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SUMMARY: Many studies have measured fluoride toxicity for aquatic organisms with various levels of water quality including the examination of spot samples and the presence of interfering factors. In the present study, the actual fluoride toxicity, the fluoride LC50, was determined without interfering factors present and then after modelling the effects of changes in temperature, water hardness, and exposure time. Fluoride toxicity decreased with increased water hardness and increased with increased temperature and exposure time. This information may help with industrial effluent discharge planning in recipient waters that have a high fluoride content so that fluoride toxicity can be avoided.
Key words: Daphnia magna; Fluoride bioassay; Fluoride LC50; Fluoride toxicity.
INTRODUCTION
In the bodies of water, the toxicity of the fluoride ion (F) is related to several parameters, such as pH, temperature, and water hardness.1-2 In unpolluted surface waters, F concentrations are usually 0.01-0.3 mg/L, although higher concentrations may occur in waters in volcanic areas.3-7 Moreover, human activities can increase F in water resources by the discharge of industrial wastewaters into recipient waters.4,8-9 The ingestion of high levels of F can cause dental and skeletal fluorosis10 as well as damaging other organs including the kidney, liver, and brain.7 In aquatic environments, a high level of F has acute and chronic toxic effects (e.g., growth reduction and even death) on organisms such as algae, plants, fish, and marine crustaceans.3,11-12 Many studies have used bioassay methods with different aquatic organisms to determine F toxicity. The fluoride LC50 was determined in these studies in the presence of constant amounts of various interfering factors.3, 13-14 In the present study, the maximum toxicity of F in an aquatic environment was measured with and without the interfering factors of temperature, water hardness, and exposure time.
MATERIALS AND METHODS
In determining the interactions between the interfering parameters, of temperature, water hardness, and exposure time, the study was performed in an aquatic environment at three different temperatures and four different levels of water hardness. The standard method was used for the measurement of hardness in the prepared solutions.15 Daphnia magna were collected from an aquatic environment and bred under standard conditions.15 To measure the maximum toxicity of F (LC50 and...