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Sources of sedimentary PAHs in tropical Asian waters: Differentiation between pyrogenic and petrogenic sources by alkyl homolog abundance |
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| Authors: | Mahua Saha Kaoruko Mizukawa Hideshige Takada Mohamad P Zakaria Bui Cach Tuyen Ruchaya Boonyatumanond Badal Bhattacharya Touch Seang Tana |
| Institution: | a Laboratory of Organic Geochemistry (LOG), Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan b Faculty of Science and Environmental Studies, Universiti Putra Malaysia, Malaysia c College of Agriculture, Can Tho University, Vietnam d Nong Lam University, Ho Chi Minh City, Vietnam e Science Education Department, De La Salle University, Manila, Philippines f Environmental Research and Training Center, Bangkok, Thailand g Department of Marine Science, University of Calcutta, Kolkata, India h Institute of Ecotoxicology and Environmental Sciences, Kolkata, India i Department of Ocean Development, Government of India, NIOT Campus, Chennai, India j Economic, Social and Cultural Observation Unit, Phnom Penh, Cambodia |
| Abstract: | We collected surface sediment samples from 174 locations in India, Indonesia, Malaysia, Thailand, Vietnam, Cambodia, Laos, and the Philippines and analyzed them for polycyclic aromatic hydrocarbons (PAHs) and hopanes. PAHs were widely distributed in the sediments, with comparatively higher concentrations in urban areas (∑PAHs: ∼1000 to ∼100 000 ng/g-dry) than in rural areas (∼10 to ∼100 g-dry), indicating large sources of PAHs in urban areas. To distinguish petrogenic and pyrogenic sources of PAHs, we calculated the ratios of alkyl PAHs to parent PAHs: methylphenanthrenes to phenanthrene (MP/P), methylpyrenes + methylfluoranthenes to pyrene + fluoranthene (MPy/Py), and methylchrysenes + methylbenza]anthracenes to chrysene + benza]anthracene (MC/C). Analysis of source materials (crude oil, automobile exhaust, and coal and wood combustion products) gave thresholds of MP/P = 0.4, MPy/Py = 0.5, and MC/C = 1.0 for exclusive combustion origin. All the combustion product samples had the ratios of alkyl PAHs to parent PAHs below these threshold values. Contributions of petrogenic and pyrogenic sources to the sedimentary PAHs were uneven among the homologs: the phenanthrene series had a greater petrogenic contribution, whereas the chrysene series had a greater pyrogenic contribution. All the Indian sediments showed a strong pyrogenic signature with MP/P ≈ 0.5, MPy/Py ≈ 0.1, and MC/C ≈ 0.2, together with depletion of hopanes indicating intensive inputs of combustion products of coal and/or wood, probably due to the heavy dependence on these fuels as sources of energy. In contrast, sedimentary PAHs from all other tropical Asian cities were abundant in alkylated PAHs with MP/P ≈ 1-4, MPy/Py ≈ 0.3-1, and MC/C ≈ 0.2-1.0, suggesting a ubiquitous input of petrogenic PAHs. Petrogenic contributions to PAH homologs varied among the countries: largest in Malaysia whereas inferior in Laos. The higher abundance of alkylated PAHs together with constant hopane profiles suggests widespread inputs of automobile-derived petrogenic PAHs to Asian waters. |
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