Heavy metal content and ecological risk warning assessment of vegetable soils in Chongming Island, Shanghai City

In order to determine the content of copper (Cu), lead (Pb), chromium (Cr), zinc(Zn) and cadmium (Cd) in vegetable field, soil samples were collected from three towns of Chongming Island, an important ecotypic island of Shanghai City. The average content of Cu, Zn, Pb, Cr and Cd in vegetable soil of the three towns is 29.2 mg · kg^-1, 91.2 mg · kg^-1, 26.5 mg · kg^-1, 79.4 mg · kg^-1 and 0.222 mg · kg^-1, respectively. Except for the content of Cd exceeded the first grade of national soil standard (GB 15618-1995), the contents of the other four heavy metals were less than the first grade of the standard, and the content of heavy metals in this field met the request of heavy metal level to produce green foods (NY/T 391-2000). The contents of Cu, Pb, Cr, Zn and Cd in the vegetable soils are 24.3%, 24.4%, 22.9%, 18.8% and 65.7% higher than the background value of Shanghai, respectively. The result of ecological risk warning assessment showed that three sampling sites were medium warning situation, ten were light warning situation, eight were warning situation and one was no warning, in all the 23 sampling sites. The total situation of Chongming Island was light warning, and the I_ER = 1.562. The order of ecological risk was Baozhen town (I_ER = 1.799) > Chengqiaozhen town (I_ER = 1.636) > Chenjiazhen town (I_ER = 1.368). The three towns were all light warning situation.