| In recent years,the heavy metals(HMs)pollution in greenhouse-vegetable soil(GS)causes great concerns as governments and people attach importance to soil qualities and potential health risks.For protecting greenhouse soil quality and food safety,it is important to investigate on the situations,causes and health risks of HMs pollution.The purpose of this study was to evaluate some factors in GS as follows:(a)the physicochemical properties(soil p H,conductivity,carbonate content,organic matter,cation exchange capacity,soil texture,etc.),(b)the total and available content of soil HMs(Cd,Cu,Zn,Cr,Pb,Ni,Mn and Co),(c)the relationship between soil HMs and planting years,(d)the spatial distributions characteristics of HMs,(e)the risk assessment of HMs in GSs.Therefore,a field investigation was conducted at GS and open field in Liangzhou District which is one of the best vegetable producing areas in Gansu province.The results and conclusions of this study would help government and farmers to control the HMs pollution and protect the food safety and production of crops in arid area.The main results were as follows:(1)The p H value of GS was lower than that of open-field soil,indicated GS was acidized in a degree,its average p H value was 7.6 in this research area(the range of p H was 7.1~8.6).The average conductivity of GS was 1791 us·cm-1,which was 8.37 times than that of open-field soil.The content of organic matter was 31.17~122.51 g·kg-1 in this research area.The organic matter content of GS was 65.11 g·kg-1,which was 1.38 times than that of open-field soil.The carbonate content of all samples differ greatly in the range of 0.47%~19.78%,and the value of GS was lower than that of open-field soil.The soil CEC was 2.22~20.90 cmol·kg-1,suggested that the fertilizer-retaining capacity was poor.(2)The total-state contents of Cd,Cr,Pb,Cu,Zn,Ni,Co and Mn in GS were 0.07~0.37,30.84~78.66,18.57~43.48,18.69~74.05,73.30~297.90,28.09~43.75,3.15~10.74,and 615.84~802.99 mg · kg-1,respectively.The average values of Cd,Cu,Zn were higher than that of open-field soil,the values of Cd,Cu,Zn,Pb,Mn were higher than the background value of soil in Gansu province.The available-state average contents of heavy metals in GS were 1.02~4.74 times and significantly higher than that of open-field soil.(3)The total-state and available-state contents of different HMs in GS presented diverse rules with the different planting years.The total-state content of Cd and Cr decreased with the increasing of planting years,and there was no significant diversity between different years.However,the available-state content of Cd raised with the increasing of planting years.The total-state content of Cd and Cr reduced with time due to the amount of annual input less than the plant uptake.The available-state content of Cd grew with the time because of the soil p H reduced during the longer cultivation years.The total-state contents of Co,and the available-state content of Co and Mn decreased with the increasing of cultivation years as a result of farmer paid attention to the entering of a majority of nitrogen,phosphorus and potassium fertilizer but neglected some trace elements.The contents of Cu,Zn,Pb and Ni in GS had no obvious change with the planting years.(4)The total-state amount of Cd,Cu,Zn,Cr,Ni and Co in GS had strong spatial autocorrelation,and the spatial variation was dominated by structural variation.Pb and Mn had moderate spatial correlation,and their spatial distribution was mainly influenced by structural factors and stochastic factors.The available-state of Cd,Zn,Pb and Co had strong spatial autocorrelation,and the spatial variation was dominated by structural variation.The available-state Cu,Cr and Ni followed moderate spatial correlation.The available-state Mn had a strong random variability.The spatial distributions of the total-state amount of Cd,Cu,Zn and Cr were relatively similar in the whole area,relatively high concentrations of the central region,which were mainly distributed in the suburbs of the city,such as Jinyang Town,Fafang Town,and Gaoba town.It was contributed to a large population and few land in the suburbs,the high level of fertilization,the refined management,and the high degree of soil maturation.The correlation analysis and principal component analysis showed that the high accumulation levels of Cu and Zn were mainly related to the high content of HMs in organic fertilizer.(5)Based on the evaluation results of "Soil Environmental Quality Standard"(GB15618-1995)and "environmental quality evaluation of greenhouse vegetable production"(HJ / T 166-2004),the HMs in GS were all at a clean level,in line with the greenhouse environment of environmental quality requirements.The evaluation of potential ecological hazard index showed that GS was slightly hazardous,Cd were mildly hazardous and the other elements were slightly hazardous.The results of the geo-accumulation index of HMs showed that the Cu and Zn of GS were mild to moderate pollution degree,and the rest were pollution-free.The geo-accumulation index of HMs in open-field soil was lower than GS,indicating that the HMs were accumulated in GS.Overall,it was necessary to strengthen the environmental management of organic fertilizer to control the input of Cu,Zn and other HMs in GS. |
PDF Full Text Request