Monitoring of Ra-226 and Ra-228 in manioc (Manihot utilissima) and its flour in uranium mining in Caetite - Tropical area in Brazil

Full text: Tropical ecosystems have few developments from the radioecology point of view. In Brazil, radioecology studies had their development mainly in the 50's decade, but a little attention has been given to the radionuclides in food. The Uranium Concentrate Unit of 'Caetite' started operation in the 90's decade, and was preceded by the environmental pre-operational monitoring program, carried out during 15 years (1982-1999), according to established licensing procedures, using biological samples from the human and animal food chain. This work shows the results of last ten years of the pre-operational monitoring program of 'Caetite' in manioc (Manihot utilissima) and it's flour. The parameters studied are Ra-226 and Ra-228. Manioc (and it's flour) was chosen because of its role as the most important component of human food chain (82 kg/year for manioc and de same for manioc flour). This study was performed in 44 results of Ra-226 and 44 results of Ra-228 analyses, in 22 samples of manioc and 22 samples of manioc flour. For the analysis, initially, the Anderson-Darling goodness-of-fit test for the maximum likelihood to the gaussian distribution is executed. With the data adjusted to the gaussian curve, an Analysis of variance (ANOVA) test is executed. If there is difference between concentrations, t Student tests are then executed. The data have shown best goodness-of-fit to the log-normal distribution. After proper transformation (y=Ln(x+1)), data have shown best goodness-of-fit to the normal distribution. The ANOVA test applied to normalized data have pointed differences in concentrations, that were identified by t Student tests as the Ra-226 values in manioc and the Ra-228 values in manioc flour. All other values are statistically equal. (author)