because it is the main food of the Iraqi people and is most commonly used for making Nan, bread, and rusk. The lowest value of the ingestion annual effective dose was found in the consumption of hot pepper by adults because the amount of hot peppers eaten by people is low. The total value of the ingestion annual effective dose due to the intake of 226Ra, 232Th, and 40K in plant crops is 269.7 µSv/y. This indicated that the radiation dose due to the consumption of plant crops in Iraqi Kurdistan Region was less than the global average value of the ingestion annual effective dose of 290 µSv/y (UNSCEAR, 2000), and poses no hazard to public health.
The activity concentration of radon gas in fertilizer samples were measured using LR-115 SSNTD and it was found to be ranging from (12.37 – 595.50) Bq.m-3, with the average value (70.76 ± 12.54) Bq.m-3. The highest activity concentration of radon was found in Total Humic (K2) fertilizer, while the lowest activity concentration of radon was found in N.P.K. Complex (NPK 6) fertilizer sample. The variation in radon activity concentration in plant fertilizer samples is due to the difference in the size of the grains and the difference in the content of 226Ra in fertilizer samples.
To investigate the effect of the usage of plant fertilizers on the radon exhalations from agricultural soils, the long-tube technique equipped with LR-115 solid-state nuclear track detector was used. The activity concentration of radon gas in virgin and agricultural soil samples were measured to be ranging from (67.71 – 221.69) Bq.m-3 and (83.51 – 230.06) Bq.m-3, respectively. The variation in the activity concentrations of radon in soil samples is due to the differences in porosity, grain size, the content of 226Ra in soil samples, and the type of fertilizer applied to the agricultural lands. The activity concentration of radon gas in the agricultural soil samples are higher than the corresponding soil samples in which no fertilizer was used (virgin soil).