الفهرس 
Metals of SoilOnly 14 pages are availabe for public view
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Abstract
When agriculture soils are polluted by heavy metals, these metals can be destroy the plants or taken up and accumulate in their tissues. Animals that graze on such contaminated plants also accumulate such metals in their tissues. Humans are in turn exposed to heavy metals by consuming contaminated plants and animals, and this has been a result in various biochemical disorders to human health. So remediation of heavy metals-polluted soils is very important from view of agriculture and environmental health. The most recent techniques of soil remediation are phytoextraction (using green plants in remediation soil).
The aim of this study is to investigate the potential of some Egyptian plant species in remediation the contaminated soil by heavy metals from various pollution sources. Such as chemical pollution; whether was single or mixed pollution and from sludge-treated soil. Also investigate the effect of nitrogen fertilizer in improving phytoextraction.
The study was conducted as three pot experiments. In first experiment, the soils were contaminated by metal salts of Zn, Pb, Cu, Cd, Ni separately beside mixture of them (6 experiments) at three addition rates beside the control. In second experiment, the soil was contaminated by composted sewage sludge at three addition rates beside the control. However in the third experiment, the contaminated- soil by mixed metals was fertilized with (NH4)2SO2 at three rates beside control. Each experiment was grown with the same three species separately. The test plants were members of Brassica species: Brassica napus (canola), Brassica Alba (white mustard) and Brassica nigra (black mustard). The treatments arranged as a factorial experiment in 4 levels of pollution × 3 plant species; the treatments were replicated 3 times in a completely randomized block design. The plants were sampled at maturity stage. The biomass was recorded for every plant treatment. All plant samples were chemically analyzed to determine plant heavy metals concentration. The plants samples of the third experiment submit to nitrogen estimation. Also soil samples were collected and chemically analyzed to estimate the available heavy metals. Some parameters are calculated to evaluation the potentials phytoextraction of each plant species such as the plants metal removal (plant biomass X plant metal concentration) and bioaccumulation coefficient (plant metal concentration / soil available metal concentration). All results of plants, soils and the calculated parameters were submit to statistical analysis to summarize the results and tabulated in the final view.
The results of the study are summarized as follows:-
First experiment:-
1. Phytoextraction of Zn polluted soil: when B. napus, B. alba and B. nigra were grown in soil polluted by Zn, B. napus, B. alba were similar in Zn removing. That’s according to the high biomass of B. napus and the high Zn concentration of B. alba. However, B. nigra was the lowest in removing Zn due to its low biomass as comparing to the other species. The available Zn in soils which cultivated by the three plants species was almost similar. Also between bioaccumulation coefficients of the three plant species there wasn’t significant difference. The BC values reveal that Brassica species have potential Zn- phytoextraction.
As relative to the control, increasing Zn pollution additions to 250 (μg/g) increased Zn removal by Brassica napus by 77% and the highest Zn addition (1000 μg/g) increased Zn removal by B. alba and B. nigra by 244%, and 150%, however, it decreased gradually the plants biomass by 69%, 58%, 41%, respectively. As expected each of the plant Zn concentration and available soil Zn increased, however, bioaccumulation coefficient decreased by increasing Zn additions.
2. Phytoextraction of Pb polluted soil: B. napus, B. alba and B. nigra which grown in soil polluted by Pb were similar in Pb-removal that’s due to the similarity in the plant biomasses and Pb-plant concentrations. The Pb- bioaccumulation coefficient of all species expressed that it has potential Pb- phytoextraction and there wasn’t significant difference between them.
Increasing Pb pollution additions (until 1000 μg/g) increased plants Pb concentration and available soil Pb concentration. However, it decreased Pb- bioaccumulation coefficient and the plants biomass except B. nigra biomass increased by 60%. The biomass increasing beside the high Pb content lead to obviously increase in Pb removal by B.nigra amounted to 353% as comparing to the control.
3. Phytoextraction of Cu polluted soil: Generally, there wasn’t significant difference in Cu- removing by B. napus, B. alba and B. nigra when grown in Cu-polluted soil. That’s due to the equality biomasses. The highest Cu- concentration was found in B. nigra. Bioaccumulation coefficient of the three species was similar and the plants have potential Cu- phytoextraction.
Increasing Cu pollution additions to the soil (to 200 μg/g soil), increased Cu concentration in both plant and soil and evidently the biomass (165%) of B. nigra and Cu removal by B.nigra and B.alba which amounted to 331% and 77%, respectively of the control. However, B.napus biomass decreased and also Cu removal by 50% as relative to the control. Bioaccumulation Coefficient also decreased and reaches to 0.95 in B. alba at highest Cu-pollution (200 μg/g) so it isn’t suitable for phytoextraction highly Cu-polluted soil.
4. Phytoextraction of Cd polluted soil: In soil polluted by Cd, the three Brassica species were similar in Cd removing. That’s due to the similarity in Cd plant concentration rather than plants biomass. B. napus was the highest biomass and the lowest in bioaccumulation coefficient.
Increased soil Cd pollution additions (to 20 μg/g) increased Cd concentrations in the plants & soil and Cd removals by the three plants. The increase in Cd removing amounted to 357%, 274%, and 806% for B. napus, B. alba and B.nigra, respectively, relative to the control. Bioaccumulation coefficient decreased for all species by increasing Cd pollution additons.
5. Phytoextraction of Ni polluted soil: The response of the three Brassica species biomass to Ni-pollution was generally similar. The concentration of Ni in Brassica species was almost negligible and similar to the control treatment under the condition of this study.
6. Phytoextraction of mixed metals polluted soil: when Brassica species grown in soil polluted by mixed metals (Zn+ Pb+ Cu+ Cd + Ni), Brassica napus was the highest in removing all metals. That is due to its high biomass. The limiting factor in metals removing by the other plant species was the concentration of plant metals. Brassica alba and Brassica nigra were similar in removing both Zn and Pb. Brassica nigra was the lowest in removing both Cu and Cd from mixed polluted soil.
Bioaccumulation coefficient of the three plants demonstrated that they have potential for phytoextraction of all metals and they similar in accumulating Zn and also similar in accumulate Cu. Brassica napus is the best in accumulating Cd, however, Brassica nigra is the lowest in accumulating Pb.
Increasing application of pollution by mixed metals gradually increased all metals removal by the plants. The highest metals removal was at highest level of pollution addition (Zn 500 µg/g + Pb 500 µg/g + Cu 100 µg/g + Cd 10 µg/g + Ni 100 µg/g). That is reveal to the effect of increasing both the plant biomass and plant metals concentration. Plant concentration of Pb & Cd reaches the highest concentration at highest addition of mixed metal. However, Zn & Cu plant concentrations increased until the second level of pollution (Zn 250 µg/g + Pb 250 µg/g + Cu 50 µg/g + Cd 5 µg/g + Ni 50 µg/g) then decreased. Available soil metals gradually increased with increasing mixed metal pollution additions, however, Bioaccumulation coefficient decreased. The BC of Pb & Cd decreased only at the highest level of pollution.
Correlation coefficient of bioaccumulation coefficient for all metals expressed that BC of Cd correlate negatively with BC of both Zn & Cu of Brassica species which grown in soil polluted by mixed metals.
Second experiment:-
Phytoextraction of heavy metals from sludge- treated soil: - The three Bassica species when grown in sludge- treated soil were almost similar in its biomass and the removal of Pb & Cd. Brassica nigra was the best in removing Zn & Cu. Available Zn & Pb and Cu was the highest in soil cultivated by Brassica nigra so its bioaccumulation coefficient of Pb and Cu was less than the other species. There wasn’t difference between the three species in BC of Zn and Cd. Bioaccumulation coefficient of the three plants demonstrated that they have potential for phytoextraction of all metals from sludge- treated soil.
Increasing sludge additions decreased the removals of Zn, Pb, Cu by B.napus and its biomass and increased the removals of Zn, Cu, Cd by B.alba and B.nigra and its biomasses and increased all metals concentration in the three Brassica species. Increasing sludge addition rates resulted in increasing the available soil metals which affect in decreasing the bioaccumulation coefficient of Zn, Cu and Cd metals by the three Brassica species. However, increasing sludge application resulted in increasing accumulation of Pb by the three plants.
Third experiment:-
Phytoextraction of mixed metals polluted soil as affected by nitrogen fertilizer:
In the polluted soil which fertilizered by (NH4)2SO4, Brassica nigra was the highest in the biomass and Brassica alba was the highest in all metals concentration. The three plant species was similar in removing Zn. Brassica napus was the less in removing Pb, Cu, Cd that’s due to its low metal concentration.
Increasing addition of (NH4)2SO4 to polluted soil decreased the biomass of the three species. On the other hand, increased Zn removal by B.napus and the removals of Zn, Pb by B. alba then the removals of the two metals decreased by increasing levels of ammonium additions. However in B.nigra, the removal of Zn decreased with increasing soil Zn addition till 80 Kg N /Faddan.
Bioaccumulation coefficient proved that the three species have the ability to accumulate all metals. The three Brassica species was similar in accumulating both Cu and Cd. Brassica nigra was the lowest in accumulating Zn and Brassica napus was the lowest in accumulating Pb.
Increasing ammonium sulfate additions to the polluted soil increased significantly the accumulation of Zn in all species and the accumulation of Cu in B. napus & B. alba and the accumulation of Cd in B. napus. However the accumulation of Pb decreased in B.nigra.
In all Brassica species, the accumulation of Zn increased until limit then decrement by increasing ammonium additions.
Concerning to the plant nitrogen, there are no variation between Brassica species in N content by ammonium additions to polluted soil.
Recommendations:-
It is recommended to:
Remediate soil contaminated by single or mixed metals by growing B. napus according to its high biomass.
Remediate soil contaminated by sludge by growing B. nigra which is the best in removing Zn and Cu, or the three plant species (Brassica napus, Brassica alba and Brassica nigra) to remediate Pb and Cd from sludge-treated soil.
Addition of ammonium sulfate fertilizer to polluted soil to assist in increasing of soil metals solubility and the removal by Brassica plants.
B. nigra is highly concentrated metals but its small biomass diminishes its efficiency so it needs to increase the biomass by the genetic engineer.
Before using Brassica species to remediate the contaminated soil, environmental impact assessment must be done.