Heavy Metal(Loid)s Pollution In Surface Soil Of Beijing Urban Park And Their Risk Assessment

Urban parks play an important role in the urban ecosystem.The environmental quality of urban park soils might influence human health following long-term exposure.Especially the heavy metal?loid?in soil has become the key index to evaluate the environmental quality and ecological function of urban parks.As the capital of China,Beijing has witnessed rapid development of urban scale and urbanization process.A large number of new urban parks were built on land from industrial relocation and agricultural renovation,and there are different degrees of environmental pollution problems.In order to fully explore the concentration level,pollution sources and potential risks of heavy metal?loid?s in the soil of Beijing urban parks,we collected 121 urban park topsoil samples in Beijing,determined eight heavy metal?loid?Zn,Cr,Pb,Cu,Ni,As,Hg and Cd element content.Heavy metal?loid?s were analyzed using geostatistical,UNMIX model,conditional decision tree?CIT?,ecological risk and human health risk.The results showed that:?1?The average concentrations of Cr?63.57 mg/kg?and Ni?27.12 mg/kg?were lower than the background values,while Zn?145.68 mg/kg?,Pb?36.43mg/kg?,Cu?35.49 mg/kg?,As?11.97 mg/kg?,Hg?0.87 mg/kg?and Cd?0.49 mg/kg?were higher than the background values.Compared with China Soil Environmental Quality Standards for Development Land?GB36600-2018?,only one sample exceeded the standard screening values for mercury and arsenic,respectively.?2?From the spatial distribution analysis,Ni and Cr were evenly distributed on the whole;Hot spot analysis showed that Cu and Zn had similar accumulation patterns.The high value area of Pb and Hg were mainly concentrated in the middle of the study area.Cd accumulation was concentrated in the southwest of the study area.The high value region of As was mainly distributed in the northern area.?3?The HI value of all heavy metal?loid?s was less than 1,and the LCR value was lower than 10^-6,indicating that the heavy metal?loid?s in the soil of Beijing urban park had no significant non-carcinogenic and carcinogenic risk to children and adults.The ecological risk calculated that the majority of soil samples?73.55%?have moderate pollution risk,while a small number of samples?18.18%?have moderate to severe pollution risk.The analyses showed that:?1?heavy metal?loid?s in Beijing urban park soils is good but has a certain degree of enrichment.The spatial characteristic of the enrichment of each metal is,Ni and Cr,Cu and Zn have similar spatial distribution characteristics,while other heavy metal?loid?s have different distribution characteristics.Pb was concentrated in Beijing center area.The concentration of Hg decreased from the urban center to the surrounding areas.The accumulation of Cd is concentrated near the former Shougang site in Shijingshan district.High As were mainly located in Chaoyang district and Haidian district.?2?Through Pearson correlation analysis and spatial autocorrelation analysis,it can be found that there is a strong correlation between Pb,Zn and Cu,while the correlation between other metals is weak.Ni?C₀/?C₀+C?<25%?has a strong spatial correlation.The spatial correlations of Cr,Pb,Zn,Hg,As and Cd were not significant?25%<C₀/?C₀+C?<75%?.The spatial correlation of Cu is weak?C₀/?C₀+C?>75%?.?3?Heavy metal?loid?s in the soil of Beijing urban park are mainly from traffic emissions,industrial and agricultural production activities.The contribution rate of anthropogenic sources is much higher than that of natural sources.According to the UNMIX model analyses,three pollution sources of heavy metal?loid?s in the soil of Beijing urban parks are identified:soil parent materials and special industrial sources,mixed sources of industry and agriculture,and traffic sources.According to CIT analyses,duration of urbanization,park age,per capita GDP,traffic emissions,industrial and agricultural activity,and coal consumption are important factors affecting the accumulation of metal?loid?s in the soil of Beijing urban parks.?4?The health risk and ecological risk of heavy metal?loid?s in the soil of Beijing urban park were low.