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

Figure 4

The vertical profiles of heavy metals in soils from wastewater-irrigated and groundwater-irrigated areas. (a) Cr; (b) Pb; (c) Ni; (d) Zn.

(a)

(b)

(c)

(d)