Study On Bioavailability Prediction Of Heavy Metals In Soil Using Diffusion Gradients In Thin-films Technique Modified By Biochar

The massive relocation of urban industrial enterprises has led to an increase in the number of contaminated sites left behind,causing a large number of heavy metal pollutants to be released into the soil environment,causing the soil quality to decline,while gradually deteriorating the ecological environment and seriously threatening the lives and health of residents.In this paper,with heavy metal Cd as the target pollutant,a new type of Diffusive gradients in thin-films technique?DGT?was developed.Through aqueous solutions and soil environmental media,Cd concentration,p H,and dissolved organic matter?DOM?concentration on the extraction of available Cd concentration of the new Biochar-DGT?B-DGT?and traditional Chelex-DGT?C-DGT?.Through technical comparison,the advantages of B-DGT in the prediction of bioavailability of heavy metals in contaminated soil are revealed,with a view to constructing a test method suitable for the bioavailability of typical heavy metals in soils with different properties.The main research results obtained are as follows:?1?The prediction bioavailability of B-DGT and C-DGT technology is affected by the different concentrations of Cd in the aqueous solution:When the concentration of Cd in the aqueous solution is lower(<5 mg·L^-1),the bioavailiable state concentration of heavy metals extracted by B-DGT and C-DGT is not much different.When the Cd concentration in the aqueous solution increases,the bioavailiable state concentration of Cd extracted by B-DGT continues to increase,showing a good positive correlation;while the bioavailiable state Cd concentration extracted by C-DGT tends to decrease and gradually stabilizes.Therefore,the bioavailiable state prediction advantage of C-DGT for high-concentration Cd solutions(>5 mg·L^-1)is lower than that of B-DGT,because the binding membrane of C-DGT can easily reach adsorption saturation,while the biochar binding membrane has large adsorption capacity.Thus,B-DGT is suitable for the prediction of bioavailability under high concentration of heavy metal pollution.?2?The sensitive threshold range of C-DGT extraction available Cd affected by p H is p H<7.When the concentration of Cd in the aqueous solution is 5,10 mg·L^-1,the effect of p H change on the extraction of available Cd by B-DGT is minimal.When the concentration of Cd is 20 mg·L^-1 and the p H of B-DGT in the solution is 7,the available Cd extraction rate is the highest.?3?In the soil environment medium,the rule of available Cd extracted by B-DGT and C-DGT respectively is consistent with the trend in the water body.The available Cd concentration extracted by DGT in the same soil was positively correlated with the initial concentration of heavy metals.The available Cd concentration extracted by B-DGT was significantly higher than that of C-DGT,which was shown when linearly fitting the bioavailiable state content extracted by BCR method.It has better accuracy,and the change trend of the available Cd concentration extracted by B-DGT is significantly correlated with the change of the available Cd concentration in the soil?R²=0.9997?,especially in predicting the bioavailability of high-concentration heavy metal contaminated soil,the advantage is more obvious.It also shows that for B-DGT,the biochar material itself contains less Cd,and it has no effect on the prediction results when extracting the available Cd concentration in the soil.?4?B-DGT and C-DGT predict the bioavailability of Cd for 11 different types of soil.It is concluded that the correlation coefficient between the concentration of Cd extracted from the soil and the anion concentration in the soil is r=0.514,p>0.05,Indicating that there is a weak correlation between the two,but the correlation is not significant.For B-DGT,the correlation coefficient between the extracted Cd concentration in the soil and the anion concentration in the soil is r=0.009,p>0.05,indicating that there is no correlation between the two.The correlation coefficients between the C-DGT and B-DGT extracted available Cd concentration in the soil and the cation concentration in the soil were r=0.223,r=-0.215,p>0.05,indicating that the two and the cation concentration in the same soil There is no correlation between them.That is,when C-DGT predicts the availability of heavy metals in the soil,it is affected by the anion concentration in the soil to a certain extent,while B-DGT is hardly affected by the anion concentration in the soil,and can be widely used for bioavailability prediction of heavy metals in soils with different anion and cation concentrations.?5?The effect of soil DOM on the bioavailability of B-DGT and C-DGT in predicting soil Cd found that:There is no correlation between the C-DGT and B-DGT extraction of the available Cd concentration in the soil and the DOM concentration in the soil,that is,C-DGT and B-DGT predict the availability of heavy metals in the soil without being affected by the soil's DOM concentration.Therefore,the developed B-DGT can be applied to predict the bioavailability of heavy metals in different DOM types of soil.Considering the above research results comprehensively,B-DGT can effectively predict the bioavailability of heavy metals Cd in different types of contaminated soil,and is more accurate than the results obtained by traditional DGT technology.