Study On The Joint Toxicity Of Antibiotics And Triazole Fungicides To Chlorella Pyrenoidosa

In the natural water environment,there are many kinds of pollutants,including antibiotics and triazole fungicides,which coexist in various forms and concentrations,and form a variety of complex mixed pollutants.These complex mixed pollutants are bound to have an impact on aquatic organisms,thus causing potential risks to all kinds of organisms and human health,but their ecotoxicity data are seriously insufficient.At present,most researches focus on the single toxicity of antibiotics or triazole fungicides,while the joint toxicity research is extremely scarce.Therefore,it is urgent to study the joint toxicity of antibiotics and triazole fungicides to the sensitive species of green algae.In this paper,three typical antibiotics?Doxycycline hyclate?DOX?,Erythromycin?ERY?and Oxytetracycline?OXY??and three typical triazole fungicides?Myclobutanil?MYC?,Propiconazole?PRO?and Tebuconazole?TCZ??were selected as the target pollutants,to study the single toxicity and its mechanism of Chlorella pyrenoidosa;The combined toxicity interaction of binary and six component mixtures were analyzed by Isobolograms,Concentration Addition?CA?,Independent Action?IA?and Model Deviation Ratio?MDR?;In this basis,the mixed system with the largest interaction in binary mixed system was selected to study the effect of sequential exposure on the joint toxicity of Chlorella pyrenoidosa.The main results are as follows:?1?The results on single toxicity of antibiotics and triazole fungicides to Chlorella pyrenoidosa and its toxic mechanism showed that the order of the toxicity of the six target pollutants to Chlorella pyrenoidosa was PRO>DOX>TCZ>ERY>MYC>OXY;The activities of superoxide dismutase?SOD?and catalase?CAT?in Chlorella pyrenoidosa were promoted by the exposure of six target pollutants;In addition,the total protein?TP?and chlorophyll a?Chla?contents in Chlorella pyrenoidosa were inhibited in varying degrees.These phenomena are all the reasons for the inhibition of the growth of Chlorella pyrenoidosa.?2?The results on the joint toxic interaction of antibiotics and triazole fungicides to Chlorella pyrenoidosa showed that the type of toxic interaction of binary mixed system to Chlorella pyrenoidosa was related to concentration range and component concentration ratio,and the largest interaction occurred in the mixed system of antibiotics and triazole fungicides,while the interaction of six mixed system was not obvious in general.The synergistic effect of binary mixture?MDRCA and MDRIA greater than 5.90?is significantly greater than that of six component mixture(MDRCA and MDR_IAA 1.90).Therefore,by contrast,the largest interaction between pollutants occurs in binary mixture.?3?The results on the joint toxicity of antibiotics and triazole fungicides to Chlorella pyrenoidosa showed that the combined toxicity of antibiotics?DOX?and triazole fungicides to Chlorella pyrenoidosa was the most obvious.The toxicity of DOX and any triazole fungicides to Chlorella pyrenoidosa was enhanced when they were exposed in reverse order.Therefore,the joint toxicity of antibiotics and triazole fungicides to Chlorella pyrenoidosa would be changed by the sequential exposure,and the sequential exposure was closely related to the exposure time and concentration,which is also one of the key factors to determine the toxicity..