Detail Is combustion the major source of chlorinated dioxins and dibenzofurans to the environment? A mass balance investigation Bibliografi Author: Baker, John Isaac ; Hites, Ronald A. (Advisor) Topik: CHEMISTRY; ANALYTICAL|ENVIRONMENTAL SCIENCES Bahasa: (EN )    ISBN: 0-599-66861-X     Penerbit: Indiana University     Tahun Terbit: 2000     Jenis: Theses - Dissertation Fulltext: 9962759.pdf (0.0B; 0 download) Abstract Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) are byproducts from the manufacture of chlorinated chemicals; however, ubiquitous environmental contamination by PCDD/F has historically been attributed to combustion sources. Despite significant growth in the available data for emission and deposition, it still appears that total PCDD/F deposition exceeds emissions. We focused our efforts to explain this phenomenon by first examining the possibility that deposition was biased high. To improve estimates of PCDD/F deposition to the oceans, we collected air samples at Bermuda and Barbados. A total 58 air samples were analyzed for PCDD/F and we used these data to calculate a total deposition to the world's oceans of about 1 t/yr as compared to a previous estimate of 12 t/yr to land. To investigate whether recent time-trends have biased high land deposition estimates obtained from soil measurements, we analyzed PCDD/F in two dated sediment cores from Siskiwit Lake, a remote lake on Isle Royale in Lake Superior. We used these data to compare soil concentrations, obtained from Ryan Island on Siskiwit Lake, to sediment concentrations. We calculated similar values from both media indicating that land deposition has not been overestimated. Further examination of these sediment cores provided preliminary evidence that another atmospheric source of PCDD/F exists. Finally, we conducted a global mass balance by first developing a method to estimate PCDD/F emissions from countries where these data are lacking. Second, we accounted for PCDD/F degradation in the atmosphere through reactions. Finally, we compared the remaining PCDD/F after reaction with depositional estimates. We found that most of the mass balance discrepancy is due to the octachlorinated dibenzo-p-dioxin (OCDD) congener. We explain this finding by providing evidence that OCDD is generated photochemically from pentachlorophenol (PCP) in water, and we suggest that the photochemical synthesis of OCDD from PCP in atmospheric condensed water is the most significant source of OCDD to the environment. Opini Anda Klik untuk menuliskan opini Anda tentang koleksi ini! Lihat Sejarah Pengadaan  Konversi Metadata   Kembali

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