Study On Heavy Metal Pollution In Surface Soil Around Qinghai Lake

Soil heavy metal pollution poses a serious threat to ecological environment quality,crop growth and human health,which has become a hot issue in the world.Qinghai Lake area is an internationally renowned tourist resort,and it is also an important agriculture and animal husbandry products supply area.Therefore,it is an applied topic with theoretical value and practical value to evaluate the contamination status of heavy metals in surface soil around Qinghai Lake.A total 87 samples from surface soil were collected to test for the concentration and existing forms of Cd,Cr,Pb,As,Cu,Zn,Ni,Mn,Co.The physicochemical properties including pH value,magnetic susceptibility,soil granularity and organic matter were also analyzed.Based on the experimental date,the concentration level,spatial distribution,pollution source and correlation with physicochemical properties of heavy metals in soil were explored.At the same time,the pollution level,potential ecological risk and human health risk of heavy metal in surface soil around Qinghai Lake were evaluated.According to these researches,the main results were as follows:(1)The concentration of Cd,Cr,Pb,As,Cu,Zn,Ni,Mn and Co in surface soil around Qinghai Lake were 0.05～5.57,11.50～60.93,7.46～35.09,0.96～18.52,2.06～74.38,17.30～98.62,6.23～31.62,190.94～878.18 and 3.29～23.09 mg/kg.Heavy metals except for Cd,were approximately equal to or less than the background value of Qinghai Province.The mean concentration of Cd was 4.53 and 1.16 times of the background value of Qinghai Province and the screening value of soil pollution risk control standards for agricultural land,respectively.(2)The concentration of Cr,Pb,As,Cu,Zn,Ni,Mn and Co in surface soil were all significantly correlated with clay,silt,organic matter,low-frequency magnetic susceptibility and high-frequency magnetic susceptibility,however,which showed a negative correlation with sand and pH.Those heavy metals were negatively correlated with frequency magnetic susceptibility,weakly.It is worth pointing out that there was no obvious correlation between Cd and physicochemical properties.(3)The modified BCR fractional analysis shown that Cd,Mn and Co were main acid-soluble form of the total concentration in surface soil around Qinghai Lake,which indicating these heavy metals had strong mobility and high environment risk.Zn,Mn,Pb and Cu,Cd,Pb,Co were mian reducible form and oxidizable form of the total concentration,respectively,which indicating potential mobility and risk.The residual form of Cr,Ni and As was all more than 65%,which indicating lower bioavailability and toxicity.(4)Single factor pollution index method,geo-accumulation index method,Nemero pollution index method,and pollution load index method were used to assess the pollution degree of heavy metals in surface soil around Qinghai Lake,the results shown that the major pollutant element is Cd,Pb and Co,followed by Cr、As、Cu、Zn、Ni and Mn,and there were also pollution sample.(5)The results of potential ecological risk index method shown that the research area reached the degree of moderate ecological risk according to the background value of Qinghai Province.The results of health risk shown that the non-carcinogenic risk index of children and adults were less than 1,which indicating no significant non-carcinogenic risk.The carcinogenic index of Cd ranged from 1.0×10-6～1.0×10-4,indicating that Cd was in an acceptable range.Ni and Co less than l.0×10-6,which indicating that Ni and Co were no carcinogenic risk.The non-carcinogenic risk and carcinogenic risk of heavy metal exposure pathways were in order of direct ingestion>respiratory inhalation>skin absorption.The non-carcinogenic risk and carcinogenic risk of children was greater than that of adults.(6)The spatial distribution of Cd in surface soil around Qinghai Lake had the order of west>north>northeast>southeast>south.Cr,Pb,As,Cu,Zn,Ni,Mn and Co followed the same spatial distribution,which were higher in north and south and lower in northeast and southeast.The results of Nemero pollution index method shown that west,north,northeast and southeast all reached the heavy pollution level,south reached the light pollution level.The results of pollution load index method shown that south and north accumulated to moderate pollution level,while west,northeast and southeast were not polluted.(7)The results of multivariate analysis shown that heavy metals in surface soil could be classified as 2 sources.Cr,Pb,As,Cu,Zn,Ni,Mn and Co were affected by nature,traffic and coal combustion,Cd was affected by traffic and agriculture.