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Item Assessing neurotoxic potential of titanium dioxide nanoparticles and bulk form using the fish model, Nile tilapia (Oreochromis niloticus)(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Samanthika, A.L.C.; Pathiratne, A.Titanium dioxide nanoparticles (nano TiO2) and bulk TiO2 are widely used worldwide in various sectors. Hence they can be released inevitably into the inland water bodies posing health threats to the aquatic ecosystems. Cholinesterase (ChE) activity can be used as a biomarker for screening neurotoxicity in organisms exposed to the environmental contaminants. The objective of the present study was to evaluate the neurotoxic potential of environmentally relevant concentrations of nano and bulk TiO2 using Nile tilapia as the tropical fish model. Groups of fish which had been acclimated to the laboratory conditions for two weeks were exposed continuously to relatively low concentrations (50 and 100 μg/L) of nano or bulk TiO2 for 7 or 14 days (n= 7). The control fish were exposed only to aged tap water. The experimental design also included 7 day nano or bulk TiO2 exposure groups which had been transferred to aged tap water for another 7 days to evaluate potential recovery of the toxicity. Neurotoxic potential was assessed using ChE activity measurements in the brain, gill and liver tissues by a standard spectrophotometric method. ChE activities (mean±SEM in nmol/min/mg protein) in gills were elevated significantly(P <0.05) in the fish exposed to 50 and 100 μg/L bulk TiO2 for 7 days (102±9 and 105±7 respectively) compared to those of the control fish (71 ± 5) whereas brain ChE activities were not affected. Liver ChE activities were significantly elevated at 100 μg/L continuous exposure to bulk TiO2 for 7 and 14 days (279±15 and 315±15 nmol/min/mg protein respectively) compared to those of the control fish (155±12) and were not restored to normal levels after 7 days post exposure. A consistent ChE activity stimulation pattern was not evident with respect to bulk and nanoTiO2 exposures. In the fish exposed to both concentrations of nano TiO2, ChE activities in brain and gill tissues were not significantly different from those of the control fish. However ChE activity in liver tissues of the fish exposed to 100 μg/L of nano TiO2 was elevated significantly (P < 0.05) at 7 days exposure and post exposure periods. The results revealed that environmentally relevant concentrations of nano and bulk TiO2 may pose neurotoxic risks to the fish populations inhabiting the contaminated water bodies and the bulk form of TiO2 is not ecotoxicologically inert as previously assumedItem Survival and cholinesterase activity of Asian common toad (Duttaphrynus melanostictus) tadpoles following short term exposure to a carbosulfan-based pesticide(Sri Lanka Association of Fisheries and Aquatic Resources., 2017) Samarakoon, H.M.T.R.; Pathiratne, A.Carbosulfan, a carbamate pesticide widely used in agriculture especially in the Asian region has received less attention in ecological impact assessments particularly to non-target amphibians. In this study, short term effects of a carbosulfan-based pesticide (Marshal®) on survival and cholinesterase (ChE) activity of tadpoles of Duttaphrynus melanostictus, a non-target amphibian in tropical Asia were evaluated. Based on the concentration-toxicity response patterns, estimated median lethal concentration (LC50) and median ChE inhibitory concentration (IC50) for 96 h were 24 and 2.1 mg/L carbosulfan respectively. For the ChE inhibition for 96 h, the lowest observable effect concentration and no observable effect concentrations of carbosulfan were 0.6 and 0.3 mg/L respectively. Upon transfer to pesticide-free water by 14 days, ChE activities of the tadpoles were restored to normal levels. Since the tadpoles exposed to 0.3 mg/L carbosulfan have not exhibited lethality, morphological deformities, abnormal behavior or statistically significant ChE depression, it is unlikely that the carbosulfan-based pesticide could induce neurotoxic effects for D. melanostictus tadpoles at the concentration of ≤ 0.3 mg/L of active ingredient under short term exposure.Item Effects of biological and technical factors on brain and muscle cholinesterases in Nile tilapia, Oreochromis niloticus: implications for biomonitoring neurotoxic contaminations(Springer-Verlag., 2008) Pathiratne, A.; Chandrasekera, L.W.H.U.; De Seram, P.K.C.Influence of body length, body weight, gender, sexual maturity, and tissue storage on brain and muscle cholinesterases (ChE) in Nile tilapia was evaluated considering its potential use in biomonitoring neurotoxic contaminations in tropical environments. Results show that ChE activities in both tissues decreased significantly with increased total length (4–24.5 cm) or body weight (1–186 g) of the fish and the relationships were curvilinear. Comparisons of the slopes and elevations of the regression lines of the logarithmic ChE and body size relationships of males with those of females indicated that gender had no significant effect on the body size-specific ChE activities. Response of the ChE of sexually mature males to chlorpyrifos exposure was similar to that of females. Gonadal maturity stage of this fish does not seem to influence ChE activities. Storage of tissues at –80°C for 28 days had no significant effect on ChE activities in the control fish and the fish exposed to carbofuran. However, a partial reactivation of brain ChE activities was observed in the fish exposed to carbosulfan after 28 days of storage. The results emphasize the importance of consideration of body size of the fish and storage time of the tissues in order to formulate accurate conclusions about the neurotoxic chemical exposure when ChE of the fish is used in biomonitoring programs.