Annual Research Symposium (ARS)
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Item Monitoring anti-cholinesterase contamination in Bathalagoda reservoir, Sri Lanka(University of Kelaniya, 2008) Hemachandra, C.K.; Pathiratne, A.; Pathiratne, K.A.S.Organophosphosphorus and carbamate pesticides are widely used in Sri Lanka for agricultural pest management. They may enter inland water bodies draining agricultural watersheds and affect aquatic fauna including fishery resources. These pesticides are considered as anti-cholinesterases as they could inhibit the cholinesterase enzymes including acetylcholinesterase which plays an important role in maintaining normal functioning of the nervous system. Hence monitoring of anticholinesterase contaminations in inland water bodies is important yet difficult due to low persistence of many of these pesticides. In the present study, anticholinesterase contaminations in Bathalagoda reservoir, located in the vicinity of agricultural lands in Kurunagala District were monitored bimonthly during the period September 2007 to June 2008 using brain and muscle cholinesterases (ChE) of feral Nile tilapia (Oreochromis niloticus), as a biomarker (n=IO). ChE activities were measured using standard methods established for this fish. The results show that ChE activities in brain and muscle tissues in feral fish were depressed significantly in comparison to the laboratory reared control fish by 57-72% and 59-78% respectively in September 2007 and December 2007. There were no significant gender specific differences in the ChE levels of the feral fish at each sampling stage. The brain and muscle ChE activities in the fish collected from the reservoir at each sampling stage were negatively correlated (p < 0.05) with the rainfall in the area. The depression of ChE levels in the brain and muscle tissue of feral tilapia may indicate the exposure of fish to anti-cholinesterase contaminations present in the reservoir during rainy periods.Item Evaluation of the Potential of Selected Polycyclic Aromatic Hydrocarbons in Inducing Xenobiotic Biotransformation Enzymes in Nile Tilapia(University of Kelaniya, 2007) Hemachandra, C.K.; Pathiratne, A.; Pathiratne, K.A.S.Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous contaminants of much ecotoxicological concern in the aquatic ecosystems. They can be biotransformed in fish liver by the phase 1 CYP1A1 dependent activation enzymes such as 7-ethoxyresorufin- 0-deethylase (EROD) and the phase II detoxification enzyme, Glutathione S-transferase (GST). The present study was carried out to evaluate the potential of selected P AHs in the natural environment in inducing hepatic xenobiotic biotransformation enzymes viz. EROD and GST in Nile tilapia, a widely distributed food fish in freshwater ecosystems. The fish (n = 5-6) were treated with naphthalene (20 ~-tg/g) or phenanthrene (20 and 40 ~-tg/g) or fluoranthene ( 1, 5, and 20 11glg) or corn oil alone as the carrier (controls) and enzyme activities were determined at 1 day and 3 days after the treatment using standard methods. The results showed that the EROD activity of the fish was not affected significantly by the treatment of fish with 1 11g/g fluoranthene. However all the other PAH treatments significantly depressed the EROD activity of the fish in comparison to the controls. Hepatic GST activity of the fish was significantly increased (up to 2 folds) by the P AH treatments in a dose dependent manner. Liver somatic index of the fish was not affected by the P AH treatments. The results revealed that naphthalene, phenanthrene and fluoranthene lack the inducing ability of hepatic EROD which could produce damaging side effects through the formation of reactive intermediates that could bind covalently with cellular DNA, RNA and proteins.Item Estimation of agricultural drainage and phosphorous loading to Embilikala and Malala lagoons in the Bundala wetland systems(University of Kelaniya, 2000) Priyankarage, S.C.; Matsuno, Y.; Mallawaarachchi, A.P.; Pathiratne, K.A.S.Item Investigation of growth parameters of CuInTe2 thin films by electrodeposition technique(Research Symposium 2009 - Faculty of Graduate Studies, University of Kelaniya, 2009) Chandima, A.M.B.; Pathiratne, K.A.S.; Darmadasa, M.; Wijesundera, R.P.; de Silva, D.S.M.Copper indium di-telluride (CuInTe2) is a promising semiconductor material for photovoltaic applications because of its suitable optoelectronic properties. Among the various deposition techniques available for the preparation of CuInTe2 thin films, method of electrodeposition is an attractive technique because of its simplicity, low cost and possibility of making large area thin films. In this investigation, potentiostatic electrodeposition of CuInTe2 thin films on fluorine doped tin oxide (FTO) was studied using a three electrode electrochemical cell containing an aqueous solution of CuCl, InCl2 and TeO2. pH of the solutions was adjusted by adding ultra pure HCl. The counter electrode was a graphite rod and reference electrode was Ag/AgCl. Electrolytic solutions were prepared with deionised water and 99.995 % pure chemicals. Prior to the film deposition FTO substrates were degreased in acetone and rinsed with deionised water followed by 2 min ultra-sonication. Cyclic voltammograms were used to investigate the growth parameters; deposition potential, concentration, proportion of CuCl, InCl2 and TeO2, pH, temperature and stirring speed of the bath. In order to grow the photoactive CuInTe2 thin films, set of samples were prepared by slightly changing the deposition potential using the growth parameters obtained from cyclic voltammetric curves. Photoactive performance (Voc and Isc) of the films were characterized using I-V measurements in PEC containing aqueous solution of Na2S2O3. Highest photoactivity is given when the film deposited at -600 mV Vs Ag/AgCl for 20 min in the electrolyte containing aqueous solution of 1 mM CuCl, 20 mM InCl2 and 2 mM TeO2. Deposition temperature, pH and stirring speed of the bath were room temperature, 1.5 and 125 rpm respectively. Annealing temperature and time were 4000C and 20 minutes respectively. The preliminary results of this study suggest the possibility of growing photoactive p-CuInTe2 thin films by single step electrodepostion technique.Item Electrochemical deposition of CdS thin films using ammonium thiocynate as the sulfur source(Book of Abstracts, Annual Research Symposium 2014, 2014) Ariyasingha, N.M.; de Silva, D.S.M.; Pathiratne, K.A.S.Use of a complexing agent containing sulfur atoms which can form a charge complex with Cd2+ ions could provide a condition necessary to bring atoms or ions of both the elements Cd and S together in the form of a charge complex to the electrode surface thereby facilitating the formation of CdS on the electrode surface over other materials. In the present study, electrochemical conditions necessary to electrodeposits thin films of CdS using ammonium thiocynate as the complexing agent was studied.Item Electrochemical deposition and characterization of CdTe thin films(Book of Abstracts, Annual Research Symposium 2014, 2014) Kumarasinghe, K.D.M.S.P.K.; Chinthana, H.R.D.; de Silva, D.S.M.; Pathiratne, K.A.S.The semiconductor cadmium telluride (CdTe) has been widely used in applications of photovoltaics, sensors and detectors because of its direct band gap with high atomic number and electron density. With its narrow and direct band gap, stability with high absorption coefficient and other optoelectronic properties, it is the most ideal material for photovoltaic structures. A solar cell made of polycrystalline CdTe thin film is one of the most promising low cost materials for photovoltaic applications. CdTe was grown using different techniques such as physical vapor deposition, chemical vapor deposition, molecular beam epitaxy, close space sublimation, liquid phase deposition and electrodeposition. Electrodeposition has demonstrated numerous advantages due to its simplicity, low cost and scalable manufacturing techniques. CdTe films have been electrodeposited on fluorine doped tin oxide (FTO) coated glass substrates which have sheet resistance less than 20 ?/sq. A conventional three electrode cell was used for the deposition where a high purity graphite rod and saturated calomel electrode (SCE) were presented as the counter electrode and as the reference electrode respectively. Prior to the deposition of semiconductor layers FTO glass substrates were cleaned by a sequence of steps which included wiping out with detergent, ultrasonic washing in detergent solvents and then with deionised water followed by degreasing using acetone, methanol and isopropyl alcohol. CdTe thin films have been prepared by potentiostatic electrodeposition from acidic solution containing CdSO4, CdCl2 and TeO2. The deposition mechanism was investigated by cyclic voltammetry. The thickness of the film can be controlled by the charge passed during the deposition, and it is possible to obtain p-type and n-type materials by changing the deposition potential. Photoelectrochemical (PEC) cell measurements were carried out in order to determine the electric conductivity type of electrodeposited layers.The PEC values were determined for both as deposited and heat treated materials.The electrodeposited thin films were characterized and investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible absorption spectroscopy. The CdTe thin films were found to posses a bandgap of (1.44�0.02) eV, which is in a good accordance with those reported in the literature.Item Eletrodeposition of CdS thin films using different sulfur sources for CdS/CdTe solar cells(Book of Abstracts, Annual Research Symposium 2014, 2014) Kumarasinghe, K.D.M.S.P.K.; Chinthana, H.R.D.; de Silva, D.S.M.; Pathiratne, K.A.S.Cadmium Sulphide (CdS) and Cadmium Telluride (CdTe) are two promising photovoltaic materials for thin film solar cells. CdS is a wide band gap n-type semiconductor, which can act as a window layer. The function of CdS is to allow energetic shorter wavelength photons to pass for the incidence at the hetero-interface with minimum absorption loss. The high optical band gap of CdS (~2.42 eV) assists this function. Among the different techniques, electrodeposition is one of the most suitable low cost methods, because the material can be deposited on the desired area of the substrate thus providing a film of reproducible quality. CdS films were prepared by electrodeposition technique from CdCl2 as cadmium precursor and Na2S2O3 or (NH4)2S2O3 as sulfur precursor in aqueous medium. For the electrodeposition of CdS three electrode system was employed using glass/FTO as the working electrode (cathode), saturated calomel electrode as a reference electrode and high purity graphite rod as a counter electrode (anode). Electrochemical deposition method through the influence of the concentration of precursor species, deposition potential, deposition temperature and pH offers excellent control over the properties of thin CdS layers using a potentiostatic approach. The changes in the morphology and properties of the films prepared from different sulfur sources were studied. The CdS layers grown using Na2S2O3 as sulfur precursor show thickness below 100 nm. Voc and Jsc obtained for initial solar cells with CdS films grown using Na2S2O3 as sulfur precursor had higher values compared to that of CdS semiconductor layers grown using (NH4)2S2O3. The photoelectrochemical (PEC) cell measurements were used to identify the electrical conductivity type of the layers and it was found that as grown and heat treated material layers were of n-type for both CdS layers which were grown using different sulfur sources. Upon heat treatment, the material layers show enhanced PEC signal indicating improved optical properties. The optical absorption measurements were carried out in order to evaluate the band gap of the resulting materials. All samples exhibit a band gap value of 2.42 0.08 eV without any noticeable differences as expected. Electrodeposited CdS films were characterized by XRD for determination of bulk structure and SEM for surface analysis.Item A low cost electro-deposition procedure for growth of n- type cds semiconductor material used in fabrication of cds/cdte thin film solar cells(Book of Abstracts, Annual Research Symposium 2014, 2014) Chaturangi, R.A.; Kumarasinghe, K.D.M.S.P.K.; Pathiratne, K.A.S.; de Silva, D.S.M.CdS/CdTe thin film solar cells have exceeded the efficiencies of nearly 20% and 16% in laboratory and industrial scale devices respectively. Owing to the large band gap of 2.42 eV of CdS semiconductor, it is used as the window material in these devices. A low cost electro-deposition experimental procedure which utilizes electro-purified analytical grade chemicals and a method which does not produce wastes need to be discarded into the environment is described here. CdS thin films with thickness <100 nm was potentiostasticaly electro-deposited utilizing EG & G Princeton Applied Research Model 366 A bipotentiostat on fluorine doped tin oxide(FTO) conducting glasses which function as working electrodes in three electrode cells comprising of silver/silver chloride reference electrodes and graphite counter electrodes. Prior to use, conducting glasses were mechanically cleaned in a dust free environment. Electro-purified CdCl2 and Na2S2O3 were used as the Cd and S sources for depositing thin films of CdS on FTO glasses. Ranges of working electrode potentials, relative proportions of the two salts and the pH in the electroplating baths which could yield CdS thin films that showed satisfactory photovoltaic activities were estimated. Bath temperature and deposition time were kept at previously established values of 470C and 1 hour for all depositions. Also all CdS thin films were annealed at 400 0C for 10 minutes in air prior to estimation of their photovoltaic properties. It was found that, deposition potentials in the range of -1300 to �1500 mV with respect to silver/silver chloride electrode, concentration ratios of [Cd]/[S] = 10:1 to 15:1 having [Cd] concentrations in the range of 10 to 15 mmol dm-3 in solution and pH in the range of (1.2�1.4) in the plating bath could produce CdS thin films with optical band gaps lying in the range of (2.3 � 0.1) eV. X-ray diffraction studies showed that all CdS deposits were to consist of cubic lattice structure. Current- Voltage measurements indicated that, the thin films grown were of n-type in electrical conductivity. Photo-electrochemical cell experiments produced open circuit voltages and short circuit current densities in the ranges of -150 to -250 mV and 3.75 to 20 ?A cm-2 respectively indicating the level of photovoltaic activity that the deposits of CdS could demonstrate. Studies are in progress for further improvements of the electro-deposition procedure.Item A kinetic study on slow natural degradation of polycyclic aromatic hydrocarbons in Bolgoda Lake waters and a technique for rapid destruction of them in the aquatic environment(Proceedings of the Annual Research Symposium 2005-Faculty of Graduate Studies, University of Kelaniya, 2005) Pathiratne, K.A.S.; de Silva, O.C.P.Polycyclic aromatic hydrocarbons (PAHs) are unique environmental contaminants that exhibit strong toxic, carcinogenic and mutagenic properties. They are generated through incomplete combustion of organic matter such as fossil fuels (petrol, diesel, and natural gasses, etc.), wood and many other organic compounds used in variety of industrial and domestic processes. Once formed, they are adsorbed on to particulate matter and deposited on ground and in water bodies through continuous atmospheric fallouts. During rainy seasons, PAHs deposited on ground surfaces are washed into water bodies through surface runoff. A recent study revealed that water and sediment in Bolgoda lake to contain PAHs above safe levels. Further, the levels observed during dry seasons were found to increase after heavy rains, followed by gradual degradation during dry periods. As a part of the present investigation, the kinetics of degradations of four selected PAHs; naphthalene, phenanthrene, pyrene and chrysene (2, 3, 4 and 5 member ring compounds) found in Bolgoda lake were carried out. Four different environmental matrices given below (a) to (d): (a) Bolgoda lake water exposed continuously to incandescent radiation of a 60 W tungsten lamp at room temperature. (b) Bolgoda lake water kept in dark at room temperature. (c) Deionized water with pH and electrical conductivity (EC) adjusted to those of Bolgoda lake water, exposed continuously to incandescent radiation of 60 W tungsten lamp at room temperature (d). Deionized water with pH and EC adjusted to those of Bolgoda lake water, kept in dark at room temperature. These four different media could represent unique environmental components found in Bolgoda lake that could be responsible for degradations of PAHS in the Bolgoda lake. The results indicate that pseudo first order rate constants corresponding to degradations of all four PAHs in the four different media at room temperature decrease in the order a > b > c > d. Also, in all four media the order of the pseudo first order rate constants for degradations of the four PAHs found to vary as chrysene > naphthalene > pyrene > phenanthrene. As the other part of the investigation, the suitability of a modified Fenton based oxidation process to enhance the rate of degradation of PAHs in aquatic environment was investigated. The effect of initial concentration of H2 O2 & Fe2+ ions, pH of the solution and the presence of triton X-100, a surfactant which could bring non polar PAHs and polar Fenton reagents in close proximity to facilitate degradation reaction were examined for 3,4 and 5 member ring compounds: phenanthrene, pyrene and benzo(a)pyrene found in local aquatic environments. Pseudo first order rate constants for degradations of all three PAHs found to increase with increasing initial H2 O2 concentrations and initial Fe2+ concentration in aqueous media. High degradation rates were observed for concentration ratios, [H2 O2 ]:[Fe2+] in the range of ~50 to ~100. Decrease of pH of solutions, also increased the rates of degradation of all three PAHs. Presence of Triton X-100 at low levels, (1% v/v in the solution) found to increase the degradation rates of all three PAHs. Under all conditions studied, the pseudo first order rate constants for degradation of Benzo(a)pyrene were found to be the largest among the three PAHs .Item Induction of pollutant responsive biomarkers, ethoxyresorufin–Odeethylase, glutathione S-transferase and biliary fluorescent aromatic compounds in tilapia inhabiting Bolgoda North Lake, Sri Lanka.(Proceedings of the Annual Research Symposium 2005-Faculty of Graduate Studies, University of Kelaniya, 2005) Chandrasekera, L.W.H.U.; Pathiratne, A.; Pathiratne, K.A.S.The presence of organic contaminants in aquatic systems poses a serious threat to environmental health. Biomarkers are sub-lethal biological measures of the response to and effect of pollutants in living organisms. Use of biomarkers has been identified as a powerful and cost-effective approach to obtain information on the state of the environment and the effect of pollutants on living biological resources. This study presents results of a part of the research project which focuses on evaluation of the use of biomarkers in food fish tilapia as tools in monitoring pollution in inland waterbodies in Sri Lanka. In the present study, activities of two enzyme biomarkers, ethoxyresorufin-O-deethylase (EROD) & glutathione S-transferase (GST) and biliary fluorescent aromatic compounds (FACs) in Nile tilapia (Oreochromis niloticus) collected from Bolgoda North Lake were evaluated in comparison to the baseline levels of the control fish in order to assess the biomarker responses in this fish. The results revealed that EROD and GST activities of tilapia inhabiting Bolgoda North Lake were significantly elevated several folds in comparison to the baseline levels. Liver somatic index and microsomal and cytosolic protein levels in the gill and liver tissues of fish collected from the lake were also elevated significantly compared to the controls. Induction of EROD and GST enzymes indicate the exposure of fish residing in the lake to organic contaminants such as polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB). Analysis of biliary FACs in the fish showed recent uptake of naphthalene, pyrene and benzo(a)pyrene type PAHs. Occurrence of PAHs in the colloids and sediments of Bolgoda North Lake has been confirmed by chemical analysis. Results suggest that EROD and GST in liver and gill tissues and FACs in bile in this fish are promising biomarkers of organic contaminations especially PAHs in the aquatic environments.