Prediction And Early-warning Forecast On Heavy Metals And Their Pollution Status In Agricultural Soils In Zhejiang Province,china Based On Input-output Inventory

Heavy metal pollution of agricultural soils is one of the most increasing concerns globally.It is essential for accurate determination of input and output pathway of heavy metals to estimate the accumulation or depletion of heavy metals in agricultural soil.Hence,input and output inventory,a quantitative analysis method of heavy metals balance in agricultural soils,has been widely used.In the present study,we firstly made a general review of previous inventories in different regions,which will improve the compilation of inventories.Secondly,input and output inventory of heavy metals in agricultural soil of Zhejiang Province was established to determine the dominant pathways of soil heavy metal input and output and relative contributions,and to perform prediction and early warning forecasting pertaining to the geochemical accumulation of soil heavy metals.Heavy metal balance in agricultural soils in Zhejiang Province was also assessed with PROTERRA-S model and the results were compared with input and output inventory to give a more comprehensive understanding of heavy metal accumulation in the agricultural soils of Zhejiang Province.To further identify the status and sources of heavy metals pollution in agricultural soil in Zhejiang,the concentrations and spatial distribution patterns of heavy metals were assessed.Sources of the heavy metals were identified using principal component analysis?PCA?and positive matrix fraction?PMF?model.To assess their potential risks,the potential ecological risk indices?RI?was applied,along with the health risk assessment method recommended by US Environmental Protection Agency.To better understand the natural Hg emission processes in the agricultural soils,soil-air exchange of Hg at four seasons in the agricultural soils of Quzhou in situ in January,March,July and September of 2018 was investigated using a dynamic flux chamber coupled with a Mercury Vapor Analyzer.The main results of the present study were summarized as follows:?1?Inventory of heavy metals inputs to and outputs from agricultural soils in Zhejiang Province was developed.Atmospheric deposition was responsible for47.88%and 76.87%of the total Cr and Pb inputs in the agricultural soils in Zhejiang Province,respectively.Livestock manures accounted for approximately 54⁸5%of the total As,Cu,and Zn inputs.Livestock manure and irrigation were the main sources of Hg,accounted for 50.25%and 38.63%of the total inputs,respectively.Ni was mainly derived from atmospheric deposition?57.86%?,followed by irrigation?22.69%?.As for Cd,the relative contributions of atmospheric deposition,irrigation,and livestock manure were similar.Crop harvest and leaching were found to be the dominant output pathways of the soil elements Cd,Cu,Hg,and Zn,being responsible for 74.43⁸3.62%of the total outputs.Surface runoff was the dominant output pathway for As,Cr,Ni,and Pb,accounting for approximately 73.36%,46.32%,54.16%,and 48.11%of the total outputs,respectively.According to prediction and early warning,Cd is the priority control pollutant in the agricultural soils in Zhejiang Province.?2?Applied PROTERRA-S model to simulate Cd input and output fluxes revealed that 65.75%of the regional Cd was supplied by atmospheric deposition,30.96%by livestock manure and 3.29%by chemical fertilizer application.However,input and output inventory of Cd in agricultural soil of Zhejiang Province showed that atmospheric deposition was responsible for 34%of the total Cd inputs,followed by livestock manure?31.34%?and chemical fertilizer?3.97%?input.PROTERRA-S model simulated results showed that crop harvesting and leaching accounted for34.52%and 49.32%of the total Cd output,respectively.Input and output inventory of Cd showed that crop harvesting and leaching accounted for 39.18%and 35.25%of the total Cd output,respectively.Considerable variability could be ascribed to the differences in the determination of the main input and output pathways,and the methods used for fluxes assessment.Irrigation as one of dominant input pathways in input and output inventory,however,is excluded in PROTERRA-S model.Pesticide and sewage sludge input are observed and evaluated in PROTERRA-S model,surface runoff is neglected.It is necessary to verify and improve PROTERRA-S model performance for practical application in the further.Considering these two methods have certain limitations,it is important to integrate these methodologies from mutual authentication to obtain more comprehensive understanding of heavy metal accumulation in agricultural soils in Zhejiang Province.?3?The overall pollution status of heavy metals in agricultural soil of Zhejiang Province was identified.Heavy metals exhibited different patterns spatially from GIS maps,may indicating their different sources and mechanisms to control the patterns.PCA result indicated that Cr,Cu,and Ni were mainly inherited from industrial practices,while Cd and Hg were associated with agricultural activities.As,Pb and Zn were probably associated to atmospheric deposition.Based on PMF model,the source1 profile was dominated with Cd,Hg and Pb,categorized as application of pesticides and fertilizers.Source 2 had predominant loadings of Ni and Cr,and Cu categorized as industrial use and discharge.The source 3 profile was mainly consisted by As,identified as representing coal combustion.Potential ecological risk indexes of heavy metals decreased in the following sequence:Cd>Hg>Pb>As>Cu>Ni>Cr>Zn,and RI of all of the cities were lower than 150,indicating that these cities had low potential ecological risk levels.The HI values of the eight kinds of heavy metals were all less than 1.0 for both children and adults,indicative of a lack of non-carcinogenic risk by heavy metals in these populations.Most of the carcinogenic risk values for As and Cd were above 10^–6,but were lower than the highest acceptable risk of 10^–4,indicating the cancer risks were within acceptable levels.?4?Seasonal variation of Hg exchange fluxes between soil and air were investigated,and the major variables controlling the Hg fluxes were evaluated.The soil-air Hg exchange flux averaged from 58.14 ng/m²/h to 160.3 ng/m²/h,indicating that agricultural soil is a significant Hg source for the atmosphere in Quzhou City,Zhejiang Province.The seasonal variations in soil-air Hg flux were observed,with low values in the winter time?58.14 ng/m²/h?,elevated values in the spring?98.92ng/m²/h?,peaked in the summer?160.3 ng/m²/h?,and decreased values in the autumn?109.1 ng/m²/h?.Hg evasion from soils showed a clearly diurnal pattern that Hg release into the atmosphere reached maximum at 11 a.m.,and fell to minimum at 2a.m.and 8 p.m.,respectively during spring and summer.Whereas,soil-air Hg flux exhibited a similar diurnal pattern during autumn and winter that it peaked at 1 p.m.,and fell to minimum at 6 a.m.and 11 p.m.,respectively.Environmental factors controlling soil-air exchange of Hg differed in different seasons.Soil temperature was the major variable controlling Hg fluxes during winter and spring.Soil temperature and TGM were significant in explaining the Hg fluxes in summer,and showed antagonism between each other.O₃ and TGM play dominant roles in influencing the Hg fluxes in autumn.Empirical models for estimating Hg evasive flux from soils were developed based on regression analyses,and atmospheric O₃ concentration was parameterized in the models for the first time.Measured and modeled Hg fluxes in four seasons showed significant linear correlations?R²=0.61,P<0.001?,indicating these models can be applied to estimate the Hg release into the atmosphere through evasion from soils.