The Acute Biological Toxicity And Toxic Mechanism Of Bromate In Water

The process of ozonation has been widely used in water treatment processes because of its advantages.If there is bromide ions in the water,they can be oxidized by ozone,and the byproducts-bromate could induce renal cell tumors in test rats,which is a big threat to the water quality security.In this article,the toxicological risk of the bromate was investigated in a systematic way,the acute toxicity of bromate and interaction characteristics on some kinds of typical creatures with different trophic levels which are usually used for toxicology tests were studied to explore the bromate's toxic mechanism,and meanwhile,to seek for sensitive detection creatures and indicators for bromate's toxicity.With the sensitive detection indicators,the comprehensive toxicity of bromide-containing water after ozonation was evaluated.Our results offered academic support for further understanding bromate's toxic mechanism and provided reference basis for establishing biotoxicology standard to ensure the safety of water.The differences may be existed in the toxicity effects of bromate on different creatures,therefore several creatures and indicators are needed for comprehensive assessment of bromate's toxic effects and for determination of sensitive detection creatures.In this study,some typical toxic-detection creatures for with different trophic levels were selected as research objects.It was found that the 96 h EC₅₀ of potassium bromate on Scenedesmus obliquus and Microcystis were 738.18 mg/L and 195.39 mg/L,respectively,the 48 h EC₅₀ and LC₅₀ on Daphnia magna were 154.01 mg/L and 198.52 mg/L,respectively,the 48 h EC₅₀ and LC₅₀ on Moina were 161.80 mg/L and 175.68 mg/L,respectively,the 96 h LC₅₀ on zebrafish was 931.4 mg/L,and the 14 days LD50 of bromate in Wistar rats and ICR mice were 215 mg/kg and 464 mg/kg,respectively.It was indicated that the sensitivity of the test creatures to the toxic effects of bromate were different,in which the Daphnia magna,the Moina and the Microcystis were the most sensitive,and the Scenedesmus obliquus was less sensitive,and the zebrafish was less sensitive than the Scenedesmus obliquus,while the Chlorella vulgaris and the luminescent bacteria were the least sensitive.There was no obvious cumulative toxicity and genetic toxicity of bromate and the results did not exhibit significant differences on growth and development,organ development organization form and liver function of rats,however,bromate reduced the white blood cell count in rats and had influences on kidney function,glucose metabolism and lipid metabolism.According to the results that the Microcystis and Daphnia magna were more sensitive to the toxic effects of bromate,the bromate's toxic mechanism on algae cells and Daphnia magna was investigated in this study.It was found out that the combined toxicity effect of bromate caused the growth inhibition of algae cells and the activity inhibition as well as the death of Daphnia magna.The main toxic mechanism of bromate on algae was that an excess of reactive oxygen species?ROS?in algae cells caused by bromate can lead to the peroxidation damage,the physiological dysfunction and the cellular structure damage of algae cells.And the main toxic mechanism of bromate on Daphnia magna was that bromate caused the impairments in the antioxidant system,the nervous system and the energy metabolism.Among the detection creatures and indicators used in this study,the cell membrane integrity of Microcystis,Ca²⁺/Mg²⁺-ATPase activity of Daphnia magna and the white blood cell count in rats were significantly influenced by bromate,thus they can be used as important indicators to evaluate the bromate's toxic effects.In the ozonation processes of bromide-containing water,many other byproducts generated besides bromate,so the bromate's toxic effects can not reflect the total toxic effects of bromide-containing water after ozonation.Thereinto,the dibromoacetic acid is a common byproduct in the treated water.We studied the joint toxic effects of the dibromoacetic acid and the bromate on Daphnia magna,and found out that there were two types of combination modes for these two byproducts: the synergistic effect and the partly additive effect,which indicated that the joint effects of byproducts do have some risks to increase water toxicity,thus it is necessary to investigate the comprehensive toxicity of bromide-containing water.Based on the obvious influence of bromate on the Ca²⁺/Mg²⁺-ATPase activity of Daphnia magna,the survival rate and the Ca²⁺/Mg²⁺-ATPase activity of Daphnia magna were used as indicators to investigate the influences of organic matters on comprehensive toxicity of bromide-containing water after ozonation.The organic matters such as starch,bovine serum albumin and humate were added into the bromide-containing water to represent the polysaccharide,amino acid,and humus in the water,respectively.It was found that the toxicity of water treated by ozonation could be influenced by the concentration of bromide,dissolved organic carbon?DOC?concentration,ozone concentration and chlorination.When no bromide existed in the water,there was no significant influence on water toxicity by ozonation.The water toxicity increased with the increase of bromide concentration,and it reached to the maximum when the bromide concentration was 4 mg/L.After that,the water toxicity did not increase with the increase of bromide concentration.The chlorination can further increase the water toxicity after ozonation.The optimum concentration of ozone differed with the different concentration of DOC.The water toxicity increased whether the ozone concentrations were higher or lower than the optimum concentration of ozone.Among the three organic matters investigated in our experiments,the water toxicity bromide-containing water after ozonation was maximum with the addition of humate,the water toxicity was less with the addition of bovine serum albumin than with humate,and it was minimum with the addition of starch.The Ca²⁺/Mg²⁺-ATPase activity of Daphnia magna was more sensitive to water toxicity and it can better reflect the water toxicity,thus it can be used as an important indicator for evaluating the security of water safety.