Characteristics Of Cd-Pb Accumulation And Contribution In Vegetables From Atmospheric Deposition

With the development of industrialization and accelerated urbanization,the problem of heavy metal pollution has become increasingly prominent.Heavy metals can directly or indirectly enter into the interior of vegetables through dry and wet atmospheric deposition,triggering the risk of heavy metal accumulation and thus threatening human health.Therefore,it is especially important to clarify the heavy metal accumulation effect of atmospheric deposition on vegetables,to reveal the accumulation process of heavy metals in vegetables by atmospheric deposition,and to analyze the contribution and distribution of heavy metals in vegetables by atmospheric deposition.This paper takes lettuce,a vegetable popular among Chinese residents,as the research o bject,takes Cd and Pb,which are more prominent in pollution,as the target heavy metals,and adopt atmospheric precipitation(dry deposition)and atmospheric precipitation(wet de position)as the simulation scenario,and adopts a fully designed experiment with potted h ydroponics and potted soil cultivation,focusing on the differences in the effects of atmosp heric deposition state,atmospheric deposition method,atmospheric heavy metal concentratio n and other factors,analyzing the accumulation effect of atmospheric deposition on vegeta ble Cd and Pb,revealing the enrichment and migration process of atmospheric deposition on vegetable Cd and Pb,and analyzing the contribution and distribution characteristics of atmospheric deposition on vegetable Cd and Pb by constructing contribution coefficients an d distribution ratios.1.Atmospheric deposition mainly caused the accumulation of heavy metals in vegetables through two pathways: atmosphere → soil → roots and atmosphere → leaves,while the accumulation caused by atmospheric action on the stems was not obvious;the higher the atmospheric concentration of heavy metals promoted the accumulation of heavy metals in vegetables,the accumulation of Pb was higher than that of Cd,natural dustfall(leaf/soil mix dustfall)significantly increased the risk of Cd accumulation in vegetables,and foliar precipitation(spraying)promoted the increase of Pb accumulation in vegetables.2.The organ distribution characteristics of heavy metals in vegetables were significantly different for different atmospheric deposition states and deposition methods,and their accumulation was in the order of leaves > roots > stems.For Cd,mixed leaves/soil dustfall significantly promoted the accumulation of roots and stems Cd,and the leaves Cd content was higher under foliar precipitation.For Pb,roots,stems and leaves Pb accumulation was significant under surface dustfall,foliar dustfall and foliar precipitation.3.The enrichment and transport characteristics of heavy metals in vegetables are obviously different for different atmospheric deposition states and deposition methods.The heavy metal enrichment coefficients of vegetables to the atmosphere were Cd>Pb and leaf>stem>root,and the situations with higher enrichment coefficients were low atmospheric concentrations of heavy metals,surface precipitation(irrigation)and foliar precipitation,which mainly affected the roots,stems and leaves,respectively.The migration characteristics of heavy metals from stems and leaves to roots of vegetables were as follows: Cd was negatively migrated(mainly accumulated in roots)and Pb was positively migrated(mainly accumulated in leaves);the situation with higher migration coefficient were high atmospheric heavy metals concentrations,foliar precipitation,which showed that the migration coefficient of 1 < stems < migration coefficient of leaves,that is,Cd and Pb from roots and stems easily migrate to leaves for enrichment.4.The transformation characteristics of vegetable heavy metals were obviously different for different atmospheric deposition states and deposition methods.The intensity of vegetable Cd activity was in the order of leaves > stems > roots,low atmospheric heavy metal concentration inhibited vegetable Cd activity,and the treatments of surface dustfall,foliar waterfall and foliar dustfall had significant inhibitory effects on roots,stems and leaves Cd activities,respectively.The intensity of vegetable Pb activity was leaves>roots>stems in order,high atmospheric heavy metal concentration inhibited vegetable Pb activity,and surface precipitation and natural dustfall had prominent inhibitory effects on roots leaves and stems Pb activity,respectively.Therefore,under the dual stress of atmospheric deposition and soil pollution,vegetable roots and stems Cd and Pb tend to exist in a less active form and accumulate gradually,making it difficult to migrate to the leaves.5.The contribution characteristics of heavy metals in vegetables were obviously different for different atmospheric deposition states and deposition modes.The atmospheric contribution coefficients of heavy metals in vegetables showed that Cd<Pb.For Cd,the atmospheric contribution coefficients of each organ were in the order of stem<root<leaf,and the high concentration increased the atmospheric contribution to vegetable Cd.For Pb,the atmospheric contribution coefficients of each organ were in the order of stem<leaf<root,and the low concentration increased the atmospheric contribution to vegetable Pb.The contribution of Cd and Pb from precipitation irrigation to roots,stems and precipitation spraying to leaves dominance was obvious.6.The distribution of Cd and Pb in vegetables subjected to soil input and atmospheric deposition stress,soil > atmosphere(Cd:54.6% > 45.4%;Pb:53.1% > 46.9%).Soil mainly affected the accumulation of Cd and Pb in roots,with a contribution of 59.7% and 59.4%,respectively,while atmospheric deposition mainly affected the accumulation of Cd and Pb in stems and leaves,with a contribution of 51.3% and 54.2%,respectively.This paper only explored the accumulation of heavy metals in vegetables through simulated atmospheric deposition experiments,and was largely limited to the comparative analysis of surface effects and semi-qualitative and semi-quantitative process exploration and contribution distribution analysis.It is suggested that subsequent studies should be combined with plant physiological and biochemical analyses and isotope tracing to further investigate the intrinsic mechanisms of atmospheric deposition on heavy metal accumulation in crops and to improve the accuracy of the analysis of the contribution of atmospheric deposition to heavy metal accumulation in crops.