Sources and distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments, Thailand

To assess the distribution of polycyclic aromatic hydrocarbons (PAHs) and identifying the main source of the pollutants in coastal, canals, riverine and the upper Gulf of Thailand, surface sediments were collected from urban canals (n = 8), the Chao Phraya River (n = 11), estuarine (n = 9), coastal area (n = 14) and the upper Gulf of Thailand (n = 28) and analyzed for 3-7 rings of PAHs. Sources pollutants and media of transport (ambient air, asphalt, tire, crankcase oil, soot, street dust, and street runoff) were collected from heavy traffic road in Bangkok and rural area. The research finding indicated that PAHs contaminations in Thai sediments as low to moderate. Especially, urban canals were detected at high concentration ranging from 512 to 8399 ng/g (2290 ± 2556 ng/g; n = 8). On the other hand, the coastal areas were detected at low concentration ranging from 6 to 228 ng/g (50 ± 56 ng/g; n = 14). Among the possible sources of PAHs, cluster analysis categorized that, street dust, street runoff, and canal sediment were into a single group, and indicated that street dust and street runoff are the major source and major carrier, respectively, of PAHs to urban canals. Multiple regression analysis of PAH profiles identified tire debries as major contributors of PAHs to street dust and the urban canal sediment, followed by diesel vehicle exhaust. Ruchaya Boonaytumanond, Environmental Research and Training Center, Technopolis, Pathumthani, 12120, Thailand, Tel: 66-2-5774182, Fax : 66-2-5771138, [email protected] Introduction Thailand is a developing country in tropical Asian countries, where inputs of organic pollutants from urban sources have been increasing. Especially, Bangkok is a mega-city with ~7 million inhabitants and various pollutants are derived from both point and non-point sources and it are transported to aquatic environment. Polycyclic aromatic hydrocarbons (PAHs) and their derivatives are widespread in the environment as organic pollutants. PAHs are an important class of environmental contaminants to study because some of those compounds are carcinogenic and/or mutagenic potential. The objectives of study were to assess the status of PAHs and to identify the main sources of the pollutants. Materials and Method The Gulf of Thailand is located in the western side of the South China Sea, surrounded by Thailand, Vietnam, Cambodia and Malaysia. The upper Gulf located between latitudes 13°30′N and 12°60′N and longitudes 100°00′E and 101°00′E. The sediments were collected from coastal areas (a), canals (b), estuarine (c) and the upper Gulf of Thailand (d) as shown in Figure 1. The Choa Phraya River is the main river in which passes through the Bangkok and discharges it’s water to the upper Gulf of Thailand. Addition, potential source materials (asphalt, tire, crankcase oil, vehicle exhaust soot) and transport media (street dust, and street runoff and ambient air) were collected from Bangkok area and analyzed for PAHs. The sediment samples were analyzed for 3-7 benzene rings by pressurized solvent extraction (ASE 200; Dionex) with dichloromethane (DCM)/acetone (3:1, v/v). Polar components were removed by using silica gel column. PAHs fractionation was carried out through a fully activated silica gel column and eluted with hexane/DCM (3:1, v/v). PAHs were analyzed by gas chromatography / mass spectrometry (GC-MS). Detailed instrumental conditions were described previously [Ruchaya et al., 2006]. Results and discussion All analyses were calculated on a dry weight basis and Total PAHs” means the sum of 17 PAHs. Total PAH concentrations in the surface sediments ranged from 6 to 8399 ng/g. The distribution of PAHs in sediments from urban canals ranging from 512 to 8399 ng/g, (2290 ± 2256 ng/g, n = 8), the Chao Pharya River from 33 to 594 ng/g (263 ± 174 ng/g, n = 11), estuary of the Chao Phraya River from 30 to 724 ng/g (179 ± 222 ng/g, n = 9), coastal area from 6 to 82 ng/g (50 ± 56 ng/g, n = 14), and the upper Gulf of Thailand from 73 to 741 ng/g (183 ± 195 ng/g, n = 30). It indicated that PAH contaminations in Thai sediments are categorized as low to moderate on global comparison. Figure 1 Sampling location (a) coastal areas , (b) Chao Phraya River and canals, (c) estuary of the river and (d) the upper Gulf of Thailand Source identification of PAHs in Bangkok was carried out from source materials and transport media. PAH profiles of the street dust samples were explained mainly by tires, diesel vehicle soot, and used engine oil, indicating that those are the major sources of PAHs in the street dust. Tires in particular contributed to the PAH profiles of all street dust samples. Our statistical approaches identified tire debris and soot from diesel-powered vehicles as the major and secondary contributors, respectively, to PAHs in street dust and canal sediments in Bangkok. On the cluster analysis, street dust, street runoff, and canal sediment were categorized into a single group, indicting that street dust and street runoff are the major source and major carrier, respectively, of PAHs to urban canals. References Ruchaya, B., Gullaya, W., Ayako T., Hideshige T. (2006). Distribution and origins of polycyclic aromatic hydrocarbons (PAHs) in riverine, estuarine and marine sediments in Thailand. Marine Pollution Bulletin, 52, 942-956. (B)