Contribution of ⁴⁰K arising from agropastoral activities to the total effective dose by plant ingestion in the Far-North, Cameroon

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 ⁴⁰K-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 mean activity concentrations of ²³⁸U, ²³²Th and ⁴⁰K were 41, 59 and 529 Bq/kg respectively. The total effective dose to the public and the risk of cancer morbidity were generated by RESRAD-ONSITE code version 7.2. 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 (⁴⁰K) from plant ingestion is the major 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 ⁴⁰K 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.