Evaluation Of Heavy Metals And Selenium In Soils Of Gua Jiayu Regions In Beijing

Heavy metal pollution in orchard soil has become one of the main contents in the survey of heavy metals pollution in soil.As one of the main areas producing peach in Beijing,the investigation of soil heavy metal content and distribution characteristics in Guajiayu Region is crucial.The contents,spatial structure,sources and pollution assessment of heavy metals from 122 topsoil samples in Guajiayu region were systematically analyzed by Geostatistical methods,Principal Component Analysis(PCA),including mercury(Hg),arsenic(As),cadmium(Cd),chromium(Cr),lead(Pb)and total selenium(Se).There are following conclusions:(1)The average contents of Hg,As,Cd,Cr and PB were 0.04,10.47,0.17,80.66 and 22.48 mg/kg respectively and the coefficient of variation was between 16%and 29%.Total contents of Se ranged from 0.06 to 0.76 mg/kg with an average of 0.30 mg/kg.86.88%of sampling points were beyond high level of Se content,of which 20.49%in the selenium-rich soil.The average content of As and Se were significantly different in land uses and there was no significant difference in Hg,Pb,Cd and Cr.The average content of six heavy metals were significantly different at different altitudes.(2)The characteristics of spatial structure suggested that Hg,As and Cr had strong spatial autocorrelation as well as Cd and Pb moderately spatially correlated.Besides,the optimal fitting models were Gaussian model for Hg and Cr and exponential model for As,Cd.and Pb.Spatial variability showed that Se had a weak spatial correlation and its optimal fitting model was exponential model.The areas with high Pb and As were concentrated in the central low-altitude areas,and the high contents of Cr were predominated in the high-altitude areas such as the southeast and southwest corners.The contents of Hg and Cd were relatively low in northwest,but were mainly distributed in southwest and east.Se element wholly exhibited a northwest ribbon-shaped distribution and the areas with seleniun-rich soil showed obvious spatial cluster pattern.(3)Correlation analysis showed that there was a significant positive correlation between elevation and Hg,Cd and Cr(P<0.01)and a significant negative correlation with As and Pb(P<0.01)respectively.Principal component analysis found that Pb,As,and Cr were classified as the first principal component,accounted for 40.21%of the value of contribution,following Hg and Cd as the second principal component with 25.74%of the value of contribution.Traceability analysis showed that sources and spatial distribution of Pb,As,Cr,Hg and Se were significantly influenced by structural factors such as soil parent material,altitude.Natural factors like soil parent rnatrial and topography combined with random factors such as land uses impacted on the content and spatial distribution of Cr.(4)According to the assessment of heavy metal pollution,soil background value as an evaluation criteria in Beijing can more accurately reflect accumulation of heavy metals in investigated areas.The single factor pollution grade displayed that As and Cd elements caused mild pollution and the environment affected by Hg and Pb elements were still clean,as well as the pollution grade of Cr elements was moderate pollution.The comprehensive pollution grade of this area was still clean.The average value of potential ecological risk coefficient of Cd element represented moderate ecological hazard,while the other elements triggered mild ecological hazard.Potential ecological risk index(RT)was 81.84,which was a mild ecological hazard.The average cumulative index of Cr was 0.91,which was in mild to moderate pollution,and the other four elements were in non-pollution level.(5)Referring to the national secondary standard of soil environmental quality and the secondary standard of soil environmental quality of agricultural land,the current soil environmental quality in agricultural land can be fully reflected.The single factor pollution index of Hg?As?Cd?Cr?Pb elements reached safety grade,which the nemerow comprehensive pollution index were clean and the potential ecological risk coefficients were all in a slight ecological hazard,which the comprehensive potential ecological risk index were slight risk and the land accumulation index were in a pollution-free level.There was a certain accumulation of heavy metals in the soils of Hangjiayu area,most of which maintained the natural level and were suitable for crop growth,and there was selenium-rich soil spread over the region.