Study On The Basic Characteristics And Biological Toxicity Of Leachate From Tanning Sludge

Tannery sludge leachate is a kind of harmful wastewater with high concentration of heavy metals produced by tannery sludge landfill.If the leachate of tannery sludge is not handled properly,the pollutants in it will pollute the surrounding environment and endanger human health through the food chain.In this paper,producers(plants),decomposers(Qinghai Lake bacteria)and consumers(zebrafish)in the ecosystem were used as the toxicity test organisms of tannery sludge leachate.Seed germination and luminous intensity of luminescent bacteria were tested by leachate of tannery sludge diluted with ultra-pure water.The acute toxicity test of leachate from tannery sludge to zebrafish was carried out and its semi-lethal concentration to zebrafish was studied.At the sublethal concentration,the changes of superoxide dismutase(SOD),catalase(CAT),peroxidase(POD),acetylcholinase(Ach E)and propylene glycol(MDA)were used as the research index.Finally,through tunel detection,histological observation and DNA damage study,to understand the expression of apoptosis,tissue and organ damage and genotoxicity of zebrafish under the stress of tannery sludge leachate and the resistance mechanism of alleviating the influence of leachate,in order to compare the damage to human body caused by toxic substances in tannery sludge leachate after entering the environment,and to explore the acute toxic effect and response mechanism of human contact with pollutants in leachate.In this paper,it is found that tannery sludge leachate has obvious toxic effects on producers(plants),decomposers(Qinghai Lake bacteria)and consumers(zebrafish)in the ecosystem,and the main conclusions are as follows:(1)The seed germination rate of the sludge leachate treatment group was lower than that of the control group.The leachate of tannery sludge could inhibit the germination of plant seeds,and the semi-inhibitory rates of seed germination of ryegrass,white clover and red clover were 27.70%,22.96%and 29.70%,respectively.When the concentration of leachate is low,the seed coat of plant seeds can effectively protect plants from the effects of pollutants.The effects of leachate on seed bud growth of three kinds of plants were promoted at low concentration and inhibited at high concentration.When the concentration of leachate is low,the nutrient elements such as nitrogen and phosphorus will promote the growth of plant buds,while when the concentration of leachate increases,the accumulation of toxic substances will exceed the self-defense limit of seed coat or other plants,and then inhibit the growth of buds.Sludge leachate shows the prospect of resource utilization in urban greening,and after effective treatment,it can provide effective nutrient elements for urban green plants.(2)The luminous intensity of luminous bacteria in the tannery sludge leachate treatment group was lower than that in the control group.The leachate of tannery sludge can inhibit the luminous intensity of luminous bacteria,and its inhibition rate is positively correlated with the concentration of leachate,and there is no phenomenon that low concentration pollutants promote the luminous intensity of bacteria in the research results of others.The luminous intensity inhibited by leachate was rated by two toxicity evaluation methods:luminous intensity semi-inhibition rate of luminous bacteria and biological toxicity of industrial waste.it was found that the toxicity of tannery sludge leachate was rated as high toxicity and high toxicity respectively.According to the regression equation of inhibition rate,it is estimated that the sludge leachate diluted to 6.11%still has low toxicity.(3)Under the stress of leachate from tannery sludge,zebrafish swimming slowly,breathing slowly,Gill cover opening frequency decreased,and a large number of zebrafish died a few hours later.The 24h-LD₅₀,48h-LD₅₀,72h-LD₅₀ and 96h-LD₅₀ of leachate to zebrafish were 4.32%,3.47%,2.57%and 2.13%respectively,and their biological toxicity was extremely toxic.Leachate from tannery sludge at sublethal concentration can cause oxidative stress,cause oxidative damage and affect the nervous system of zebrafish.After long-term adaptation,zebrafish can overcome the oxidative stress and nervous system interference caused by low concentration sludge leachate.(4)Under the stress of sublethal concentration of tannery sludge leachate,a large number of cells of zebrafish showed apoptosis after 7 days,and the apoptosis rate was positively correlated with the concentration of leachate.The effect of leachate on apoptosis of zebrafish organs was liver tissue cell>Gill tissue cell>muscle tissue cell.Leachate has little effect on the histology of muscle tissue;leachate can cause a large number of proliferation and exfoliation of Gill tissue cells,and even cause Gill lamella enlargement and Gill filament bleeding;leachate has the most obvious effect on liver histology,causing hepatocyte membrane lysis,nuclear fusion and significant expansion of hepatic sinusoids.(5)Leachate from tannery sludge threatened zebrafish to cause hepatocyte comet tailing,and the length of comet tail increased with the increase of leachate concentration.Leachate from tannery sludge is genotoxic to zebrafish,and it is speculated that the genotoxicity caused by DNA damage is related to oxidative stress caused by exposure to heavy metals.Organisms have a certain resistance to pollutants in sludge leachate.If the human body is exposed to tannery sludge leachate for a long time or eats water and food contaminated by leachate for a long time,it may affect health,bring about diseases related to antioxidant system and nervous system,and even cause cancer.