No abstract

Mercury (Hg) is a toxic element released into the environment mainly by anthropic activities. Consequently, the improvement for Hg determination in environmental samples is of great interest. Instrumental Neutron Activation Analysis (INAA) is considered an adequate method to determine several elements. However, Hg determination by INAA is often hampered by its volatility, which causes losses. The aim of this study was to establish adequate irradiation conditions for Hg determination in environmental samples by INAA. The following parameters were evaluated: irradiation time, container for irradiation and spectral gamma ray interferences. For the study, aliquots of certified reference materials (CRMs) and tree bark samples were irradiated together with Hg synthetic standard at the IEA-R1 nuclear research reactor. Gamma ray activities of 197Hg and 203Hg were measured in a spectrometer coupled to a HGe detector. Obtained results indicated that polyethylene capsules or envelopes can be used as container for sample irradiation and the Hg impurities in these containers were negligible. Irradiation time of one hour was adequate for Hg determination and in long irradiations of 8 h problems of spectral interference of 198Au and 75Se were observed. In addition, Hg loss during the irradiation of 1 h and after irradiation was not observed. Quality control of Hg results, obtained in the CRMs analyses using one hour of irradiation, indicated good precision and accuracy with HORRAT < 2 and |Z score| < 2. The experimental conditions established in this study were applied to tree bark samples. Detection limits in these analyses were between 0.14 and 1.9 µg g-1.

Tree barks have proven to be a valuable source of information on air quality. Nowadays, studies with this biomonitor are constantly being developed. However, data of several factors that affect the accumulation of the pollutants in the barks, such as bark porosity, duration of the deposition on the bark and dispersion or variability of pollutants in a defined area, are scarce in the literature. The aim of this study was to evaluate the spatial variability of chemical elements concentrations accumulated on Sibipiruna (Cenostigna pluviosarum) barks in order to examine their aerial dispersion in two small urban areas of the Metropolitan Area of São Paulo. The neutron activation analysis (NAA) applied in the analyses consisted of irradiation the aliquots of the sample together the synthetic element standards at the IEA-R1 nuclear reactor. Concentrations of the As, Br, Ca, Co, Cr, Cs, Fe, K, La, Mn, Rb, Sb, Sc, V and Zn were determined in tree barks using short and long irradiations. Results obtained in the analyses of the tree bark samples indicated that the variability of element concentrations depends on the element, study area and numbers of trees. The variability of element concentrations in general was higher for elements presenting low concentrations. Quality control of the analytical results was evaluated by the analysis of INCT-MPH-2 Mixed Polish Herbs Certified Reference Material and these results presented good accuracy with values of standardized difference or |ζ score| ≤ 2, indicating that the procedure of NAA applied is suitable for the analyses.

Tree barks are considered a promising indicator of air pollution monitoring, because of its accumulation of aerosol particles, simplicity of species identification and wide geographical distribution. However, there are no established protocols for its sampling as well as there are no detailed studies on its usability as an alternative or complementary indicator of atmospheric pollution. In this study, barks from very common tree species, Sibipiruna (Poincianella pluviosa) and Tipuana (Tipuana tipu), were analyzed to define experimental conditions for their use as biomonitor of air pollution. Bark samples collected at the São Paulo city were cleaned and ground for analysis. Instrumental neutron activation analysis (INAA) was applied for the determination of As, Br, Ca, Co, Cr, Fe, K, Sb, Sc and Zn and graphite furnace atomic absorption spectrometry (GF AAS) for Cd and Pb. Results obtained in these analyses indicated that species of trees, bark surface layers taken for analysis as well as tree trunk diameter or tree age should be considered for use tree bark as a biomonitor. Analytical control of results carried out by analyzing certified reference materials demonstrated that INAA and GF AAS techniques can provide reliable data for element concentrations with standardized differences, |Enscore | < 1.