Effects Of Physicochemical Properties On The Bioavailability Of Pb And Cd In Soils In Wetland Systems

As one of the important types of ecosystems,wetland is an important target for environmental protection and global change research.At present,wetland has become the main reservoir of heavy metals.When the wetland soil is contaminated by heavy metals such as lead(Pb)or cadmium(Cd),the bioavailability of heavy metals changes due to the transformation between heavy metals,which affects the toxicity of heavy metals.This process is affected by soil texture,soil water holding capacity,organic matter,pH etc.Therefore,the study of the role of heavy metal pollutants in the stabilization process of wetland soils under different environmental factors will be more practical.By simulating wetland climatic conditions,using a combination of field sampling and indoor simulation,When heavy metals(Pb,Cd)are contaminated and transferred to the soil,the contents of Pb and Cd(full amount,effective state)and bioavailability with time under different gradient wetland soil water content,organic matter content and water pH.(1)After Pb and Cd enter the simulated wetland system with 2cm of flooding,0% organic matter and pH=7,in the early stage of stabilization,Pb has a certain effect on the bioavailability of Cd;Cd has little effect on the bioavailability of Pb.The bioavailability ratio of Pb and Cd fluctuated around 1 in the late stage of stabilization.When the soil environment of the wetland simulation system is contaminated by heavy metals such as Pb and Cd,the interaction between the two heavy metals is small.(2)In a wetland simulation system that changes the pH,moisture,or organic matter gradient,the available content and bioavailability of Pb and Cd decreased with time,while The total content of Pb and Cd changes little with time.At the end of the experiment,compared with the initial heavy metal content,the available content and bioavailability decreased by 73% to 93%.The total amount of Pb and Cd changed little with time,and the change range was about-5% to 5% compared with the total content of Pb and Cd on the 0th day.(3)The results show that the lower the pH,the greater the toxic effect of heavy metals on organisms,and the impact of heavy metal pollution on soil under acidic soil conditions is greater than that of alkaline environment.The higher the organic matter content,the lower the available content and bioavailability,while the total amount of heavy metals in the soil environment increased.When the water content of the wetland soil is different,the effective content and bioavailability of Pb and Cd in the submerged 2cm and dry-wet conditions are lower than other water conditions;The effective state and bioavailability of Pb and Cd in the dry and wet alternate state are higher than the continuous flooding state.