RESCON 2025

Permanent URI for this collectionhttps://ir.lib.pdn.ac.lk/handle/20.500.14444/5252

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Nocturnal beetle assemblages and their taxonomic and functional diversity across sub-montane habitats in Riverston, Sri Lanka
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Wijerathna, W. M. H. U.; Ranasinghe, U. G. S. L.; Benjamin, S. P.
Beetles represent a significant portion of Sri Lanka's insect fauna. However, little is known about how their diversity patterns and ecological functions vary across sub montane habitats. In this study, the diversity and the functional structure of nocturnal beetle assemblages across three habitat types, central forest (CF), forest edge (FE) and grassland (GR), were investigated in Riverston, northern Knuckles Conservation Forest. Field surveys were conducted during 2019 and 2020, including dry and rainy seasons using UV light traps (total 72 trapping events). Beetles were identified to family level and classified into six feeding groups (Herbivores, Predators, Scavengers, Fungivores, Moss feeders, and Xylophagous). Assemblages were analysed for taxonomic and functional diversity using abundance data. In total, 10,133 beetles from 65 families were recorded. FE supported the highest abundance and richness (44.52%, 58 families), followed by CF (35.72%, 56) and GR (19.74%, 46). The most common family was Staphylinidae in FE (18.4%) and GR (24.7%), while Pselaphidae dominated in CF (43.8%). Shannon and Pielou indices showed no significant differences (FE; H′ = 2.58, J = 0.23, CF; H′ = 2.30, J = 0.18, GR; H′ = 2.55, J = 0.29; p = 0.3679), indicating stable alpha diversity. However, Bray-Curtis dissimilarities revealed moderate beta diversity between habitats (CF–FE = 0.61, CF–GR = 0.59, FE–GR = 0.46). CF had the highest functional richness (4.82) and RaoQ (0.72), while FE showed the highest divergence (0.71) indicating the presence of functionally distinct taxa. FE had the most even functional distribution (0.75). NMDS of functional composition revealed distinct separation between CF and GR (73.2% dissimilarity). This study highlights that habitat structure plays a critical role in shaping the functional composition of beetle communities, even when taxonomic diversity appears stable. These findings underscore the importance of conserving a mosaic of habitats to ensure the maintenance of overall beetle biodiversity. A future study will extend to additional sub montane locations to assess the consistency of these patterns across a broader spatial scale and further inform habitat-based conservation strategies.
Development of simple and low-cost paper fluidic devices coupled with amperometry for separation and detection of pharmaceutical compounds
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Wijerathne, A.M.M.P.; Nawaruwan L., H.P.G.; Dissanayake, D.M.L.R.; Wijesinghe, M.B.
The advancement and characterisation of cellulose chromatography paper-based microfluidic devices mark a significant step forward in analytical chemistry, particularly for point-of-care diagnostics and environmental monitoring. Hydrophobic patterning on chromatography paper was used to define hydrophilic flow channels, directing the sample from an inlet to a defined location for subsequent analysis. This simple yet elegant development led many to recognise paper as a substrate material for applications where low-cost and portability are critically important. Carbon ink was used to fabricate the working electrode on the paper-based microfluidic device, and silver paste was used as the pseudo-reference electrode to keep the device simple and low-cost. A 350 V difference was applied along the paper channel to create the fluidic flow. As the electrolyte 10.00 mmol L⁻¹ borate buffer solution at pH 9 was used. Amperometric analysis was carried out using a homemade instrumental setup. When subjected to amperometric analysis, the developed paper-based microfluidic device produced distinct peaks for ascorbic acid and acetaminophen. Migration times of 120 s and 85 s and peak currents of 0.28 µA and 0.31 µA for acetaminophen and ascorbic acid, respectively, were obtained for a separation distance of 1.5 cm. The R² value for the calibration curve of ascorbic acid was 0.94. Future efforts may focus on constructing calibration curves for acetaminophen based on the peak areas of amperograms and reducing the peak width for more accuracy. This study successfully demonstrated the detection and separation of two key electrochemically active analytes, ascorbic acid and acetaminophen. Further, instead of power-free fluid transport via capillary action, paper electrophoresis was used to obtain narrow peaks by increasing the fluid flow rate.
Banana peel powder as a green corrosion inhibitor for stainless steel grade 202 in hydrochloric acid medium
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Alliyadde, P.O.; Priyantha, N.
Corrosion is a persistent issue in acidic environments, especially for stainless steel (SS) Grade 202, which is prone to localized attack in the presence of chloride ions. While synthetic corrosion inhibitors are widely used, their toxicity and environmental impact have prompted the need for green and sustainable alternatives. In this study, the corrosion inhibition potential of banana peel powder (BPP) was evaluated for SS Grade 202 in 0.50 mol L⁻¹ HCl medium. BPP extract was prepared by mixing 10.0 g of dry powder with 80.0 mL of distilled water, followed by refluxing to enhance the release of active compounds, such as tannins, flavonoids and polyphenols, which are known for their surface-adsorbing and corrosion-inhibiting properties. Fourier transform infrared spectroscopy of the extract identified characteristic functional groups at 1700 cm⁻¹ for C=O and 3300 – 3500 cm⁻¹ for O-H involved in corrosion inhibition through surface adsorption, while verifying the refluxing process preserved the chemical integrity of the extract. Mass loss measurements demonstrate significant reduction in corrosion rate from 50% to 15% with increase in the extent of the BPP extract, where the addition of 2.0 – 4.0 mL extract to 40.0 mL of 0.5 mol L⁻¹ HCl solution showed 70% inhibition efficiency. Electrochemical impedance spectroscopy revealed an increase in polarization resistance from 1.70 Ω cm² to 3.40 Ω cm², with the diameter of the semi-circle increasing proportionally, indicating the formation of a protective layer on the metal surface. Tafel slope analysis showed a decrease in corrosion current density from 20.80 μA cm–² to 6.20 μA cm–² along with modified slope values, confirming the ability to suppress both anodic metal dissolution and cathodic reactions through corrosion inhibition. Open circuit potential measurements displayed positive potential shifts, reflecting enhanced thermodynamic stability of the metal surface in BPP containing solutions. Atomic absorption spectroscopy confirmed the release of metal ions into the corrosive medium during corrosion. Overall, the results establish BPP as an effective, biodegradable, and environmentally friendly corrosion inhibitor for SS Grade 202 in HCl medium.
Investigation of the presence of SO₄²⁻ in humic substances extracted from drinking water
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Abeysinghe, A.M.G.R.D.; Bandara, A.; Jayarathne, L.; Makehelwala, M.
Humic substances (HS) are a fraction of dissolved organic carbon. There are two main fractions of HSs: humic acid (HA) and fulvic acid (FA). Recent research on HS in water indicates that they can bind with charged species, such as metals and ligands, leading to severe health problems. Further, recent studies have highlighted the increase of manganese (Mn²⁺) levels in ground water in some areas in Sri Lanka, and it is hard to remove manganese by filtration. Therefore, this study focused on the investigation of the presence of SO₄²⁻species bound to HAs in drinking water with and without Mn²⁺. First, the presence of humic substances was confirmed by extracting HA from some selected well water samples in Sri Lanka and characterised using Fourier transform infrared (FTIR) spectroscopy by identifying major functional groups present in the most acceptable model structure of HAs and comparing them with authentic standards. To identify the potential interactions of SO₄²⁻ with HAs, two methods were followed: adding SO₄²⁻ directly from a SO₄²⁻ source and adding through a metal salt. By comparing the FTIR spectra and Raman spectra, the effective binding of SO₄²⁻ with HAs could be proven. Overall, this study was able to prove that SO₄²⁻ binding happens through an elimination/exchange reaction and electrostatic interaction with HAs, and SO₄²⁻ followed by metal binding causes sulphate to bind via the metal.
Development of an electroanalytical detection scheme for fipronil insecticide
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Sriyananda, B.G.W.M.; Perera, K.L.H.S.; Navaratne, A.N.
Fipronil is a widely used insecticide with serious health hazards. This study aimed at comparatively evaluating the performance of glassy carbon electrode (GCE) and stearic acid-modified GCE (SAGCE), for rapid, inexpensive detection of Fipronil in aqueous samples. Electrochemical behaviour of Fipronil was studied using a GCE. Cyclic voltammogram (CV) for GCE was obtained under optimised conditions (0.5 mmol L⁻¹ Fipronil in 0.1 mol L⁻¹ HClO₄/acetone solution 50:50 v/v; scan rate 50 mV s⁻¹; potential range –0.1 V to +1.8 V), which peaked at 1.5 V. When the Fipronil concentration was gradually increased, the peak current (PC) of the CVs increased with a linear variation between 0.04 and 3.00 mM (slope = 6.695; R² = 0.979), where the slope corresponds to sensitivity. Scan rate dependence was assessed using the Randles-Sevcik relationship, and the slope of 0.5 of the log (peak current) vs. log (scan rate) plot indicated that the oxidation reaction was diffusion-controlled, permitting chronoamperometric analysis. Amperogram was obtained with 0.26 mM increments of Fipronil concentration at 60 s intervals for 10 times, resulting in 4 μA increments until six additions. To reduce the noise level and increase detection limits, SAGCE was designed. The above analyses were repeated, resulting in a linear variation in PC increment between 1.28 and 3.28 mM (slope = 3.521; R² = 0.988). Diffusion control of the oxidation reaction at SAGCE was confirmed by scan rate dependence analysis, which resulted in a slope of about 0.5 in the log (peak current) vs.log (scan rate) plot permitting chronoamperometry. An amperogram obtained under similar conditions showed 3 μA increments. The SAGCE reduced noise level; however, exhibited lower sensitivity compared to GCE. By optimising the thickness of the SA coating on the working electrode to leverage PC, this can potentially be developed into a method for low-cost pesticide monitoring in resource-limited settings.
Electroanalytical detection of imidacloprid using stearic acid-nano TiO₂ modified glassy carbon electrode
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Hewagampalage, J.M.; Navaratne, A.N.
Imidacloprid, one of the world’s most widely used insecticides, has emerged as a hidden environmental threat due to its long-term persistence in ground water and soil. In addition, contamination of food with imidacloprid residues can have serious impact on both human and animal health. Hence, its detection in environmental samples is important. Among different analytical techniques, electroanalytical techniques provide a simple and cost effective method for imidacloprid detection. In this study, a simple, novel electrochemical method based on stearic acid and TiO₂ nanoparticles was developed for the detection of imidacloprid. TiO₂ nanoparticles were synthesised using the sol-gel method and characterised by scanning electron microscopy, Fourier transform infrared spectroscopy and powder X-ray diffraction, which indicated that TiO₂ nanoparticles with an average diameter of 24.46±1.32 nm were successfully synthesised. The glassy carbon electrode (GCE) was modified with stearic acid-nano TiO₂ suspension using simple drop casting method. The electrochemical behaviour of imidacloprid at the bare GCE and at the stearic acid-nano TiO₂ modified GCE were studied using electroanalytical techniques, namely, cyclic voltammetry (CV) and steady state amperometry. CV analysis resulted in a single reduction peak at –1.2 V, indicating the electroactivity of imidacloprid. Electrode fouling observed in amperometric studies with the bare GCE was overcome with the stearic acid coating, while the sensitivity of the electrode was enhanced by incorporating TiO₂ nanoparticles. The modified electrode developed provides an amperometric sensor to detect imidacloprid with a linear dynamic range of 1.19×10⁻⁴ mol L⁻¹ to 6.97×10⁻⁴ mol L⁻¹ . It exhibited a minimum detection limit of 8.77×10–6 mol L⁻¹, which is closer in value for similar type of modified electrodes reported in literature, and a limit of quantification of 2.92×10–5 mol L⁻¹, offering a potential tool for imidacloprid detection in environmental samples.
Electrochemical investigation of thiamethoxam on bare and stearic acid/silver particles modified glassy carbon electrode
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Jayasinghe, J.H.L.K.; Navaratne, A.N.
The intensive use of pesticides contributes to environmental contamination and potential health risks, requiring the development of sensitive detection methods. Thiamethoxam (TMX) is one of the most widely used neonicotinoid pesticides in modern agriculture. Among the existing analytical detection techniques, such as high-performance liquid chromatography and gas chromatography, electrochemical methodologies offer a promising alternative, due to their cost-effectiveness and efficiency. In this research, cyclic voltammetry, square wave voltammetry, and amperometry were employed to obtain electrochemical responses under various conditions. The results revealed an irreversible reduction peak at –1.24 V vs. the Ag/AgCl/KCl reference electrode, attributed to the characteristic reduction of the nitro group to hydroxylamine derivative of TMX, occurring via a diffusion-controlled process in pH 9.0 Britton-Robinson buffer according to the peak current-scan rate relationship. Although electrochemical sensors are a more effective method, electrode fouling can occur when pesticide molecules block the active surface of the bare electrode, resulting in a lower electrochemical signal, which suggests the necessity of electrode modification. Nanomaterials exhibit different properties with specific characteristics compared with the same materials with micrometer-scale dimensions. Undesirable characteristics of nanoparticles, such as the tendency to agglomerate, high surface energy, and attractive van der Waals forces between particles, which limit applications, can be overcome using stearic acid, which functions as a capping agent to maintain the stability of nanoparticles. Silver nanoparticles act as an electrocatalyst, which enhances the rate at which the electron transfer takes place at the electrode surface. The scanning electron microscopy images revealed that the synthesised particles are in an aggregated form, with a particle size of around 127 nm. The stearic acid/silver particles modified glassy carbon electrode shows a higher current response as well as lower background noise in comparison to the bare glassy carbon electrode.
Development of a detector for 3-nitro-tyrosine using electrogenerated chemiluminescence with bipolar electrochemistry
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Rajasinghe, S.M.; Lakmina, N.; Wijesinghe, M.B.
Biomarker 3-nitro-L-tyrosine (3-NT), associated with nitrosative stress, has been linked to various pathological conditions, including neurodegenerative and cardiovascular diseases. Therefore, its detection is important; however, traditional detection methods, such as mass spectrometry and chromatography, require expensive instrumentation and expertise. Electroanalytical techniques are of choice owing to their ability to detect in real-time and low-cost. However, it is usually susceptible to high noise. Translating the current signal to an optical signal, which exhibits simultaneous oxidation and reduction at the extremities of a bipolar electrode (BPE), may provide better detection limits, as optical signals are less susceptible to environmental noise. In this study, a novel electrochemiluminescence (ECL)-based detector utilising BPE was developed for the detection of 3-NT. The objective was to establish a cost-effective and highly sensitive detection method suitable for biomedical and environmental applications. The detector setup consisted of a BPE coupled with luminol-H₂O₂-based ECL reporting, where the reduction of 3-NT at the cathodic pole induced light emission at the anodic pole. The experiments optimised the luminol-to-H₂O₂ ratio of 2:13 and applied potential of 2.6 V to achieve maximum ECL intensity. The system was evaluated using image-based intensity analysis captured via a smartphone camera. Results demonstrated a linear correlation between 3-NT concentration and ECL intensity, with R² of 0.93, linear dynamic range of 1.00 μmol L⁻¹ to 80.00 μmol L⁻¹, calibration sensitivity of 0.075 luminescence intensity per μmol L⁻¹ and a detection limit of 1.00 μmol L⁻¹, significant improvement upon conventional methods such as cyclic voltammetry. The BPE-ECL platform developed has proven to be a robust, low-cost alternative to high-end detection techniques, offering advantages such as miniaturisation, portability, and potential integration with microfluidic devices for point-of-care diagnostics. Future improvements could include a continuous flow system at the anodic pole, coupled with an electrophoretic microchip at the cathodic pole, to detect multiple biomarkers separated by electrophoresis.
Valorisation of banana pseudostem (bps) waste for defluoridation of drinking water
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) De Silva, J.; Piyumanthi, P.G.A.P.T.; Batugedara, B.D.I.M.; Senanayake, S.A.M.A.I.K.
Dental and skeletal fluorosis are prevalent in the dry zone of Sri Lanka, among people who utilise drinking water with high fluoride levels. This study investigated the possibility of banana pseudostem (BPS) derived fibres and cellulose to remove fluoride in drinking water. BPS fibres and cellulose were extracted through sequential mechanical and acid hydrolysis methods, respectively. They were characterised using; scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and physicochemical analysis. Fluoride removal efficiency was studied following batch adsorption experiments using SPADNS spectrophotometric method. The extraction yields of BPS fibres and cellulose resulted in 5% and 3%, respectively. SEM images confirmed successful extraction and fibrous morphology, which aligned with macrofibrils in BPS fibers (width ≈ 87 µm) and aggregated rod-like structures in microcrystalline cellulose (10 – 25 µm width). FTIR spectra highlighted hydroxyl, alkene and ether, as functional groups essential for fluoride binding. XRD confirmed the semi-crystalline nature of cellulose I allomorph, supporting structural integrity during adsorption. Physicochemical analysis emphasised the adsorptive dominance of BPS fibres; higher water holding capacity (16.96±0.02 g g-1), higher swelling capacity (5.00±0.02 mL g-1) and lower moisture content (13.16±0.08%) compared to those of cellulose. Adsorption optimisation identified 0.4 g adsorbent dosage, 0.5 mg L-1 fluoride concentration, pH 2 and 10, and 90 min contact time as the ideal conditions. However, 1.5 mg L-1 fluoride concentration and pH 7 were used, in accordance with WHO guidelines and to depict typical fluoride levels and pH in groundwater (7.2 - 8.2) of Sri Lanka. Under these optimised conditions, BPS fibres achieved a removal efficiency of 63.19±0.03%, outperforming cellulose (35.81±0.07%). Post-adsorption SEM-EDX analysis confirmed the fluoride adsorption by the detection of fluorine (F) peaks. According to the results, BPS fibre is highlighted as a promising defluoridation biomaterial by serving as a blueprint for future development of bio-waste-based adsorbents for sustainable water purification.
Development of an eco-friendly lantana-based bioadsorbent for effective aluminium removal from industrial wastewater
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Sadushani, M.D.C.; Dharmapriya, T.N.; Karunathilaka, R.M.M.K.; Abeysinghe, A.M.S.R.; Priyantha, N.
Aluminium (Al) contamination in industrial wastewater, especially under acidic conditions, poses environmental and health risks. Conventional treatments such as chemical precipitation produce hazardous sludge. This study explores the use of invasive plant Lantana camara as a low-cost biosorbent for Al removal. Three approaches were applied to leaves and stems of L. camara as raw material, chemical surface modification, and thermal conversion to biochar. In a typical experiment, adsorbent (1.00 g) was added to 50.0 mL of 100 mg L-1 Al solution, shaken for 1.0 h at 150 rpm at room temperature, and analysed through atomic absorption spectroscopy. As the raw biosorbent exhibits insignificant Al removal, it is necessary to modify it for efficiency improvement. Alkaline treatment of raw biosorbent with 0.1 mol L-1 NaOH achieves a removal efficiency of 71.2% for leaves, and 36.0% for stems, while acidic treatment with 0.5 mol L-1 HNO3 results in 61.2% and 23.6% removal for leaves and stems, respectively. Sequential acid–base treatment (0.2 mol L-1 NaOH followed by 0.5 mol L-1 HNO3) shows maximum efficiencies of 90.4% and 93.1% for leaves and stems, respectively. Furthermore, thermal conversion of leaves into biochar showed Al removal efficiencies of 90.5%, 90.7%, 91.4%, and 92.0% at pyrolysis temperatures of 250 °C, 300 °C, 350 °C and 600 °C, respectively. Dosage optimisation reveals that even 0.10 g of leaf biochar achieves 80.6% Al removal, increasing progressively to 87.1%, 95.6%, 96.6%, 97.3%, and 99.1% at dosages of 0.25, 0.50, 0.75,1.00, and 2.00 g, respectively. Al removal increases from 73.0% at 3 min to 81.1% at 50 min with only slight improvements at 60 (83.8%) and 90 min (86.0%), making 50 min the optimal shaking time. Thermal treatment outperforms chemical modification in adsorption, structure, and sustainability. X-ray fluorescence spectroscopy shows high native Ca and K, enabling effective ion exchange. Utilising L. camara provides a sustainable solution for Al removal while aiding in invasive species control, ecological balance, and resource recovery.
Computational study of linear and non-linear optical properties in novel Heptazine derivatives
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Jayaweera, J.P.C.C.; Kodikara, M.S.
The development of advanced optoelectronic and photonic technologies is critically dependent on the discovery of new materials with superior non-linear optical (NLO) properties. Heptazine, a highly efficient electron acceptor having a planar conjugated structure, presents a promising core structure for octupolar D₃A-type NLO systems. Symmetrical substitution of peripheral hydrogens by electron-donating groups considerably enhances the NLO response. Notably, organometallic s-hepatazine systems display exceptional multi-photon absorption activity. Surprisingly, there have been no experimental or theoretical second-order NLO studies on these organometallic heptazine derivatives. This study employed density functional theory (DFT) and time-dependent DFT (TD-DFT) at the CAM-B3LYP/6-31+G(d)/SDD level of theory, selected after testing various methods and basis sets, and led to results consistent with previously reported work. This approach was applied to explore novel heptazine derivatives bearing amino (NH₂) and dimethylamino [N(CH₃)₂] donor groups, and nitro (NO₂) acceptors, substituted at the 2,5, and 8 positions of the heptazine ring, either directly or indirectly attached, through linkers such as –C₆H₄– and –C₆H₄–C≡C–C₆H₄–. Instead of organic donor groups, the Ru(dHpe)₂Cl unit was attached to the heptazine core in organometallic systems. Extending the 𝜋-conjugation in donor-substituted derivatives results in an increase in the first, second and third-order polarisabilities due to improved electron delocalisation, while the NO₂ substituted heptazine analogues show lower values. The replacement of the organic donor groups by the organometallic unit leads to a significant increase in the first and second order polarisabilities. Natural bond orbital analysis confirms that the donor groups increase the negative charge on the core, enhancing delocalisation and polarisability. The efficacy of s-heptazine as the core structure was investigated for organometallic molecules. Heptazine derivatives showed the largest NLO coefficients compared to triazine and commonly used benzene core geometries. The lower HOMO-LUMO energy gap in heptazine can be attributed to this prediction. Based on the TDDFT calculations, 2,5,8-tri(donor)-s-heptazines show red-shifted bands. When NO₂ groups are substituted, the low-energy band is blue-shifted. Moreover, Ru complexes enhance NLO via metal-to ligand charge transfer, with heptazine giving the highest response. Building on this, future work may explore frequency-dependent NLO behavior and conformational effects on organometallic systems.
Sri Lankan laterite – an adsorbent for tetracycline in aqueous media
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Sachintha, U.S.T.; Wijekoon, I.M.; Koralegedara, N.H.
Antibiotics and their residues are considered as emerging contaminants, as their accumulation in the environment causes antibiotic resistance among microorganisms. Hence, accumulation, prevention, and immediate removal of antibiotics are essential. Laterite (LT), a naturally occurring iron-rich soil, is a well-known adsorbent for many environmental contaminants. However, its application in antibiotic adsorption is limited. Hence, this study investigates the adsorption potential of raw LT in removing tetracycline (TC), a widely used antibiotic that is frequently detected in aquatic environments. Batch adsorption experiments were conducted to assess the TC removal potential of LT under different conditions. TC solutions of known concentrations (1, 4, 17, 50, 72 mg L-1) were thoroughly mixed with LT over specified contact times (5, 10, 30, 60, 120, 180, 240 min) and analysed for TC concentrations using a UV spectrophotometer (at λmax= 352.1 nm). The effects of pH (3, 4, 5, 7, 10), adsorbent dosage (5, 10, 15, 20 g L-1), and the soil organic matter (OM) were investigated. Optimum removal was observed at pH 5 -7 with 10 g L-1 adsorbent dosage, and in the absence of OM. The low adsorption observed at both acidic (pH < 5) and alkaline pH (pH > 7) is attributed to electrostatic repulsion between LT and TC due to their similar surface charges (pHzpc of LT = 5.8 and pKa of TC is 3.3, 7.7, and 9.7). As TC exists in its zwitterionic form at pH 3.3 - 7.7, the maximum adsorption is observed at pH 5 - 7. TC Adsorption data followed the Langmuir isotherm model (R² = 0.9981), indicating monolayer adsorption on a homogeneous surface. Kinetics data aligned the best with the pseudo-first-order model, suggesting that an electrostatic attraction-initiated interaction between LT and TC. Furthermore, Fourier transform infrared spectroscopic analysis confirmed the complexation between TC and Fe and Al groups of LT by changes in relevant peak positions and intensities, indicating electrostatic attraction followed by hydrogen bonding and metal-ligand coordination. These findings highlight the potential of laterite as a sustainable, low-cost, and eco-friendly adsorbent for TC removal in contaminated water systems.
Computational studies on antibacterial activities of 6β-Hydroxybetunolic acid and its derivatives
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Herath, H.M.K.D.; Ranatunga, R.J.K.U.; Jayasinghe, S.
Antibiotic resistance is a major global health threat. Developing novel antibacterial agents with enhanced mechanisms against specific strains, supported by computational drug design, offers a promising solution to this challenge. Previous studies have shown that 6β hydroxy betulinic acid (6β-HBA) possessed strong antibiotic activity (16 mg L⁻¹) against methicillin-resistant Staphylococcus aureus (MRSA) which has limited antibiotic activity. However, its synthetically modified derivatives demonstrated reduced antibacterial activity. Therefore, in this study, 𝘪𝘯-𝘴𝘪𝘭𝘪𝘤𝘰 investigations were conducted to elucidate the mechanism underlying the antibacterial effects of 6β-HBA. Lupane-type triterpenoids feature a hydroxyl group at the C-6 position. The synthesised derivatives involved modifications at the C3-OH to C3-OAc, C6-OH to C6-C=O, and C17-COOH group to C17-COOR. Preliminary computational investigation on ligand interactions with penicillin binding protein 2a (PBP2a) from MRSA was carried out, using molecular docking and molecular dynamics (MD) simulations. Molecular docking analyses revealed strong binding affinities (–8.3 kcal mol⁻¹) for 6β-HBA and the derivatives which had free C17-COOH group, with PBP2a. Further validation through MD simulations confirms the stability of the ligand-protein complexes of 6β-HBA and identified key interactions with active site residues, such as ASP665, TYR664, and ASN624, of PBP2a, which are essential for inhibiting bacterial cell wall synthesis. However, no such interactions were observed for the synthetic derivatives without free COOH at C17. These 𝘪𝘯-𝘴𝘪𝘭𝘪𝘤𝘰 results directly support and explain previous findings, where modification of the C17-COOH group led to a dramatic increase in MIC values and a complete loss of antibacterial activity against Gram-positive bacteria, including MRSA. Moreover, C3-OAC protected compound showed promising interactions with the acetate group and protein residues, which is again corroborated with the strong antibacterial activity obtained in 𝘪𝘯-𝘷𝘪𝘵𝘳𝘰 studies. Thus, this study provides molecular-level evidence that C17-COOH and the C3-OAc groups are essential for effective protein binding and highlights their critical role in designing potent antibacterial agents.
Environmental impact of inhalational agents used in operating theatres in Sri Lanka: a retrospective multi-centre audit
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Samarasinghe, S.U.D.; Abeysundara, A.B.; Samarasinghe, A.; Warnasuriya, D.G.H.; Munasinghe, P.
Inhalational anesthetic agents, particularly isoflurane and sevoflurane, are potent greenhouse gases that contribute to healthcare-related environmental pollution, especially in settings that lack proper scavenging systems. Despite global awareness, there is a scarcity of data on the environmental impact of anesthetic practices in low-resource settings, such as in Sri Lanka, highlighting a critical research gap. A retrospective audit assessed 315 theatre sessions, conducted over one month at National Hospital-Kandy, Teaching Hospital-Peradeniya and Dental Hospital-Peradeniya. Data were collected on volatile agent usage, surgery duration, fresh gas flow rates, and the availability and functionality of anesthetic gas scavenging systems (AGSS), using anesthesia theatre records maintained manually by doctors. Agent usage and CO₂ equivalent (CO2e) emissions were calculated using established equations to determine the volatile agent consumption and CO2 equivalent. AGSS were unavailable in 204 sessions (64.8%), AGSS were present but not connected in 56 (17.8%), and AGSS were present merely venting gases into the external environment without proper degradation in 24 sessions (7.6%). Only 31 sessions (9.8%) used a properly functioning AGSS. The mean minimal alveolar concentration (MAC) fraction of agent consumption was 1.03%. Out of the total MAC fractions, the mean MAC fraction of isoflurane is 1.02% while sevoflurane is 1.13%. A total of 3519.5 mL of volatile agent fluid was used, but only 368.0 mL (10.50%) was effectively scavenged. More than 89% was released directly to the environment. Total emissions during the study period of one month amounted to 35.713 kg CO2e, isoflurane contributing 34.738 kg CO2e and sevoflurane 0.975 kg CO2e. Additionally, 16.5% of sessions used N₂ O/O₂ mixtures, compounding the environmental burden. The audit reflects major deficiencies in AGSS implementation in Sri Lankan operating theatres, resulting in significant environmental and occupational risks. Urgent interventions, including infrastructure improvement, staff education and adoption of low-flow or total intravenous anesthesia techniques, are needed to promote sustainable anesthetic practices.
Altitude-driven variations in airborne bacterial communities: a comparative study from Piduruthalagala and Colombo, Sri Lanka
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Gunathilaka, H.M.S.A.T.; Dissanayake, C.; Gunasekaran, E.; Thotawatthage, C.; Magana-Arachchi, D.N.
Understanding the diversity and distribution of airborne bacteria is a critical concern. This study examined the differences in airborne bacteria at two varying altitudes in Sri Lanka: Piduruthalagala Mountain (PT) and Lotus Tower (LT). Eight samples were collected on filter papers from each location using an Envirotech APM 550 fine particulate air sampler. After 30 minutes of sample collection, the filter papers were cut into fine pieces and shaken in 8 mL of distilled water at 100 rpm for 2 h. After centrifugation, the filtrate was cultured on Luria-Bertani (LB) culture media. Bacterial DNA was extracted using Boom’s method. Sample preparation was conducted, followed by 16S Metagenomic Sequencing Library Preparation targeting the 16S V3-V4 region. The DNA of 45 culturable isolates were extracted, comprising 25 from PT and 20 from LT. The PCR amplicons and metagenomic samples were sequenced per the manufacturer’s instructions at Macrogen Inc., South Korea. The isolates exhibited taxonomic diversity, comprising 46 species from the Gammaproteobacteria, Betaproteobacteria, and Firmicutes phyla. 16S rRNA amplicon metagenome sequencing identified 80 bacterial species, including 21 phyla, 20 classes, 17 orders, 12 families, and 22 genera. Pseudomonadota was the most dominant phylum, followed by Firmicutes. Cyanobacteria were present at all sites; LT showed a higher abundance (0.48%) than PT (0.16%), likely due to its proximity to Beira Lake and the sea. The genera Brevundimonas, Fenollaria, Prevotella, Peptoni, Enterococcus, and Corynebacterium were exclusively found at high-elevation sites. The average Simpson index for the LT site was 0.6645 for bottom samples and 0.7733 for top samples. At the PB site, it was 0.8333 for the top, and 0.7307 for the bottom samples. Overall, the samples collected from higher altitudes exhibited greater alpha diversity. The viable microbes originating from high altitudes shape microbial dynamics in lower elevations. This research offers a framework for analyzing airborne microbial communities on both local and regional scales.
Panicum maximum- derived cellulose nanoparticles incorporated membrane for targeted CO₂ capture in air purification
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Nilmani, A.H.M.Y.; Navarathne, J.M.S.G.B.; Priyantha, N.; Wijesinghe, M.B.
Air pollution poses a profound threat to the environment, imperiling human health, ecosystems, biodiversity, and exacerbating climate change. Carbon dioxide (CO₂), released through industrial processes, burning fossil fuels and deforestation, stands out as the most significant contributor to atmospheric degradation. This study presents the development of an advanced, sustainable cellulose nanoparticle (CNP) based membrane engineered for effective CO₂ removal from contaminated air. CNPs were isolated from Panicum maximum through a chemical treatment followed by delignification, bleaching and acid hydrolysis. The scanning electron microscopy, granulometry and X-ray diffraction confirm the formation of CNPs with diameters less than 100 nm. These CNPs were subsequently integrated into cotton fabric substrates in the presence of polyvinyl alcohol (PVA) as the binding agent. These modified cotton fabrics (MCFs) were tested with untreated bare cotton fabrics (BCFs) serving as controls. A custom-built experimental system comprising calibrated CO₂ and pressure sensors, a controlled CO₂ injection unit, and test chambers was employed to evaluate the filtration efficacy of the membranes. Initial trials at ambient CO₂ concentrations (~430 ppm) demonstrated a substantial reduction of 90 ppm (decrease to 340 ppm) with MCFs, whereas BCFs showed no change. Pressure fluctuations mirrored CO₂ removal patterns, confirming membrane performance. Further tests at elevated CO₂ levels (2,000 and 5,000 ppm) revealed concentration-dependent removal efficiency. Although absolute reduction was less pronounced at higher concentrations, MCFs still achieved meaningful CO₂ capture, particularly at lower CO₂ loadings. These findings validate the potential of CNP-coated cotton membranes as scalable filtration media for CO₂ mitigation. Future work will focus on optimizing fabrication parameters such as nanoparticle loading, PVA concentration, membrane thickness and functionalization, to further enhance the CO₂ filtration capacity and operational robustness for practical air purification applications.
Controlled complexation of Zr(iv) and Hf(iv) with Amino derivatives of 2,6-pyridinedicarboxylates: a computational approach for separation efficiency enhancement
(Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka, 2025-11-07) Adhikari, D.M.; Hettiarchchi, C.V.; Ranatunga, R.J.K.U.
Extraction of ultra-pure zirconium and hafnium would be a value addition to the zircon (ZrSiO₄) ore available in Sri Lanka. However, extracting the ultra-pure Zr and Hf has become impossible to countries such as Sri Lanka due to the complexity, environmental impact and the cost of the currently available methods. Among them, fractional crystallisation is the simplest method with the least environmental impact, although its separation efficiency is low. In this study, a theoretical approach was taken to improve the separation efficiency of fractional crystallisation through complex formation with 2,6-pyridinedicarboxylate (PDA). Initially, the reaction energy for each ligation step during the formation of [M(PDA)₃]²⁻ starting from [M(H₂O)₉]⁴⁺ was calculated with density functional theory (DFT) using ORCA 5.0. However, based on the calculated reaction energies, it was not possible to separate Zr(IV) and Hf(IV) with the formation of [M(PDA)₃]²⁻, due to similar reaction energies in the latter steps. However, in the initial step, there is a significant difference between Zr(IV) and Hf(IV) complex formations. Consequently, calculations were extended to determine the reaction energies with amino derivatives of PDA for the initial step. If one of the metals shows significant favorability to ligate with a particular amino derivative, it is possible to stoichiometrically drive the ligation toward a particular metal ion. Thereafter, the remaining complex substitutions can be performed with 2,6-PDA, leading to complexes with differing physical properties. The calculations, performed at the hybrid B3LYP functional, and def2-TZVP basis set, accounting for the basis-set superposition error, indicate that 4-amino-PDA show the highest favorability to ligate with Zr(IV) in the initial step among other amino derivatives of PDA. Therefore, it is possible to crystallize [Hf(PDA)₃]²⁻, if a controlled amount of 4 amino-PDA is used in the initial step. It is expected that properties of dipole-moment and solubility be significantly different for the two complexes, allowing easier and more efficient separation.
Preliminary study on impact of herd size on antipredator vigilance of spotted deer (axis axis) at Wilpattu national park, Sri Lanka
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Suriyabandara, S.M.D.; Wijesundara, C.S.
Several studies across the globe have shown that predators control prey animals not only by direct killing, but also by creating a landscape of fear, the spatial variation in a prey animal's perception of predation risk. Various animals show different strategies to offset the perception of predation risk in landscape of fear. Herding is also one method used by different animals, such as ungulates. This aspect is essential in managing predator and prey species within protected areas. In the present study, how the vigilance behavior of spotted deer (Axis axis) changes with respect to the herd size was examined. The study was conducted in May and June 2025, in Wilpattu National Park, Sri Lanka. Twenty focal animals of Axis axis were sampled during this study (male-6, female-14). Vigilance behavior of one animal was studied between 2 – 5 min. The number of animals in the herd of the focal animal and the proportion of time spent by the focal animal on antipredator vigilance behavior, i.e., raised head posture above the horizontal line with its ears in an upright position were recorded. A Pearson correlation test was conducted to assess the relationship between the herd size and vigilance behavior. Mean herd size observed was 8.66±2.18 individuals per herd. According to the results, there is a strong negative correlation between Axis axis herd size and antipredator vigilance (Pearson correlation = –0.499, p = 0.025). This shows that the herd size has a strong impact on vigilance behavior of axis deer and when the herd size increases axis deer becomes less vigilant. These findings suggest that Axis axis exhibit reduced antipredator fear responses when occurring in large herds. Therefore, it can be identified that large herds support Axis axis to offset the fear towards predators and increase the proportion time spent on fitness enhancing activities such as foraging.
Evaluating the catch efficiency of yellowfin tuna (Thunnus albacares) in Sri Lanka’s longline fisheries across western and eastern waters of the Indian ocean
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Wijenayake, K.D.V.N.; Haputhantri, S.S.K.; Gamage, T.R.I.
The study was conducted to evaluate the efficiency of capturing yellowfin tuna (Thunnus albacares) using live, dead, and artificial lures in longline fishery in Sri Lanka. Data were collected from fishing operations conducted in the coastal waters of the Western and Eastern regions of Sri Lanka within the Indian Ocean. Primary data were obtained through structured interviews with longline fishermen from 150 commercial vessels operating at five major landing sites (Dikkowita, Negombo, Tangalle, Nilwella, and Kottegoda) during the period from September to December 2024. Catch per unit effort (CPUE) was calculated and analysed using the Kruskal-Wallis test. Significant differences in CPUE were observed among bait types for both the number of fish caught and total weight (p = 0.001). Dead bait demonstrated the highest catch efficiency (0.513±0.376 individuals per 100 hooks; 0.221±0.160 kg per hook), followed closely by artificial lures (0.506±0.394 individuals per 100 hooks; 0.210±0.184 kg per hook), while live bait recorded the lowest efficiency (0.429±0.429 individuals per 100 hooks; 0.176±0.205 kg per hook). No statistically significant difference in CPUE (p > 0.05) was observed between the Western and Eastern regions of the Indian Ocean; however, dead bait showed slightly higher efficiency in the Western region. Although live bait showed the highest median CPUE values, its use was constrained by high costs, storage challenges, and limited availability. Artificial lures were identified as a competitive and cost-effective alternative, offering a sustainable option to reduce dependence on natural baitfish. Variations in regional factors such as prey availability, water clarity, and predator behavior were also considered to have influenced bait performance and catch efficiency.
Identification and prevalence of Dinurus euthynni infecting Auxis thazard (frigate tuna) from southern and northeastern marine waters of Sri Lanka
(Postgraduate Institute of Science (PGIS) University of Peradeniya, Sri Lanka, 2025-11-07) Gamage, T.R.I.; Rajapakse, R.P.V.J.; Wijenayake, K.D.V.N.; Anupama, N.M.T.
Auxis thazard (Frigate tuna) is an economically important tuna species found in Sri Lankan coastal waters. Endoparasite infections can cause inflammation, congestion, and hemorrhage in vital organs such as the stomach, liver, and intestines of fish. The digenean fauna of this species is still inadequately documented. The aim of this study was to identify the digenean parasitic trematode, Dinurus euthynni, parasitising Frigate tuna and compare its prevalence in northeast coast (Trincomalee) and southern coast (Galle) of Sri Lanka. A total of 50 specimens, 25 each from Galle and Trincomalee, were dissected. Parasites were extracted from their stomach, cleaned with 0.9% saline water, and preserved in 70% aqueous ethanol solution. Morphological identification was based on characteristics including a dorsoventrally flattened, narrow, elongate body with rounded anterior and posterior ends, a short fore body and well-developed ecsoma longer than the body, and with irregular tegument covered with prominent plications. The oral and ventral suckers were well-developed, muscular and transversely oval. Phylogenetic analysis was conducted using the second internal transcribed spacer (ITS2) and cytochrome c oxidase subunit 1 (COX1) gene regions. The identified local sequence was 100% similar to the sequence identified from Rio de Janeiro, Brazil, bearing accession no. OP458340.1. The parasites measured between 4479 – 14562 µm and the length of ecsoma ranged between 2107 – 8141 µm. A total of 79 specimens of D. euthynni were recorded across both sites. The prevalence was higher in Galle (52%) compared to Trincomalee (28%). The mean abundance was 2.5±0.7 in Galle and 0.6±0.2 in Trincomalee. According to the Mann Whitney U test, there was a significant difference in parasite abundance between sites (p = 0.032). This study reports the identification of D. euthynni and marks the first attempt to study its infection in Sri Lankan marine food fish.

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