fibre crops as alternative land use for radioactively contaminated arable land

Journal of Environmental Radioactivity 81 (2005) 131e141

www.elsevier.com/locate/jenvrad

Fibre crops as alternative land use forradioactively contaminated arable land

H. Vandenhove*, M. Van Hees

Belgian Nuclear Research Centre, SCK-CEN, Department of Radiation

Protection Research, Radioecology Section, Boeretang 200, 2400 Mol, Belgium

Accepted 5 January 2005

Abstract

The transfer of radiocaesium, one of the most important and widespread contaminants

following a nuclear accident, to the fibre crops hemp (Cannabis sativa L.) and flax (Linumusitatissimum L.) as well as the distribution of radiocaesium during crop conversion werestudied for sandy soil under greenhouse and lysimeters conditions.

Soil parameters did not unequivoqually explain the transfer factors (TF) observed.

TFs to flax stems ranged from 1.34 to 2.80! 10�3 m2 kg�1. TFs to seeds are about a factorof 4 lower. During the retting process for separating the fibres from the straw, more than 95%of the activity was removed with the retting water.

For hemp, the TF to the stem was about 0.6! 10�3 m2 kg�1. For hemp, straw and fibreswere mechanically separated and TF to straw was about 0.5! 10�3 m2 kg�1 and to fibres1.0! 10�3 m2 kg�1.

Generally, the TFs to the useable plant parts both for hemp and flax, are low enough toallow for the production of clean end-products (fibre, seed oil, biofuel) even on heavilycontaminated land. Given the considerable decontamination during retting, contaminationlevels in flax fibres would only exceed the exemption limits for fibre use after production in

extreme contamination scenarios (O12 300 kBqm�2). Since hemp fibres are mechanicallyseparated, use of hemp fibres is more restricted (contamination !740 kBqm�2). Use of stems

* Corresponding author. Tel.: C32 14 332114; fax: C32 14 321056.

E-mail address: [email protected] (H. Vandenhove).

0265-931X/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jenvrad.2005.01.002

mailto:[email protected]

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132 H. Vandenhove, M. Van Hees / J. Environ. Radioactivity 81 (2005) 131e141

as biofuel is restricted to areas with contamination levels of !250 and 1050 kBqm�2 for flaxand hemp, respectively. Use of seeds for edible oil production and flour is possible almost

without restriction for flax but due to the high TFs to seed observed for hemp (up to3! 10�3 m2 kg�1) consumption of hemp seed products should be considered with care.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Fibre crops; Hemp; Flax; Radiocaesium; Soil-to-plant transfer; Alternative land use; Chernobyl

deposition

1. Introduction

Following the Chernobyl accident, large areas in the CIS were severelycontaminated with radioactive fall-out and application of corrective actions remainsan issue. When agricultural production is hampered in such territories because ofhigh activity levels in food products, the development of more integrated andecologically-based approaches is required. Many studies have hence been conductedto test the effect of different physical and chemical countermeasures (Shaw et al.,1992; Alexakhin, 1993; Konoplev et al., 1993; Lembrechts, 1993; Nisbet, 1993; Vovket al., 1993; Melin et al., 1996; Vandenhove et al., 1996; Valcke et al., 1997; Smolderset al., 1997; Waegeneers et al., 2001). In contrast, information on long-term effect ofcountermeasures and especially the change to non-food crops is still limited. GOPA(1996a,b) assessed the suitability of biofuel production from rapeseed in Belarusand Ukraine including consideration of cultivation on contaminated lands. Thefeasibility of the use of willow short rotation coppice for energy production oncontaminated arable land has been evaluated by Vandenhove et al. (1999, 2001)(considering radioecological, radiation protection, technical and economic criteria)and Gommers (2001) (radioecological assessment).

We have investigated the feasibility of the production of fibre crops oncontaminated areas. Two fibre crops, hemp (Cannabis sativa L.) and flax (Linumusitatissimum L.) were studied. For both crops extensive knowledge is available onthe use of the fibre for textiles and many other high value applications. The varioususes of flax fibres include fabric, insulating material, composite material and paperenforcers. Flax seeds are used in the food industry and the oil extracted from seedshas multiple uses (food industry, additives in paints, basis of linoleum) (FlaxCouncil, 2003). The disadvantage of this crop is that it requires fertile, fine-texturedsoils and that it is a demanding crop. Hemp fibres are used for clothes, insulatingmaterial, building material, litter. Oil from hemp seeds is used in lacquers, colours,cosmetics. Seeds also serve as a source of protein for man and animals. Seed extractsare used in the pharmaceutical industry. Hemp is also advocated as a bioenergy crop(Hempflax, 2003). Biewinga and van der Bijl (1996) carried out a study on energycrops in Europe and they concluded that this crop scores among the highest on bothecological and economic criteria. Industrial hemp has also been tested in the

133H. Vandenhove, M. Van Hees / J. Environ. Radioactivity 81 (2005) 131e141

remediation or conditioning of soils contaminated with heavy metals or polycyclicaromatic hydrocarbons (Campbell et al., 2002; Linger et al., 2002; Loser et al., 2002).

When advocating an alternative crop not only must the fate of radionuclides in thecrop cultivation system be considered, but also the radionuclide behaviour duringprocessing and hence the expected radionuclide concentration in end-products.

However, information on the radionuclide transfer to fibre crops is limited. Forexample, GOPA (1996a,b) reports a radiocaesium transfer factor (TF) for flax of0.18 and 0.23! 10�3 m2 kg�1 for seeds and straw, respectively, but no information isavailable on the radiocaesium transfer to fibres. We found no information onradionuclide transfer to hemp.

The transfer of radiocaesium, one of the most important and widespreadcontaminants following a nuclear accident, to the fibre crops hemp and flax and thedistribution of the activity during crop conversion is investigated in present study.Crops were grown in lysimeters or in pot experiments in a greenhouse.

2. Materials and methods

Radiocaesium TF to hemp (C. sativa L.) and flax (L. usitatissimum L. var.Natasha) was studied under greenhouse and lysimeters conditions on a sandy soil(Orthic podzol ). A sandy soil was selected for this experiment since in the entirecontaminated area of Ukraine, Belarus, and Russia, the proportion of dry sandysoils under agricultural land use amounts to 28.7% and for Belarus is as high as 60%(Van der Perk et al., 1999, 2004).

For the potted soil experiment, 10-L buckets were filled with 14 kg sandysoil (Orthic podzol ), brought to field capacity (20%). Soil was contaminated with134Cs 1 month prior to start-up. Final soil contamination was 309G 23 kBq kg�1

(75.6G 1.7 MBqm�2) for flax and 326G 27 kBq kg�1 (79.7G 2.9 MBqm�2)for hemp.

For the lysimeter plots the contamination was distributed over 25 cm depth.Homogeneous contamination was achieved by removing the 25 cm layer of soil whichwas wet with distilled water containing 134Cs in a container. Soil was thoroughlymixed and transferred back into the lysimeter. For flax, contamination was done 1month prior to sowing and the contamination density was 29.89G 1.86 kBq kg�1

(9.0G 0.6 MBqm�2). For hemp, contamination was 2 years old at the start ofexperiment and the contamination density was 13.30G 0.18 kBq kg�1 (4.0G0.05 MBqm�2).

Initial soil nutrient statuswas considered adequate for thepotted soil experiment andfor the cultivation of flax on the lysimeters. For hemp, the lysimeter soil was fertilised14 days after sowing (27.2 g KNO3, 23.5 g NH4NO3 and 15.3 g KH2PO4 per m

2).At the start of the experiment, soil was characterised. Exchangeable cations and

134Cs were measured in an 1 M NH4Ac extract, cations by atomic absorptionspectrometry (AAS) and 134Cs by gamma-counting. The CEC was determined by thesilver thiourea method (Chhabra et al., 1975) at the pH of the soil. At the end of theexperiment, soil was analysed for exchangeable cations, cations in soil solution and


exchangeable Cs. The composition of the soil solution was measured at field capacity(10 kPa). To collect the soil solution, a disposable 60 mL syringe without plungerwas filled with nylon fibre and soil sample. The syringe was transferred to acentrifuge tube and centrifuged for 30 min at ca. 50! g. The soil solution wasfiltered through a 0.45-mm membrane filter (Millipore), and the concentrationsof KC, Ca2C and Mg2C were measured. The RIP value of the soil was measured bythe simplified procedure of Wauters et al. (1996). Total and exchangeable Cs wasmeasured with a Minaxi, autogamma 5000 series-gamma counter, Packard,3! 3¼$, counting efficiency w30%. All soil analyses were done in triplicate. Allcontamination data were calculated back to the time of sowing as reference date. Thesoil’s characteristics are listed in Table 1.

All 8 pots (2 plants! 4 replicates) were placed in a greenhouse. Sowing densitywas 14 g and 4 g seeds per m2 for flax and hemp, respectively. Day (length 12 h) andnight (12 h) temperatures were 21e25 �C and 13e15 �C, respectively. Light intensityat canopy height was 600 (SE 30 mmol) of photons m�2 s�1. Soil moisture wasadjusted with distilled water to constant weight each second day. In the potted soilexperiment, flax was harvested after 146 days and hemp after 186 days. For thelysimeter experiment, flax was harvested after 134 days and hemp after 138 days. Theflax stem was air-dried prior to retting. The leaves, seeds and chaff were dried at60 �C. Hemp stem, leaves and seeds were dried at 60 �C. Flax was ret (removingstraw and liberating fibres with water through rotting) according to Belgian practice(Valcke, 2002). Flax was put in cold (13 �C) water for 12 h. The cold water wasdecanted and the plant material was then transferred to water of 24 �C. Every 12 h,the temperature was increased with 2 �C (final temperature 34 �C) and with everytemperature increase, 10% of the water was removed and clean water at thecorresponding temperature was added. Biomass loss and concentration of Cs in thedifferent washing waters was measured to assess the amount of activity removed with

Table 1

Some soil characteristics of the soil used in the greenhouse and lysimeter experiment at the start and at the

end of the experiment

Parameter Greenhouse Lysimeter

Hemp Flax Hemp Flax

Exchangeable cations

at start (meq kg�1)

K 1.98G 0.08 0.77G 0.04 3.62G 0.28

Ca 24.8G 1.1 63.1G 4.0 50.6G 3.6

Mg 3.55G 0.18 5.38G 0.21 10.50G 0.93

Exchangeable cations

at end (meq kg�1)

K 0.74G 0.02 0.43G 0.05 1.13G 0.22 1.76G 0.15

Ca 20.54G 0.98 21.59G 0.48 57.9G 8.3 44.1G 8.9

Mg 2.73G 0.09 2.85G 0.07 4.98G 0.27 8.97G 0.74

Soil solution

cations at end (meq L�1)

K 0.41G 0.03 0.15G 0.03 0.92G 0.02 0.86G 0.03

Ca 6.71G 0.88 6.56G 0.56 7.66G 0.20 3.30G 0.08

Mg 2.62G 0.38 2.04G 0.17 1.58G 0.05 1.67G 0.05

CEC at start (meq kg�1) 56.6G 2.1 77.6G 4.7 76.2G 8.6

RIP at start (meq kg�1) 485G 9 154.5G 6.8 166.8G 3.4

Exchangeable Cs at start (%) 51G 4 26G 2 46G 3

Exchangeable Cs at end (%) 28G 3 20G 3 15G 3 30G 1


the retting water from both fibres and straw. For hemp the straw was mechanicallyremoved to obtain the fibres as done in practice (Hempflax, 2003).

Cs and K-activity was analysed in different plant compartments: straw, fibres,seeds and chaff. K in plant material was measured with AAS.

Statistical analysis was carried out using Statistica.

3. Results and discussion

3.1. Soil characteristics

Some characteristics of the soils used in the experiment are presented in Table 1.The soil radiocaesium interception potential (RIP), a measure of the soil Cs-fixationcapacity, was a factor of 3 higher for the potted soil than for the lysimeter soil. Theavailable Cs-content was about 50% of total Cs for the recently contaminated soiland 26% for the soil contaminated 2 years prior to the start of the experiment. Theexchangeable Cs-content decreased two-fold in the course of the experiment.

Exchangeable K-contents varied by a factor of 2 between soils. Changes in soilcharacteristics during the course of the experiment were most pronounced forexchangeable K-content. In the greenhouse experiment, there was a two-fold andfour-fold decrease in exchangeable K-content for hemp and flax, respectively. In thelysimeter experiment, decrease was with a two-fold for flax and there was a 50%increase for hemp, partially due to the fertilization. Soil solution K concentration atthe end of the experiment was significantly lower in the greenhouse soil than in thelysimeter soil and always lower for flax than for hemp.

No such systematic decreases in the course of the experiment were recorded forthe bivalent cations.

Table 2

Yield figures (ton ha�1) for flax and hemp for different plant parts

Plant part Flax Hemp

Greenhouse Lysimeter Greenhouse Lysimeter

Stem 2.72G 0.41 0.83G 0.32 5.86G 0.37 11.1G 2.8

Stem after

rettinga1.80G 0.39 0.64G 0.29

Straw 1.30G 0.23b 0.21G 0.10b 3.69G 0.41 7.4G 2.0

Fibre 0.49G 0.12b 0.43G 0.26b 1.89G 0.16 3.2G 0.8

Seeds 0.004c 0.062G 0.029 0.63G 0.09 2.6G 0.5

Chaff 0.004c 0.082G 0.023

Leaves 0.93G 0.03 1.76G 0.22 4.9G 1.8

a During flax retting part of the biomass (w25%) was removed with the retting water.b Amount of straw and fibre from the retted biomass.c No standard deviation was calculated since material from the 4 replicates was combined due to very

low yield.


3.2. Biomass production

The biomass production figures are presented in Table 2. The yield of hemp wasalways lower in the greenhouse experiment than for the lysimeter experiment, andthis, for all plant compartments. The better nutrient status of the lysimeter soil maypartially account for this, notwithstanding that growth conditions in greenhousemay be presumed to be more favourable. The fibre production figures obtainedwas high compared with FAO (2003) figures for France and Ukraine (1.6 and0.5 ton ha�1, respectively). The same is true for the hemp seed production figures (0.7and 0.1 ton ha�1 for France and Ukraine, respectively, FAO, 2003). Biewinga andvan der Bijl (1996) mention hemp total yields ranging from 3.7 to 11 ton ha�1, inagreement with our stem yield figures.

Flax yield was always larger in greenhouse than on the lysimeters. Fibre yieldfigures were at the low end of the FAO (2003) recorded yield figures (0.3e1.2 ton ha�1). Flax generally requires fine-textured soils to attain high yields.

3.3. Transfer to plant compartments

Transfer factors to the different plant compartments are given in Table 3. Forflax, the TFs are significantly higher in the greenhouse experiment than for thelysimeters for each plant compartment. This observation contrasts with the fact thatthe RIP of the lysimeter soil is three times lower than that of the greenhouse soil.However, the soil K-status of the greenhouse soil was inferior, and at the end of theexperiment soil solution potassium concentrations was as low as 0.15 mM for thegreenhouse soil whereas in the lysimeter soil, soil solution potassium concentrationwas 0.9 mM. It has been previously shown in solution culture that Cs uptakeincreases exponentially below a K-solution concentration of 0.25e0.5 mM, (Shawet al., 1992; Smolders et al., 1996; Waegeneers, 2002). In soil, root uptake leads todepletion of K near the root. At the rootesoil interface solution concentration isreported to be 0.1e0.8 times that in bulk soil concentration (Waegeneers, 2002). Flaxgrown on sandy soil under greenhouse conditions would probably have beenexposed to K concentrations at the root surface low enough to enhance Cs-transfer.

Table 3

Transfer factors to flax and hemp for different plant compartments

Plant part Flax TF (!10�3 m2 kg�1) Hemp TF (!10�3 m2 kg�1)

Greenhouse Lysimeter Greenhouse Lysimeter

Stem 2.80G 0.69 1.34G 1.18 0.55G 0.07 0.70G 0.15

Stem straw 0.042G 0.016a 0.016G 0.013a 0.43G 0.08 0.57G 0.12

Stem fibre 0.060G 0.012a 0.023G 0.009a 0.86G 0.16 1.10G 0.22

Seeds 0.53 0.286G 0.070 1.77G 0.41 3.03G 0.68

Leaves 2.72G 0.50 NDb 1.90G 0.35 2.67G 0.60

a TF calculated on the retted material. Flax stems were too fragile and fine to remove fibres

mechanically.b Not determined since it was difficult to collect leaves at the field.


Transfer factors to the flax seeds are a factor 4 lower than to the total stem. Thisdifference between straw (stem) and seeds is observed for most crops (GOPA,1996a). Transfer factors found for seeds were rather large compared to earlierrecorded transfer factors (GOPA, 1996a: 0.11e0.29! 10�3 m2 kg�1; Vandenhoveet al., 2002: 0.04e0.07! 10�3 m2 kg�1). Transfer factors to leaves and stems arecomparable. Higher Cs-TF to various plant compartments are generally associatedwith larger K-levels in these compartments (Fig. 1). However, since most of the Csand K were leached from the straw and fibres during the retting process, caution isrequired in the comparison of concentrations of these elements between compart-ments.

The effective transfer factors to the flax fibres and straw obtained after rettingwere a factor of 40e60 lower than to the stem. This was due to the retting process:almost all of the radioactivity (w99%) was removed with the retting water, theactivity in the cold water accounting for 90% of the removal. This resulted in analmost radioactivity free end-product. The final activity in the straw was 30e50%lower than for the fibres.

For hemp, the TFs to the different plant compartments were always significantlylower for hemp cultivated on greenhouse soil than on lysimeter soil. This is despitethe aging of Cs at the lysimeter site and the more limiting K-status towards the endof the experiment for the greenhouse soil. The only parameter that might partiallyexplain this observation is the soil RIP value which was lower for the sandy lysimetersoil.

The TFs were highest for the seeds and leaves, followed by fibres and straw. Thesame trend is found for the K-levels in the various compartments (Fig. 1). Theexcellent linear regression between Cs and K contents in the different hemp

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

fibr

e

leav

e

stra

w

stra

w

fibr

e

leav

e

leav

e

seed

stra

w

fibr

e

seed

stra

w

fibr

e

seed

F F F H H H H F F F H H H H

Greenhouse

3.6 ±0.26

0.016 0.006 0.007 0.006

Lysimeter

Fig. 1. K contents in the different plant parts of flax and hemp. Values for K-content in flax fibres and

straw (bast) are obtained after retting.


compartments of hemp grown in greenhouse and lysimeters (Fig. 2) clearly illustratessimilar distribution patterns for K and Cs.

3.4. Consequences of a radioactive contamination

Hemp and flax products may have different end-uses. Table 4 gives informationon the restriction to soil contamination levels taking into account control limits for137Cs in Belarus and Ukraine and the TFs observed in present experiment.

K (plant)= 0.94 Cs (Plant) + 0.20R2 = 0.98

K(plant) = 9.53 Cs (Plant) - 0.08R2 = 0.75

0

0.2

0.4

0.6

0.8

1

1.2

0.010.0080.0060.0040.0020 0.0140.012

Cs in plant parts of hemp (Bq kg-1) Cs in plant parts of hemp (Bq kg-1)

Lysimeter

0.00.20.40.60.81.01.21.41.61.8

0.100.080.060.040.020.0 0.160.140.12

Greenhouse

Fig. 2. Relation between Cs and K-contents for different plant compartments of hemp.

Table 4

Maximal 137Cs soil contamination levels in function of end use of product and observed transfer factors

Flax TF

(!10�3 m2 kg�1)

Use Decontamination

factor

Limit

Bq kg�1Max soil cont.

kBqm�2

Stem fibre 0.06 Fibre O100 740a 12 300

Stem fibre 0.06 Building material:

boards, chips,

fibre board

O100 1850a 31 000

Stem 3 Biofuel 1 740a 247

Seeds 0.5 Oil 10e50 185 3700c

Seeds 0.5 Flour 1.3e2b 370 962

Hemp

(!10�3 m2 kg�1)

Stem fibre 1 Fibre 1 740a 740

Stem fibre 1 Building material:

boards, chips,

fibre board

1 1850a 1850

Stem 0.7 Biofuel 1 740a 1057

Stem 0.7 Litter 1 1850a 2643

Seeds 3 Oil 10e50 185 610

Seeds 3 Flour 1.3e2b 370 160

a Szekely et al. 1994.b IAEA, 1994; all other values were from GOPA 1996a.c Maximal 137Cs soil contamination levels calculated using the lower value for the decontamination

factor listed (values indicated in italic).


Conclusions made are thus for sandy soil and are the most restricted since finertextured soils have generally lower transfer factors.

When evaluating the data presented in Table 4, it should be born in mind thatcontamination levels at the time of the accident in excess of 1480 kBqm�2

(40 Ci km�2) occurred over a surface of 3100 km2 for the whole Former SovietUnion (GOPA, 1996a), representing about 1% of the area contaminated above37 kBqm�2 (1 Ci km�2).

Given the large decontamination during the retting process, the contaminationlevels in the flax fibres will in almost all circumstances be below the limit for use.Care should be taken for the treatment of the waste water (retting water) whichcontains about 99% of the activity.

Given the high TF to the stem (3! 10�3 m2 kg�1), use of flax straw (total stem) asbiofuel is restricted to areas with contamination below 250 kBqm�2. Use for seedsfor the extraction of oil results in an almost contamination free end-product. Use ofstraw as biofuel after retting is possible in almost all contamination scenarios. Use ofseed flour would be restricted to sandy areas with a contamination level below1000 kBqm�2.

Use of hemp fibre should be restricted to areas with soil contami-nation! 740 kBqm�2. Hemp in Europe is also advocated as one of the mostefficient and ecologically sound bioenergy crops (Biewinga and van der Bijl, 1996).With the TFs observed, burning of the hemp should be limited to areas witha contamination! 1050 kBqm�2. Use of hemp fibre in building material should belimited to hemp from areas with 137Cs contamination below 1850 kBqm�2. Giventhe high TFs observed for hemp seed, vegetable oil extraction from hemp seedshould be limited to seeds from areas with less than 600 kBqm�2. And flourproduction from hemp seeds should be restricted to seeds from areas with less than160 kBqm�2, and will hence almost always be banned.

4. Conclusions

There was no clear relation between the TFs observed and the soil characteristics.As is generally the case for Cs, improved K-fertilization and soil amendments whichincrease the soil RIP tend to decrease the TF. The TFs exemplified here can beregarded as almost worst-case scenario TFs: obtained for sandy soil, with low RIP,and a moderate to low K-status.

Generally, the TFs to the useable plant parts both for hemp and flax, are low enoughto allow production of a clean end-product (fibre, seed oil, biofuel) even on heavilycontaminated land. Given the large decontamination level during retting, contami-nation levels in flax fibres will only exceed the exemption limits for fibre use underconditions from extreme contamination scenarios. Since hemp fibres are mechanicallyseparated, use of hemp fibres is more restricted (contamination! 740 kBqm�2). Useof stems as biofuel would be restricted to areas with contamination levels of!250 and1050 kBqm�2 for flax and hemp, respectively. Use of seeds for edible oil productionand flour would be possible almost without restriction for flax but due to the high TFs


to seed observed for hemp (up to 3! 10�3 m2 kg�1) consumption of hemp seedproducts should be considered with care.

Flax is, however, a more demanding crop than hemp in terms of soil properties(higher fertilization, finer textured soils required) and in terms of productionpractice. Hence the choice of most appropriate alternative land use considering thetwo crops considered here would depend on soil type, climatic conditions andrequirements for final product use.

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