Ni and Pb were not detected in plant tissues; this may be
because of negligible amounts of heavy metals in municipal
sewage effluent because the size and amount of industrial
activities in Zabol region are small. However, effluents discharged
from minor available industrial units (like batteries
and dairy products manufacturers) are a matter of concern, because
high concentrations of certain elements can be hazardous,
and hence, the influence of these metals should be
considered.Because of the low dynamics of toxic heavy metals, they
possibly accumulate in the lower parts of the plant such as
the root and stem. Nevertheless, Madejo´ n et al. (2006) reported
the presence of some heavy metals in the leaves of olive
and holm oak trees. In fact, the quantity of element absorption
by a plant depends on several factors, including the total quantity
of the elements applied through sewage application