上海市奉贤区农田土壤-农产品中的重金属含量特征和污染评价

Content characteristic and pollution assessment of heavy metals in farmland soils and agricultural products in Fengxian District,Shanghai

为分析奉贤区农田土壤和农产品的重金属污染状况,采集粮田、菜田和果园3种作物的农田土壤及其对应农产品,分别测定土壤8种重金属元素(Hg、As、Cd、Cr、Pb、Cu、Zn和Ni)和农产品5种重金属元素(Pb、Cd、Cr、As和Hg)的含量特征,采用单项污染指数法、综合污染指数法、积累指数法和富集因子等方法对土壤-农产品中重金属元素进行污染风险评价,并将地统计学与因子分析相结合分析农田土壤重金属的空间分布特征。结果表明:与上海市土壤背景值相比,奉贤区农田土壤Hg、Cd、Cr、Zn和Ni的平均含量较高,分别是背景值的1.40、1.36、1.06、1.15倍和1.44倍。单项及综合污染指数值显示土壤重金属处于无污染水平;但Cd、Ni、Hg元素的积累指数值显示无-中度污染水平,其中有4.92%农田土壤处于Hg元素的中度污染。在空间分布上,Hg呈连片分布;As、Cd整体含量低,南北区域分布;Cr、Zn呈条带状分布,自南往北递增状态;Pb呈散点状分布;Cu元素整体含量高,呈东西梯度分布;Ni元素呈岛状分布。因子分析中,因子1包括Cu和Zn,因子2是Pb,因子3包括Cd、Cr,因子4是Ni,因子5是As和因子6是Hg。奉贤地区土壤重金属含量主要受到工业源、农业源、交通源和自然源影响较大,应加强污染源控制,降低风险水平。农产品样中的5种重金属均未超出标准限量值,单项及综合污染指数值显示农产品重金属属于清洁水平。经土样和农产品样中的重金属含量相关性分析,两者无相关,农产品对土壤重金属的富集因子较小。不同土地利用方式对土壤和农产品中重金属含量影响较大,菜地土壤和农产品对Cd较为敏感,吸收能力较强,而果园土壤和农产品对各重金属吸收总体较弱。在农业生产中可以根据作物吸收重金属特性来调整种植结构,以减轻重金属污染。综合来看,奉贤区土壤-农产品系统中重金属累积程度低,但局部农田土壤中重金属含量存在轻微污染,需引起重视。

To analyze the contamination status of heavy metals in farmland soils and agricultural products in Fengxian District,the topsoil and agricultural product samples were collected in grain field,vegetable field and orchard.The content characteristic of eight heavy metals(Hg,As,Cd,Cr,Pb,Cu,Zn and Ni)in soil and five heavy metals(Pb,Cd,Cr,As and Hg)in agricultural products were determined The pollution status was evaluated by single pollution index,comprehensive pollution index,geoaccumulation index and enrichment factor.The geostatistics method combined with factor analysis was applied to analyze the spatial distribution and sources of soil heavy metals.The results showed that the average contents of Hg,Cd,Cr,Zn and Ni in Fengxian farmland soils were 1.40,1.36,1.06,1.15 and 1.44 times of the background values in Shanghai soils,respectively.The single pollution index and comprehensive pollution index revealed that heavy metals in soils were uncontaminated,while the geoaccumulation index indicated that Cd,Ni and Hg were at uncontaminated to moderately contaminated level,of which Hg in 4.92%samples was at moderately contaminated levels.The content of Hg was continuously distributed in the region.The As and Cd were low and distributed between the north region and the south regions.The Cr and Zn were distributed in strips and increased from the south region to the north region.The Pb was distributed as scattered dots.The Cu was high and decreased gradient from the west region to the east region,but the Ni was distributed as an island.Factor analysis demonstrated that Cu and Zn could be attributed to Factor 1,and Factor 3 was the main contributors to Cd and Cr.In addition,Factor 2,4,5,and 6 showed heavily loadings for Pb,Ni,As and Hg,respectively.The heavy metal contents in Fengxian District were mainly affected by industrial source,agricultural source,traffic source and natural source.Therefore,it is necessary to strengthen the source controlling and reduction strategies.The contents of heavy metals in 64 agricultural product samples were all lower than the limit standards.The single pollution index and comprehensive pollution index indicated that the products belonged to clean level.Although the contents of heavy metals showed similarity between soil and product samples in a certain level,but no significant correlation was detected,which result to the low enrichment factor.The heavy metal content in soil and agricultural product from different land use were significantly different:Cd was sensitive in vegetable field and had a high absorbing ability,while orchard was contrary to vegetable field where the pollution index was lower.In order to reduce heavy metals pollution,the planting structure could be adjusted according to the heavy metals absorption characteristic in different crops.In sum,the accumulation of heavy metals in the soil-product system of Fengxian District was relatively low,but the content of heavy metals in soil was slightly polluted in local farmland,which should be paid enough attention.