OCCURRENCE OF ORGANIC POLLUTANTS: PAHs IN WATER BODIES AROUND KELANITISSA AND KERAWALAPITIYA POWER PLANTS IN SRI LANKA

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds with more than one benzene ring formed due to natural processes such as forest fires and anthropogenic activities. These ubiquitous contaminants have gathered an interest due to their toxicity and carcinogenic activity. Exposure to PAHs has also been linked with cancer, cardiovascular disease and poor fetal development. PAHs are considered as persistent organic pollutants because of their stable chemical structure and inherent resistance to decomposition. In this study, the water bodies near two diesel fueled power plants in Sri Lanka i.e., Kerawalapitiya and Kelanitissa were selected to determine the presence of PAHs in surface water and its sediment. In the preliminary sampling rounds, the presence of PAHs were identified. With increased sample size, three sampling rounds were carried out. In addition to water and sediment from Hamilton canal and Sebastian canal, water samples from wells near both power plants were analyzed. PAHs in water samples were extracted to dichloromethane and analyzed by HPLC with UV-DAD (254 nm) and HPLCFLD (excitation at 250 nm, emission at 410 nm). Sediment samples were pretreated before the analysis and then, PAHs were extracted to methanol by ultrasonication. The presence of low, medium and high molecular weight PAHs in water and sediment samples obtained from both sites were detected. Total concentration of PAHs in surface water samples obtained from Sebastian canal during rainy season (April 2015), *Corresponding author Email: sri@kln.ac.lk; https://orcid.org/0000-0001-9038-7306 DOI: http:://doi.org/0.4038/josuk.v12i0.8014 This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution and reproduction in any medium provided the original work is properly credited.


INTRODUCTION
Polycyclic aromatic hydrocarbons (PAHs) are a diverse and ubiquitous class of chemical contaminants present in the environment. These PAHs are emitted as a result of carbonization and incomplete combustion of organic matter. Incomplete combustion of fossil fuels for industrial plants, heating and diesel powered motor vehicles, combustion sources inside house and workplaces are some sources of PAHs to the environment (Masih, 2012). These PAHs are also identified as semi-volatile organic compounds (SOCs) (Sehili and Lammel, 2007) and class of persistent organic pollutants (POPs) due to their increased resistance to oxidation and degradation with high molecular weights (Abdel-Shafy and Mansour, 2015). An increased attention has been given on PAHs since some of them are known to be mutagenic or carcinogenic (Ross and Nesnow 1999;Salamone et al., 1979).

According to Europe Union and United States Environmental Protection
Agency (US EPA), sixteen PAHs act as "priority pollutants" with different levels of risks in cancer (Lerda, 2010). The presence of PAHs is noted in air, soil, vegetation, ice, and water. PAHs originated from one place can be transported to another by the means of long-range atmospheric transport. As a result of their characteristics of lower water solubility, low vapor pressure, low reactivity they exist in both gas and particulate phases (Park et al., 2002). The fate and the potential of Long-Range transport of PAHs in atmosphere is greatly influenced by the partitioning between gas and particulate phases. Usually, PAHs with low molecular weight (i.e., 2-3 aromatic rings) are in equilibrium with particulate phase and gas phase whereas high molecular weight PAHs consisting of more (i.e., 4-6 aromatic rings) are mainly in the particulate phase (Wu et al., 2006). PAHs in the atmosphere can be subjected to degradation and deposition.
The PAHs can reach water bodies mainly through dry and wet deposition, road runoff, industrial wastewater, leaching from creosote-impregnated wood, petroleum spills, and fossil fuel combustion. Because of their hydrophobic properties, PAHs in aquatic environments also rapidly become associated with the particulate matter. This causes the occurrence of PAHs in sediment of water bodies (Patrolecco et al., 2010). In rivers, sediment act as a storage compartment for PAHs. Therefore, by estimating the amounts of PAHs in the environment, the level of organic contamination can be identified (Mastran et al., 1994).
Several studies have been conducted worldwide in pursuit of determining the level of pollution in coastal areas and inland lakes (Karyab et al., 2013;Patrolecco et al., 2010;Lai et al., 2011). In Sri Lanka, studies have been performed to monitor the occurrence of PAHs in Bolgoda Lake, Beira Lake and Weras Ganga located in Western province. Phenanthrene and Pyrene had been identified in the northern end of Weras Ganga by using fish species Nile Tilapia (Oreochromis niloticus) as a biomarker (Pathiratne et al., 2010). Sediment and water samples from Bathalagoda reservoir also have been studied and the PAH amount has been identified as lower than that of Beira lake.
In this study, the main objective was to identify the presence of PAHs in water bodies and its sediment around Kelanitissa and Kerawalapitiya power stations and to quantify them. AES Kelanitissa power station and Kerawalapitiya power stations are diesel fuel fired combine cycle powered power stations. As most of the PAHs in urban environments are pyrogenic in origin, there is a huge possibility of finding PAHs near the two power stations. Therefore, surface water samples and sediment samples from Hamilton canal near Kerawalapitiya power station and Sebastian canal near Kelanitissa power station were tested for the presence of PAHs. In order to confirm the atmospheric deposition of PAHs to water bodies, water samples from few wells close to each power station were tested. Sebastian canal is found around Kelanitissa power station which is located in Peliyagoda, Western Province, Sri Lanka. The estimated terrain elevation above sea level is 11 meters. It is a highly industrialized area with high traffic emission.
The Hamilton Canal which is located close to (i.e., within 2 km radius) the Kerawalapitiya power plant in Western Province Sri Lanka. The sampling sites of Hamilton canal is within the perimeter of 2 km from the Kerawalpitiya power station.
Surface water and sediment samples were collected from the canal within a radius of 2.5 km.

Sample Collection
Surface water samples close to the bank were collected from each site to amber bottles. In the first and second sampling round in 2015, 4 sub-sites were selected from each site for water and sediment sampling. In the third sampling round in 2016, eight sub-sites from Sebastian canal and five sub-sites from Hamilton canal were selected.
Five liters from each sub-site were collected. At each sampling point in Hamilton and Sebastian canals, the approximate flow rate was measured. Sediment samples containing soil at a thickness of 2.0-5.0 cm were collected to labelled containers by using a Peterson grab sampler. At each site, the depth from the surface was noted. Sediment sampling was done at the same location where the water sampling was done and stored under 10 ˚C until the extraction.

Sample Preparation
Water samples (2.0 L) were extracted using dichloromethane (3 x 50.0 mL) after filtration to remove any solid particles (Durchmesser 250 mm rundfilter The samples were sonicated at 50˚C for 1 hour. In order to further purify extracts from sediment samples, a cleanup procedure was performed. Methanol extract of sediments were concentrated into nearly 0.5 mL using the rotary evaporator. The residue was prepared for column chromatography by dissolving in dichloromethane (2.00 mL). Silica column chromatography was performed to remove the interferences before the HPLC analysis (Stationary phase-Silica, mobile phase-dichloromethane).
Fractions (10.0 mL each) were collected until the absorbance at 254 nm was constant.
Next, similar fractions were combined and evaporated to dryness by rotary evaporation.
Subsequently, the residues dissolved in Acetonitrile (0.05 mL) were stored at 10 ˚C after filtering through 0.45 micron PTFE syringe filters.

Analytical procedure
Water and sediment sample were analyzed for PAHs including EPA priority pollutants using HPLC system (Agilent 1200 series) with UV-DAD (254 nm) and Fluorescence (excitation: 250 nm, emission: 410 nm) detectors. The revered phase column chromatography was done using VYDAC C-18 PAH column. Acetonitrile: water (using a gradient program, Table 1.) was used as the mobile phase at 0.5 mL min -1 flow rate. A gradient method that began from 55:45 of acetonitrile and water was applied. Then, the proportion of acetonitrile was gradually increased up to 100:0 by a binary pump (Agilent 1200 series). After that, each sample (20 µL) was injected and HPLC traces were obtained.      (Table 5).  To identify whether the possible source of PAHs to the surface of water bodies might be due to atmospheric deposition, well water samples were analyzed by using the same procedure.     (Figure 4). W3 samples obtained near Kereawalapitiya plant also contained higher amount of BkF (0.339 µg/L) than the guideline value ( Figure 5). BkF is listed as a probable carcinogenic PAH by the US EPA (Lerda, 2010). In this study all the well water samples were taken from wells used by public for their household purposes including drinking and bathing.
Therefore, the presence of these carcinogenic PAHs might pose a serious health issue.   (Table 13) in July 2015.    Recovery studies for both water and sediment samples were done using a low molecular weight PAH (Anthracene) and a medium molecular weight PAH (Fluoranthene).