| With the rapid development of society and economy,a large amount of heavy metals present in soils,decline in the soil quality,resulted in deterioration in the soil structure and function,finally direct harm to human health and development.Therefore,the research and evaluation about pollution status of heavy metals would have a great implication to land classification management,agricultural safety,prevention and cure of soil pollution and ecological civilization construction.Farmland soil in Yongdeng county was collected,examined and through mathematical statistics analysis to study the distribution properties of heavy metals in the farmland.Multi factor comprehensive evaluation,Nemerow index and Principal component analysis were used to make risk evaluation on the 8 kinds of heavy metals(cadmium,mercury,arsenic,lead,zinc,chromium,copper,nickel)from 228 surface soil samples collected in 5 different areas.The main conclusions are as follows:(1)The analysis result of agricultural soil in Yongdeng showed that the content of all kinds of heavy metals in soils is higher than the average content in Gansu province except for mercury.The maximum value of chromium,copper and zinc in this region occurred in Datong river;the maximum value of nickel occurred in Minle-Wushengyi hill belt;the maximum value of cadmium and lead occurred in middle reaches of Zhuanglang river valley;and the maximum value of mercury and arsenic occurred in downstream in Zhuanglang river valley.The cadmium in soil of the region are normally distributed,6 elements such as mercury,arsenic,lead,chromium,copper and zinc in soil is right-skewed while nickel left-skewed.(2)The risk assessment of heavy metals based on “Soil environmental quality: standard for soil pollution risk management and control of farmland(Trial)” showed that the farmland in Yongdeng wholly was in good condition,only in some sites the Arsenic content of soil was close to the threshold value.(3)The risk assessment of 8 heavy metals in 5 regions based on Multi factor comprehensive evaluation and Nemerow index showed low pollution(hazard)and high cleanliness in study areas.Some sites in middle lower belt in Zhuanglang river valley has reached the clean warning limit pollution level,the content of arsenic and cadmium was relatively high and accumulated in distinct degrees,this is because the region is the concentration area of chemical raw materials,chemical products manufacturing and farm-use land in Yongdeng.(4)The result based on principal component analysis showed higher correlation coefficient between cadmium and lead,chromium and nickel,copper and zinc.To a certain extent,this can reflect the homology and difference of these heavy metals.Soil quality of the 5 research regions wholly was in good condition,the soil quality follows the sequence: Minle-wushengyi low mountain and hills>Qinwangchuan basin>Datong river belt>Zhuanglang river valley downstream belt> Zhuanglang river valley midstream belt.The result indicated that the soil environment of Zhuanglang middle lower belt was bad.(5)Main measures taken in the prevention and cure of heavy metal pollution are as follows: fertilize scientifically and reasonably;carry out intensive investigation on the soil pollution of farmland and determine the scope and degree of farmland pollution;strengthen the protection and ensure the safe use of farmland;strengthen management and control of pollution sources,increase investment to prevent and cure soil pollution;introduce technical methods to improve the soil environmental quality of farmland.The prevention and treatment measures for each region should be targeted and accurate. |
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