Toxicity Of Cationic Blue SD-GSL And Its Biological Decolorization Products To Aquatic Plants

Decolorization is a key step in the treatment of azo dye wastewater.Currently,biological decolorization of azo dye wastewater using domesticated microorganisms is the mainstream treatment technology,but there are few reports on the ecotoxicity of azo dyes and decolorization products.In this study,Chlorella vulgaris and Lemma minor L.were used as the test organisms.Through the determination of various indicators,the toxic effects of azo dye cationic blue SD-GSL and decolorized products on aquatic plants were studied,with a view to providing a scientific basis for the ecological risk control of azo dye wastewater.Cationic blue SD-GSL was decolorized using Bacillus thuringiensis ZHT-7 and Halomonas sp.YCN-6 respectively,to obtain a decolorized product.The cationic blue SD-GSL and the two biological decolorization products were separated by macroporous adsorption resin XAD-8 to obtain the corresponding hydrophobic acid substance（HOA）,hydrophobic alkali substance（HOB）and hydrophilic substance（HI）.Chlorella vulgaris and Lemma minor L.were selected as the test organisms for the toxicity test.The algal cell density,the number of Lemma minor L.leaves,chlorophyll a,total chlorophyll,photosynthetic activity,superoxide dismutase（SOD）activity,malondialdehyde（MDA）and other indicators to study the effect of each separated component on the growth and activity of aquatic plants.Through the EC₅₀value,the toxic effect of each component was evaluated.Further,using high-performance liquid chromatography-mass spectrometry,the separated components of the product decolorized by the cationic blue SD-GSL by Bacillus thuringiensis ZHT-7 were qualitatively analyzed to explore the relationship between the molecular structure of the components and the toxic effects.The results showed that the components of cationic blue SD-GSL and biological decolorization products can inhibit Chlorella and Lemma minor L..Except for the increase of MDA content,all other indicators showed a downward trend with the increase of the component concentration.The toxic effects of the same components on Chlorella vulgaris and Lemma minor L.are quite different.From the perspective of the inhibitory effect on growth,the EC₅₀value of each component on Chlorella vulgaris（915.6～2949.2 mg/L）is higher than that on Lemma minor L.（176.5～514.2 mg/L）;From the perspective of the inhibitory effect of photosynthesis,the EC₅₀values（334.7～749.6mg/L）of Chlorella vulgaris in each component are lower than those of Lemma minor L.（511.2～866.2 mg/L）;In view of antioxidant capacity,the EC₅₀value of each component for Chlorella vulgaris is lower than that for Lemma minor L..In general,among the three components separated by macroporous adsorption resin,the hydrophobic acid substance has the strongest toxic effect on Chlorella vulgaris and Lemma minor L.,while the hydrophilic substance has the weakest toxic effect.However,comparing with the separated components of the cationic blue SD-GSL,the components of the biological decolorization product have a stronger toxic effect on Chlorella vulgaris and Lemma minor L.In the product of the decolorization of cationic blue SD-GSL by Bacillus thuringiensis ZHT-7,the hydrophobic acid substance may be benzothiazoles,and the hydrophilic substance may be anilines.