The Use of Neutron Activation Analysis in Environmental Pollution Studies

摘要

Environmental samples and localized species from a marine environment, water samples for public drinking, sediment core samples from a polluted marine environment, soil samples from tin-tailing dump sites, air particulate matter and leachates from landfills were analyzed for their trace, toxic elemental contents, chemical species and natural radioactivity in an attempt to assess the safety levels of these pollutants in these matrices by means of instrumental neutron activation analysis (INAA) and other related nuclear techniques. Complementary techniques such as the graphite furnace atomic absorption spectrometry (GFAAS), ICP-MS, ion chromatography and pre-concentration steps particularly in the speciation studies were also incorporated in these studies for specific elemental determinations prior to irradiation in a neutron flux of about 5.1X10~8 n.m~(-2).s~(-1) from a TRIGA Mk.II reactor. Pre-concentration of the chemical species of As and Se was done using a mixture of ammonium pyrrolidinethiocarbamate-chloroform (APDTC-CHCl_3) while activated carbon derived from agricultural wastes was used in the iodine speciation. Some of the specific chemical species have to be separated prior to the final quantitative determination to reduce interference and enhance the sensitivity of the INAA technique. These include arsenic, selenium and iodine species present in various matrices. The more toxic inorganic arsenic, selenium, iodine and a host of other trace elements were detected in these samples by quantifying their respective y-rays emitted from the radioisotopes. The amounts of As(III) present vary from about 1.8 ng/g to 15.5 ng/g in localized marine species, 0.1 ng/g to more than 5.0 ng/g in treated public drinking water while the more toxic inorganic Se(IV) is present in the range of 1.5 μg/L to about 4.5 μg/L. The distribution patterns of pollutants were presented on maps and deductions were made from these patterns to address pollution issues. Results obtained from the analysis of sediment core samples taken from a fairly polluted marine environment were analyzed for the REE contents to determine the concentrations of La, Ce, Sm, Eu, Tb, Dy and Yb using instrumental neutron activation analysis. Core samples were divided into strata of between 2 to 3 cm intervals and prepared in the powdered form before irradiating them in a neutron flux of about 5.0X10~(12) n.cm~(-2).s~(-1) in a TRIGA Mk.II reactor. Down-core concentration profiles of La, Ce, Sm, Eu, Tb, Dy and Yb in 3 core sediments from three sites are obtained. The shale- normalized REE pattern from each site was examined and later used to explain the history of sedimentation by natural processes such as shoreline erosion and weathering products deposited on the seabed and furnishing some baseline data and/or pollution trend occurring within the study area. The shale-normalized REE patterns also showed that LREE in the sediment samples exhibit enrichment relative to HREE particularly, La and Sm showing enrichment compared to the ratios in shale. REE concentrations of 124 μg/g at the surface of sediment collected at two of the three sites were found to decrease to 58 and 95 μg/g, respectively. This was of particular interest when it is used to explain the anomalies occurring in the marine sediment as a result of geochemical processes over a long period of time. The air pollution trend in the Asia Pacific region was also studied for source emission identification with samples collected using the Gent Stack Sampler and modeling was done using the Chemical Mass Balance-7 and Statgraphic software. About 100 filters were analyzed and close to about 60% of the mass within the paniculate matter group has been identified. All determinations were validated using suitable SRMs.