Occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in Bolgoda and Beira Lakes, Sri Lanka.

The pollution of polycyclic aromatic hydrocarbons (PAHs) has been widely used to assess the potential impact of anthropogenic activities on aquatic environments because their occurrence in water is closely tied to urban activities. Many PAHs possess mutagenic and carcinogenic properties (Menzie et al. 1992). PAH distribution and toxic potentials have therefore been the focus of numerous studies in waterways including the Great Lakes (USEPA Report 1994), Yanisei Bay (Dahle et al., 2003), and the Fraser River basin (Yunker et al., 2002). Sri Lanka, a small island nation with a dense population of about 20 million people, faces a multitude of environmental stresses ranging from deforestation to traffic congestion and the deterioration of water quality. This study was undertaken to understand the occurrence, sources, and potential impacts of PAHs in the waterways of Sri Lanka. Two lakes, Beira and Bolgoda, were selected for the study due to their economic value and high level of pollution. Beira Lake, situated in downtown Colombo, the capital city of Sri Lanka, is highly polluted. Sources of pollution are multifarious. For instance, clusters of communities have sprung up along the edges of the lake in recent times and many shacks have been built. These communities are generally not connected to municipal sewer systems and substantial quantities of domestic sewage and untreated wastewaters are discharged directly into the lake. Small industries have also grown rapidly around the lakes, most of which are not believed to have adequate facilities to treat industrial wastewater, especially organic wastes. In addition, Sri Lanka has experienced an upsurge of motor vehicles, including millions of three-wheelers and minivans that are powered by leaded gasoline and diesel fuels. Traffic congestion and severe air pollution due to vehicle emissions are now common daily occurrences and are considered a major potential source of PAHs in the lakes. Although Bolgoda Lake is situated some distance from Colombo, it is heavily polluted due to the growing number of towns with an attendant increase in small businesses and various industries along its shores. These new developments have undoubtedly impacted the lake through the discharge of PAHs and other anthropogenic chemicals present in industrial wastewater and from street runoffs. The lake, additionally, receives a large quantity of pollutants from the industrial zone in the north. The pollution caused by PAHs has led to various studies on the distribution and origin of PAHs in the environment (Yunker et al., 1996; Budzinski et al., 1997). Based on the proportions of different PAHs, most studies aim to distinguish PAHs of petrogenic sources from those of pyrolytic origins. The PAHs of petrogenic origin, prevalent in coals and fossil fuels, are formed from diagenesis of sedimentary organic material under low to moderate temperature and tend to consist of low-molecular-weight PAHs with two to three aromatic rings (Potter et al., 1998). The pyrolytic PAHs, on the other hand, are formed at much higher temperatures (greater than 500 degrees C for example) and consist mainly of four or more aromatic rings (Commins, 1969). Thus, an increase in the proportion of higher-molecular-weight PAHs is taken to be indicative of contaminations of mainly pyrolytic origin. The prevalence of high-molecular-weight PAHs in the urban dusts (Wise et al., 1988) and in atmospheric particles (Sicre et al., 1987) illustrates the chemistry of their formation at high temperature. The purpose of this study was to determine the PAH concentrations and distribution with respect to sampling location, origin and sources in two polluted lakes.