Evaluation Of Combined Toxicity Of Heavy Metals And Antibiotics To Microcystis Aeruginosa

The evaluation of the combined toxicity of pollutants to organisms has always been the research focus in the field of environmental toxicology.Antibiotics and heavy metals are typical and common pollutants in China's water environment at present,and their toxicity evaluation is an important basis for pollution control.The toxicity evaluation work at present is mainly to carry out toxicity test research on single heavy metals or antibiotics,which has achieved relatively fruitful results.However,most of the heavy metals and antibiotics in the water environment are not single,but combined pollution.Therefore,it is necessary to evaluate their combined toxicity.Most of the current combined toxicity evaluation methods were based on the assumption that the concentration of pollutants and the toxic effect are linear,while the relationship between the concentration of most pollutants and the toxic effect was non-linear.Therefore,it is necessary to establish a more reliable method to evaluate the combined toxicity.Phytoplankton is the primary producers of aquatic ecosystems and plays a vital role in the stability of aquatic ecosystems.Phytoplankton is usually used as a test organism for toxicity evaluation,because of its strong sensitivity to water quality and easy cultivation.In this study,Microcystis aeruginosa was selected as the test organism.Through a single pollutant and a combined test of pollutants to evaluate a nonlinear combined toxicity evaluation method.Based on this,the combined toxicity of heavy metals and antibiotics was studied.The main conclusions of this study are as follows:(1)In this study,a nonlinear combined toxicity evaluation method was proposed to evaluate the combined toxicity of five heavy metals on Microcystis aeruginosa.The results of the new evaluation method indicate that the combined toxicity of Cu+Cd,Cu+Cr and Zn+Cr to Microcystis aeruginosa was synergistic when combined at low concentrations,and it was antagonistic when combined at high concentrations.When Pb+Cu combined at low concentration,there were no interaction between the two heavy metals.When combined at high concentration,the combined toxicity to Microcystis aeruginosa was synergistic.The combined toxicity of Zn+Cd,Pb+Cr,Pb+Cd,Pb+Zn and Cr+Cd to Microcystis aeruginosa was antagonistic,and the combined toxicity of Cu+Zn to Microcystis aeruginosa was synergistic.The above results have been verified at both the antioxidant system and antioxidant enzyme level.(2)The combined toxicity of three antibiotics to Microcystis aeruginosa was evaluated.The results showed that through the analysis of the nonlinear combined toxicity evaluation method,it was found that tetracycline+sulfadiazine was synergistic at low concentration and antagonistic at high concentration.Sulfadiazine+sulfamethoxazole and tetracycline+ sulfamethoxazole were synergistic.The results of the gene and antioxidant enzyme system reaction show that the main reason for the different toxic effects of the three antibiotic combinations on Microcystis aeruginosa was the different degree of damage caused by the combined antibiotic combination against the oxidation system and cell membrane.(3)The combined toxicity of three heavy metals and three antibiotics to Microcystis aeruginosa was evaluated.The results showed that tetracycline+Pb,tetracycline+Cd,sulfadiazine+Cu,sulfamethoxazole+Cd were synergistic at low concentration and antagonistic at high concentration.Tetracycline+Cu,Sulfamethoxazole+Pb,Sulfamethoxazole+Cu were synergistic,Sulfadiazine+Pb,Sulfadiazine+Cd were antagonistic.