Study On Heavy Metals Pollution In Soil And Vegetables In Suburbs Of Shanghai

This paper takes 8 suburbs of Qingpu,Jiading,Jinshan,Minhang,Pudong,Baoshan,Songjiang and Chongming in Shanghai as the research objects.The content of lead,arsenic,mercury,cadmium,and chromium was determined by the digestion of agricultural soil and vegetable samples in that 8 suburbs in Shanghai.The average contents,coefficient of variation,data distribution and other information of the soil samples were compared with the national soil ecvironmental secondary standards and the Shanghai soil background value.The average contents,pollution index and other information of the vegetable samples were compared with the national food hygiene standards,also they were compared with each district or themselves.Based on the researc,we get the following conclusions:The pH value of agricultural soil in each district is increasing from southwest to northeast,and it's speculated that the pH value of the eastern soil,may be washed with salinity,is much higher than the western inland.The concentration of heavy metals in agricultural soils is quite different between each district.Pb is the least affected by the spatial difference,and the Hg is the largest one on the contrary.In the 8 districts,both the concentrations of cadmium and mercury are present at a maximum data over the national soil environmental secondary standard.The maximum value of Cd in the six districts is excessive,accounting for the 8 districts 3/4?Minhang District of southern Shanghai,Songjiang District and Qingpu District of western Shanghai,Jiading,Baoshan and Chongming District of northern Shanghai?,the excessive value of Hg is accounted for the8 districts 5/8?Minhang District of southern Shanghai,Songjiang District and Qingpu District of western Shanghai,Jiading and Chongming District of northern Shanghai?.And the average value of cadmium in Chongming District of northern Shanghai and mercury in Qingpu District of western Shanghai are excessive 4.6 times and 4.8 times with the national soil environmental secondary standard.Compared with the soil background value of Shanghai,the average value of Cd in 7 districts is excessive,Hg in 6 districts is excessive.And the other three elements were as follows:arsenic accounted for 2 districts,lead accounted for 5 districts,and chromium accounted for one district.The detection rate,average content and maximum value of heavy metals in soil showed the regular that the data is increasing from east to west and from south to north in Shanghai.The minimum value of cadmium in some of the northern part is higher than that of soil background.It can be seen that the distribution level of Cd and Hg in agricultural land in Shanghai is high.The single pollution index and the total one of the vegetable sampling from these 8districts were less than 1,which proved that the samples fit the national food safety and hygiene standards,indicating that the heavy metals of the vegetables in city suburban do not exist obvious risk and hazard to human health.Four of the five kinds of heavy metal elements weren't excessive expect the Cd.But the Cd exceeded the standard rate is low,only 0.15%.The content of different heavy metal elements in vegetables is quite different,which is related to the enrichment behaviour of heavy metals in vegetables.The levels of five heavy metals in different kind of vegetables showed the value in leafy vegetables was highest,indicating that leafy vegetables enrich heavy metals stronger than other types of vegetables.The enrichment of other four elements in the cowpea was the weakest among the nine kinds of vegetalbes except the Hg element.It is consistent with the same result that the leafy vegetables enrich stronger with the heavy metal elements in the literature.The highest of average content of Cr was 0.046 mg·kg^-1 in Jiading District of northern Shanghai,As element and Pb was 0.0078 and 0.029 mg·kg^-1 in Qingpu District of western Shanghai,and the highest content of Cd was 0.022 mg·kg^-1 in Minhang District in the southern of Shanghai.It shows the same result with the soil data increasing from east to west and from south to north in Shanghai.It can be seen that heavy metal content of urban vegetables is mainly affected by the heavy metal content in soil in this survey.The content of heavy metals in agriculture soil and its crops in Shanghai has been effective controlled than the past under under the supervision and monitoring of state and relevant departments.Only the individual soil or vegetables exceeded.It is still impacted by the human activities in the investigation point.But because of the low failure rate,there is no obvious risk of human health.It is only necessary to monitor the heavy metal content of agriculture soil and its crops continuously.This study has certain practical significance to know the distribution of heavy metals in the suburbs of vegetables and soil.Only by strengtherning the monitoring and supervision of heavy metal elements,controlling and using fertilizers and pesticides rationaly,arranging the vegetable production areas far away from industrial areas and other sources of pollution reasonably to ensure the quality of vegetables,can the risk of contamination reduce.