Assesment of water pollution in Gediz River by using Daphnia magna toxicity tests

The objective of this thesis was to evaluate water pollution in Gediz River by performing toxicity tests with Daphnia magna used frequently as bio-indicator species in ecotoxicological studies. The samplings were done twice by taking water samples from five different stations of Gediz River in spring and summer. Some chemical parameters of water samples of each station (Fe, Mn, Cl-, NH3-N, S-, K, NO3--N, PO43-,Ca and Mg) were analyzed by spectrophotometric method in the laboratory. Acute toxicity tests were performed in accordance with the standard "Daphnia sp. Acute Immobilization Test" protocol (OECD, 2004; Test Guideline 202) by using static system. Chronic toxicity tests were also performed in accordance with the standard "D. magna Reproduction Test" protocol (OECD, 1998; Test Guideline 211) by using semi-static renewal system. The data were evaluated by using SPSS statistics programme with probit regression analysis, One Way ANOVA variance analysis and the Post Hoc Tukey test. According to the results of 48 hours tests, acute toxic effects of water samples obtained from the 1st, the 2nd and the 5th station in spring, from the 5thstation in summer were determined on D. magna. The EC50 values of these water samples were calculated as 57,53; 55,01; 28,28; 18,68, respectively. As a result of chronic toxicity tests, however, it was detected that the water samples of Gediz River did notshow serious chronic toxicity on D. magna. Moreover it was also determined that the water samples have beneficial effects on growth, development and reproduction of D. magna. It is concluded that Daphnia toxicity tests, one of the standard ecotoxicological assays, do not seem to be suitable for assessing the effects of organic pollution on aquatic systems. Besides, the beneficial effects observed in chronic toxicity tests should also be explained as hormetic responses of lower concentrations of pollutants in river water, that are accumulated in sediments at high concentrations.