Ordination of environmental data using principal component analysis: the case of the radium isotopes (Ra-226 and Ra-28) in surface waters in an area associated with NORM/TENORM mining

The radium isotopes Ra-226 and Ra-228 were analyzed in surface water at six points, during eighteen months, from June 2006 to December 2007, in the neighborhood of a mine of phosphate associated with uranium in the region of Santa Quiteria, state of Ceara, Brazil. The soluble fraction (which passes through filter of 0.45 micron) and the particulate fraction (which is retained on the 0.45 micron filter) were analyzed using the Principal Component Analysis, PCA, a method for ranking environmental data, and were analyzed also by F test for testing the difference between radionuclides and the difference between the two analyzed fractions. The PCA has identified four groups of samples. Results of Ra-226 in soluble fraction are grouped in the negative part of axis 1 (Factor 1) and axis 2 (Factor 2). Results of Ra-228 in particulate fraction are grouped in the positive part of axis 1 (Factor 1) and in the negative part of axis 2. Results of Ra-226 in soluble fraction are grouped along the positive part of axis 1 (Factor 1). Finally, results of Ra-228 in the particulate fraction are grouped in the positive part of axis 1 (Factor 1) and axis 2 (Factor 2). This last group has two discrepant points (01 and 06). There is no statistical difference between the two analyzed fractions but there are statistical differences between analyzed radionuclides. Therefore, three conclusions can be identified: The use of PCA with radionuclides and analyzed fractions as parameters permits the grouping of collecting data by their environmental similarities; the mean concentration of Ra-226 was statistically higher than that of Ra-228; and there is no statistical difference between soluble and particulate fractions. (author)