Understanding of automobile-derived pollution in tropical Asian waters

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Surface sediment samples were collected at 143 riverine and coastal locations in the tropical Asian countries (i.e., Thailand, Cambodia, Laos, Malaysia, Philippines, Vietnam, Indonesia, and India) in 2003-2005. Polycyclic aromatic hydrocarbons (PAHs) together with hopanes and benzothiazoles were analyzed for the sediment samples by gas-chromatograph equipped with mass spectrometer (GC-MS) following accelerated solvent extraction (ASE) of freeze-dried sediments, two-step silica gel column chromatography. Total PAH concentrations ranged from 6 ng/g-dry sediment to 265,000 ng/g. The concentrations of sedimentary PAHs were categorized as low to middle in comparison on global scale. The lower concentrations can be ascribed to dilution by soil which is intensively supplied by surface runoff associated with frequent and heavy rain inherent in the tropical climate zone.PAH profiles in sediments from urban areas in the tropical Asia except for Kolkata, India, exhibited strong petrogenic signatu … More re. A ratio of methylphenanthrenes to phenanthrene (MP/P ratio), which has been utilized for source-discrimination of PAHs, was more than 2 in many locations in all the cities examined in the tropical Asia, indicating that wide-spread inputs of petrogenic PAHs occur in urban areas in the tropical Asia. This extensive inputs of petrogenic PAHs provides striking contrast with dominance in pyrogenic inputs in developed countries where MP/P ratios are less than unity in many cases.Bioaccesibility of sedimentary PAHs were studied by in vitro extraction method using aqueous solution of sodium dodecylsulfate (SDS) as simulated digestive fluid. Bioaccessibility of PAHs (proportion of PAHs extracted with SDS to PAHs ultrasonically extracted with DCM) was〜30% to〜70% for Malaysian sediments whose MP/P ratios were〜3 to〜7, whereas those for Japanese sediments with MP/P ratio less than 2 were〜5% to〜40%. This suggests that petrogenic PAHs found in tropical Asian waters are more bioavailable than pyrogenic PAHs. The higher bioaccessibility is consistent with higher PAHs concentrations with higher MP/P ratios observed in mussels collected from Malaysian west coast than those from Tokyo Bay.Detailed sources of the petrogenic PAHs were estimated through intensive statistical analyses (cluster analysis and multi regression analysis) of PAHs and hopane profiles. Also analyses of benzothiazoles, molecular markers of tire-wear particles and street dusts, and heavy metals were applied to assist the source-identification. The analyses indicated that the petrogenic PAHs are derived from automobiles and the street dust was identified as the dominant pathway of PAHs to the aquatic environments. Furthermore, used crankcase oil, tire-wear particle, asphalt, and diesel exhaust were identified as primary sources of the PAHs to the street dust and sediments. Predominant contribution of street dust was supported by positive correlation between PAH concentrations and several metals abundant in tire (e.g., Cd, Zn). Less