The Removal Potential Of Iris Pseuacorus Toward Atrazine And Its Response Characteristics Under The Combined Pollution Of Atrazine-Cadmium

Organism and heavy metals can successively or simultaneously enter the environment through a variety of ways,and the interaction between organism and metal ions will change their own physicochemical property,migration transformation regularity and biological toxicity.They tend to pose a greater threat to the environment.Atrazine（ATZ）is a low toxic triazobenzene herbicide that inhibits plant photosynthesis and easily enters surface runoff and groundwater.Cadmium（Cd）is one of the most toxic heavy metals,which can be deposited into the soil,leached with wastewater,or taken up by plant roots and quickly transported to the edible plant parts,thereby entering the human food chain,and has received increasing attention worldwide.ATZ contains five electron-donor atoms that can potentially participate in the formation of metal/ATZ complexes.To some extent,this increases the risk of human exposure to ATZ through the food chain.And the synergistic effect of various pollutants will cause more serious ecotoxicological problems.Based on a 3 week hydroponic experiment,the removal potential of I.pseuacorus toward ATZ and its response mechanisms under the combined pollution of ATZ-Cd²⁺was evaluated by contrasting the absorption characteristics of pollutants and the physiological characteristics of plant growth between the compound pollution and ATZ pollution.The results of the study are as following:1.Cd²⁺has a negative effect on ATZ degradation,and ATZ has a longer half-life in the presence of Cd²⁺,thereby suggesting that the coexistence of Cd²⁺could prolong the persistence of ATZ in water.This is likely due to the inhibition of dealkylation of ATZ by Cd²⁺.The ATZ metabolite concentrations increased with increasing initial ATZ levels and experimental duration in both the single and combined treatments.In the presence of Cd²⁺,the DEA content was significantly greater during the early stage of the experiment（within the first 4 days）,while the DIA content was significantly lower and the HYA content was significantly higher throughout the experimental period.Deethylation reactions may proceed at several times the rate of deisopropylation and hydrolytic dechlorination reactions;this trend was similar to that in the absence of Cd²⁺.Thus,Cd²⁺affected not only the N-dealkylation of ATZ,but also the further degradation of intermediate compounds in the degradation of ATZ in water.2.I.pseuacorus had a certain degree of tolerance to ATZ single and ATZ-Cd²⁺compound pollution.The tolerance of single ATZ pollution was higher than ATZ-Cd²⁺combined pollution,and the tolerance of plants supplemented with Cd²⁺at 5 mg·L-1 was also significantly higher than that of plants supplemented with Cd²⁺at 10 mg-L-1 in combined pollution.With the extension of stress time and the increase of Cd²⁺concentration,the relative growth rate of I.pseuacorus decreased gradually.And the root length and root surface area also showed a decreasing trend,indicating that the toxic effect of compound pollution was stronger.EC50 decreased with the extension of pollution stress time and the increase of Cd²⁺concentration,indicating that both stress time and Cd²⁺concentration would increase the severity of ATZ toxicity to plants.3.Plant can obviously promote the degradation of ATZ in culture medium,but the coexisting pollutant Cd²⁺will enhance the persistence of ATZ in the environment.At the same concentration of ATZ,the degradation rate of ATZ with plant pollution was significantly higher than that without plant treatment.And with or without plants,the degradation rate of ATZ under single ATZ pollution condition was higher than that under ATZ-Cd²⁺combined pollution condition.In the presence of plants,the half-life of ATZ was significantly shortened,but in the presence of Cd²⁺,the half-life of ATZ was significantly prolonged.These indicated that plants could accelerate the degradation of ATZ in samples and shorten the residence time of ATZ in water environment.However,under single ATZ pollution and combined ATZ-Cd²⁺pollution,ATZ could be detected in both stems,leaves and roots of I.pseuacorus.The results showed that plant roots could transfer to leaves rapidly after absorbing ATZ.In the single ATZ pollution treatment,leaves content of ATZ was generally higher than that in the combined ATZ-Cd²⁺pollution treatment.It showed that Cd²⁺could restrict the transfer of ATZ from roots to leaves.Both ATZ concentration and exposure time were significant factors which affected Cd²⁺content in plants,and the exposure time had a greater importance.4.Cd²⁺can promote PSⅡ electron transport of I.pseuacorus under ATZ stress.The response of photosynthetic system to ATZ and Cd²⁺stress is mainly reflected in the process ofPSⅡ electron transport.In this experiment,from the generation of K-band and L-band,and the change of the initial slope of OJIP curve in this experiment,it can be found that the electron transfer rate of P680 to QA under the compound pollution is higher than that of single ATZ pollution,and both of them decreased with the increase of ATZ concentration.It indicated that the interaction of ATZ and Cd²⁺can promote PSⅡ electron transfer rate of the donor side to be faster.On the PSⅡ acceptor side,according to the rising degree of J in each pollution treatment,we found that both single ATZ pollution and ATZ-Cd²⁺combined pollution blockedPSⅡ electron transport on the QA downstream.With the increase of ATZ concentration,the blocking ability was stronger.In addition,although combined pollution could blockPSⅡ electron transport on the QA downstream,its blocking ability is smaller than that of single ATZ pollution.It showed that the interaction of ATZ and Cd²⁺will weaken the blocking ability ofPSⅡ electron transport on the QA downstream.I.pseuacorus can regulate its antioxidant system against to the membrane lipid peroxidation damage,and reduced the toxic effects of ATZ and Cd²⁺.The MDA content of single ATZ pollution was significantly higher than that of combined ATZ-Cd²⁺pollution,indicating that the presence of heavy metal Cd²⁺ can reduce the degree of membrane lipid peroxidation by ATZ.And the activities of SOD,CAT and APX in single ATZ pollution were also generally higher than those of combined pollution,which may be due to the low peroxidation degree of combined pollution itself,and leading to a lower activity of antioxidant enzymes.It may also be that the presence of Cd²⁺can inhibits the regulatory capacity of the antioxidant system.