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Translocation and accumulation of Cr, Hg, As, Pb, Cuand Ni by Amaranthus dubius (Amaranthaceae) fromcontaminated sitesJohn J. Mellem a , Himansu Baijnath b & Bharti Odhav aa Department of Biotechnology and Food Technology, M. L. Sultan Campus , DurbanUniversity of Technology , Durban, South Africab School of Biological and Conservation Sciences , University of KwaZulu-Natal , WestvilleCampus, Durban, South AfricaPublished online: 31 Mar 2009.

To cite this article: John J. Mellem , Himansu Baijnath & Bharti Odhav (2009) Translocation and accumulation of Cr, Hg, As,Pb, Cu and Ni by Amaranthus dubius (Amaranthaceae) from contaminated sites, Journal of Environmental Science and Health,Part A: Toxic/Hazardous Substances and Environmental Engineering, 44:6, 568-575, DOI: 10.1080/10934520902784583

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Journal of Environmental Science and Health Part A (2009) 44, 568–575Copyright C© Taylor & Francis Group, LLCISSN: 1093-4529 (Print); 1532-4117 (Online)DOI: 10.1080/10934520902784583

Translocation and accumulation of Cr, Hg, As, Pb, Cuand Ni by Amaranthus dubius (Amaranthaceae) fromcontaminated sites

JOHN J. MELLEM1, HIMANSU BAIJNATH2 and BHARTI ODHAV1

1Department of Biotechnology and Food Technology, M. L. Sultan Campus, Durban University of Technology, Durban, South Africa2School of Biological and Conservation Sciences, University of KwaZulu-Natal, Westville Campus, Durban, South Africa

Phytoremediation is an emerging technology where specially selected and engineered metal-accumulating plants are used for bioreme-diation. This study was undertaken to evaluate the potential of Amaranthus dubius for phytoremediation of chromium (Cr), mercury(Hg), arsenic (As), lead (Pb), copper (Cu) and nickel (Ni). Locally gathered soil and plants of A. dubius were investigated for themetals from a regularly cultivated area, a landfill site and a waste water treatment site. Metals were extracted from the samples usingmicrowave-digestion and analyzed using Inductively Coupled Plasma–Mass Spectroscopy. The mode of phytoremediation, effect ofthe metals on the plants, ability of the plant to extract metals from soil (Bioconcentration Factor) and the ability of the plants tomove the metals to the aerial parts of the plants (Translocation Factor) were evaluated. The survey of the three sites showed thatsoils were heavily contaminated with Cr, Hg, Cu and Ni. These levels were far above acceptable standards set for soils and above thestandards set for the Recommended Dietary Allowance. Specimens of A. dubius from the three sites showed that they could tolerateHg, sequester it from the soil, and translocate it to the shoots. Cr could only be removed from the soil and stored in the roots, withlimited amounts translocated to the aerial parts. Pb, As, Ni, and Cu have some degree of transportability from the soil to the roots butnot to aerial parts. The ability of A. dubius to be considered for phytoremediation has to be viewed with caution because translocationof the metals to the aerial parts of the plant is limited.

Keywords: Phytoremediation, Amaranthus dubius, inductively coupled plasma–mass spectroscopy, bioconcentration factor, translo-cation factor, Cr, Hg, As, Pb, Cu, Ni.

Introduction

Both aquatic and terrestrial habitats are becoming progres-sively polluted due to discharge of pollutants generatedfrom various industries, from transportation and fossil fuelburning. Many industries discharge their untreated wastew-ater and industrial wastes containing various proportionsof heavy metals into natural water bodies and on land.Heavy metals include lead (Pb), cadmium (Cd), zinc (Zn),mercury (Hg), arsenic (As), silver (Ag), chromium (Cr),copper (Cu), iron (Fe) and the platinum group elements.The remediation of heavy metals is based on physicochem-ical technologies meant primarily for intensive in situ or exsitu treatment of relatively highly polluted sites. As such,this is not suitable for the remediation of vast, diffusely

Address correspondence to Professor B. Odhav, Department ofBiotechnology and Food Technology, M. L. Sultan campus,Durban University of Technology, P. O. Box 1334, Durban 4000,South Africa. E-mail: odhavb@dut.ac.zaReceived October 21, 2008.

polluted areas where pollutants occur only at relatively lowconcentrations and superficially.[1]

In this context, phytoremediation appears a very validoption since it is best suited for the remediation of thesediffusely polluted areas and at much lower costs than othermethods.[2] The idea of using plants to remove metals fromsoils came from the discovery of different wild plants,often restricted to naturally mineralized soils that accu-mulate high concentrations of metals in their leaves.[3,4]

Phytoremediation can be accomplished by severalmeans including phytoextraction,[2] phytostabilization,[5]

phytovolatilization[4,6] and phytodegradation.[6] There aremany factors which determine the effectiveness of phytoex-traction in remediating metal-polluted sites.[7] The selectionof a site that is conducive to this remediation technology isof primary importance. Phytoextraction is applicable onlyto sites that contain low to moderate levels of metal pol-lution, because plant growth is not sustained in heavilypolluted soils.

Soil metals should also be bioavailable, or subject toabsorption by plant roots. The land should be relatively

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free of obstacles, such as tree trunks or boulders, and havean acceptable topography to allow for normal cultivationpractices, which employ the use of agricultural equipment.As a plant-based technology, the success of phytoextractionis inherently dependent upon several plant characteristics.The two most important plant characters include the abilityto accumulate large quantities of biomass rapidly and theability to accumulate large quantities of environmentallyimportant metals in the shoot tissue,[2,8−10] the combinedaction of which results in most metal removal.

Ebbs et al.[11] reported that Brassica juncea, while havingone-third the concentration of Zn in its tissue, is more ef-fective at Zn removal from soil than Thlaspi caerulescens,a known hyperaccumulator of Zn. This advantage is dueprimarily to the fact that B. juncea produces ten-times morebiomass than T. caerulescens. Plants being considered forphytoextraction must be tolerant of the targeted metal, ormetals, and be efficient at translocating them from rootsto the harvestable above-ground portions of the plant.[7]

Other desirable plant characteristics include the ability totolerate difficult soil conditions (i.e., soil pH, salinity, struc-ture, water content), the production of a dense root system,ease of care and establishment, and few disease and insectproblems. Although some plants show promise for phy-toextraction, there is no plant which possesses all of thesedesirable traits with the “perfect plant” continuing to bethe focus of many plant-breeding and genetic-engineeringresearch efforts.

The majority of hyperaccumulating species discoveredso far are restricted to tropical areas.[3,12] The first hy-peraccumulators characterized were members of the fami-lies Brassicaceae and Fabaceae. Although the number ofmetal-accumulating taxa identified to date has been re-ported to be 397, there is a continuous search for novelphytoextracting plants which are adapted to particularecosystems and climates.[13] Studies have demonstrated thatthe ability to accumulate heavy metals varies greatly be-tween species and between cultivars within a species.[14]

Particular emphasis has been placed on the evaluation ofshoot metal-accumulation capacity of the cultivated Bras-sica species (mustard) because of their relation to wildmetal-accumulating mustards.[2]

Although the largest numbers of temperate-climate hy-peraccumulating species belong to the Brassicaceae,[3] in thetropics the Euphorbiaceae is the best represented group.[15]

Other field trials for the continuous phytoextraction ofmetals have been reported: Thlaspi caerulescens and Si-lene vulgaris for Cd and Zn, respectively; Brassica oleracea,Raphanus sativus, Thlaspi caerulescens, Alyssum lesbiacum,Alyssum murale and Arabidopsis thaliana for Zn, Cd, Ni,Cu, Pb and Cr, respectively.[16]

There is ongoing research by Bigaliev et al.[17] on metaluptake by five species of Amaranthus viz. A. hybridus,A. hypochondriacus, A. paniculatus, A. retroflexus and A.tricolor, and two hybrids between A. hybridus and A.hypochondriacus. The metals Cd, Cu and Zn were used

in the experiments and revealed different levels of accu-mulation and toxicity in the plant seeds, roots, stems andleaves. Other recent studies include A. dubius and A. hy-bridus, which were grown in farm soil containing differentamounts of water soluble salts of Cd, Pb, Hg and Ni.[18]

In A. dubius at the highest contamination level Hg waspresent in the roots (336 ppm) after 5 weeks. Both Ama-ranthus species showed increased levels of Ni and Cd inthe leaves. Jonnalagadda et al.[19] investigated the impact ofcoal mine dump-contaminated soil on metal uptake by A.dubius and A. hybridus. Both these species recorded highmanganese (Mn) accumulation. Although no Hg was de-tected in the soil or plants, plants of A. hybridus had higherelemental concentrations than those of A. dubius.

The quick growth of amaranths and their great biomassmakes them some of the highest yielding leafy crops whichwould be beneficial as a primary food source, thus prevent-ing starvation and malnutrition in the third-world coun-tries. Grubben[20] mentioned that because of their highyield, ability to grow in hot weather conditions, high nutri-tive value, their pleasant taste, and the fact that they growall year; makes the amaranth a popular vegetable. Howeverthere are disadvantages to amaranths namely: (i) It is re-garded as an aggressive and invasive weed in cultivated farmand disturbed lands; (ii) it contains high levels of nitrogenand when eaten in excess by ruminants, the consumed herbsare converted to highly toxic nitrates by microorganisms inthe rumen resulting in severe poisoning, bloating or evendeath; and, (iii) amaranths being C4 plants are excellent in-dicators of heavy metal pollution and problems may ariseif contaminated plants are cooked and eaten by humans.The aim of this study was to investigate the potential ofnaturally growing A. dubius, from a regular cultivated area(RCA), a landfill site (LS) and a waste water treatmentsite (WWT), to accumulate heavy metals from the soil. Toachieve this aim our objectives were to collect and analyzeplants and soil for Cr, Hg, As, Pb, Cu and Ni from the3 sites; determine translocation of the metals from soil toplant; compare the metals accumulated by A. dubius at eachsite and evaluate the plant portal in which the particularmetal is stored.

Materials and methods

Site identification

A site in the Durban South area (RCA) of Merebank, thatis regularly cultivated for various crops, was chosen as alocation in which heavy metals were not expected. This siteis close to several industries. The Springfield Landfill Site(LS) is a highly disturbed area, as a result of the constantturning of soil due to solid waste dumping. The samples inthis study were collected from an area that showed mini-mum active disturbance. The specimens from the NorthernWaste Water Works (WWTS) were collected from dry sewersludge.

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Sampling

Duplicate samples of plant material (500 g dry weight) werecollected from the 3 sites in June 2005. Each replicate con-sisted of subsamples collected from different points in theirrespective sampling area. Plants were harvested withoutdamaging the roots and rinsed in distilled water to removedust, soil and mineral particles. Samples were then sepa-rated into roots, stems and leaves and dried at 60◦C for48 h in a convection oven. Samples were milled to a finepowder using a Waring Commercial Laboratory Blender,placed in aluminum covered 500 mL Schott bottles andstored.

The top 10 cm of soil between plants at each site wascollected in duplicate, air dried for two days, sieved andstored in Schott bottles in a cupboard until analysis. Soilsamples (1 g) were digested in 5 mL of 69.5% nitric acidand 2 mL 30% hydrogen peroxide using microwave diges-tion. Once samples were cooled to room temperature thesolutions were filtered through Whatman No 1 filter paperto remove any undigested particles. The filtrate was ana-lyzed for heavy metal content using Inductively CoupledPlasma–Mass Spectroscopy (ICPMS).[21] The metals (Cr,Hg, As, Pb, Cu and Ni) found at each of the three siteswere compared to acceptable limits.[22]

Extraction

Metal extraction using the microwave digestion procedure.The heavy metals were extracted using a microwave diges-tion procedure described by Zunk and Planck.[23] This tech-nique was found superior to the standard wet digestion pro-cess and has been used when the concentrations of metalsin the sample are low.[24,25] A high performance microwavedigestion unit [Milestone Microwave Laboratory Systems]was used to digest the plant material. Samples were weighedout in the digestion vessel and HNO3 and H2O2 added.[26]

The vessels were placed into a sample holder and then intothe microwave digestor. The microwave digestor parame-ters were set as 5 steps with the samples in the vessels beingexposed to different temperatures for different periods oftime. The power ranged from 0–600 Watts and time from1–5 min. The samples were then cooled for ± 45 min, de-canted into a 25 mL volumetric flask and made up to thelevel with distilled water.[27,28] Sample vessels were removedafter 1h, cooled for ± 45 min at room temperature andbrought up to 25 mL with distilled water. This was filteredwith Whatman No. 1 filter paper to remove any remainingparticulate, and stored in a refrigerator for metal analysisusing ICPMS.

Heavy metal analysis

Inductively coupled plasma mass spectroscopy (ICPMS).The metals were analyzed using ICPMS according to theprocedure outlined by Zayed et al.[21] and Wang et al.[24] In

this system samples are decomposed to neutral elements athigh temperature argon plasma and analyzed based on theirmass to charge ratios. Four steps are involved: (i) sampleintroduction; (ii) aerosol generation; (iii) ionization by anargon plasma source; and (iv) mass discrimination. Resultsfrom ICPMS were obtained as mg/L and represented asparts per million (ppm).

Translocation factor

To evaluate the potential of this species for phytoextraction,the Translocation Factor (TF) was calculated. This ratiois an indication of the ability of the plant to translocatemetals from the roots to the aerial parts of the plant.[29] Itis represented by the ratio:

TF = Metal concentration (Stems + Leaves)Metal concentration (roots)

Metals that are accumulated by plants and largely storedin the roots of plants are indicated by TF values < 1, withvalues greater indicating translocation to the aerial part ofthe plant.[29]

Bioconcentration factor

The Bioconcentration Factor (BCF) of metals was usedto determine the quantity of heavy metal absorbed by theplant from the soil. This is an index of the ability of theplant to accumulate a particular metal with respect to itsconcentration in the soil[30] and is calculated using the for-mula:

BCF

= Metal concentration in plant tissue (whole plant/portal)Initial concentration of metal in substrate (soil)

The higher the BCF value the more suitable is the plant forphytoextraction.[9] BCF Values > 2 were regarded as highvalues.

Results

Metal levels in soil samples from a regular cultivated area,landfill site and wastewater treatment site

Metal concentrations in the soil from the three sites areshown in Figure 1. There is a variation in the concentra-tion of each of the metals at the different sites. Chromiumconcentration ranged from 48 ppm–1129.5 ppm; Hg con-centration 0.25 ppm–1.85 ppm; As concentration 3.5 ppm–9.35 ppm; Pb concentration 28 ppm–52 ppm; Cu concen-tration 18 ppm–105 ppm and Ni concentration 15 ppm–65ppm. Cr was the highest in the RCA (Fig. 1 A). Mercurywas highest in the LS (Fig. 1 B). Arsenic was highest in theWWTS (Fig. 1 C). Lead was high in both LS and WWTS(Figs. 1 C and D respectively). Copper and Ni were highin both LS and WWTS (Figs. 1 E and F, respectively).

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Metal accumulation by A. dubius in contaminated sites 571

Fig. 1. Heavy metal content in soil from the three sites (regular cultivated area-RCA, landfill site-LS and waste water treatmentsite-WWTS): A-Cr (soil); B-Hg (soil); C-As (soil); D-Pb (soil); E-Cu (soil); F-Ni (soil). Bars denote mean ± standard deviation(n = 3).

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Table 1. Guidelines for Land Application and Storage in NovaScotia with maximum contamination levels for soil compared tomaximum concentration levels found at the three sites.

Maximum concentration Maximum acceptableMetal (ppm) concentration for soil

Cr 1129.5 – RCA 64Hg 1.85 – LS 0.5As 9.35 – WWTS 12Pb 52 – WWTS 60Cu 105 – WWTS 63Ni 65 – WWTS 32

(Regular cultivated area-RCA, landfill site-LS and waste water treatmentsite-WWTS).

A comparison of the maximum levels of the variousheavy metals in the soils compared to acceptable standards(Table 1) showed that Cr, Hg, Cu and Ni were above the stip-ulated standards. The remaining heavy metals were withinacceptable ranges.

Metal concentrations in plant samples from regularcultivated area, landfill site and wastewater treatment site

Amaranthus dubius from the RCA showed Cr to be thepredominant metal species present with 59 ppm - roots,16 ppm - stems and 31 ppm - leaves. This site was alsocharacterized by high levels of Hg and Pb. In the LS thepredominant metal accumulated was Cu (39 ppm - roots,8 ppm - stems and 15 ppm - leaves). The metal accumulationin WWTS varied with Cr (45 ppm - roots, 4 ppm - stemsand 5 ppm - leaves), Hg (1 ppm - roots, 3 ppm - stems and4 ppm - leaves) , Cu (40 ppm - roots, 9 ppm - stems and 16ppm - leaves) and Ni (20 ppm - roots, 3 ppm - stems and 5ppm - leaves) (Table 2).

A comparison of the maximum levels of the variousheavy metals in the leaves (edible portion of A. dubius) com-pared to RDA standards showed that all the metals (Cr, Hg,As, Pb, Cu and Ni) were above the stipulated standards.[31]

The concentration of heavy metals in the different portalsfrom all three sites show a high level of metal accumulationin the roots except for Hg which was higher in the leavesof plants from the RCA and WWTS, and Pb which washigher in the stems and leaves from the RCA and stems inthe LS. The highest amount of Cr (107 ppm) was foundin the RCA, the highest amount of Hg (8 ppm) was foundin the LS, the highest amounts of As (22 ppm) and Pb (55ppm) were present in the LS. The highest amount of Cu(70 ppm) and Ni (27 ppm) were found in plants harvestedfrom WWTS (Table 2).

Comparison of metal concentration in the soil and plantsfrom a regular cultivated area, landfill site and wastewatertreatment site

A comparison of the predominant metals in the soil andplants is shown in Table 3. In the RCA there is a very high

Table 2. Heavy metal content of A. dubius from the three sites.

Metal Organ RCA LS WWTS

Cr Roots 58.935 ± 2.737 19.395 ± 1.973 44.680 ± 2.206Stems 16.590 ± 1.994 9.710 ± 2.008 3.790 ± 0.014Leaves 31.585 ± 2.242 5.860 ± 2.531 5.240 ± 0.509

Hg Roots 1.470 ± 0.240 4.730 ± 0.608 1.040 ± 0.339Stems 1.060 ± 0.368 1.620 ± 0.552 2.560 ± 0.834Leaves 3.065 ± 0.658 1.805 ± 0.290 4.245 ± 0.771

As Roots 0.775 ± 0.035 14.300 ± 0.990 2.785 ± 0.516Stems 0.565 ± 0.092 1.935 ± 0.940 0.245 ± 0.078Leaves 0.495 ± 0.134 5.350 ± 0.495 0.880 ± 0.113

Pb Roots 4.090 ± 0.127 16.760 ± 1.075 16.625 ± 0.460Stems 6.225 ± 1.280 20.500 ± 3.536 1.210 ± 0.721Leaves 25.990 ± 1.004 17.650 ± 0.495 8.970 ± 0.382

Cu Roots 20.950 ± 2.899 43.020 ± 2.390 39.920 ± 1.018Stems 8.930 ± 1.315 10.205 ± 0.955 8.505 ± 0.559Leaves 10.435 ± 2.029 16.455 ± 0.940 15.830 ± 1.457

Ni Roots 5.620 ± 0.877 12.090 ± 1.117 19.535 ± 1.181Stems 2.965 ± 0.191 6.935 ± 2.213 2.855 ± 0.629Leaves 3.290 ± 0.410 5.765 ± 0.940 4.755 ± 0.488

(Regular cultivated area-RCA, landfill site-LS and waste water treatmentsite-WWTS) – [mean ± standard deviation (n = 3)].

concentration of Cr in the soil and in plants harvested. Highlevels of Pb were found in soil and plants from LS. The soiland plants from WWTS samples showed high levels of tracemetals (Ni and Cu). No link in the concentration of Hg andAs in soil and plant samples was observed.

Translocation of metal from soil to aerial parts (TF values).The potential of A. dubius to translocate metals from the

Table 3. Relative metal accumulation in soil and plant samplesfrom the three sites (ppm).

RCA LS WWTS

CrSoil 1129.5 48.0 236.0Plant 107.1 34.9 53.7

HgSoil 0.25 1.9 0.4Plant 5.6 8.2 7.8

AsSoil 6.1 3.5 9.4Plant 1.8 21.6 3.9

PbSoil 28.0 47.7 52.0Plant 36.3 54.9 26.8

CuSoil 24.5 18.0 105.0Plant 40.3 69.7 64.3

NiSoil 30.0 15.0 65.0Plant 11.9 24.8 27.1

(Regular cultivated area-RCA, landfill site-LS and waste water treatmentsite-WWTS).

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Table 4. Metal accumulation characteristics of A. dubius at thethree sites to determine the indirect movement of each metalfrom the roots to the aerial parts of the plant and the trend ofmovement of each metal from the soil to plant.

RCA LS WWTS

Metal TF† BCF‡ TF† BCF‡ TF† BCF‡

Cr 0.817 0.095 0.803 0.728 0.202 0.228Hg 2.806 22.380 0.724 4.408 6.543 17.629As 1.368 0.301 0.509 6.167 0.404 0.418Pb 7.877 1.297 2.276 1.151 0.612 0.515Cu 0.924 1.646 0.619 3.871 0.609 0.612Ni 1.113 0.396 1.050 1.653 0.389 0.418

Regular cultivated area-RCA, landfill site-LS and waste water treatmentsite-WWTS.† Translocation factor (ratio of metal concentration in aerial portals tothose in roots) - values > 1 are regarded as high.‡ Bioconcentration factor (ratio of metal concentrations in plant tissueto those in soil) - values > 2 are regarded as high.

roots to the aerial parts of the plant (leaves and stems) isshown in Table 4. TF values > 1 were found for Hg, As,Pb and Ni at the RCA. TF values > 1 were also found forPb and Ni from LS, and for Hg from WWTS. All other TFvalues were < 1.

Index of plant to accumulate metal with respect to soilconcentration (BCF values). The Bioconcentration Factor(BCF) index represents the ability of A. dubius to extractheavy metals from the soil. The highest BCF value wasfound for Hg followed by As. The BCF index at the RCAwas highest for Hg followed by Cu, Pb, Ni, As and Cr.The BCF index of the metals at the LS was the highest forAs followed by Hg, Cu, Ni, Pb and Cr. At the WWTS thehighest BCF index was for Hg followed by Cu, Pb, As, Niand Cr. From the results obtained heavy metal levels in theplant tissues never exceeded the respective metal levels ineach site. The higher the BCF of A. dubius the more suitableit is for phytoextraction of metals as can be seen in Table 4.

Discussion

Plants are known to sequester, degrade and stimulate thedegradation of organic contaminants in soil.[32] The seques-tration of heavy metal by plants is an effective method of re-ducing heavy metal contamination in soil.[33] Sequestrationof toxicants by plants is an important area of phytoremedi-ation research. Plants are known to accumulate a variety oftoxicants from soil. In view of its demonstrated potential,phytoremediation has been gaining importance in the reha-bilitation of contaminated sites including municipal solidwaste dumpsites.

In this study, high levels of Cr, Hg and As concentra-tions were found in the soil and plants from the RCA.

In relation to the acceptable standards set for soils as perthe Guidelines set for Land Application and Storage inNova Scotia (Table 1) and the standards set for the Rec-ommended Dietary (Daily) Allowance (RDA), the valuesfound in this study were unacceptable. Heavy metals suchas methylated forms of Hg, As and Pb have been reportedto have no known bio-importance in biochemistry andphysiology with consumption at low concentrations beingtoxic.[22] The most common health effect from exposure toCr is contact dermatitis, skin inflammation or rash. Largerdoses of Ni, such as accidental ingestion, have been shownto have more adverse health effects ranging from stomachaches to heart failure. However, these effects occurred af-ter exposure to levels of 50,000 to 100,000 times greaterthan levels normally encountered in food or drinkingwater.

At the inception of this study the RCA site was chosenbecause it is a site where constant turning of the soil wouldhave resulted in very little Cr, As and Hg pollution. How-ever, the results of this study showed very high levels of Cr(Fig. 1A and Fig. 2A). This could have been due to the factthat this area is surrounded by a paper and pulp industry,petroleum industry and the Durban International Airport.The high Cr level in the soil from the RCA may be at-tributed to contaminants which may have leached into thearea. Heavy metal contamination may also be as a result ofatmospheric pollution due to the proximity of the RCA toDurban International Airport.[34,35] The LS is a dumpingground for many industries and hence the high levels of Cr,Pb, Cu and Ni found were as expected.

Landfills hold waste containing a wide range of organicmolecules of both natural and xenobiotic origin.[36] TheWWTS receives both domestic and industrial solid wasteand had high levels of Cr, As, Pb, Cu and Ni in the soil pos-sibly as a result of leaching. As the sludge is a concentratedmedium the presence of these metals is expected.[37]

Plants from all three sites are not safe for consumptionbecause of the high level of metal accumulated in the leaveswhich serve as the edible part of the plant (Table 2). Thevariation in uptake of the heavy metals depends on the ab-sorption capacity of each metal by the plant that may bealtered by human and environmental factors. Of the 3 sitestested, a correlation between the heavy metal concentra-tion in the soil and plants could not be made as there wasvariation in metal concentrations. Cr, Pb, Cu and Ni werepresent in high concentrations in the soil and plants of A.dubius. Ni and Cu showed a consistency in concentrations.Thus high concentrations of heavy metals in the soil andthe ability of A. dubius to tolerate these metals without anytoxicity to the plant is difficult to determine.

Conclusion

Initial survey showed that the RCA, LS and WWTS siteshave higher than legislated levels of Cr, Hg, Cu and Ni.

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There was a marked relationship between the levels of Crand Cu in the soil and plants from all three sites, but forHg, Pb, Ni and As the levels in the soil were higher relativeto their uptake, and hence the concentrations in plantswere lower. Despite this, the BCF index which indicates themovement of metals from soil to plant, indicated that allof the metals tested (Cr, Hg, As, Pb, Cu and Ni) could bebioremediated using A. dubius.

Acknowledgments

This work was supported by the postgraduate grants fromthe Durban University of Technology and the NationalResearch Foundation.

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