The Investigation Of Cadmium Pollution In Long Jiang River And Its Impact On Fish And Other Aquatic Organisms

Cadmium (Cd) is a kind of toxic heavy metals, it has the characteristics of high toxicity, biodegradable, easy residues, and it is one of the "top five" toxic elements in the environment. In recent years, the heavy metal pollution incidents occurred frequently, they were serious harmful to the people’s health, and the local water environmental ecology. Guangxi Longjiang cadmium pollution incident was took place in2012January, which caused the significant social influence. In order to reduce the concentration of cadmium in Longjiang River and ensure the safety of water supply in the downstream, the technique of "weak alkaline chemical precipitation removal of cadmium" by adding soda or lime and polymeric aluminum chloride was used to transform ion water cadmium into cadmium precipitation to the bottom of river.In order to fully understand the Longjiang River cadmium pollution incidents and the impact on downstream water and the change trend of Cd content in the sediment after emergency measures, the investigation was launched for sediment cadmium content on the Longjiang River and the lower reaches of the Liujiang River river, the geoaccumulation index and potential ecological risk index was applied to quantitative evaluation on the potential ecological risk. Lalang, which suffered most seriously for the river cadmium pollution, Sancha and Dashi, which been affected serious for the contaminated sediment after emergency control, were chosen to carry out the experiments of fish in situ visualization which included the toxicity poisoning and detoxification experiments, In simultaneous monitored the three in situ observation points in the water, sediment, aquatic plant heavy metal cadmium, cadmium in the food chain (Research water or sediment, aquatic plants and fish) in the migration and accumulation process. The impact of the accidents on Longjiang Fish and other aquatic organisms had been analysed. The research results obtained were as follows:(1) The accident caused the Longjiang River cadmium pollution exceed the standard Cd content has the varying degree, the most serious exceed the standard of nearly9times, in the emergency disposal, polluted river water Cd content is up to standard and is still downward trend; the lower reaches of the Liujiang River section in each stage were not exceed the standard of water content of Cd, show the cadmium pollution accidents on the lower reaches of the Pearl River water quality is not affected.(2) Contaminated river due to the emergency of doing a lot of flocculant, first showed significantly increased Cd content in sediment, but after the flood scouring and dilution, Cd content in sediment has an overall decline, especially in lower reaches of the Liujiang River River, flood period, Cd in the sediment content is close to the background value, plus the Liujiang River safflower reservoir blocking and closure, the cadmium pollution incident impacts on river sediment has not yet spread to the downstream.(3) It indicated that, with two kinds of evaluation results, although sediment Cd content tended to decrease, the degree of pollution was still serious, and ecological risk level was high. Further observation and study of Cd in the sediment needed to be implemented for water ecological environment.(4) The Cd content of Longjiang water had been up to standard and tended to be stable, Cd content in the submerged plant also decreased gradually, after that in situ fish, Cd content exceeding the standard in muscle could be recovered with blocking food pollution source.(5) In the flood period, the emergence of a large number of dead fish phenomenon, by dissecting it was clear that:water content of sediment and sediment floes jamed gill, caused fish suffocation. Therefore, the flood period to death of fish is not directly responsible for Cd poisoning.(6) Submerged plants, fish and other organisms had been in the stage of recovery in Longjiang water quality compliance,, but as the cadmium content in the sediment was still at a high level, it could be changed by submerged plant into bioavailable, for entering the food chain, the Longjiang river sediment cadmium pollution still has the potential ecological risk.The above conclusion indicated that, with the Longjiang River cadmium pollution emergency in the "weak alkaline chemical precipitation emergency cadmium removal technology", the Longjiang river water quality standards to recovered soon, the residents regained the safty potable water, protected the water in lower reaches of the Liujiang River not affecting; after that the content of Cd in aquatic organisms gradually decline included the submerged plants, fish (partition food source), and had been in the stage of recovery. Due to the addition of sediment Cadmium Forms sink to bottom, caused the increase of river sediment cadmium content in Longjiang, it could be absorbed by submerged plants into bioavailable, and then transferred into the food chain, so there was still the potential ecological risks.