Effects Of Accumulators And Their Biochar On Heavy Metal Migration And Morphology Changes In Polluted Mining Areas In Southwest China

The problem of heavy metal contamination caused by mining activities is a major challenge to soil quality and safety in China.The number of contaminated mine sites is large and the actual situation is complex,only some of them have been treated,and there are still a large number of remaining mine sites in the process of natural recovery.The process of plant growth,extinction and the utilisation of its derivatives is often a potential secondary pathway for the migration of heavy metals from contaminated mine sites.For mine sites in natural recovery,the growth to decay process of typical pioneer plants can have an impact on soil heavy metals;for contaminated mine sites in ecological management,the disposal of hyperaccumulator biomass is often a thorny issue for phytoremediation techniques.In this study,the hotspot issues of typical plants and heavy metals in polluted mine sites were explored in separate experiments,and the effects of the growth and decay of Miscanthus floridulus on soil heavy metals in natural restoration were investigated.The main findings of the study are as follows:(1)The results of the sampling survey of Miscanthus floridulus in the contaminated mine site in its natural state showed that Miscanthus floridulus is a potential multi-metal enrichment plant and that the growth of Miscanthus floridulus has some activating effect on the inter-root soil heavy metals.The mean concentrations of Cr,Ni,Cu,Zn,As,Cd and Pb in the aboveground part of the mango were 33.76,7.42,9.71,38.83,0.27,0.42 and 3.27 mg/kg,respectively,while the mean concentrations of Cr,Ni,Cu,Zn,As,Cd and Pb in the below-ground part were69.27,16.47,23.88,46.59,1.49 and 1.49,respectively.In the analysis of the inter-and noninter-root soils of Miscanthus floridulus,it was found that the average concentrations of soil heavy metals in the inter-root soil were in the order of Cr > Cu > Ni > Zn > Pb > As > Cd,and the average concentrations of soil heavy metals in the non-inter-root soil were in the order of Cr > Cu > Pb > Ni > Zn > As > Cd.The highest concentrations of Cr and Cu and the lowest concentrations of Cd were found in both the inter-and non-inter-rooted soils of Miscanthus floridulus at the mine site.The pH of the inter-rhizosphere soil is lower and the sum of the soluble(F1)and reducible(F2)forms of most of the metal weak acids is greater.(2)In soil incubation experiments simulating the decay of Miscanthus floridulus,the addition of Miscanthus floridulus increased soil organic matter,raised soil pH and,to varying degrees,promoted the activation of soil heavy metal forms.The order of the weakly acid soluble state(F1)of the soil was Cd > Zn > As > Cu > Ni > Pb > Cr,which was 1.12,1.04,1.38,1.19,1.05,1.93 and 1.09 times higher than the control weakly acid soluble state(F1)of the heavy metals,respectively;and except for As,the order of activation by the addition of Miscanthus floridulus and pH adjustment was Pb >Cd>Cu>Ni>Zn>Cr.Compared with the control treatment,the concentration of the weakly acid soluble state(F1)of heavy metals increased by17.13,3.17,2.73,2.41,2.34 and 1.83 times with the addition of five knotted mangoes and pH adjustment,respectively.(3)The mean Zn,Cd and Pb contents of Boehmeria nivea(L.)Gaudich biochar were585.82,12.34 and 65.57 mg/kg,respectively,and the mean Zn,Cd and Pb contents of Sedum plumbizincicola biochar were 24120.89,385.64 and 43.28 mg/kg,respectively,and the high Zn,Cd and Pb contents of Sedum plumbizincicola biochar were Cd contents were the key influencing factors limiting the resourcefulness of its super-enriched plant biomass.In the pot experiment,Boehmeria nivea(L.)Gaudich biochar treatment(ZM)had no significant effect on maize growth and soil Zn and Cd contents,indicating that ramie biochar has potential use or has some use value.In contrast,the total biomass of maize treated with Sedum plumbizincicola biochar(JT)was reduced by 44.4%,root volume,root surface area and total projected area by35.1%,28.1% and 28.1% compared to the control,and the Zn content in the upper part of the maize ground and roots was 16.0 and 21.7 times higher than the control,and the Cd content was 11.6 and 25.8 times higher than the control.In the analysis of the sum of the weakly acid soluble(F1)and reducible(F2)states of elemental Zn in the soil,it was found that the highest percentage was 62.10% in the Sedum plumbizincicola biochar treatment,while the percentage was 6.77% and 16.09% in the control and Boehmeria nivea(L.)Gaudich biochar treatments,respectively.