Sources of sedimentary PAHs in tropical Asian waters: Differentiation between pyrogenic and petrogenic sources by alkyl homolog abundance

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 (Sigma PAHs: approximately 1000 to approximately 100,000 ng/g-dry) than in rural areas ( approximately 10 to approximately 100g-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+methylbenz[a]anthracenes to chrysene+benz[a]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 approximately 0.5, MPy/Py approximately 0.1, and MC/C approximately 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 approximately 1-4, MPy/Py approximately 0.3-1, and MC/C approximately 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.

Petroleum-related hydrocarbons in deep and subsurface sediments from South-Western Barents Sea

“…a hopanogram) may yield information on the particular source and has been used to determine specific oils (e.g. Boehm et al, 2001;Bartolomé et al, 2007;Saha et al, 2009). Due to a large number of isomers and low biomarker levels in more recent sediments, GC-MS analysis of biomarkers requires a fine-tuned analytical method and a thorough sample purification procedure.…”

Distribution and Source of Sedimentary Polycyclic Aromatic Hydrocarbon (PAHs) in River Sediment of Jakarta

“…Anthropogenic sources of PAHs include the combustion of organic matter from wood or fossil fuels as well as biomass. Forest fires, vehicle engines combustion by gasoline or diesel fuel, industrial operations and garbage incineration are classified as pyrogenic sources [8]. The other sources are petrogenic, including crude oil and petroleum products such as kerosene, gasoline, diesel fuel, lubricating oil and asphalt.…”

“…Climate conditions and socio-economic circumstances could be some of the factors affecting the distribution of PAHs. Both petrogenic and pyrogenic PAHs were recorded in many studies [8][9][10][11]. Studies of these compounds have been conducted in many countries, but there is only limited data from Indonesia, although industrialization, urbanization, and motorizations have been increasing significantly since several decades ago.…”

Distribution, input pathway and mass inventory of black carbon in sediments of the Gulf of Thailand, SE Asia

“…However, a vast majority of the existing studies on the sedimentary BC in the coastal margins were geographically within high-latitude regions (e.g., Europe and America), such as the Northern European shelf (Sanchez-García et al, 2012), the Gulf of Cadiz (Sanchez-García et al, 2013), the Gulf of Maine (Gustafsson and Gschwend, 1998;Flores-Cervantes et al, 2009), the pan-arctic estuaries (Guo et al, 2004;Elmquist et al, 2008); the Washington coast (Dickens et al, 2004), etc., however, only little attention has been paid to the continental shelf of Asia (e.g., Wang and Li, 2007;Sun et al, 2008), particularly for the Southeast Asia (SE Asia), a tropical region, which has been identified as a major BC emission source region due to frequent forest fires, biomass burning and escalating fossil fuel utilisation (Streets et al, 2003). Moreover, the tropical coastal margins in SE Asia also serve as an important source emission region for coastal BC export due to the inherent nature of rapid transferring of land-based materials into the aquatic system via strong rain and surface runoff (Nittrouer et al, 1995;Zakaria et al, 2002;Saha et al, 2009). Therefore, the coastal sediments from tropical SE Asia may be an important reservoir for the exported BC from the adjacent landmass.…”

“…The Gulf of Thailand (GOT), a shallow and semi-enclosed shelf sea in SE Asia, has been subjected to a huge BC emission from biomass burning, forest fires and fossil fuel consumption from the adjacent regions (Saha et al, 2009;Sahu et al, 2011;Huang et al, 2013). Because of the nutrient-rich, shallow waters and their confined nature, the ecosystem of the GOT is especially vulnerable to human activities (Srisuksawad et al, 1997), and increased anthropogenic activities around the GOT have induced severe environmental pollution, especially for the upper Gulf with significant river export of land-based contaminants (e.g., the Chao Phraya River) (Wattayakorn et al, 1998).…”