This study was aimed at monitoring the environmental pollution of a
loamy sand soil cultivated with different tree woody species, i.e., Morus alba,
Khaya senegalensis, Acacia saligna and Populus nigra and irrigated with treated
contaminated wastewater through drip irrigation system. Some heavy metals, i.e,
Cd, Co, Ni and Pb were determined in each of irrigation water, irrigated soil and
grown woody trees, whether the expected phytoremediators were able to
accumulate and translocate these heavy metals, from lower plant part tissues to
the upper ones, taking into consideration their concentrations in irrigation water
and irrigated soil. In order to achieve this target, two areas were selected in
Egypt, i.e., a) Egyptian Chinese friendship woody forest of the previous four tree
species at Sadat City, Minufiyah Governorate, Egypt which irrigated with a
primary treated wastewater and b) Egyptian-Japanese woody forest at Wadi AlNatron, Behaira Governorate, which irrigated with natural underground water, as
a control for Acacia saligna only.
The obtained results showed an always seasonal difference as regards
different studied heavy metal concentrations in irrigation water during 2010 that
was noticeably higher than 2009. However, Ni and Pb concentrations in
irrigation water of Sadat City area exceeded the permissible values of Egypt
contaminated water. Also, Ni concentration in the natural underground water of
Wadi Al-Natron area exceeded the permissible limit values of fresh water. As for
heavy metal concentrations in the soil, data revealed that Cd concentrations were
found in a low concentration at soil supporting Populus nigra vs a high
concentration in subsurface layer (20-40 cm) in the soil supporting Acacia
saligna. The highest concentration of Ni was occurred at subsurface layer (20-40
cm) of soil supporting Acacia saligna and Khaya senegalensis. On the other
hand, soil Pb and Co concentrations were almost similar for the four tree species.
Concerning the metal concentrations in tree species, there were
insignificant differences for Cd concentrations in different tree stems, however,
the different distribution pattern of Co concentrations in stem could be
categorized in an ascending order of Populus > Morus > Khaya > Acacia. Co
and Ni concentrations in leaves were also taken an ascending order of Morus >
Khaya > Acacia > Populus. Pb concentrations in leaves were taken ascending
order of Morus > Acacia > Khaya > Populus. All metals were successfully
transported from roots to stems for all the investigated tree species. In Morus
alba metals showed translocation preferences of Pb > Ni > Co > Cd vs Cd > Pb
> Ni > Co in Khaya, Cd > Ni > Co > Pb in Acacia and Pb > Co > Ni > Cd in
Populus. In addition, Morus alba exhibited Ni and Co highest translocation
factor values that were found only at the highest temperature degrees.
Moreover, Ni and Co concentrations in plant were found to be affected by
soil pH, organic matter and irrigation water salinity these may be assisting
naturally to accelerate soil phytoremediation processes at warm climate under
desert regions. So, it could be recommended that using Morus alba and Populus
nigra for metal removal from soil is only technically feasible in short time period if more metal can be made available by adding chemicals to soil that increased
their concentrations. It is essential in case of using Morus alba as a
phytoremediator to discard any fruit or leaves, however, it is also recommended
to study the effect of accumulated metals in Morus leaves on silk warm as a
biological indicator. The metal amounts extracted by plants can be put into
perspective by calculating a theoretically decrease in soil metal concentrations
from the known plant maximum metal concentrations in order to calculate the
concentration factor, i.e., CF = metal concentration in plant tissue/its
concentration in the soil. This could be achieved according to the number of
planted trees/fed. Also, it should be following up Ni concentration in the natural
underground water at the Egyptian-Japanese forest to avoid Ni pollution.