The Optimization And Research Of Daphnia Magna Toxicity Testing

The variety of urban wastewater pollutants was complex and the potential toxiceffects had increased. Instead of a real, direct reflection of the wastewater toxicity onliving organisms, conventional physical and chemical testing index could only analyzeand evaluate wastewater quality from a limited perspective. Relying on the control ofthe emission limit value of industrial wastewater pollution parameters alone could notmeet the requirements of risk assessment and management of environment safety. Whilebiological toxicity test is a good supplement to chemical analysis, which could predictthe interaction between poison to a certain extent, and can be used to seek safetyconcentration to aquatic organisms of chemical substances and industrial waste water.This can be used to provide scientific basis for reasonable wastewater dischargestandard and can also be used to check the degree of effective wastewater treatment andtest the degree of water pollution. Biological toxicity data has an irreplaceable role inwater pollution control and water quality security.This experiment selects Daphnia magna which is stipulated by the national standardas the testing organism. The main contents of study were as follows:(1) In view of theproblems arising from the the preparation stage of Daphnia magna toxicity test, yeastextract was used to optimize the cultivation methods, and then verify the sensitivity ofDaphnia neonates.Typical heavy metals, organic compounds and urban sewage from asewage treatment plant were selected to examine the stability and reliability of theDaphnia magna which is cultured by yeast extract, and the results of Daphnia magnatoxicity test could be used to evaluate of pollution levels of pollutants and the treatmenteffect of urban sewage secondary treated water.(2) Aiming to the each processing stage effluents of semi-coking wastewater, Daphnia magna acute toxicity test andconventional physical and chemical measurement were conducted. And then, combiningbiological toxicity indicators with conventional index to analyze and evaluate thetreatment effect of each treatment unit and expose the relationship between the twoindices.The further coagulation treatment on final effluent of wastewater was conducted.The treated water was operated with Daphnia magna acute toxicity test again to analyzethe results of the further treatment and the weakening of toxicity.(3) Photobacteriumwas used for acute toxicity analysis of semi-coking wastewaters, comparing the resultwith the result of Daphnia magna acute toxicity test to analyze and discuss thesensitivity and applicability of two testing organismsAccording to above researches, the main conclusions are as follows:(1) During thecultivation of Daphnia magna, adding appropriate yeast extract could shorten thegrowth cycle of Daphnia magna and increase the number of spawns, while thesensitivity still could be kept in the range which the national standard requires.(2)Heavy metals and organic compounds treatment plant were used to Daphnia magnaacute toxicity test, the results were similar to the experimental results which have beenpublished, proving that the cultivation Daphnia magna method is reliability. Thebiological toxicity of the top five heavy metals in the test were as follows: mercury,copper, cadmium, chromium, zinc; The biological toxicity of the top four organiccompounds in the test were as follows: odium dodecylbenzenesulfonate, acetaminophen,phenol, ciprofloxacin.(3) This method was also applied on urban sewage, suggestingthat D. magna can distinct the influent and effluent clearly. This method can beconsidered practical in actual water samples test.(4) When the effluents of each watertreatment unit were diluted, the logarithmic of dilution and24-hour immobilizationproportion as well as48-hour lethal proportion had a a negative linear realationship.Chemical indices and acute toxicity indices of semi-coking wastewater were decreasedafter treatment, while its acute toxicity increased after extraction process and extraction,then reduced gradually. The ammonia stripping and coagulation-agitation-sedimentationwere the dominating processes to remove the biological toxicity of semi-cokingwastewater.(5)The Daphnia magna acute toxicity indicators had a good linearrelationship with TP, NO3-N, TOC had a good linear relationship, while had a certain linear correlation with NO2-N and COD, and had a relatively weak linear correlationwith NH4-N.(6) When the semi-coking wastewater was treated, its effluent had met thecoking chemical industrial pollutants emission standards. However, the residue wasstill of biological toxicity, which need further treatment. Coagulation treatment couldreduce the biological toxicity of effluent.(7) Photobacterium and D. magna are bothtesting organisms according National Standard. For the test of semi-coking wastewater,both of them could reflect the toxicity of water samples clearly. The sensitivity appearedin Daphnia magna acute toxicity test was higher than that in the photobacterium acutetoxicity test.