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Remedial ability of maize (zea-mays) on lead contamination under potted condition and non-potted field soil condition

  • This study presents the remedial ability of maize on lead (Pb) contaminated soil. Soil samples were collected randomly from the site and subjected to physico-chemical tests before experimentation. The samples were contaminated artificially at six different concentration levels of lead nitrate (Pb(N03)2). Experimental design was 4-factorial combination (6×6×2×1). The study duration was 10 weeks, and during this period, Pb contents of the soil were analyzed in intervals of two weeks. Analyzed physico-chemical properties of the soil showed that the soil was loamy with pH 6.82, electri-cal conductivity 1.62 dS/m and adequate macro nutrient elements. The average percentage removal of Pb from the soil was 2.25% and 3.67% for potted and non-potted experiments, respectively. Similarly, the average percentage of Pb in the roots was 1.10% and 1.68% for potted and non-potted experiments, respectively. The result of this study indicated that extraction of Pb by the plant system increased with the increase of lead concentration in the soil as well as in the extent of vegetation attained by the crop. It also clearly showed that the non-potted experiments demonstrated greater influence on removal of Pb from the soil system than the potted experiments.
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  • [1]

    Abioye, O.P., Ijah, U.J.J., Aransiola, S.A., 2013. Remediation Mechanisms of Tropical Plants for Lead-contaminated Environment. Soil Biology. Berlin, Heidelberg: Springer Berlin Heidelberg, 59-77.
    [2]

    Adriano, D.C., Bollag, J.M., Frankenberger, W.T., Sims, R.C., Wenzel, W.W., Adriano, D.C., Salt, D., Smith, R., 1999. Phytoremediation: A Plant-Microbe-based Remediation System. Bioremediation of Contaminated Soils. U. S.: American Society of Agronomy, Crop Science Society of America, Soil Science Society of America.
    [3]

    Appel, C., Ma, L.N., 2002. Concentration, pH, and surface charge effects on cadmium and lead sorption in three tropical soils. J. Environ. Qual. 31, 581. doi: 10.2134/jeq2002.5810
    [4]

    Blaylock, M.J., Salt, D.E., Dushenkov, S., Zakharova, O., Gussman, C., Kapulnik, Y., Ensley, B.D., Raskin, I., 1997. Enhanced accumulation of Pb in Indian mustard by soil-applied chelating agents. Environ. Sci. Technol. 31, 860-865. doi: 10.1021/es960552a
    [5]

    Brady, N.C., Weil, R.R., 1999. The Nature and Properties of Soils, 12th ed. Prentice Hall. Upper Saddle River, N J.
    [6]

    Donahue, S., Auburn, A.L., 2000. Soil Quality-Urban Technical Note No. 3. Soil Quality Institute 411. USDA and NRCS 36832334-844-4741X-177.
    [7]

    EPA, 1993. 40CFR Part 503-Standards for use and disposal of sewage sludge: Final rules. Federal Register 58: 9248-9415. http://www.gadnr.org/epd/Files_PDF/techguide/wpb/smplasguidelinerev_June2006.pdf.
    [8]

    EPA, U. S., 1993. Clean Water Act (Sec. 503, 58(32)). Washington: U. S. Environmental Protection Agency.
    [9]

    Foth, H.D., 1990. Fundamentals of Soil Science. New York: John Wiley and Sons.
    [10]

    Fuhrmann, M., Lasat, M.M., Ebbs, S.D., Kochian, L.V., Cornish, J., 2002. Uptake of cesium-137 and strontium-90 from contaminated soil by three plant species; application to phytoremediation. J. Environ. Qual. 31, 904. doi: 10.2134/jeq2002.9040
    [11]

    Iloeje, N.P., 1981. A New Geography of Nigeria, New Revised Edition. Longman, Great Britain.
    [12]

    Kabta, P., Pendias, H., 1984. Trace Elements in Soil and Plants. Boca Raton, Fla, USA: CRC Press.
    [13]

    Karishma, B., Prasad, S., 2014. Effect of agrochemicals applicationon accumulation of heavy metals on soil of different landuses with respect to its nutrient status. IOSR J. Environ. Sci. Toxicol. Food Technol. 8, 46-54.
    [14]

    Lasat, M.M., 2002. Phytoextraction of toxic metals. J. Environ. Qual. 31, 109.
    [15]

    Perkin-Elmer, 1968. Analytical methods for Atomic Absorption Spectrometry. Perkin-Elmer Corp Norwalk Connecticut plant in Ghana. J. of Plant Soil Environ. 56(5), 244-251.
    [16]

    Shen, Z.G., Li, X.D., Wang, C.C., Chen, H.M., Chua, H., 2002. Lead phytoextraction from contaminated soil with high-biomass plant species. J. Environ. Qual. 31, 1893.
    [17]

    Tiwari, S., Tripathi, I.P., Tiwari, H.L., 2013. Effects of lead on environment. Inter. J. of Emerg. Res. in Manag. &Technol. 2(6), 1-5.
    [18]

    Tu, C., Ma, L.Q., Bondada, B., 2002. Arsenic accumulation in the hyperaccumulator Chinese brake and its utilization potential for phytoreme-diation. J. Environ. Qual. 31, 1671.
    [19]

    Yusuf, A.A., Arowolo, T.O.A., Bamgbose, O., 2002. Cadmium, copper and nickel levels in vegetables from industrial and residential areas of Lagos City, Nigeria. Glob. J. Environ. Sci. 1. DOI: 10.4314/gjes.v1i1.2390.
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Remedial ability of maize (zea-mays) on lead contamination under potted condition and non-potted field soil condition

    Corresponding author: Uche Jenice Chiwetalu, jenice.chiwetalu@esut.edu.ng; caohuicong@njfu.edu.cn
  • a. Agricultural and Bio-resources Engineering Department, Faculty of Engineering, Enugu State University of Science and Technology, Enugu, Nigeria
  • b. Agricultural and Bioresource Engineering Department, Faculty of Engineering, University of Nigeria Nsukka, Enugu State, Nigeria

Abstract: This study presents the remedial ability of maize on lead (Pb) contaminated soil. Soil samples were collected randomly from the site and subjected to physico-chemical tests before experimentation. The samples were contaminated artificially at six different concentration levels of lead nitrate (Pb(N03)2). Experimental design was 4-factorial combination (6×6×2×1). The study duration was 10 weeks, and during this period, Pb contents of the soil were analyzed in intervals of two weeks. Analyzed physico-chemical properties of the soil showed that the soil was loamy with pH 6.82, electri-cal conductivity 1.62 dS/m and adequate macro nutrient elements. The average percentage removal of Pb from the soil was 2.25% and 3.67% for potted and non-potted experiments, respectively. Similarly, the average percentage of Pb in the roots was 1.10% and 1.68% for potted and non-potted experiments, respectively. The result of this study indicated that extraction of Pb by the plant system increased with the increase of lead concentration in the soil as well as in the extent of vegetation attained by the crop. It also clearly showed that the non-potted experiments demonstrated greater influence on removal of Pb from the soil system than the potted experiments.

1.   Introduction
  • The increase in exploitation, production and consumption of the mineral resources in earth, coupled with the exponential growth of the world's population over the past 200 years have resulted in environmental buildup of waste products, of which heavy materials are of particular concern (Appel and Ma, 2002). The major causes of soil lead contamination in urban and populated environment are the weathering, chipping, scraping, sanding and sand blasting of structures bearing lead-based paint.

    These activities find their end point mainly on the soil resulting pollution of the soil and the environment in general because the pollutant can be transferred from soil to surface water, ground water, be absorbed by plants and transferred to herbivores and humans, thus affecting the entire food chain. Soil is an important aspect of both rural and urban environment, and land management is the key to soil quality (Donahue and Auburn, 2000). However, it is advisable that applicators of industrial waste or sludge must be abided by the regulatory limits set by the U.S. Environmental Protection Agency (EPA, U.S., 1993). Preventing heavy metal pollution with numerous technologies is nearly impossible and such reliable means of cleaning this dangerous metal like lead are envisaged. Traditional techniques of heavy metal soil remediation are costly and may cause secondary pollution. Series of approaches are being practiced in order to reclaim land contaminated with lead (Abioye et al., 2013). Phyto-remediation is known to be the use of plants in cleaning up contaminated environments (soil and water), offering the most environmentally friendly approach for soil and water remediation (Abioye et al., 2013). In phyto-extraction process, plants remove contaminants from soil by accumulating them in plant tissues, and it is a promising cleanup technology for a variety of metal contaminated soil (Fuhrmann et al., 2002; Lasat, 2002). This method of cleaning up contaminated soil is cheaper than the conventional cleanup methods and does not require extensive excavation, disposal costs and loss of topsoil associated with traditional remediation practices (Blaylock et al., 1997).

    However, successful phyto-extraction needs plants produce high biomass and accumulate large number of contaminants in the biomass from the soil (Tu et al., 2002; Shen et al., 2002). Research result has demonstrated that plants were effective in cleaning up contaminated soil (Adriano et al., 1999). Maize, rice, peas and Indian mustard have been classified as tolerant plants with relatively higher accumulation ability and higher biomass compared with other plants. Maize, which is cultivated in different parts of the globe under diverse environment, has profuse and fine branched root system. The matured root system extends downwards to approximately 2 m and laterally to approximately 1.5 m. It has also numerous root hairs which play an important role in absorption of water, nutrients and contaminants from the soil. Similarly, vegetables have also been found to absorb heavy metals from the soil as well as from surface deposits on part of vegetables exposed to polluted air (Yusuf et al., 2002). These contaminants extracted from the plant system can successfully be harnessed from the harvested plants and further be used as ore or other products (Brady and Weil, 1999). Literatures have shown that of all the metals lead is the most common soil contaminant (EPA, 1993). Figs. 1 and 2 are Pb mine sites at Amaeka in Ezza south L.G.A., Ebonyi State, South East of Nigeria. This study compared the remedial ability of zea mays for lead contaminated soil under potted and non-potted field condition for effective bioremediation of contaminated soils.

    Figure 1.  Lead mine sites at Amaeka, Ebonyi State, Nigeria

    Figure 2.  Lead contaminated sites at Amaeka, Ebonyi State, Nigeria

    Environmental risk due to soil pollution is of particular importance for agricultural areas, as extensive reliance on agrochemicals for agricultural productions has immensely resulted in the accumulation of various heavy metals in the soil leading to serious consequences. Thus, pollution of heavy metals poses a threat to country's food production. There is a growing public concern over the potential accumulation of heavy metals in agricultural soils globally owing to the rapid urban and industrial development and the increasing reliance on agrochemicals in the last decades (Karishma and Prasad, 2014). Lead is one out of four metals that have the most damaging effects on human health which is a potent poison and is harmful in even small amount, and it is one of a limited class of elements that can be described as purely toxic which is an important environmental contaminant because of its known toxicity to humans and other living organisms. Many other elements, including heavy metals such as chromium, manganese, molybdenum, nickel, and selenium, although toxic at high levels, are actually required nutrients at lower levels. Lead is a relatively corrosion resistant, dense and malleable metal that has been used by humans for at least 5000 years (Tiwari et al., 2013). Lead contamination has been identified globally as one of the major causes of environmental degradation and several ill health most especially in the developing countries. Hence, phyto-remediation of Pb contaminated agricultural soil using maize under two different conditions was envisaged. Therefore, the objectives of the study are to determine the physical and chemical properties of the soil samples before experimentation, to design an experiment that will serve as a guide for the phyto-remediation of lead contaminated soil for potted and non-potted field conditions, to analyze the soil sample in two weeks intervals, to determine the quantity of lead removed from the soil and Pb contents of the root, and to compare the results obtained for the two experimental conditions.

2.   Materials and methods
  • This experiment was carried out at Agricultural and Bio-resource Engineering Research Farm, behind Faculty of Engineering complex, Independence Layout Enugu, Enugu North L.G.A., Enugu State, Nigeria. Enugu (N6°24′, E7°30′) has an area of 67 km2 and a population of 198 723 (census in 2006). Enugu is in the savanna zone of the country (Iloeje, 1981). The soil in the area is of rolling grassland and occasional forest patches. The soil type is loam with scanty gravels and pH of 6.5–7.8. The vegetation of Enugu urban area is rainforest vegetation to derived Guinea savannah vegetation.

  • Maize (Oba Super 11), soil auger, 120 cm3 plastic container, plastic bags, disposable hand gloves, wipes, permanent ink marker, distilled water oven, aqua reqia, conical flask, lead (II) nitrate (Pb(NO3)2), filter papers, and digital weighing balance and atomic absorption spectrophotometer.

  • The experimental design was 4-factorial combination (6 × 6 × 2 × 1) of six different levels of Pb concentration grown under potted field condition, six different levels of Pb concentration grown under non-potted field condition, two different study conditions and one plant species, zea-mays (Oba super 11). Six different sample containers were perforated and filled with 10 kg of soil and used for the potted experimentation. For non-potted, the ground condition was modified (tilled) at six different spots and filled with contaminated soil of different levels of concentration (200–1000 mg/kg) to a depth of about 60 cm. The six containers were labeled A–F and grown with maize crop (Oba super 11). The plastic containers (120 cm3 buckets) used were perforated at the bottom and by the sides for aeration of the soil system. The plastic containers were planted with three viable seeds of maize crop each, which was thinned to one seedling after 10 days of germination. Similarly, three viable seeds were also planted in the non-potted field experimental set ups. The Figs. 35 show the experimental site before planting of maize, non-potted field experiment and potted field experiment, respectively.

    Figure 3.  Experimental site before planting

    Figure 4.  Non-potted field experiment

    Figure 5.  Potted field experiment

    The set-up of the experiment is as follows: sample A, ordinary soil without contamination (0 mg/kg); sample B, soil contaminated with lead at 200 mg/kg potted experiment; sample C, soil contaminated with lead at 400 mg/kg potted experiment; sample D, soil contaminated with lead at 600 mg/kg potted experiment; sample E, soil contaminated with lead at 800 mg/kg potted experiment; sample F, soil contaminated with lead at 1000 mg/kg potted experiment; sample G, ordinary soil without contamination 0 mg/kg non-potted experiment; sample H, soil contaminated with lead at 200 mg/kg non-potted experiment; sample I, soil contaminated with lead at 400 mg/kg non-potted experiment; sample J, soil contaminated with lead at 600 mg/kg non-potted experiment; sample K, soil contaminated with lead at 800 mg/kg non-potted experiment; sample L, soil contaminated with lead at 1000 mg/kg non-potted experiment.

  • The seeds used for this study were purchased from ENADEP (Enugu State Agricultural Development Program). Each experimental set-up was sown with three seeds and were thinned after 10 days of germination, leaving the healthiest and sound seedling to grow for the study.

  • Lead (II) nitrate (Pb(NO3)2) salt was used as the source of Pb at a concentration of 0, 200, 400, 600, 800 and 1000 mg/L. These concentrations were obtained by adding equivalent quantity of lead nitrate in 1000 mL volumetric flask containing distilled water. Example, 200 mg/L lead (II) nitrate (Pb(NO3)2) salt was obtained by dissolving 0.2 g of lead in 1000 mL distilled water. The same method was applied to obtain 400, 600, 800 and 1000 mg/L lead (II) nitrate salt (Pb(NO3)2) salt. The different concentrations obtained were used to contaminate the collected soil samples to the required levels of contamination. The different concentrations obtained were mixed thoroughly with the measured 10 kg of uncontaminated soil in order to spike the soil (Kabta and Pandias, 1984).

  • The 2 g of soil each (oven dried) were weighed and placed into conical flasks that were previously washed with HNO3 and distilled water, 4 cm3 of perchloric acid, 25 cm3 concentration. 5 cm3 concentration HNO3, H2SO4 were added under a fume hood. The contents were mixed gently at low to medium heat on hot plate under fume hood. Heating continued until dense white fumes disappeared, then each mixture was allowed to cool and then 40 cm3 distilled water was added and boiled for a minute under the same hot plate. The solution was allowed to cool and then filtered for atomic absorption spectrometry readings in accordance with Perkin-Elmer (1968).

  • The pH was determined using digital pH meter. The 2 g of soil sample was weighed into a 100 mL beaker and the meter probe inserted, a value of about 6.82 read from the meter screen. Similarly, the electrical conductivity of the sample of the soil sample before experimentation was determined as 1.67 dS/m using a digital conductivity meter (model DDS-307). The result are shown in Table 1. The crop used was zea mays (Oba super 11) because this specie of maize is a high yielding crop variety which has high potential to adapt to adverse climatic conditions and can adapt easily in different environments. It is the most cultivated maize variety in Enugu.

    Item pH EC (dS/m) CEC (cmol/kg) OM (%) Clay (%) Sand (%) Silt (%) Gravel (%) BD (g/cm3) MC (%)
    Value 6.82 1.67 2.6 23 37 39 0.8 1.28 11.07
    Notes: EC, electrical conductivity; OM, organic matter; BD, bulk density; MC, moisture content; CEC, cation exchange capacity

    Table 1.  Soil properties before experiment

3.   Results and discussion
  • The characteristics of soil used for this study before contamination are shown in Table 1. The soil type is loamy, with almost equal proportion of silt and sand. It indicates that the soil has 50% lower than clay, sand and silt. The pH of the soil before experimentation was 6.82, showing that the soil was slightly acidic near to neutral level. The bulk density (BD) of the soil was 1.28 g/cm3, and this may be ascribed to the soil being in its natural state with some level of compaction as a result of human and animal activities in the soil. Moisture content (MC) of the soil obtained was l1.07%, showing that the soil before experiment was in stress zone. Organic matter (OM) content of the soil was within the acceptable range of 2%–3%. The electrical conductivity (EC) result obtained indicated that the value fell within the acceptable range for clay soil (0.2–8.0 dS/m). The EC value is also an indication that the soil is fertile (1.1–5.7 dS/m), i.e., optimal range in the soil.

  • The macro nutrient element result (Table 2) showed that the percentage of potassium (K) obtained from the soil before the start of the experiment was above the average value (0.83%) required in a soil. However, the normal range of K is between 0.3% and 2.5%. Phosphorous (P) was found above the average range of 0.6%. Nitrogen (N) was obtained to be 0.45% which was also adequate because the minimum level for N in the soil is about 0.14%.

    Item K (%) Mg (cmol/kg) Ca (cmol/kg) N (%) P (%)
    Value 1.70 13.5 1.94 0.45 0.93

    Table 2.  Soil macro nutrient elements

  • Table 3 presents the result of the analyzed Pb content in the soil (potted and non-potted experiments) at week two. The results showed that there was little reduction in the concentration of lead in the contaminated soils of the different treatment levels for potted and non-potted condition. The result also showed that Pb uptake by the crop was generally influenced by the stage of growth attained by the crop as well the concentration of lead in the soil. However, extraction of Pb by maize under non-potted condition was a little higher than that of potted grown condition, which can be attributed to the confinement of the plant root system by the containers. It can been seen from the values obtained for the amount of lead removed. The quantity of Pb removed at this stage of growth (week two) was relatively low because of the age of plant. Moreover, the quantity removed was also influenced by the increase in concentration because more lead was found in the soil solution with exception of 800 and 1000 mg/L. Non-potted experiment showed that about twice the quantity of lead removed during week two of potted experiment was removed in same week two for non-potted experiment. It was attributed to non-restriction of plant's root development under this set and as well infiltration of the contaminants beyond the root zone of the planted crop.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantityremoved Atomic Adsorption Spectrophotometer value Concentration Quantity removed
    0 0 0 0 0 0 0
    200 3.97 198.50 1.50 3.94 197.00 3.00
    400 7.95 397.50 2.50 7.93 396.50 3.50
    600 11.90 595.00 5.00 11.88 594.00 6.00
    800 15.94 797.00 3.00 15.90 794.50 5.50
    1000 19.98 999.20 0.80 19.88 994.00 6.00

    Table 3.  Analyzed Pb concentrations of soil at week two of experiment (mg/L)

    Fig. 6, Fig. 7 show the quantity of Pb removed at two weeks experimental period for potted and non-potted experiments, respectively. The results showed gradual increase in removal of Pb from the soil with increase in Pb concentration of the samples for both conditions. However, at 800 and 1000 mg/L there was a decline in Pb removal for potted experiment. It can be attributed to the high Pb concentration in the soil system. In addition, the roots developed by maize at this stage were still tender and not sufficient enough to extract large concentration of Pb in their system. At 800 mg/L non-potted experiment, there was a little decline and a rise at 1000 mg/L in the trend of removal of Pb from the soil. This can be linked with some environmental factors since the root of plants is not confined in a container.

    Figure 6.  Quantity of Pb removed and sample concentration for potted experiments

    Figure 7.  Quantity of Pb removed and sample concentration for both potted and non-potted experiments

    The results obtained in week four are presented in Table 4. It can be seen that extraction of lead slightly increased for the different concentrations and the two study conditions. The changes in the amount of Pb removed may be influenced by the stage of growth attained by the crop. It can been seen from Table 4 that at week four, the crop has more developed root system and vegetative cover that can accumulate more Pb in their system than when they were in week two that the crops are still in their early or initial growth period. The higher quantity of lead removed by the crop grown under non-potted experiment was attributed to its growth condition.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity removed Atomic Adsorption Spectrophotometer value Concentration Quantity removed
    0 0 0 0 0 0 0
    200 3.94 197.00 3.00 3.94 197.00 3.00
    400 7.90 395.00 5.00 7.84 392.00 8.00
    600 11.79 589.50 10.50 11.64 582.00 18.00
    800 15.82 791.00 9.00 15.62 781.50 11.50
    1000 19.88 994.00 6.00 19.72 986.00 14.00

    Table 4.  Analyzed Pb concentration of soil at week four of experiment (mg/L)

    In week six of the experiment, there was similar results as obtained for week four. Table 5 shows that the removal of lead was influenced by the stage of growth attained by the crop and the concentration of lead in the soil, and a slight increase in the quantity of lead removed by the crops was found. It was attributed to the stage of growth attained by the crop. At this stage, the crop is at its developmental stage and has more developed root system and vegetative cover that are capable of extracting more Pb than when they are in their initial stage of development. This observation was for both studied conditions, though the non-potted experimental crops significantly extracted more Pb than the potted ones.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity removed Atomic Adsorption Spectrophotometer value Concentration Quantity removed
    0 0 0 0 0 0 0
    200 3.88 194 6 3.64 182 18
    400 7.88 394 6 7.48 374 26
    600 11.72 586 14 11.50 575 25
    800 15.66 783 17 15.54 777 23
    1000 19.76 988 12 19.58 979 21

    Table 5.  Analyzed Pb concentrations of soil at week six of experiment (mg/L)

    The results of the analyzed soil Pb at week eight are shown in Table 6. The extraction of lead by the crop was high in week eight for both studied conditions. The quantity of Pb removed was more than double the quantity removed for 200 and 400 mg/L in week six. This is related with the growth stage of crop. At week eight, maize has syreached their peak in vegetation and high osmotic reactions were expected to take place by the crops at this stage.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity removed Atomic Adsorption Spectrophotometer value Concentration Quantity removed
    0 0 0 0 0 0 0
    200 3.71 185.5 14.5 3.52 176 24
    400 7.69 384.5 15.5 7.40 370 30
    600 11.56 578.0 22.0 11.40 570 30
    800 15.52 776.0 24.0 15.32 766 34
    1000 19.60 980.0 20.0 19.48 974 26

    Table 6.  Analyzed Pb concentration of soil at week eight of experiment (mg/L)

    The results obtained in the last week of the experiment (week ten) are shown in Table 7. Lead extraction by the plant roots for both studied conditions was found to be the highest in week ten. The non-potted plants proved to extract more Pb than the potted plants because of the restriction by their containing vessels. At this stage, the crops have developed cob (maize fruit) awaiting full maturity. Osmotic reactions were also very high and affected the quantity of lead absorbed by the roots of the crop to a great extent. Furthermore, Pb in soil solution is expected to be reduced in later weeks since much of which has been absorbed by the plant root.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity removed Atomic Adsorption Spectrophotometer value Concentration Quantity removed
    0 0 0 0 0 0 0
    200 3.54 177 23 3.30 165 35
    400 7.60 380 20 7.14 357 43
    600 11.38 569 31 11.16 558 42
    800 15.28 764 36 14.98 749 51
    1000 19.38 969 31 19.22 961 39

    Table 7.  Analyzed Pb concentration of soil at week ten of experiment (mg/L)

    The results of the analyzed Pb concentration of the roots in week two of the experiment are shown in Table 8. About 0.6–5.55 mg/L of lead was found in the roots of the planted crops for the different treatment levels and also for the two studied conditions. The difference in the Pb concentrations of the roots and soil might be as a result of translocation and infiltration of the contaminants. However, the Pb concentrations of other plant parts were not analyzed.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity in root Atomic Adsorption Spectrophotometer value Concentration Quantity in root
    0 0 0 0 0 0 0
    200 3.976 198.8 1.2 3.952 197.60 2.40
    400 7.958 397.9 2.1 7.945 397.25 2.75
    600 11.908 595.4 4.6 11.892 594.60 5.40
    800 15.950 797.5 2.5 15.908 795.40 4.60
    1000 19.988 999.4 0.6 19.890 994.45 5.55

    Table 8.  Analyzed Pb concentration of plant root at week two of experiment (mg/L)

    The results presented in Table 9 showed a similar trend with those in Table 8. However, more Pb was found in the roots of the crop at week four, compared with that of week two. The increase in the Pb content in the roots can be attributed to a more developed root system by the planted crop.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity in root Atomic Adsorption Spectrophotometer value Concentration Quantity in root
    0 0 0 0 0 0 0
    200 3.964 198.20 1.80 3.963 198.15 1.85
    400 7.925 396.25 3.75 7.880 394.00 6.00
    600 11.848 592.40 7.60 11.818 590.90 9.10
    800 15.863 793.15 6.85 15.808 790.40 9.60
    1000 19.910 995.50 4.50 19.753 987.65 12.35

    Table 9.  Analyzed Pb concentration of plant root at week four of experiment (mg/L)

    The results of Pb concentration in the roots in week six are shown in Table 10. At week six, maize crop is in its developmental stage with a more defined and developed root system. Osmotic reactions are expected to be higher too, causing extraction of more minerals including contaminants found in the soil by the roots. Nevertheless, some quantity of lead maybe translocated to other part of the crop influencing Pb availability in the root.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity in root Atomic Adsorption Spectrophotometer value Concentration Quantity in root
    0 0 0 0 0 0 0
    200 3.952 197.60 2.40 3.854 192.70 7.30
    400 7.950 397.50 2.50 7.786 389.30 10.30
    600 11.874 593.70 6.30 11.792 589.60 10.40
    800 15.837 791.85 8.15 15.806 790.30 9.70
    1000 19.874 993.69 6.31 19.874 993.69 8.80

    Table 10.  Analyzed Pb concentration of plant root at week six of experiment (mg/L)

    The analyzed Pb concentrations of the root at week eight are shown in Table 11. Maize at week eight has attained high vegetative stage with well developed roots capable of adsorbing minerals from the soil. Increase in the Pb content in the roots at this stage was as a result of the stage of growth attained by the crops. The concentration of lead found in the roots of the crops was obtained to be within 5.87–14.47 mg/L for both studied conditions. However, in week four the lead content of the root was within 1.80–12.35 mg/L.

    Sample concentration Potted condition sample Non-potted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity in root Atomic Adsorption Spectrophotometer value Concentration Quantity in root
    0 0 0 0 0 0 0
    200 3.883 194.13 5.87 3.804 190.22 9.78
    400 7.876 393.81 6.19 7.760 388.00 12.00
    600 11.835 591.77 8.23 11.744 587.20 12.80
    800 15.807 790.34 9.66 15.711 785.53 14.47
    1000 19.842 992.09 7.91 19.783 989.15 10.85

    Table 11.  Analyzed Pb concentration of plant root at week eight of experiment (mg/L)

    Similarly, higher concentrations of Pb were found in the roots of maize at week ten than those in week eight. This is related with the age of the crops and root development. At this stage, the crops have fully developed and absorption of minerals by plants' roots from the soil was high, thereby influencing the quantity of Pb absorbed by the roots. The Pb concentration in the root of maize was the highest at week ten (Table 12).

    Sample concentration Potted condition sample Nonpotted condition sample
    Atomic Adsorption Spectrophotometer value Concentration Quantity in root Atomic Adsorption Spectrophotometer value Concentration Quantity in root
    0 0 0 0 0 0 0
    200 3.812 190.59 9.41 3.716 185.78 14.22
    400 7.836 391.81 8.19 7.660 382.99 17.01
    600 11.748 587.40 12.60 11.658 582.88 17.12
    800 15.709 785.47 14.53 15.585 779.24 20.76
    1000 19.741 987.05 12.95 19.683 984.16 15.84

    Table 12.  Analyzed Pb concentration of plant root at week ten of experiment (mg/L)

4.   Conclusions
  • In conclusion, the results of this study showed that extraction of Pb by the plant system increased with the increase in concentration of lead in the soil and in the extent of vegetative growth or cover (time). In addition, the non-potted crops had greater influence on removal of Pb from the soil system than those grown under potted condition. Similarly, more Pb was found in the roots of crops for non-potted experiments than potted experiments. Furthermore, Pb concentration increased adsorption capacity because higher dosage of Pb was found in soil medium for root extraction. However, it is expected that lead extraction by the plant system will decrease at the late stage (week twelve and beyond) of the plant growth stage because of reduction in the osmotic reaction in the plant system as a result of age and less availability of lead in the soil medium. Finally, the results of this study indicate that maize is tolerant to Pb.

Reference (19)

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