Évaluation de la contribution du potassium-40 généré par les activités agropastorales à la dose efficace totale par ingestion de plantes

Abstract

This study assesses the level of radioactivity, its corresponding dose and risk in areas of intense agropastoral activities in the Mayo-Sava, Mayo-Tsanaga and Mayo-Kani Divisions of the Far North region of Cameroon. The ultimate aim is to show that beyond the geological structure and mineralogical composition of the soil, agricultural fertilizers and animal droppings from livestock farming can contribute significantly to the elevation of the K-induced radioactivity level in an environment. Natural radionuclide analysis was carried out on 55 soil samples collected from the three aforementioned localities, using a laboratory NaI (Tl) gamma spectrometer. The 40 mean activity concentrations of 238 232 40 U, Th and K were 41, 59 and 529 Bq/kg respectively. 40 The total effective dose, the risk of cancer morbidity and the absorbed dose rate were ge- nerated by RESRAD-ONSITE 7.2 and RESRAD-BIOTA 1.8 respectively. The 0.7 mSv/year maximum total effective dose was estimated at time t= 38 years, with contributions of 56%, 37.3%, 3.9%, 2.1%, 0.7% and 0.07% from plant ingestion, external exposure, meat ingestion, milk ingestion, soil ingestion and inhalation, respectively. Potassium-40 ( K) from plant ingestion is the ma jor contributor. The doses in the initial year of agropastoral activity and the total excess cancer risk were 0.3 mSv/year and 1, 165 × 10−3 respectively. The K contributions to effective dose from plant ingestion obtained in this work are high compared to areas where agropastoral activities are not intensive. This may be due to the various fertilizers and animal droppings distributed in nature which are very rich in potassium. Although potassium is essential to life, it is nevertheless necessary for radiation protection to take into account this type of radiological exposure which is not without harmful effects on the environment and health. As for absorbed dose rates generated by the RESRAD-BIOTA 1.8 code, the level of public exposure to natural radioactivity reported is low in the present work. However, K contributes the ma jority of the total absorbed dose rate from plants and animals. This contribution is estimated at 98.6% in Mayo-Sava and Mayo-Tsanaga and 98.2% in Mayo-Kani. For the total absorbed dose rate from terrestrial animals, the contribution of K is estimated at 91.7% in Mayo-Tsanaga and Mayo-Sava, and 97.9% in Mayo-Kani. Finally, the results generated by the RESRAD-BIOTA 1.8 code are in perfect agreement with those generated by the RESRAD- ONSITE 7.2 code.