| dc.description.abstract | In this study, we have established an analytical protocol for high-precision Sr-Nd-Pb isotope ratio measurements on a variety of environmental materials, including airborne particles, riverine materials, and solid waste. We have successfully used this technique to better constrain metal sources and transport in the highly human-impacted environment of Taiwan. Detailed information on the literature review and methodology are given in Chapter 1.
In Chapter 2, we present a comprehensive approach for tracing possible Pb sources in PM10 in central Taiwan by using chemical characteristics, Pb isotope ratios, and reanalysis datasets (ECMWF). The results suggested that Pb in PM10 was predominantly contributed from oil combustion and oil refineries during the local events (48–88%), whereas the lowest contributions were from coal combustion (< 21%). During periods of high wind speed, the contribution from natural sources increased significantly from 13 to 31%. Despite Pb represented only a small portion of PM10, a strong correlation (r = 0.89, p < 0.001, multiple regression analysis) between PM10 mass and the concentrations of Pb, V, and Al was observed in the study area, suggesting that the sources of PM10 in central Taiwan can be possibly tracked by using chemical characteristics and Pb isotopes in PM10. Moreover, the Pb isotopic signatures of PM10 collected during the LRT event confirmed the impact of airborne pollutants from Mainland China, and the chemical characteristics of the PM10 significantly differed from those collected during local events.
In Chapter 3, we further applied Pb isotope ratios to study the characteristics of aerosols and transport from Chiang Mai (Thailand) to Mt. Lulin (Taiwan) during the Southeast Asia biomass burning season. We analyzed the inorganic compositions (water-soluble ions and trace metals) of size-fractionated aerosols collected at both sites. The chemical and Pb isotopic signatures from biomass burning in Chiang Mai aerosols are characterized by high non-sea-salt K+ concentrations, high Fe concentrations, and high 206Pb/207Pb (208Pb/207Pb) isotope ratios, suggesting greater contributions from crustal materials during biomass burning, consistent with those observed in previous studies. Aside from biomass burning signatures, we also found that aerosols with high contents of trace metals had lower 206Pb/207Pb (208Pb/207Pb) isotope ratios, indicating oil combustion and/or other industrial activities are possible sources of the observed enrichments of trace metals. The analysis of Mt. Lulin aerosols showed that biomass burning from Southeast Asia might be an important aerosol source influencing aerosol compositions at Mt. Lulin, especially for the fine particles (<0.95 µm). The chemical analyses of size-fractionated aerosols demonstrated that more information about sources of aerosols could be obtained through this approach.
Applications of the Sr-Pb isotope ratios for studying metal sources and transport in two highly polluted rivers (i.e. Agongdian River and Ji-Shuei River) in southern Taiwan are further discussed in Chapter 4. Of special interest is that in the Agongdian River, upstream waters are characterized by high Sr and Pb isotope ratios; on the other hand, most effluents collected from wastewater treatment units had low Pb isotope ratios. This makes it possible to estimate relative contributions from natural and anthropogenic sources. Time-series studies were carried out in both river catchments. A simple isotope-mixing model estimated that a major portion of Sr could be originated from upstream waters (63~76%), whereas contributions from industrial sources are relatively small (25~36% and 0.3~0.4% for industrial sources with low 87Sr/86Sr and other industrial effluents, respectively) in the Agongdian River. Contributions of Pb vary significantly, with 9-85% and 15-91% originating from natural and industrial sources, respectively. The results of Pb isotope analyses further suggested that high concentrations of Pb during the rain events were most likely natural Pb derived from crustal materials.
In Chapter 5, we further evaluate the potential of using Sr-Nd-Pb isotope ratios to distinguish sources of solid wastes from the same types of industries. Materials including solid waste (slag) and auxiliary materials were analyzed to further constrain sources of Sr-Nd-Pb in slags from three steel smelting plants. The results show that Sr-Nd-Pb isotope ratios in slags and auxiliary materials have great potential for discriminating reductive or oxidative slags from the three plants. However, isotope ratios of slags can be significantly different over time, most likely due to different sources of auxiliary materials. The measured isotope data of the auxiliary materials indicated that Sr and Nd isotope ratios in slags were mainly controlled by lime and ferro-silicon, and Pb isotope ratios were most likely related to ferro-silicon or ferromanganese, implying that these auxiliary materials are the key to discriminate the origins of the slags. Our results demonstrated that sources of slags can be discriminated by the combined Sr-Nd-Pb isotope ratios, and thus serves as a probe for tracing sources of slags if the databases for plants and associated materials are better constrained.
Overall, this study demonstrates the robustness of using Sr-Nd-Pb isotope ratios to trace sources and transport pathways of metal pollution in a variety of environmental materials, and has great potential for studies in environmental forensics and model validations. The multi-tracer approach developed in this study should provide important information for tracing metal sources and transport pathways in the environment increasingly impacted by human activities. | en_US |