Stress Effects Of Microplastics And Heavy Metals On Escherichia Coli

Studies have shown that more than 100,000 microplastic particles are ingested in the human gut through diet every year,and scholars are also continuously studying the pollution and toxicity of microplastics in the water environment,terrestrial ecosystems and soil organisms.Due to the small particle size and large specific surface area of microplastics,they are often used as carriers for the migration and accumulation of small molecular pollutants in the environment.Therefore,the comprehensive environmental effects and biological toxicity of pollutants carried by microplastics are more complicated.Microplastics carrying pollutants will accumulate in the gastrointestinal tract after entering the organism.Intestinal microbes are important regulators of the physiological process of organisms.The combined pollution of microplastics carrying pollutants will change the structure of the intestinal microbial population and disturb its originality.some physiological homeostasis.However,how the carryover of microplastics affects the toxic behavior of harmful chemicals against specific gut bacteria and the mechanisms of microbial metabolic dysregulation caused by the combined ingestion of microplastics with other pollutants has been poorly studied.In this context,this topic takes polystyrene microplastics as the research object,first discusses the composite effects of microplastics and heavy metals,and based on this,further studies the effects of single polystyrene microplastics,heavy metals and the combination of the two on intestinal microbes in the large intestine.The stress effect of Bacillus,supplemented by kinetic model,was used to explore the mechanism of Escherichia coli biometabolism imbalance,and revealed the law of cytotoxicity produced by microplastics combined with heavy metals.The main experimental conclusions are as follows:(1)The experimental results of the adsorption of heavy metal ions by PS show that this adsorption study conforms to the pseudo-second-order kinetic model and the Freundlich isotherm adsorption model,which is a coexisting process of physical adsorption and chemical adsorption.By calculating the change of Gibbs free energy?G,it is found that the?G value of the six heavy metal ions tested in the experiment increases with the increase of adsorption capacity,which further indicates that the higher adsorption capacity of PS to heavy metal ions requires more external energy.In the same solution system,the difference in?G values of PS microplastics for different heavy metal ions is small,indicating that the adsorption reaction rates of PS to heavy metal ions are almost similar.In different solution systems,the type of salt significantly affected the adsorption of heavy metal ions on microplastics.(2)The experimental results of the stress effect of PS on E.coli showed that different particle sizes of 0.1,1,5 and 10?m and different concentrations of PS of 1,10,50 and 100mg/L had no significant inhibitory effect on the viability of E.coli.In the case of far higher than the exposure concentration of microplastics in the environment,the inhibition rate of E.coli viability was also less than 5%;using E.coli protein content,LPO activity level,and total antioxidant capacity as indicators,the biochemical reactions of E.The results of the investigation showed that PS with different concentrations and particle sizes had no significant difference in the level of total protein content,LPO activity level,and total antioxidant capacity,so a single PS had no significant inhibitory effect on the activity of Escherichia coli.(3)The experimental results of the stress effect of heavy metal ions(Cr³⁺,Pb²⁺,Cu²⁺,Ni²⁺,Cd²⁺,Mn²⁺and Mix)on Escherichia coli showed that the apoptosis of Escherichia coli first went through a rapid decline stage,and then slowly declined until all apoptosis.The mathematical model fitting of the stress effect of Escherichia coli is more in line with the logistic function model.The difference of the maximum inhibitory concentration of heavy metal ions is about 8?g/L,and the difference of the minimum inhibitory concentration is less than 4?g/L;The cytotoxicity EC₅₀values of Cr³⁺,Pb²⁺,Cu²⁺,Ni²⁺,Cd²⁺,Mn²⁺and Mix ion types were 33.17?g/L,30.74?g/L,31.87?g/L,34.34?g/L,36.75?g/L,33.63?g/L,33.23?g/L,respectively.(4)The experimental results of the stress effect of PS complex heavy metal ions on Escherichia coli showed that the mathematical model fitting was more in line with the logistic function model.The cytotoxicity EC₅₀ of seven heavy metal ion types were39.79?g/L,33.90?g/L,35.41?g/L,36.75?g/L,41.23?g/L,38.63?g/L,35.58?g/L,respectively.In the experiments of two types of stress effects,Pb²⁺and Cd²⁺have the strongest inhibitory effect,but under the same conditions,the inhibitory effect of PS complex heavy metal ions is significantly reduced,and the survival rate of E.coli is increased by 10.16%.And it was found that the cytotoxicity of Cr³⁺was greatly weakened when exposed to the same level as other heavy metals due to its adsorption characteristics by PS.