phytoremediation of polychlorinated biphenyl-contaminated...

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Phytoremediation of polychlorinated biphenyl-contaminated soils: the rhizosphere effect Tesema Chekol a, * , Lester R. Vough b , Rufus L. Chaney c a Battelle Memorial Institute, 1204 Technology Drive, Aberdeen, MD 21001, USA b Department of Natural Resource Sciences, University of Maryland, College Park, MD 20742, USA c USDA-ARS, Animal Manure and By-Products Laboratory, Beltsville, MD 20705, USA Received 20 October 2003; accepted 28 January 2004 Abstract The objective in the first phase of this study was to screen alfalfa, flatpea, sericea lespedeza, deertongue, reed canarygrass, switchgrass, and tall fescue for phytoremediation of polychlorinated biphenyl (PCB)-contaminated soil. During the second phase, the focus was rhizosphere characterization to optimize PCB phytoremediation. Aroclor 1248 (PCB) was added to soil at 100 mg kg 1 of soil. In the first phase, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls and the two most effective species were selected for further study. During the rhizosphere characterization study, soil irradiation did not affect PCB biodegradation, but planting significantly increased PCB biodegradation; 38% or less of the initial PCB was recovered from planted pots, compared to more than 82% from the unplanted control soils. Presence of plants significantly increased the biological activity (microbial counts and enzyme activity) of both irradiated and unirradiated soils. Greater bacterial counts and soil enzyme activity were closely related to higher levels of PCB biodegradation. The data showed that Aroclor 1248 biodegradation in soil seem to be positively influenced by the presence of plants and plant – bacteria interactions. Our results suggested that phytoremediation could be an environmentally friendly alternative for PCB-contaminated soils. D 2004 Elsevier Ltd. All rights reserved. Keywords: PCB; Soil contamination; Phytoremediation 1. Introduction Contamination of soils and waters with polychlorinated biphenyls (PCBs) has often resulted from the manufacture, handling, use, and disposal of these chemicals. Moreover, their extreme persistence in the environment and ability to bioconcentrate in the food chain makes them great environ- mental and human health risks that need remedial action (Cousins et al., 1998; Hickey, 1999). Due to the fact that engineering-based remedial technologies are expensive and disruptive, there is a growing interest in developing new remediation technologies that are environment friendly and less expensive (Cunningham et al., 1996). Phytoremedia- tion, use of plants for remediation, is one such highly appealing technology (Schnoor et al., 1995; Wenzel et al., 1999). Past plant – PCB interaction experiments were done main- ly for the purpose of looking into the food chain transfer (Webber et al., 1990; Gan and Berthouex, 1994). The possibility of PCB uptake and translocation by corn (Zea mays L.), cabbage (Brassica oleracea var. capitata L.) and carrot (Daucus carota L.) from contaminated sewage sludge was explored and carrots had the highest PCB concentration in the plant tissues followed by cabbage and corn (Webber et al., 1990). However, these concentrations, with the exception of peel layer of carrots, were very small and not related to the soil PCB contamination levels. Other reports have also confirmed that the risk of PCB translocation into the corn grain or stover to be negligible (Gan and Berthouex, 1994). Use of ectomycorrhizal fungi has shown some promise in PCB remediation, particularly the lower chlorinated con- geners (Donnelly and Flecher, 1995). In this mutually beneficial system of plant – fungus interaction, PCB degrad- ing ectomycorrhizal fungi were better adapted and this was one crucial step in overcoming the competitive disadvan- tages encountered in other introduced degraders. 0160-4120/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2004.01.008 * Corresponding author. Tel.: +1-410-306-8641; fax: +1-410-306- 8422. E-mail address: [email protected] (T. Chekol). www.elsevier.com/locate/envint Environment International 30 (2004) 799 – 804

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www.elsevier.com/locate/envint

Environment International 30 (2004) 799–804

Phytoremediation of polychlorinated biphenyl-contaminated soils:

the rhizosphere effect

Tesema Chekola,*, Lester R. Voughb, Rufus L. Chaneyc

aBattelle Memorial Institute, 1204 Technology Drive, Aberdeen, MD 21001, USAbDepartment of Natural Resource Sciences, University of Maryland, College Park, MD 20742, USA

cUSDA-ARS, Animal Manure and By-Products Laboratory, Beltsville, MD 20705, USA

Received 20 October 2003; accepted 28 January 2004

Abstract

The objective in the first phase of this study was to screen alfalfa, flatpea, sericea lespedeza, deertongue, reed canarygrass, switchgrass,

and tall fescue for phytoremediation of polychlorinated biphenyl (PCB)-contaminated soil. During the second phase, the focus was

rhizosphere characterization to optimize PCB phytoremediation. Aroclor 1248 (PCB) was added to soil at 100 mg kg� 1 of soil. In the first

phase, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls and the two

most effective species were selected for further study. During the rhizosphere characterization study, soil irradiation did not affect PCB

biodegradation, but planting significantly increased PCB biodegradation; 38% or less of the initial PCB was recovered from planted pots,

compared to more than 82% from the unplanted control soils. Presence of plants significantly increased the biological activity (microbial

counts and enzyme activity) of both irradiated and unirradiated soils. Greater bacterial counts and soil enzyme activity were closely related to

higher levels of PCB biodegradation. The data showed that Aroclor 1248 biodegradation in soil seem to be positively influenced by the

presence of plants and plant–bacteria interactions. Our results suggested that phytoremediation could be an environmentally friendly

alternative for PCB-contaminated soils.

D 2004 Elsevier Ltd. All rights reserved.

Keywords: PCB; Soil contamination; Phytoremediation

1. Introduction

Contamination of soils and waters with polychlorinated

biphenyls (PCBs) has often resulted from the manufacture,

handling, use, and disposal of these chemicals. Moreover,

their extreme persistence in the environment and ability to

bioconcentrate in the food chain makes them great environ-

mental and human health risks that need remedial action

(Cousins et al., 1998; Hickey, 1999). Due to the fact that

engineering-based remedial technologies are expensive and

disruptive, there is a growing interest in developing new

remediation technologies that are environment friendly and

less expensive (Cunningham et al., 1996). Phytoremedia-

tion, use of plants for remediation, is one such highly

appealing technology (Schnoor et al., 1995; Wenzel et al.,

1999).

0160-4120/$ - see front matter D 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.envint.2004.01.008

* Corresponding author. Tel.: +1-410-306-8641; fax: +1-410-306-

8422.

E-mail address: [email protected] (T. Chekol).

Past plant–PCB interaction experiments were done main-

ly for the purpose of looking into the food chain transfer

(Webber et al., 1990; Gan and Berthouex, 1994). The

possibility of PCB uptake and translocation by corn (Zea

mays L.), cabbage (Brassica oleracea var. capitata L.) and

carrot (Daucus carota L.) from contaminated sewage sludge

was explored and carrots had the highest PCB concentration

in the plant tissues followed by cabbage and corn (Webber et

al., 1990). However, these concentrations, with the exception

of peel layer of carrots, were very small and not related to the

soil PCB contamination levels. Other reports have also

confirmed that the risk of PCB translocation into the corn

grain or stover to be negligible (Gan and Berthouex, 1994).

Use of ectomycorrhizal fungi has shown some promise in

PCB remediation, particularly the lower chlorinated con-

geners (Donnelly and Flecher, 1995). In this mutually

beneficial system of plant–fungus interaction, PCB degrad-

ing ectomycorrhizal fungi were better adapted and this was

one crucial step in overcoming the competitive disadvan-

tages encountered in other introduced degraders.

T. Chekol et al. / Environment International 30 (2004) 799–804800

Actual PCB phytoremediation studies are very limited

and the reported cases refer mainly to plant tissue culture or

soil microcosm studies (Mackova et al., 1997; Epuri and

Sorensen, 1997). For example, hairy root cultures of Sola-

num nigrum L. were reported to cause 40% mineralization

of commercial PCB mixtures after 30 days of incubation

(Mackova et al., 1997). Enhanced mineralization of Aroclor

1260 was also reported in planted soil microcosm compared

to that in unplanted control (Epuri and Sorensen, 1997).

Available literature is very sketchy and phytoremediation

of PCB-contaminated soils is a largely untouched area of

research. This study was conducted to determine if some

forage and conservation crops could be used for phytor-

emediation of PCB-contaminated soils. The specific objec-

tives were to screen several legume and grass species for

their effectiveness in enhancing soil Aroclor 1248 biodeg-

radation and to determine rhizosphere characteristics, in-

cluding enzymes and microbial population and composition,

associated with contaminant biodegradation.

2. Materials and methods

Three legumes and four grass species were screened in the

first phase. The legumes were alfalfa (Medicago sativa L.),

flatpea (Wagner pea), (Lathyrus sylvestris L.) and sericea

lespedeza (Lespedeza cuneata Dum.-Cours.). Grass species

were deertongue (Panicum clandestinum L.), reed canary-

grass (Phalaris arundinacea L.), switchgrass (Panicum vir-

gatum L.), and tall fescue (Festuca arundinacea Schreb.).

The two sets of experiments were conducted at the

Department of Natural Resource Sciences growth chambers

facility. The growth chambers were Model BDR8 (Con-

viron, Winnipeg, Canada). The first phase of the trials

involved crop species screening, while in the second phase,

plant species that performed best in the first phase were

further evaluated for their rhizosphere characteristics.

Growth chamber temperatures were maintained at 25/16

jC, and the light regime was 16/8 h day/night cycle, with

photosynthetic photon flux rate of 400–500 Amol m� 2 s� 1

from metal halide bulbs. The relative humidity in the

chambers was set at 65F 5%.

The soil for these studies was obtained from a forested

area with no cropping and pesticide application history at

the Central Maryland Research and Education Center-

Clarksville Facility. The soil is classified as Hatboro

(course-loamy, mixed, nonacid, mesic, Typic Fluvaquent).

Soil testing results showed pH (1:1 water) 6.1; OM content

2.6% and CEC 5.72 cmol/kg.

Soil for the irradiation experiment in the second phase of

the study was irradiated at the University of Maryland

Radiation Engineering Facilities. The irradiation was done

at 25 krad/h for 100 h at 25 jC with a total of 2.5 mrad g-

irradiation from a Co60 source. The irradiated soil was used

to assess the impact of plants on contaminant biodegrada-

tion in the absence of microorganisms.

Both the analytical standard and pure chemical Aroclor

1248 were obtained from ChemService, West Chester, PA.

The targeted contaminant concentration of 100 mg/kg of soil

was used for this experiment. Right after spiking, the soil was

left under exhaust hood for 3 days with periodic mixing to

allow the solvent (hexane) to evaporate, subsequently cov-

ered and allowed to age at room temperature for 4 weeks

before transfer to pots and seeding. There were three repli-

cates of plant species treatment and unplanted control pots.

The unplanted control was used to assess contaminant

biodegradation in the absence of plant rhizosphere.

Constant soil moisture (f 28%) was maintained through

periodic refilling of reservoir of the Moisture Replacement

System (MRS) developed by Sardanelli and Kenworthy

(1997). This system consisted of plant pots with wick

inserts, a holding rack to support the pots, and an enclosed

bottom water reservoir with a disposable plastic lining.

During the second phase, the MRS was connected to a

permanent water source and refilling of the reservoirs was

regulated with a programmable One-Station DC controller

(The Drip Store, Valley Center, CA). Deionized water

flowing into the reservoirs in the irradiated chambers was

filtered using a microbial filter, 0.2 AM Super cap capsules

(VWR Scientific, Bridgeport, NJ).

The experimental design for the crop species screening

study was split-plot in a Randomized Complete Block

Design (RCBD). The chemical treatments in each box were

used as main plots, whereas the crop species were the sub-

plot treatments. Split–split-plot in a Randomized Complete

Block Design (RCBD) was employed for the second phase

study. Soil irradiation was the main plot level treatment and

chemicals and crop species were the sub and sub–sub-plot

treatments, respectively. Data was analyzed using Proc

MIXED and multiple mean comparisons were done with

Tukey–Kramer test (SAS, 2001).

At the end of each experiment, composite soil samples

were placed in QorpakR glass containers and stored in the

freezer (� 50 jC) until extraction. For bacterial and fungal

enumeration, subsamples were placed in WhirlpakR bags

and stored at 4 jC, until the microbial assays were per-

formed. In addition, plant biomass was separated into shoot

and root mass. Any plant part above the soil surface was

considered as the shoot weight and conversely, the biomass

below the soil surface was included in the root weight.

Soil–root mass was taken out of the pots, roots were

separated from the soil by shaking, and the soil was sieved

to remove any root fragments. Both shoot and root weights

are reported on a dry weight basis.

Soil PCB extractions and analysis were done using meth-

ods described by Lopez-Avila et al. (1995). Extraction was

done using a Microwave Extraction Unit (CEM, Mathews,

NC). Ten grams oven-dry equivalent weight (ODE) of soil

were quantitatively transferred into the Teflon-lined extrac-

tion vessels and 40 ml of 1:9 acetone/hexane was added to

each vessel. The extraction was performed at 110 jC for 10

min at 100% power (1000 W). The vessels were allowed to

Table 2

Aroclor 1248 levels (mg/kg) in irradiated and unirradiated soils after 4

months of plant growth

Treatment Soil PCB

(mg/kg)

Irradiated soil

Unplanted control 86c*

Reed canarygrass 31a

Switchgrass 39b

Unirradiated soil

Unplanted control 82c

Reed canarygrass 23a

Switchgrass 28a

*Means followed by the same letter are not significantly different as

determined by Tukey–Kramer multiple comparison procedure ( P < 0.05).

T. Chekol et al. / Environment International 30 (2004) 799–804 801

cool to room temperature before opening and 10 ml of the

extract was transferred into 40 ml hexane. Samples were

filtered into amber vials through 0.2 Am filter, the first 2–3ml

of filtrate was discarded and the remainder was retained for

analysis.

Gas chromatographic analysis of Aroclor 1248 was per-

formed using a Hewlett-Packard 5890 Series II gas chro-

matograph (Hewlett-Packard, Palo Alto, CA) equipped with

an electron capture detector (ECD). A J&WMegaboreR DB

608 GC column (30 m� 0.53 mm id) was used (J&W

Scientific). The column was temperature programmed at 80

jC as an initial (0.1 min), followed with two ramps at 15 jC/min to 180 jC and then at 4 jC/min to 300 jC. Injector anddetector temperatures were maintained at 270 and 330 jC,respectively. The column was operated with a helium carrier

gas at a flow rate of 1.3 ml/min. The detector makeup and

anode purge gases consisted of 5% methane and 95% argon.

The run time was set at 37 min.

Total Aroclor 1248 levels were quantified using area

counts of 10 major peaks of a 0.8 mg/kg Aroclor 1248

standard. Quality assurance–quality control checks were

conducted with each analysis. These included use of stand-

ards with known concentrations, material blank measure-

ments, repeat analysis, and fresh spike recoveries.

Microbial enumeration was accomplished using a mod-

ified Harris and Sommers (1968) plate dilution frequency

technique.

Rhizosphere dehydrogenase activity was assayed using a

modified Dick et al. (1996) method. Twenty grams (ODE)

of rhizosphere soil was thoroughly mixed with 0.2 g CaCO3

and three replicate samples of 6 g soil were placed in three

test tubes. In each tube, 1 ml of a 3% 2,3,5-triphenyltetra-

zolium chloride (TTC) and 2.5 ml distilled water were

added. Samples were then incubated while shaking at

medium speed for 24 h at 37 jC. After 24 h, 10 ml methanol

was added to each tube and samples were vortexed. The soil

suspension was filtered through a glass funnel plugged with

absorbent cotton. The filtrate was diluted with methanol to a

100 ml volume and intensity of the reddish color was

Table 1

Residual Aroclor 1248 levels (mg/kg) in soil after 4 months of plant growth

in PCB-amended soil

Treatment PCB

(mg/kg)

Legumes

Alfalfa 23a*

Flatpea 28ab

Sericea lespedeza 29ab

Grasses

Deertongue 28ab

Reed canarygrass 27a

Switchgrass 31ab

Tall fescue 33b

Control (no crop) 82c

*Means followed by the same letter are not significantly different as

determined by Tukey–Kramer multiple comparison procedure ( P < 0.05).

measured at 485 nm using a spectrophotometer. Dehydro-

genase activities in the samples were calculated by using

calibration graphs prepared from 500, 1000, 1500 and 2000

mg triphenyl formazan (TPF)/100 ml standards. Results are

presented as mg TPF/kg soil.

3. Results and discussion

3.1. Soil Aroclor 1248 levels

At the end of the 4-month species screening experiment,

all the planted treatments had significantly lower levels of

PCB compared to the unplanted control pots (Table 1).

Although no complete congener specific analysis was con-

ducted for this study, analysis on the major component of

Aroclor 1248, tetrachlorbiphenyl, showed that this congener

accounted for about 38% of the total the PCB in soil. This

shows that the composition of the final Aroclor 1248 was

very close to the initial (40% tetrachlorbiphnyl). It should be

noted, however, quantitation of individual congeners is

more accurate than estimating Aroclors and there is a need

for congener-specific measurement in future PCB phytor-

emediation studies.

This study is in complete agreement with the findings

of Epuri and Sorensen (1997) regarding the use of tall

fescue in PCB phytoremediation. However, due to the

Table 3

LS mean root and shoot weights (g) in control and PCB-amended soil

Species Root weight (g) Shoot weight (g)

Control 100 mg/kg Control 100 mg/kg

Alfalfa 25a* 8b 24a 5b

Flatpea 53a 33b 45a 44a

Sericea lespedeza 37a 19b 54a 50a

Deertongue 140a 128a 37a 28a

Reed canarygrass 145a 140a 64a 53a

Switchgrass 90a 89a 65a 66a

Tall fescue 139a 127a 68a 63a

*Means within variable and rows followed by the same letter are not

significantly different as determined by Tukey–Kramer test ( P< 0.05).

Table 6

Bacterial and fungal counts (MPN/g) in PCB-amended soils

Treatment Bacterial counts (� 107) Fungal counts (� 104)

Initial End Initial End

Irradiated soil

Unplanted control 0f* 3.9d 0e 0.9d

Reed canarygrass 0f 4.6c 0e 2.5c

Switchgrass 0f 4.5c 0e 2.9b

Unirradiated soil

Unplanted control 2.3e 4.9c 1.5d 3.1b

Reed canarygrass 2.1e 6.2a 1.2d 4.4a

Switchgrass 2.5e 5.6b 1.6d 4.5a

*Means within variable (bacteria and fungi) followed by the same letter

are not significantly different as determined by Tukey–Kramer multiple

comparison procedure ( P < 0.05).

Table 4

Root/shoot ratios of crop species in the control and PCB-amended soil

Species Root/shoot ratio

Control 100 mg/kg

Alfalfa 1.04 1.68

Flatpea 1.18 0.75

Sericea lespedeza 0.68 0.37

Deertongue 3.73 4.57

Reed canarygrass 2.27 2.64

Switchgrass 1.38 1.34

Tall fescue 2.04 2.03

T. Chekol et al. / Environment International 30 (2004) 799–804802

more comprehensive nature of this study, tall fescue,

although better than the unplanted controls, did not per-

form as well compared to other species. As a result, this

species was not considered for further detailed rhizosphere

evaluation. Based on the results from the screening study,

reed canarygrass and switchgrass were further evaluated

for their phytoremediation abilities under irradiated and

unirradiated soil conditions.

Results from the rhizosphere effects study showed that soil

irradiation did not significantly affect PCB biodegradations

(Table 2). However, planting significantly improved the

biodegradation of PCB in both irradiated and unirradiated

soils. More than 82% of the initial PCB was recovered from

the irradiated and unirradiated unplanted control soils com-

pared to less than 39% in the planted treatments. After 4

months of plant growth in the irradiated soil, planting with

reed canarygrass and switchgrass resulted in a 70% and 61%,

respectively, biodegradation of the initial PCB levels. In the

unirradiated soils, only 23% and 28%, respectively, of the

initial PCB levels were recovered from reed canarygrass and

switchgrass planted pots compared to 82% in the unplanted

control pots.

These results clearly showed that planted treatments had

significantly lower levels of PCB compared to unplanted

controls and reed canarygrass and switchgrass were the

most effective species for phytoremediation of PCB-con-

taminated soils. Moreover, statistically significant differ-

ences observed in soil Aroclor 1248 levels between

Table 5

Root and shoot weights (g) of reed canarygrass and switchgrass grown in

control and PCB-amended soils

Treatment Root weight (g) Shoot weight (g)

Control PCB Control PCB

Reed canarygrass

(unirradiated soil)

157a* 136a 61a 50a

Reed canarygrass

(irradiated soil)

156a 133b 57a 48b

Switchgrass

(unirradiated soil)

87a 86a 67a 62a

Switchgrass

(irradiated soil)

86a 66b 60a 57b

*Means within variable and rows followed by the same letter are not

significantly different as determined by Tukey–Kramer test ( P< 0.05).

planted and unplanted soils and lack thereof between the

planted irradiated and unirradiated soils suggested that

planting was the most important factor for a successful

phytoremediation of PCB in soil.

3.2. Plant species biomass

Root weights of all legume species and root and shoot

weights of alfalfa were significantly reduced because of

soil PCB contamination (Table 3). PCB spiking of the soil

did not significantly affect the biomasses of all grass

species and shoot weights of flatpea and sericea lespede-

za. This effect could be a result of greater sensitivity to

PCB of the root system and/or beneficial microorganisms

in the legume rhizospheres compared to those in the grass

species.

Root/shoot ratios of the plant species under investigation

changed as a result of PCB amendment of the soil (Table 4).

There was a slight decrease in the root/shoot ratios of most

of the plant species used in this experiment. The increase in

the root/shoot ratios of alfalfa was attributable to a more

pronounced negative effect of PCB on the shoot growth of

this crop.

Soil irradiation significantly reduced the root weights of

reed canarygrass and switchgrass in PCB spiked soil, but

did not affect shoot weights (Table 5). The decrease in the

root weights observed in the irradiated soil could be due to a

Table 7

Correlations (R2) of microbial counts and plant biomass to Aroclor 1248

biodegradation

Variables Bacterial

counts

Fungal

counts

Shoot

weight

Root

weight

Bacterial counts

Fungal counts 0.68*

Shoot weight 0.63* 0.34

Root weight 0.72* 0.45 0.87**

Soil PCB levels � 0.67* � 0.40 � 0.94*** � 0.95***

*Significance at P < 0.05.

**Significance at P < 0.01.

***Significance at P < 0.0001.

Table 8

Soil dehydrogenase activity and Aroclor 1248 levels

Treatment Soil dehydrogenase

activity (mg/kg/24 h)

Soil PCB

(mg/kg)

Irradiated soil

Unamended no crop 33f* 0

Unamended reed canary 386c 0

Unamended switchgrass 256d 0

Amended no crop 23f 86c

Amended reed canary 368c 21a

Amended switchgrass 299cd 39b

Unirradiated soil

Unamended no crop 218d 0

Unamended reed canary 604a 0

Unamended switchgrass 471b 0

Amended no crop 130e 82c

Amended reed canary 601a 23a

Amended switchgrass 450b 28a

*Means within column followed by the same letter are not significantly

different as determined by Tukey–Kramer multiple comparison procedure

( P< 0.05).

T. Chekol et al. / Environment International 30 (2004) 799–804 803

combined negative effect of soil irradiation and PCB on the

rhizosphere of reed canarygrass and switchgrass. Soil spik-

ing with PCB alone did not significantly affect the root and

shoot weights of these grasses.

3.3. Microbial assays

Microbial data at the end of experiment (Table 6)

showed that bacterial and fungal counts in the irradiated

soil were slightly increased compared to the initial counts.

The increase in both counts could be a result of prolif-

eration in the previously nonculturable organisms stimu-

lated by the favorable environment in the growth

chambers and/or some level of contamination during the

growing period.

Planting significantly increased the microbial numbers in

both the irradiated and unirradiated soil.

Plant shoots and root weights were significantly

correlated to Aroclor 1248 biodegradations in the soil

(Table 7). Bacterial counts were also significantly corre-

lated to the PCB biodegradation, plant biomass and fungal

counts.

These observations indicated that plant biomass was the

most important factor for Aroclor 1248 biodegradations in

the soil, hence selection of plant species and cultivars for

PCB phytoremediation. In addition, the positive correlation

observed between plant biomass and the number of bac-

teria in soil could be indicative of the proliferation of

bacteria stimulated by greater supply of nutrients from a

vigorous plant. These correlations could be an indication

for the biologically mediated biodegradations of PCB in

soil.

3.4. Rhizosphere dehydrogenase activity

Results presented in Table 8 showed that PCB amend-

ment and irradiation caused a reduction in the dehydroge-

nase activity of soils. It should be noted that dehydrogenase

activity of the soil was significantly reduced due to

irradiation. However, with the exception of unplanted

control treatment in the unirradiated soil, the reductions

associated with soil PCB amendments were not statistically

significant.

In this study, the presence of plants significantly in-

creased the dehydrogenase activity of both irradiated and

unirradiated soils. Moreover, higher soil dehydrogenase

activities significantly correlated with higher levels of

PCB biodegradation in both the irradiated and unirradiated

soils. Based on these observations, it could be concluded

that planting increased the biological activity of soils

measured as dehydrogenase activity. The increased biolog-

ical activity appeared to be responsible for the significantly

higher levels of PCB biodegradation in the planted pots

compared to unplanted controls.

Results from these experiments showed that use of forage

crops for phytoremediation of PCB-contaminated soils was

an effective and environmentally friendly means of remedi-

ation. To the best knowledge of the authors, this study was

the first of its kind to show that plants in general, and forage

crops in particular, are very effective for phytoremediation

of PCB-contaminated soils.

References

Cousins IT, Mclachlan MS, Jones KC. Lack of an aging effect on the soil –

air partitioning of polychlorinated biphenyls. Environ Sci Technol

1998;32:2734–40.

Cunningham SD, Anderson TA, Schwab P, Hsu FC. Phytoremediation

of soils contaminated with organic pollutants. Adv Agron 1996;56:

55–114.

Dick RP, Breakwell DP, Turco RF. Soil enzyme activities and biodiver-

sity measurements as integrative microbiological indicators. In: Doran

JW, Jones AJ, editors. Methods of soil analysis: Part 2. Microbio-

logical and biochemical properties. Soil Science Society of America.

Madison, WI: Special Publication #49, 1996. p. 247–72.

Donnelly PK, Flecher JS. PCB metabolism by ectomycorrhizal fungi. Bull

Environ Toxicol 1995;54:507–13.

Epuri V, Sorensen DL. Benzo(a)pyrene and hexachlorobiphenyl con-

taminated soil: phytoremediation potential. In: Kruger EL, Ander-

son TA, Coats JR, editors. Phytoremediation of soil and water

contaminants. Washington, DC: American Chemical Society; 1997.

p. 200–22.

Gan R, Berthouex P. Disappearance and crop uptake of PCBs from sludge-

amended farming. Water Environ Res 1994;66:54–69.

Harris RF, Sommers LE. Plate-dilution frequency techniques for assay of

microbial ecology. Appl Microbiol 1968;16:333–4.

Hickey WJ. Transformation and fate of polychlorinated biphenyls in soil

and sediment. In: Adriano DC, et al., editors. Bioremediation of con-

taminated soils. Agron Monogr, vol. 37. Madison. WI: ASA, CSSA and

SSSA; 1999. p. 213–37.

Lopez-Avila V, Benedicto J, Charan C, Young R. Determination of PCBs in

soils/sediments by microwave-assisted extraction and GC/ECD or

ELISA. J Environ Sci Technol 1995;29:2709–12.

Mackova M, Macek T, Kucerova T, Burkhard P, Pazlarova J, Demnerova

K. Degradation of polychlorinated biphenyls by hair root culture of

Solanum nigrum. Biotechnol Lett 1997;19:787–90.

T. Chekol et al. / Environment International 30 (2004) 799–804804

Sardanelli S, Kenworthy WJ. Soil moisture control and direct seeding

for bioassay of Heterodera glycines on soybean. J Nematol 1997;29:

625–34 [Suppl.].

SAS. Systems Release, vol. 8. Cary, NC: SAS Institute; 2001.

Schnoor JL, Licht LA, McCutcheon SC, Wolfe NL, Carriera LH. Phytor-

emediation of organic and nutrient contaminants. Environ Sci Technol

1995;29:318–23.

Webber MD, Pietz RI, Granato TC, Svoboda ML. Plant uptake of PCBs

and other organic contaminants from sludge-treated coal refuse. J En-

viron Qual 1990;23:1019–26.

Wenzel WW, Adriano DC, Salt D, Smith R. Phytoremediation: a plant–

microbe-based remediation system. In: Adriano DC, et al., editors. Bio-

remediation of Contaminated Soils. Agron Monogr, vol. 37. Madison

WI: ASA, CSSA and SSSA; 1999. p. 457–508.