Fate Of Atrazine And Its Ecotoxicological Effects In Lake Sediments

As a widely used herbicide,atrazine has been detected in groundwater,rivers and lakes where atrazine had been applied.Atrazine and its metabolites are biologically toxic,which could cause ecological damage in both groundwater and surface water sources.As a sink of various pollutants in the water body,the sediment can adsorb atrazine in the water environment.Meanwhile,the sediment is a secondary source of pollution,while the adsorbed atrazine could be released into the overlying water or absorbed by aquatic plants.When atrazine enters sediment,few attempts have assessed the biodegradation of atrazine by plants and microorganisms.The toxicological responses of submerged macrophytes and microorganisms to atrazine stress needs further investigation.Hence,this paper mainly studied the distribution characteristics of atrazine in lake sediments,the ecotoxicological effects of atrazine on submerged macrophytes and bacteria,the phytoextraction,transformation and degradation of atrazine by submerged macrophytes,and the metabolic processes of atrazine by microorganisms in sediments.The main results are as follows:?1?By detecting the concentration of atrazine in the sediments of six shallow lakes in Hubei Province,it was found that all of these lake sediments contain atrazine.The highest concentrations of atrazine in sediments appeared in Honghu Lake,Jingzhou City and Liangzihu Lake,Ezhou City,which reached 0.171 and 0.114mg·kg^-1,respectively.The equilibrium partition coefficient of atrazine desorption(K_Pd)is much larger than the adsorption equilibrium partition coefficient?K_P?of atrazine,indicating that the residue of atrazine in water is easily immobilized by the sediments.?2?Within a 60-day incubation,atrazine can significant inhibit the growth of inhibit the growth of Potamogeton crispus and Myriophyllum spicatum within the60-day incubation,while the plants will recover from the injury on the 90th day.On day 90,under the action of glutathione reductase?GR?and glutathione S-transferase?GST?,glutathione?GSH?could remove atrazine and reactive oxygen species caused by atrazine in plants.Thus,a certain concentration of GSH was useful against atrazine stress.?3?The uptake of atrazine by P.crispus and M.spicatum reached equilibrium after a 30-day incubation.On day 90,the ratio of atrazine values in P.crispus and M.spicatum to atrazine values in the sediment was 38.27±6.32 and 27.40±4.52,respectively.In P.crispus and M.spicatum,atrazine was dechlorinated and hydroxylated to hydroxyatrazine?HA?and hydroxyisopropyl atrazine?HIA?,and then HA and HIA are conjugated to HA+ctric acid/malonic acid/tartaric acid-H₂O?HA+?Cys-?-Ala?-H₂O and HIA+Glc-H₂O.Finally,all conjugates were degraded to HA,deethylatrazine?DEA?,cyanuric acid?CYA?and biuret.The formation of biuret suggested the ring opening of atrazine in aquatic plants for the first time?4?The RNA-Seq analysis showed that the top three significantly improved genes in P.crispus treated with atrazine controlled glycine-rich protein family,ribosome,hydrogen peroxide and ATP binding.According to the GO functional classification results,in biological process?BP?category,the DEGs were significantly enriched in terms of biological process,cellular process and metabolic process.The DEGs of cellular component,cell part and intracellular part were significantly enriched in cellular component?CC?category,while the molecular function,catalytic activity and ion binding were significantly enriched in molecular function?MF?category.Meanwhile,all DEGs were analyzed against the Kyoto Encyclopedia of Genes and Genomes?KEGG?database,while seven pathways were significantly enriched?P?<0.05?,including photosynthesis-antenna proteins,oxidative phosphorylation,ribosome,phagosome,photosynthesis,age-rage signaling pathway in diabetic complications and citrate cycle.Hence,the relevant metabolic pathways and molecular functions in P.crispus have changed under the action of atrazine.?5?The degradation rate of atrazine in alkaline sediments was faster than that in acidic sediments.Values of hydroxylated metabolites in the acidic lake sediments tended to be greater.Moreover,the amounts of Proteobacteria,Actinobacteria,Firmicute,Nitrospinae,Aminicenantes,Ignavibacteriae and Saccharibacteria in acidic Tangxunhu Lake sediments were significantly different from alkaline Honghu Lake sediments,while the amounts of Cyanobacteria and Saccharibacteria in sediments treated with atrazine were significantly greater than those in sediments without atrazine?P<0.05?.Notably,p H was the most relevant environmental factor in the quantitative variation of atrazine-degrading bacteria,including in Clostridium-sensu-stricto,Pseudomonas,Comamonas and Rhodobacter.With the increase of OC,CEC,p H,biuret,TN values and coarse particle ratios,the total amounts of atrazine-degrading bacteria in sediments were significantly increasedOverall,when atrazine enters water,only a small amount of atrazine would be remained in the water phase,while most of the atrazine was adsorbed by sediments rapidly.P.crispus and M.spicatum could extract,transfer and degrade atrazine in sediments.On the other hand,atrazine could induce the oxidative stress response of submerged plants to alleviate the stress of atrazine.Meanwhile,microorganisms in sediments could degrade atrazine into HA,CYA and biuret.Amounts of bacteria associated with the degradation of atrazine in sediments were mainly affected by the OC,CEC,p H,TN content and coarse particle ratios of the sediment.