OCCURRENCE OF POLYCYLIC AROMATIC HYDROCARBONS (PAHS) IN ILOILO RIVER, PHILIPPINES

Polycylic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that have received special attention due to their highly mutagenic and carcinogenic properties. The objective of this presentation is to investigate the occurrence, distribution, concentration and potential sources of PAHs in Iloilo River, Philippines using geochemical techniques. Biomarkers, which include steranes and hopanes were also analyzed in order to determine the influence of petroleum. Studies on the persistent organic pollutants are very limited in the tropical /subtropical countries in Asia. These pollutants can be quickly dispersed into the atmosphere and into aquatic systems from point sources due to mild to high tropical temperatures and heavy rainfall in the region. Six sampling stations were established along the 10-km long Iloilo River in the Philippines. In order to assess the influence of precipitation on the concentration of organic compounds in the river, sediment and water samples were collected during the wet and dry season, with a time difference of one month.

Concentration of PAHs was especially high when the sediment samples were taken during the dry season (1105.5 – 3134.3 µg/g) in comparison to the wet season (518.6 – 1304.8 µg/g). PAH concentration peaked at the middle reach of the river (Station 5) in both wet and dry seasons since the area is the confluence of Iloilo River and Dungon Creek thus receiving more organic material. Parameters including isomer ratios, the dominance of 4- to 6- ring parent PAH compounds particularly pyrene, and high parent/alkylated PAH ratios indicated a pyrogenic (combustion) source for the sediments in Iloilo River. Motor vehicles from heavy duty diesel engines were a significant source of PAH emissions. A relatively smaller contribution from pyrogenic (petroleum – derived; most from the Middle East oil) was also evident, based on hopane and sterane biomarkers. Perylene, a high molecular weight PAH of biogenic/diagenetic origin, often associated with an anoxic marine environment, was also abundant except in the upstream portion of the river.