II. THE ENVIRONMENTAL MONITORING SYSTEM IN SHANGHAI
B. The network of environmental monitoring
For determining agricultural environmental quality, soil and produce monitoring has been developed. Since 1986, 73 fixed long-term soil monitoring sites have been set up in the suburb counties, taking into account that every site carries regional significance. These sites are situated in both clean and polluted areas. Samples are collected from the mold of 0-20 cm under the surface. Variables are Cd, Zn, Cu, Pb, Mn, Cr, Hg, As and Ni.
Objects of produce monitoring are generally wheat and rice, but are substituted with vegetables in the near suburbs. Samples are collected in summer and autumn, and the variables are Cd, Zn, Cu, Pb, Mn, Cr, Hg, and As. In addition, 30 samples of soil and produce respectively are also examined for DDT and B.H.C.