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Otravy ryb kyanidy - přehledová studie
ŠVECOVÁ, Tereza
The objective of this bachelor thesis was to provide a comprehensive review of published data on the toxicity and mechanism of action of cyanides in fish and on emergency conditions caused by cyanide spills into the aquatic environment. Cyanides are present in simple form such as CN- and HCN. They also occur in complexes and organic forms. Cyanides form complexes with metals. The cyanocomplexes of cadmium and zinc are the most toxic. Conversely, cyanocomplexes with gold are the least toxic. The organic forms include nitriles, cyanogenic glycosides and cyanohydrins. Sources of cyanides are natural and anthropogenic. Anthropogenic sources are the most important sources of cyanide. The main producers of cyanide pollution and frequent sources of cyanide spills into the aquatic environment include industries involved in the extraction, treatment, and processing of metals. Information about the toxicity of different forms of cyanide to different fish species under various environmental conditions is collected and clearly presented in this bachelor thesis. When comparing the toxicity of simple and complex cyanides to the same fish species under the same environmental conditions, it is evident that, with few exceptions, the LC50 values are lower for simple than for complex cyanides. Temperature has a significant effect on the toxicity of cyanides. Cyanide toxicity decreases with increasing temperature for most fish species. Different sensitivities to cyanide have been observed in different life stages of fish. Embryos and larvae appeared to be the most resistant. In opposite, juveniles and adults were the most sensitive to cyanide. In my bachelor thesis I also made a review of published information on accidental fish kills caused by the release of cyanide into the aquatic environment in the Czech Republic and some of the world's major cyanide accidents. The source of contamination of the aquatic environment was mostly industrial wastewater from metal processing and treatment or from cyanide production in the Czech Republic. Cyanide spills have been recorded, particularly in connection with gold and silver mining in the world. The main causes of cyanide spills into the aquatic environment were the collapse of a control or safety device in detoxification tanks and tailings ponds containing cyanide wastewater. In many cases, staff failed to detect the malfunction in time.
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