| Unlike the high concentration in industrial effluents and sanitary wastewater,the heavy metals in natural water usually present the features of low concentration and wide distribution.Phytoremediation offers an innovative and promising method for heavy metal removal from water.It is an eco-friendly and effective in situ remediation technology driven by solar energy.Water hyacinth is a kind of free-floating aquatic plant with high biomass and fibrous root system.It has been proved to own great tolerance for metals and an excellent choice for phytoremediation process.Most studies regarding the phytoremediation of heavy metals focused on the removal efficiency of single metal or several metals by plants.And few studies have been reported to investigate the different uptake behaviors when plants are under the stress from more than one heavy metal.However,the competitive adsorption of heavy metals onto adsorbent such as carbon,biochar has been demonstrated.Multi-metal adsorption behavior differs from mono-metal adsorption due to competition.Therefore,present study was performed to assess the diversity of uptake behaviors of three types of heavy metal ions Cd(II),Cu(II)and Pb(II)from aqueous solutions by water hyacinth.The removal rates of Cd(II),Cu(II),Pb(II)were 98%,96%,78.5% and 79.5%,79.4%,52% respectively in mono and multi-metal mediums when initial concentrations were 0.1mg/L,1.0 mg/L,1.0 mg/L after 15 days.A significant decrease in metal concentrations was observed during the incipient 1st day in the mono-metal mediums while a moderate decrease during 1st and 5th day.In the combined contaimination of chlorine pesticide and single metals,dicofol promoted the adsorption of Cd(II)and Cu(II)by water hyacinth.And the lower concentration dicofol was,the greater removal rates could be achieved.However,the removal rate of Pb(II)showed a positive relationship with the concentration of chlorine pesticide.In the combined contaimination of chlorine pesticide and multi-metals,a high concentration of dicofol raised the removal pecentages of three metals,while a low concentration inhibited the adsorption of Cd(II)and Cu(II).All the three metals showed a much higher accumulation in roots rather than in aerial parts(shoots),which accorded with most of the previous studies.The concentrations of Cd(II),Cu(II),Pb(II)in plant roots were determined to be 279.3mg/kg,2815.7mg/kg,2198.8mg/kg in mono-metal mediums and 134.1mg/kg,2016.8mg/kg 和2089.4mg/kg in multi-metal mediums,demonstrating that no matter in mono or multi-metal solutions,root is the main position where heavy metals accumulate.The overall translocate factors are below 0.5.Moreover,the phenomenon that metal concentrations in plants treated with multi-metal water are significantly lower than in those treated with mono-metal water mediums.This result implied that the exposure to more than one type of heavy metals has impacts on the uptake of metal ions by water hyacinth.The impact factors which influence the removal rate or amount of heavy metals are explored in the study.And result showed that the heavy metal concentration,pollution load,nutirents and external temperature have significant impact on water hyacinth.Nurtrients(TN,NO3-N,NH4-N,NO2-N,TP,PO4)concentrations in the solution has also been detected,indicating that TN concentration increased considerably in the conbined contaminants treatments and TP concentration decreased in all the treatments.In the mono-metal mediums,TN concentration showed the sequence of Cd(II)<Pb(II)≈Cu(II)<Mix.Determine the content of chlorophyll,soluable sugar and MDA in plant leaves as well as the activity of of SOD to investigate the biochemical changes in water hyacinth in different treatments.Consequences implied that combined contamination imposed greatest stress on water hyacinth.Photosynthesis was impacted adversely,and a large amount of O2-accumulated in plant cells which led to severe peroxidation. |
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