Temporal evolution of 137Cs+, K+ and Na+ in fruits of South American tropical species

Concentrations of 137Cs, K and Na in fruits of lemon (Citrus limon B.) and of K and Na in fruits of coconut (Cocos nucifera L.) trees were measured by both gamma spectrometry and neutron activation analysis, with the aim to understand the behaviour of monovalent inorganic cations in tropical plants as well as the plant ability to store these elements. Similar amounts of K+ were incorporated by lemon and coconut trees during the growth and ripening processes of its fruits. The K concentration decreased exponentially during the growth of lemons and coconuts, ranging from 13 to 25gkg−1 dry weight. The incorporation of Na+ differed considerably between the plant species studied. The Na concentration increased linearly during the lemon growth period (0.04 to 0.70gkg−1 d.w.) and decreased exponentially during the coconut growth period (1.4 to 0.5gkg−1 d.w.). Even though radiocaesium is not an essential element to plants, our results have shown that 137Cs incorporation to vegetable tissues is positively correlated to K distribution within the studied tropical plant species, suggesting that the two elements might be assimilated in a similar way, going through the biological cycle together. A mathematical model was developed from the experimental data allowing simulating the incorporation process of monovalent inorganic cations by the fruits of such tropical species. The agreement between the theoretical approach and the experimental values is satisfactory along fruit development. ► Concentrations of 137Cs, K and Na in fruits of lemon (Citrus limon B.) are presented. ► Concentrations of K and Na in fruits of coconut (Cocos nucifera L.) are also showed. ► We investigated the use of 137Cs as a tracer for the plant absorption of macronutrients. ► A model was developed to simulate the temporal evolution of 137Cs, K and Na by fruits. ► This model exhibited close agreement with our results along the fruit development.