Formation Of DBPs And Their Toxicity To Zebrafish Embryos Under Chlorine/Chloramine Disinfection

At present,most studies on disinfection by-products（DBPs）only focus on the relationship between DBPs itself and the toxicity of embryo development,while little attention has been paid to the relationship between the toxicity of embryo development and the water quality（such as organic matter,bromide,iodine,etc.）as well as the disinfection factor（disinfection method）,which is closely related to the formation of DBPs.Whether the water treatment techniques and household treatment methods can change/reduce the embryonic developmental toxicity of disinfected drinking water also remains unclear.This thesis aims to obtain the key factors/techniques to control the embryonic developmental toxicity of disinfected drinking water by studying the relationship between embryonic developmental toxicity and water quality factor,water treatment technology and the household treatment methods using zebrafish and developmental abnormality rate in zebrafish（number of zebrafish abnormalities/total development indicators of zebrfish）;and identify the types of DBPs that may cause developmental toxicity through studying the relationship between various DBPs levels and developmental toxicity in zebrafish embryos.Results were as the following:1)From the rate of developmental abnormalities in zebrafish,the rank of the development toxicity in zebrafish embryo caused by different source water was:river 2（QTR）>river 1（WR）>wastewater（FS）>lake（TL）.The main water quality indexes that cause the difference of toxicity in embryonic development of source water include SUVA,UVA,nitrite（NO₂^-）,chlorophyll（Chl-a）,bromide（Br^-）,ammonia and nitrogen（NH₄⁺）.After chlorination,the embryonic development toxicity of most source water is alleviated,but some toxicity that source water does not have may increase after chlorination.The water quality related to the increased embryo development toxicity of chlorinated disinfectant water mainly includes dissolved organic carbon（DOC）and UVA.For most source water,the zebrafish embryo development toxicity increased after chloramination,and the water quality related to the increased embryo development toxicity of chloramination included DOC,SUVA,UVA,NO₂^-,NH₄⁺,bromide ion and chlorophyll.DBPs related to the developmental toxicity of chlorination included dichloroacetic acid,chloroform,dichloroacetonitrile,bromodichloroacetic acid;while DBPs related to embryonic developmental toxicity of chloramination include tribromomethane,bromodichloromethane,bromoacetic acid,dichloroacetic acid,bromochloroacetic acid,dibromoacetic acid,dichloroacetonitrile,trichloroacetic acid.2)From the rate of developmental abnormalities in zebrafish,the embryonic developmental toxicity of chlorinated water under different treatment techniques were as following:chlorine（2/8）>ozone-chlorine（1/8）=coagulation-chlorine（1/8）=ozone activated carbon-chlorine（1/8）=coagulation precipitation-chlorine（1/8）>activated carbon-chlorine（0）,suggesting that activated carbon technology is effective in relieving developmental toxicity of chlorination.The embryonic developmental toxicity of chloraminated water under different treatment technique were in the order of ozone-activated carbon-chloramine（1/8）<coagulation precipitation-chloramine（2/8）<ozonation-chloramine（3/8）<activated carbon adsorption-chloramine（4/8）<ozone-coagulation-chloramine（5/8）=chloramine（5/8）,demonstrating that ozone-activated carbon,coagulation precipitation is effective in relieving developmental toxicity.Further analysis showed that the trichloroacetic acid level in chlorinated water was negatively correlated with the mechanical beat escape reflectance of zebrafish.During chloramination,trichloromethane level were negatively correlated with the body length of zebrafish and positively correlated with the number of fetal movements.Dibromoacetonitrile and tribromomethane level were positively correlated with the rate of equilibrium damage.In general,chloraminated water has higher developmental toxicity than chlorinated water.3)From the rate of developmental abnormalities in zebrafish,developmental toxicity in zebrafish of disinfected water under different household treatments were as following:chloramination（5/8）>chloramination-filter-boiling（4/8）>chloramination-boil（3/8）=chlorination（3/8）>chloramination-heat（2/8）=source water（2/8）=chlorination-heat（2/8）=chlorination-boiling（1/8）,indicating that for chlorination,boiling is the best household treatment to reduce developmental toxicity originated from DBPs,while for chloramination,boiling or heating treatment is a better choice to alleviate the developmental toxicity of DBPs.Overall,the chlorinated water showed lower developmental toxicity than chloraminated water.Further analysis showed that bromoacetic acid,dichloroacetic acid,trichloroacetic acid,bromochloroacetic acid,dibromoacetic acid,chloroform,bromodichloromethane,dibromochloromethane,bromodichloromethane and trichloronitromethane were related with increased developmental toxicity in chlorinated water;while bromoacetic acid,dichloroacetic acid,trichloroacetic acid,dibromoacetic acid,bromochloroacetic acid,bromodichloroacetic acid,br-omochloroacetonitrile,dibromoacetonitrile,tribromomethane,bromochloroiodomethane and bromodichloronitromethane.were related with increased development toxicity in chloraminated water.In summary,the embryonic development toxicity of DBPs in disinfected drinking water can be minimized by selecting source water with less DOC,UVA,NO₂^-and other contents,adopting chlorination disinfection,and using activated carbon treatment process and boiling method.The above results can provide scientific guidance for water source management,water treatment optimization and healthy drinking water way.