Heavy Metal Residues in Soil and Accumulation in Maize at Long-Term Wastewater Irrigation Area in Tongliao, China

Figure 2

Temporal variations of the soil heavy metal concentrations at site 1. (a) Changes in the Cr concentration; (b) changes in the Pb concentration; (c) changes in the Ni concentration; and (d) changes in the Zn concentration.

(a)

(b)

(c)

(d)