| Heavy metal contamination of farmland soils in the East Dagou watershed of Baiyin City,Gansu Province,is serious,which not only leads to a decrease in the fertility of farmland soils,but also affects the safe production of crops and thus poses a threat to human health.Biochar is a solid material rich in carbon obtained by pyrolysis of agricultural and forestry wastes,which can be used for soil pollution remediation.In this paper,local agricultural waste corn cobs and walnut shells were used as raw materials for the preparation of biochar by oxygen-limited pyrolysis at 500℃.Spinach(Spinacia oleracea L)and cherry radish(Raphanus sativus L.var.radculus pers)were used as the research objects,and farmland soil in the East Dagou watershed of Baiyin City,Gansu Province was selected as the test Soil The content of heavy metals in vegetables(above ground and below ground),soil pH,soil electrical conductivity(EC),soil organic matter(SOM)were measured,and the levels of six heavy metals arsenic(As)and cadmium(Cd)were compared at different additions(1%,3%,5%)of corn cob charcoal and walnut shell charcoal.As,Cd,Cr,Cu,Pb and Zn were enriched at different additions of corn cob charcoal and walnut shell charcoal(1%,3% and 5%).The enrichment characteristics of heavy metals in the soil vegetable-system were investigated under different additions of biochar,and whether the addition of biochar could mitigate the potential health risks of heavy metals from human ingestion of vegetables.The main findings were as follows:(1)Both corn cob char and walnut shell char were alkaline and significantly increased soil pH and SOM with increasing amount of biochar addition.At the same addition amount,walnut shell char increased soil pH more significantly,and corn cob char increased SOM more significantly.The effects of the two biochars on soil EC differed,with corn cob char raising soil EC and walnut shell char lowering soil EC.(2)There were differences in the adsorption of soil heavy metals between corn cob charcoal and walnut shell charcoal.In the control group,corn cob charcoal had better adsorption effect on As,Cd and Cr,and walnut shell charcoal had better adsorption effect on Cu,Pb and Zn.In the spinach group,3% corn cob charcoal had the best adsorption effect on As and Cr,5% corn cob charcoal had the best adsorption effect on Cd and Cu,3% walnut shell charcoal had the best adsorption effect on Zn,and 5%walnut shell charcoal had the best adsorption effect on Pb;in the cherry radish group,1% corn cob charcoal had the best adsorption effect on As,Cd,Cr,Pb,and Zn.(3)Correlation analysis between above-ground heavy metals and soil heavy metals of vegetables revealed that above-ground Cr and Zn of spinach were positively correlated with soil Cr and Zn;above-ground As of cherry radish was significantly positively correlated with soil Cu and Zn,and above-ground Zn was significantly positively correlated with soil Cu and Pb.The correlation analysis of vegetable lower ground heavy metals with soil heavy metals showed that spinach lower ground heavy metals were positively correlated with soil heavy metals;cherry radish lower ground Cu was significantly positively correlated with soil Cu,and lower ground As,Cr,Zn were significantly positively correlated with soil Cu and Pb.The correlation analysis between above-ground heavy metals and below-ground heavy metals of vegetables showed that above-ground heavy metals of vegetables were positively correlated with below-ground heavy metals,and above-ground heavy metals of two vegetables mainly came from the migration of below-ground.Spinach and cherry radish were mainly sourced from the soil.(4)Consumption of vegetables is the main pathway causing health risks,As and Cd contribute significantly to human health risks,and the potential health risks of children are higher than those of adults.1% corn cob charcoal and 5% walnut shell charcoal additions significantly reduce the potential health risks of vegetable consumption in adults and children. |
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