| As indispensable food for human life, vegetables play important roles in human health. Vegetables take up metals by absorbing them from contaminated soils, as well as from deposits on parts of the vegetables exposed to the air from polluted environments.In recent years, along with industrial development, urban expansion and the scale of the constant booming township enterprises and the increasing number of the urban population, a growing interaction between humans and the soil become increasingly important.For the sake of investigate the heavy metal contamination of vegetable and soil of Lanzhou City, and explore the soil properties effects on soil heavy metal accumulation of vegetable. Soil and vegetable samples were taken from 8 locations (Anning district, Xigu district, Cheng guan district, Heping district, Dingyuan district, Zhonghe district, Pingan district, Huazhuang district) in the LAN Zhou district during April 2009. The vegetables crop plants were Indian lettuce (Lactuca sativa), scallion (Allium fistulosum), cole (Brassica campestris), leak (Allium tuberosum), cucumber (Cucumis sativus) and winter squash (Cucurbita maxima), and five heavy metals:cadmium (Cd), chromium (Cr), copper(Cu), lead (Pb) and zinc(Zn) were chose to investigate.The studied soils were generally alkaline, with mean pH values of 8.36, which was related to the special environment of the studied region described above. Generally speaking, there were no significant differences in pH between 8 districts (P>0.05). The mean value of electrical conductivity (EC) was 0.40 ds·m-1, which was not very high maybe because the ion content in the slight alkaline soil are limited, and the result was correlated with the pH value of soil. Significant differences of EC value in 8 districts were showed.Of all the soil samples, there were 97.22%of the concentrations of Cd,21.95%of Cu and 4.17%of Zn in soil samples exceeded grade I of GB 15618-1995. Compared to gradeⅡof the GB 15618-1995, among five heavy metals, only 2.78%of the concentrations of Cd in soil samples exceeded the contamination criteria. All of the concentrations of Cr and Pb in soil samples were below the safety standard of above description. All of the concentrations of five heavy metals in soil samples exceeded the background value of Lanzhou City:100%for Cd,73.61%for Cr,84.72%for Cu,61.11%for Pb and 20.83%for Zn in soil samples.There were significant differences in Cd, Cr, Cu and Zn concentrations in the soil of 8 districts in Lanzhou City. Soil contamination of Pb in Lanzhou City investigated from vegetable bases of 8 districts was better than the situation of Cd and Cu. The concentration of Pb in soil samples in 8 districts wasn't showed any significant differences.The correlation of soil Cd and Ph and EC showed significantly negative mutuality, which was accorded with Cr. Soil Cu content showed significant negative relativity with EC. Pb and Zn content showed significantly negative mutuality with pH. The pH didn't show any significant relativity with EC.Through the assessment of soil heavy metal contamination in Lanzhou City, we found that the situation of heavy metal contamination of Lanzhou City was light pollution. The main pollutant was Cd, and Cu contamination in Xigu district was more serious than other metals.Through cluster analysis in statistica soft, contamination situation of heavy metal of soil in 8 districts of Lanzhou City was joined to 3 clusters:I:Anning district, Heping district, Dingyuan district, Pingan district, Huazhuang district and Zhonghe district;II:Chengguan district; andIII:Xigu district.Heavy metal contamination in Lactuca sativa:According to GB 18406.1-2001,45.83%, 20.83%and 16.67%of the Lactuca sativa samples exceeded the safety standards for Cd, Cr and Pb contents, respectively. In the addition,25%and 29.17%of vegetable samples exceeded the safety standards for Cu and Zn content which was set in GB 15199-1994 and GB 13106-1991, respectively.Significant differences were observed between Cr, Cu, Pb and Zn content in several districts of Lanzhou City in Lactuca sativa and there were no significant differences in Cd content Lactuca sativa of in districts. Zn content in Lactuca sativa was the most and then followed by Cu, Cr, Pb and Cd. So highly content of Zn in Lactuca sativa may be dangerous to human health even though it was an essential element to human body. Zn and Pb content of Lactuca sativa in Anning district was the least; Cd and Cr content in Dingyuan district was the maximal; Cd content in Xigu and Pb content in Zhonghe was the highest. Cd, Cr, Cu and Zn contamination of Lactuca sativa in Pingan and Huazhuang were hardly the same, except for Pb content. Pb content of Lactuca sativa in 8 districts changed dramatically.Significant differences were observed in Bio-concentration factors (BCFs) of Cd and Pb in 8 districts of Lanzhou City. BCFs of Pb in Lactuca sativa in all of the districts were the least, and then the Cr, followed by Cd, Cu and Zn. The differences between Xigu and Heping district; Dingyuan, Pingan and Huazhuang were similar. The mean BCFs of five metals were ranked in the order of Zn> Cu> Cd> Cr> Pb.Soil Cd, Cr, Cu, Pb and Zn all showed significant relativity between itself contain in Lactuca sativa. Cr, Pb and Zn content in Lactuca sativa showed significant negative relativity with pH. Cd, Cr and Pb all showed significant negative relativity with EC.Heavy metal contamination in Allium fistulosum:According to GB 18406.1-2001, 35.42%,18.75%and 29.17%of the Allium fistulosum samples exceeded the safety standards for Cd, Cr and Pb contents, respectively. In the addition,12.5%and 8.33%of vegetable samples exceeded the safety standards for Cu and Zn content which was set in GB 15199-1994 and GB 13106-1991, respectively.Significant differences were observed between Cr, Cu and Zn content in several districts of Lanzhou City in Allium fistulosum. Cd and Pb content in Allium fistulosum samples among 8 districts didn't show any significant differences. Cr concentration in Allium fistulosum at different districts showed significant differences. We can observe that Cu and Cr content of vegetable in Dingyuan district were different from others at their troops. In addition, Cu and Zn content of plant in Chengguan district was higher than other districts at their teams. The lowest content of Cu was occurred at Huazhuang district. The content of Pb in plant was lower at Anning and Heping district, compared with others. Zn content of vegetable in 8 districts was the highest and Cd was the fewest, which was correspondence with above descriptions. The content of Cd and Pb in different districts weren't showing any significant difference.BCFs of heavy metals in Allium fistulosum were calculated, extraordinary significant differences in BCFs of heavy metals were observed in every district. Moreover, the BCFs were significantly different among districts in Cu and Zn accumulated in Allium fistulosum. BCFs of Pb in Allium fistulosum in all of the districts were the least, and then the Cr, followed by Cd, Zn and Cu. The differences between Xigu, Chengguan, Dingyuan and Pingan district were similar. The mean BCFs of five metals were ranked in the order of Cu> Zn> Cd> Cr> Pb. The results indicated that Pb was the hardest to be observed and accumulated in Allium fistulosum than other metals.Soil Cd, Cr, Cu, Pb and Zn all showed significant relativity between itself contain in Allium fistulosum. Cd, Cr, Cu, Pb and Zn content in Allium fistulosum all showed significant negative relativity with pH. Cd, Cr and Cu all showed significant negative relativity with EC.Heavy metal contamination in Brassica campestris:According to GB 18406.1-2001, 45.83%,35.42%and 37.50%of the Brassica campestris samples exceeded the safety standards for Cd, Cr and Pb contents, respectively. In the addition,20.83%and 31.25%of vegetable samples exceeded the safety standards for Cu and Zn content which was set in GB 15199-1994 and GB 13106-1991, respectively.Significant differences were observed between Cr, Pb and Zn content in several districts of Lanzhou City in Brassica campestris. There were no significant differences in Cd and Cu content of Brassica campestris in districts. The content Cr of vegetable in Dingyuan, Xigu and Pingan district was higher than others at the troop. Zn content in Chengguan and Anning district were the highest and lowest compared with other districts. The highest and lowest content of Cu in plant were occurred in Xigu and Pingan district, respectively. Pb content of vegetable in Zhonghe, Dingyuan, Xigu and Huazhuang district were higher than the other 4 districts. Xigu district have the highest content of Cd and Cu in Brassica campestris. Generally, Zn content of vegetable in 8 districts was the highest, followed with Cu, and Cd was the last.Significant differences were observed in the BCFs of Cd, Cr, Cu and Pb in Brassica campestris. BCFs of Cd, Cr, Cu, Pb and Zn were 0.1593,0.0073,0.2733,0.0063 and 0.2904 mg·kg-1, respectively. BCFs of Pb in Brassica campestris in all of the districts were the least, and then the Cr, followed by Cd, Cu and Zn. The differences between Chengguan and Dingyuan district were similar. The mean BCFs of five metals were ranked in the order of Zn > Cu> Cd> Cr> Pb.Soil Cd, Cr, Cu, Pb and Zn all showed significant relativity between itself contain in Brassica campestris. Cr, Pb and Zn content in Brassica campestris showed significant negative relativity with pH. Cd, Cr and Cu all showed significant negative relativity with EC.Heavy metal contamination in Cucumis sativus:According to GB 18406.1-2001,37.50%, 6.25%and 35.42%of the Cucumis sativus samples exceeded the safety standards for Cd, Cr and Pb contents, respectively. In the addition,27.08%and 37.5%of vegetable samples exceeded the safety standards for Cu and Zn content which was set in GB 15199-1994 and GB 13106-1991, respectively.Significant differences were observed between Cr, Cu, Pb and Zn content in several districts of Lanzhou City in Cucumis sativus and there aren't any significant differences were observed between 8 districts in the Cd content of Cucumis sativus. The content of Cu of vegetable in Xigu district, Heping district and Dingyuan district were higher than other districts. Cd content of plant in Dingyuan district, Cr and Cu in Xigu district, Pb content of plant in Zhonghe district and Zn content in Chengguan district were the highest compared with other districts at their teams, respectively. At the same time, Cd and Cr content of Cucumis sativus in Chengguan district, Cu in Huazhuang district, Pb and Zn in Anning district was the least, compared to the other districts.Significant differences were observed in the BCFs of Cr, Pb and Zn in Cucumis sativus. The mean BCFs of five metals were ranked in the order of Cu> Zn> Cd> Pb> Cr. The results indicated that Cr was the hardest to be observed and accumulated in Cucumis sativus than other metals.Soil Cd, Cr, Cu, Pb and Zn all showed significant relativity between itself contain in Cucumis sativus. Cd and Pb content in Cucumis sativus showed significant negative relativity with pH. Cd, Cr, Cu and Zn showed significant negative relativity with EC.Heavy metal contamination in Allium tuberosum:According to GB 18406.1-2001, 35.42%,4.17%and 31.25%of the Allium tuberosum samples exceeded the safety standards for Cd, Cr and Pb contents, respectively. In the addition,6.25%and 8.33%of vegetable samples exceeded the safety standards for Cu and Zn content which was set in GB 15199-1994 and GB 13106-1991, respectively. The descriptive statistics of the soil properties and Zn, Pb, Cu, Cr and Cd contents in the edible parts of Allium tuberosum were measured. There were no significant differences in Cd, Cr and Cu content of Allium tuberosum in 8 districts. The vegetable content of Cd in Dingyuan district, Cr and Cu in Xigu, Pb in Zhonghe and Zn in Chengguan was the highest than others. Furthermore, Cd and Cr in Chengguan, Cu content of the plant in Pingan district, Pb and Zn in Anning district was the lowest compared with others. The Cr and Cu content of Allium tuberosum in 8 districts was general, compared with other metals. All five metals of Allium tuberosum in Dingyuan district were higher.Significant differences were observed in the BCFs of Cu, Pb and Zn in Allium tuberosum. BCFs of Cr in Allium tuberosum in all of the districts were the least, and then the Cr, followed by Pb, Cd, Cu and Zn. The differences between Xigu, Dingyuan and Zhonghe district; Anning and Huazhuang; Heping and Pingan were similar. The mean BCFs of five metals were ranked in the order of Cu> Zn> Cd> Pb> Cr. The results indicated that Cr was the hardest to be observed and accumulated in Allium tuberosum than other metals.Soil Cd, Cr, Cu, Pb and Zn all showed significant relativity between itself contain in Allium tuberosum. Cr, Pb and Zn content in Allium tuberosum showed significant negative relativity with pH. Cd and Cu showed significant negative relativity with EC.Heavy metal contamination in Cucurbita maxima:According to GB 18406.1-2001, 16.67%,4.17%and 37.50%of the Cucurbita maxima samples exceeded the safety standards for Cd, Cr and Pb contents, respectively. In the addition,6.25% and 12.5% of vegetable samples exceeded the safety standards for Cu and Zn content which was set in GB 15199-1994 and GB 13106-1991, respectively.Significant differences were observed between Cd, Cr, Cu, Pb and Zn content in several districts of Lanzhou City in Cucurbita maxima. The vegetable content of Cd, Cr and Pb in Dingyuan district, Cu in Xigu district, and Zn in Chengguan district were the highest in their teams, respectively. The vegetable content of Cd and Cr in Chengguan district, Cu in Pingan district, Pb in Heping district and Zn in Anning district were the least in their teams, respectively. Generally, Zn content of vegetable in 8 districts was the highest, followed with Cu, and Cd was the last.Significant differences were observed in the BCFs of Pb in Cucurbita maxima. BCFs of Pb in Cucurbita maxima in all of the districts were the least, and then the Cr, followed by Cd, Zn and Cu. The differences between Chengguan and Zhonghe district; Xigu, Dingyuan and Pingan district were similar. The mean BCFs of five metals were ranked in the order of Cu> Zn> Cd> Cr> Pb. Soil Cd, Cr, Cu, Pb and Zn all showed significant relativity between itself contain in Cucurbita maxima. Cr, Pb and Zn content in Cucurbita maxima showed significant negative relativity with pH. Cd, Cr and Cu all showed significant negative relativity with EC.The results showed that vegetables near the city were contaminated serious, but away from urban areas were less polluted, which indicated that the transport, industrial production and other human activities influenced heavy metal contamination of vegetables. Heavy traffic, intensive industries, automobile emissions, "three wastes", and the life of coal-fired emissions were bound to spread to its surrounding suburbs, polluting of farmland, especially the vegetable base, and resulting in these suburbs vegetables heavy metal content exceeded the standard. The reason of heavy metal contamination of soil and vegetables in Lanzhou City may be:a part of the vegetable bases were generally irrigated with wastewater; vegetable bases were generally located in the outskirts of the city, subjected to the greatest impact of urbanization; many vegetables base for easy transportation were beside the road, and were affected by automobile emissions; some vegetable bases planted as many years, the history of vegetables have been twenty or thirty years or longer. According to research that soil with the extension of plant history and the increasing of curing degree, heavy metals like Zn, Pb and Cu contents in vegetables were increased. Application of fertilizers containing heavy metals may be another important reason for heavy metals contamination in vegetable. Furthermore, air pollution can not be ignored especially in industry-intensive production areas, like Xigu district.
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