Fibre crops as alternative land use for radioactively contaminated arable land

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  • 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 bre crops hemp (Cannabis sativa L.) and ax (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 ax stems ranged from 1.34 to 2.80! 103 m2 kg1. TFs to seeds are about a factorof 4 lower. During the retting process for separating the bres 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! 103 m2 kg1. For hemp, straw and breswere mechanically separated and TF to straw was about 0.5! 103 m2 kg1 and to bres1.0! 103 m2 kg1.

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

    extreme contamination scenarios (O12 300 kBqm2). Since hemp bres are mechanicallyseparated, use of hemp bres is more restricted (contamination!740 kBqm2). Use of stems

    Journal of Environmental Radioactivity 81 (2005) 131e141

    www.elsevier.com/locate/jenvrad* Corresponding author. Tel.: C32 14 332114; fax: C32 14 321056.E-mail address: hvandenh@sckcen.be (H. Vandenhove).

    0265-931X/$ - see front matter 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.jenvrad.2005.01.002

  • as biofuel is restricted to areas with contamination levels of !250 and 1050 kBqm2 for axand hemp, respectively. Use of seeds for edible oil production and our is possible almost

    without restriction for ax but due to the high TFs to seed observed for hemp (up to3! 103 m2 kg1) 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 eect of dierent 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 eect 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 bre crops oncontaminated areas. Two bre crops, hemp (Cannabis sativa L.) and ax (Linumusitatissimum L.) were studied. For both crops extensive knowledge is available onthe use of the bre for textiles and many other high value applications. The varioususes of ax bres 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, ne-texturedsoils and that it is a demanding crop. Hemp bres 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(Hempax, 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 both

    132 H. Vandenhove, M. Van Hees / J. Environ. Radioactivity 81 (2005) 131e141ecological and economic criteria. Industrial hemp has also been tested in the

  • 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 bre crops is limited. Forexample, GOPA (1996a,b) reports a radiocaesium transfer factor (TF) for ax of0.18 and 0.23! 103 m2 kg1 for seeds and straw, respectively, but no information isavailable on the radiocaesium transfer to bres. 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 bre crops hemp and ax 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 ax (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 lled with 14 kg sandysoil (Orthic podzol ), brought to eld capacity (20%). Soil was contaminated with134Cs 1 month prior to start-up. Final soil contamination was 309G 23 kBq kg1

    (75.6G 1.7 MBqm2) for ax and 326G 27 kBq kg1 (79.7G 2.9 MBqm2)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 ax, contamination was done 1month prior to sowing and the contamination density was 29.89G 1.86 kBq kg1

    (9.0G 0.6 MBqm2). For hemp, contamination was 2 years old at the start ofexperiment and the contamination density was 13.30G 0.18 kBq kg1 (4.0G0.05 MBqm2).

    Initial soil nutrient statuswas considered adequate for thepotted soil experiment andfor the cultivation of ax 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 the

    133H. Vandenhove, M. Van Hees / J. Environ. Radioactivity 81 (2005) 131e141experiment, soil was analysed for exchangeable cations, cations in soil solution and

  • exchangeable Cs. The composition of the soil solution was measured at eld capacity(10 kPa). To collect the soil solution, a disposable 60 mL syringe without plungerwas lled with nylon bre and soil sample. The syringe was transferred to acentrifuge tube and centrifuged for 30 min at ca. 50! g. The soil solution wasltered through a 0.45-mm membrane lter (Millipore), and the concentrationsof KC, Ca2C and Mg2C were measured. The RIP value of the soil was measured bythe simplied procedure of Wauters et al. (1996). Total and exchangeable Cs wasmeasured with a Minaxi, autogamma 5000 series-gamma counter, Packard,3! 3$, counting eciency w30%. All soil analyses were done in triplicate. Allcontamination data were calculated back to the time of sowing as reference date. Thesoils 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 ax 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 m2 s1. Soil moisture wasadjusted with distilled water to constant weight each second day. In the potted soilexperiment, ax was harvested after 146 days and hemp after 186 days. For thelysimeter experiment, ax was harvested after 134 days and hemp after 138 days. Theax stem was air-dried prior to retting. The leaves, seeds and cha were dried at60 C. Hemp stem, leaves and seeds were dried at 60 C. Flax was ret (removingstraw and liberating bres with water through rotting) according to Belgian practice(Valcke, 2002). Flax was put in cold (13 C) wa

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