Study On The Acute Toxicity Of New Wastewaterderived Disinfection By-products And That Combined Exposure With Metal Ions On Chinese Rare Minnow(Gobiocypris Rarus)

The shortage of fresh water resources has become an important factor that restricts the sustainable development of human beings.At the same time,at least 300 billion m³ of wastewater is produced every year in the world.Wastewater reuse has been considered as one of the effective ways to alleviate the shortage of freshwater resources.Wastewater disinfection is one of the critical water treatment technologies.However,in addition to destroying various pathogenic microorganisms,disinfectants also react with organic pollutants to generate various wastewater-derived disinfection by-products（DBPs）.With the reuse of disinfection wastewater,these wastewater-derived DBPs will also be discharged into the environment,resulting in potential exposure to environmental organisms.However,there are few studies on the potential aquatic toxicity and aquatic ecological risks of DBPs from wastewater sources,which restricts the environmental control of such substances by relevant departments.In addition,the available studies were mainly focused on the aquatic toxicity and water ecological risk assessment of aliphatic DBPs,while few studies on new phenolic DBPs were studied.It is important to point out that environmental organisms are often exposed to multiple environmental pollutants,so multi-pollutant exposures are important for accurately assessing the environmental risks of related pollutants.At present,there is no relevant research to explore the potential effects of combined toxicity of DBPs and typical metal ions on environmental organisms.Therefore,in this thesis,we selected the novel phenolic DBPs as the model compounds to study the acute toxicity effect of the model compound,to analyze the mechanism of action,to evaluate the risk of aquatic ecology,and to select the model compound with high acute toxicity,to study the effects of combined exposure with typical metal ions on aquatic organisms.The main findings are as follows:（1）Seven novel phenolic DBPs in five classes（2,4,6-trihalo-phenols,2,6-dihalo-4-nitrophenols,3,5-dihalo-4-hydroxybenzaldehydes,3,5-dihalo-4-hydroxybenzoic acids and halo-salicylic acids）and four aliphatic DBPs（dibromoacetonitrile,2-bromoacetamide,bromodichloromethane,dichloroacetic acid）were selected as model compounds,their acute toxicity to Gobiocypris Rarus and potential aquatic ecological risk were studied.Results of acute toxicity test showed that dibromoacetonitrile(LC₅₀<1 mg/L),2,4,6-trihalo-phenols and2,6-dihalo-4-nitrophenol(1<LC₅₀<10 mg/L)were classified as class I and Class II according to Globally Harmonized System of Classification and Labelling of Chemicals（GHS）,other model compounds were Class III or above,which suggested that the aquatic toxic effects of dibromoacetonitrile,2,4,6-trihalo-phenols,2,6-dihalo-4-nitrophenol should be paid more attention in the future research.The toxicity mode of action（MOA）identification results from three methods suggested that no clear and consistent MOA were obtained for those 11 DBPs currently.The species-specific aquatic toxicity analysis results highlighted that crustacean and fish were more sensitive than that of algae for most of tested compounds.Aquatic ecological risk assessment results of 11 DBPs revealed that all 7 phenolic and 2 aliphatic DBPs（2-bromoacetamide and bromodichloromethane）had low aquatic ecological risk,while dichloroacetic acid and dibromoacetonitrile had high aquatic ecological risk.The low environmental concentration was the main reason why high toxic phenolic DBPs（2,4,6-trihalophenols and 2,6-dihalo-4-nitrophenols）exhibited low ecological risk.Their ecological risk may increase with the increases of corresponding environmental concentration.Thus,more efforts should be made to determine other potential harmful effects of those high toxic phenolic DBPs and to minimize their potential ecological risk by taking appropriate measures.（2）The acute toxicity of 2,4,6-triiodophenol and dibromoacetonitrile with four typical metal ions（Hg（Ⅱ）,Pb（Ⅱ）,Cd（Ⅱ）,Cr（Ⅵ））on Gobiocypris Rarus were studied.The results showed that the acute toxic effects of the four metal ions were different,and the order of LC₅₀was Hg（Ⅱ）（0.104±0.00129 mg/L）<Pb（Ⅱ）（9.42±0.509 mg/L）,Cd（Ⅱ）（11.7±0.425 mg/L）<Cr（Ⅵ）（83.2±2.17 mg/L）.The acute toxicity of Hg（II）and Cd（II）combined respectively with2,4,6-triiodophenol and dibromoacetonitrile to Gobiocypris Rarus was studied,the binary mixture system of 2,4,6-triiodophenol and dibromoacetonitrile with Hg（Ⅱ）showed synergistic effect on Gobiocypris Rarus,while antagonistic effect wwith Cd（II）,indicating that the same metal ion has the same effect on different DBPs,and different metal ions may have different effects on the same DBP.Based on the Hg（Ⅱ）-2,4,6-TIP binary mixed system,the combined effects on aquatic organisms of different trophic levels were studied.The results showed that the effects of combined exposure have species differences,Hg（Ⅱ）-2,4,6-TIP binary mixed system has a synergistic effect on Gobiocypris Rarus,but has an antagonistic effect on Moina and Scenedesmus obliquus.In conclusion,the combined effects of metal ions and DBPs will vary depending on the types of metal ions and aquatic species.Therefore,special caution should be taken when formulating relevant water quality standards.