DR. P. PADMAVATHYJULIET SELVARANI A, M.F.ScDr. A. SRINIVASANDr. G. SUGUMARDr. P. JAWAHAR2020-09-172020-09-172020https://krishikosh.egranth.ac.in/handle/1/5810151395The present study was conducted to assess the seasonal variation of physico chemical parameters and pesticide residues at different stations of Thamirabarani river viz. Manimuthar, Kallidaikurichi, aranammalpuram, Srivaikundam and Aathur. The overall minimum and maximum values of water quality parameters such as pH, dissolved oxygen, alkalinity, hardness and total dissolved solids were between 6.4 and 7.8, 3 and 8.2 mg/l, 8 and 152 mg/l, 20.02 and 440.04 mg/l as CaCO3, 12 and 354 mg/l respectively. The range of nutrients (nitrite, nitrate and phosphate) and ammonia were between 0.001 and 0.284 μg-at-NH3-N/l, 0.115 and 5.2 μg-at-NO2-N/l, 0.142 and 0.485 μg-at-NO3-N/l, 0.096 and 4.72 μgat- PO4-P/l respectively. The BOD and COD ranged between 0.12 and 6.4 mg/l and 0.4 and 19.2 mg/l respectively. All the water quality parameters were found to be within the prescribed level. The mean organochlorine pesticide residues of water and fish tissue samples at different stations of Thamirabarani river were in the range of Below Detectable level (BDL) to 28.44 μg/l and BDL to 20.06 μg/l respectively. Among 17 OCPs, endosulfan was the most predominant pesticide in water and fresh water fishes of Thamirabarani river followed by aldrin, endrin and heptachlor. The concentration of endrin, dieldrin and aldrin ranged from BDL to 0.09, BDL to 0.095 and BDL to 0.856 μg/l respectively. Among fishes, rohu accumulated more Σ BHC (0.042 μg/kg) than tilapia (0.035 μg/kg) and catla (0.014 μg/kg) because herbivorous fishes accumulated more BHC than carnivorous fishes. The occurrence of organochlorine pesticide residues was higher in the upstream region (station I) of the river and it is mainly due to agricultural runoff from tea and rubber plantation in the hilly region. The second most pesticide contaminated station is Srivaikundam of Thamirabarani river, which might be due to the agricultural runoff from nearby paddy and banana plantations. Toxicity experiment was conducted to find out the 50% Lethal Concentration (LC50) of glyphosate and cyhalothrin on Nile tilapia (Oreochromis niloticus). The calculated LC50 of glyphosate on tilapia was 49.22 mg/l and the calculated LC50 of cyhalothrin was 2.26 g/l. The histological changes were analysed in the fish organs exposed to glyphosate and cyhalothrin. No recognizable changes were observed in different organs of control fishes, while in acute toxicity experiment, hyperplasia, lamellar fusion, necrosis and degenerated secondary gill lamellae were observed in the fish gills exposed to glyphosate and cyhalothrin. Fish liver exposed to glyphosate and cyhalothrin showed vacuoles, irregular nucleus, melanomacrophages and hepatolysis. In gonad, absence of interstitial tissue, irregular shape of spermatogonia and decrease in number of sperm cells was observed. In chronic toxicity experiment, necrosis, blood congestion, erythrocyte infiltration and fully degenerated gill were observed in fish gills exposed to glyphosate and cyhalothrin at different concentrations. The gonad showed severe alterations like broken spermatogonia, sperm aggregation, melanomacrophage formation, severe damage to interstitial tissue and death of sperm cells. The histological effects were more pronounced during chronic toxicity or long term exposure than acute toxicity exposure. The alkaline single cell gel electrophoresis (SCGE)/comet assay was performed as a three-layer procedure to evaluate the genotoxicity effects (DNA damage) of pesticides on the organs of fishes. By comparing the DNA Damage Index (DDI) of fishes exposed to glyphosate at 61.34 mg/l, the gill was highly affected followed by liver, kidney and gonad with the DDI value of 158.2, 124.43, 85.0 and 48.05 respectively. In the case of fishes exposed to cyhalothrin at 3 g/l, the gill (226.16) was highly affected followed by liver (185.43), kidney (126) and gonad (102). Comparision of DNA Damage Index of both the pesticides revealed that cyhalothrin is highly dangerous and toxic to tilapia The study concluded that responsible use of pesticides have been practiced in agricultural fields near by the aquatic ecosystem.EnglishThesis