Acumulação de Ra-226, Ra-228, Th-228 e K-40 em raízes de Ipomea batatas (L.) LAM

Abstract

Studies relative to transfer of radionuclides in soil-vegetable system to plants grown in high radioactivity (NORM) soils are important for assessing food contamination and evaluate the level of ionizing radiation to which people are expose. Furthermore, radionuclide accumulator plant such as Ipomea potatoes (sweet potato) can increase the transport of radioactive contaminants if they are developed in soils with technologically concentrated naturally occurring radioactive (TENORM). Thus, the present work aimed to determine the soil-root transfer factors of I. potatoes growing in soils with natural radionuclides from the metropolitan region of Recife, as well as to evaluate the mobility of natural radionuclides in TENORM contaminated soils simulating undesirable radioactive contamination in soils under I. potato crops. Test 1 consisted of sampling of the enriched with natural radionuclides soil (NORM), assembly of vases for sweet potato cultivation. In Test 2, the soils were doped with oil fouling, with the purpose of obtaining theoretical statistics of 250, 500, 750 and 1000 Bq kg-1. After 5 months of greenhouse cultivation, root and soils on the profiles 0-5 cm, 5-10 cm and 10-15 cm depths. Succeeding drying, milling and sieving, followed by transfer of 30 g of soil and 7 g of root to petri dishes and sealing, the capsules remained for 21 days under controlled conditions to ensure the secular balance between the radionuclides and Rn-222, followed by natural radioactivity measurement by High Resolution Gamma Spectrometry with HPGe detectors. Radionuclides Ra-226, Ra-228, Th-228 and K-40 were quantified after 80.000 seconds of measurement for geological samples and 200.000 seconds for roots. The results obtained from the test attested to the accumulation of Ra-226, Ra-228, Th-228 and K-40 in the roots of the plants. The transfer factors (FT) values for Ra-226 found ranged from 0.14 to 0.40, 0.44 to 0.76, 0.27 to 0.80 and 1.44 to 12.93, respectively. The FT values for Ra-226 demonstrated preferential accumulation compared to Ra-228 and Th-228. In the second trial, it was found that there was no vertical migration of the radionuclides between doped soils with encrusted and the sweet potato. The roots of I. batatas plants did not respond to contamination, indicating that in a hypothetical soil contamination scenario, the contaminants would not be transferred to the food chain.