ELSEVIER

J. Environ. Radioactivity, Vol. 31, No. 2, pp. 193-200, 1997

8 1997 Elsevier Science Ltd AU rights reserved. Printed in Great Britain

PII: SO265-931X(96)00097-S 0265-931X/97 $17.00 + 0.00

Usefulness of AFCF as a Countermeasure for Radiocaesium Transfer from Loamy Soil to Rye-grass and Clover

H. Vandenhove, M. Van Hees, C. Bacquoy & C. M. Vandecasteele

SCKCEN, Boeretang 200, B-2400 Mol, Belgium

(Received 20 May 1996; accepted 4 November 1996)

ABSTRACT

Promising results were obtained using ammonium-ferric-hexacyano-ferrate (AFCF) as a countermeasure to reduce radiocaesium transfer to rye-grass grown on sandy soil. In the aftermath of these results, its effieacity as a countermeasure on loamy soil was tested. AFCF concentrations of 3 and IOgm-’ reduced radiocaesium transfer from loamy soil to rye-grass by 28% and 64%, respectively. AFCF additions of iess than 3gmp2 were not effective in reducing the TF. Ploughing the soil was as effective in reducing radiocaesium transfer as were AFCF additions of IOgme2. For clover, only AFCF additions of IOgm-’ significantly reduced transfer (by 60%). As for rye-grass, ploughing was equally effective in reducing TF as the highest AFCF dose. Contrary to the results for rye-grass, however, AFCF addition rates ~fIOgrn_~ decreased the growth of clover. 0 1997 Elsevier Science Ltd

INTRODUCTION

Interest in the fate of radiocaesium in the soil-to-plant transfer was revived after the Chernobyl accident. Radiocaesium is of particular importance because of its high fission yield and relatively high volatility which led to a high contamination level outside the reactor zone. Its fairly long physica half-life (2 years for 13”Cs and 30 years for 137Cs) and its high biological availability due to its similarities with potassium, make it liable to be rapidly transferred into the food chains. AFCF [ammonium-

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194 H. Vandenhove et al

ferric-hexacyano-ferrate(II), NH,Fe(III)Fe(II)(CN),1 and related compounds were first used to reduce radiocaesium uptake by animals (Nigrovic, 1963, 1965; Madshus et al. 1966; Bozorgzadeh and Catsch, 1972; Giese, 1988) and were found to be very effective and non-toxic. Its capacity to reduce radiocaesium concentrations in rye-grass was tested on sandy soil (Vandenhove et al., 1997). On this light textured soil, transfer was reduced with a factor of 4, 25 and 225 when, respectively, 1, 10 and 1OOg AFCF m-’ were applied. Even at 1OOg AFCF rn-*, plant growth was not affected. In the aftermath of these positive results and with the objective to extend our knowledge on the effectiveness and feasibility of AFCF application in other scenarios, we set out to test the effect of AFCF additions and of homogeneous mixing (simulating ploughing) on the TF of rye-grass and clover, grown on loamy soil. The effect of AFCF appli- cation on TF reduction on loamy soil is expected to be less spectacular than on sandy soil, because of the higher radiocaesium adsorption poten- tial of the former. Nevertheless, testing AFCF on loamy soil is useful (1) to provide the decision-makers with the necessary information on condi- tions in which to apply AFCF or not and (2) to test its toxicity on loamy soil. Meeussen (1992) found that AFCF degradation (and the consequent possible release of CN-r) was related to the clay content of the soil.

MATERIALS AND METHODS

Caesium- 134 (Amersham International, Amersham, UK) and AFCF (Industrial Giese Salt, containing 60-65% AFCF and 35540% NH&l, Riedel deHaEn, Germany) were used throughout the experiments. For the transfer studies in the greenhouse, an Orthic Luvisol (referred to as ‘loamy soil’) was used. Soil characteristics are given in Table 1. For the first live treatments (Table 2) 1150g of moist (21.0%) loamy soil (sieved: 2mm) was transferred to dark 1-litre pots (diameter: 11 cm). Italian rye-grass (0.643 g) (Lolium mult$i’orum) seed was spread evenly over the soil and covered with a 0+4-cm (55-g) moist soil layer, homogeneously contami- nated with ‘34 Cs. The final contamination level per pot was I.441 kBqg-’ dry soil; the final soil depth was 10cm. The final soil depth of 1Ocm for the TF studies for rye-grass was adapted from the IUR protocol [Inter- national Union of Radioecologists (IUR), 19891. Five different concen- trations of AFCF (0, 0.3, 1, 3 and 10 gm-*) were evenly sprayed over the soil surface with 10 ml water. Homogeneous application was accomplished by placing a nylon filter (Nytal, 25 T 11-20, Prosep, Zaventem, Belgium) on the soil surface, which was rinsed with 20ml distilled water. For treat- ment 6, 1062g soil (8.4% water) was mixed with 143ml distilled water,

Radiocaesium transfer from loamy soil to rye-grass and clover 195

TABLE 1 Soil Parameters of Orthic Luvisol (Loamy Soil)

Parameter Measure

Exchangeable bases (NH4Ac, 1 M: peq g-‘) K Na Ca

Mg Exchangeable NH4+(KC1, 1 M: peq g-‘) Soil solution (keq ml-‘)

PH (Hz01

(CaC12, 0.01 M) Total C (%) Total N (%) Texture (X)

Density (g ml-‘)

K Na

NH4 Ca

Mg

<2pm 2-50 pm

50-2000 pm

6.67 2.16

120.19 11.36 0.74 0.93 2.42 0.09 6.36 I .24 7.4 6.7 1.01 0.12

23.09 65.86

6.13 1.206

TABLE 2 Treatment Description

Treatment Mode of es-134 application

Mode of A FCF application

AFCF concentration

(g m-‘l

1 Superficial Superficial 0 2 Superficial Superficial 0.3 3 Superficial Superficial I 4 Superficial Superficial 3 5 Superficial Superficial 10 6 Mixed Superficial 1 I Mixed Mixed 1

containing *34CsC1 (final contamination level: 0422 Bq g-* dry soil). Some of the mixture (115Og) was transferred to the 1-litre pot, rye-grass was sown and the remaining 55 g of moist soil was applied as the surface layer. Then, AFCF (1 g m-*) was applied on to the soil surface as described above. Treatment 6 simulates the application of countermeasures after ploughing. Treatment 7 is similar in set up as treatment 6, except that AFCF (1 gm-2) was also mixed with the soil. [For treatments 6 and 7, 1 g AFCF mP2 was used and not 10 g rne2. The latter dose was expected to be more effective but also too costly ($6000 ha-‘, see later).] The soil was

196 H. Vandenhove et al.

given an additional 20ml of water to be in agreement with the other treatments. The final contamination level was 1.227 kBq g-i dry soil. All treatments (Table 2 gives a treatment description) were set up with four replicates; plants were watered every other day and rye-grass harvested every third week. Dry weight (DW) was determined and activity measured by y-counting (minaxi, auto-gamma 5000 series-gamma counter, Pack- ard). The transfer factors (TF, Bq g-i dry plant material Bq-’ g-’ dry soil) were calculated. After every harvest, plants were given NisPisK2i-fertilizer (30 ml pot-’ of a solution containing 17 g fertilizer 1-l). A total of 14 cuts were harvested (total duration of experiment: 9.5 months).

For clover (Trzj?dium pratense), the treatments were as for rye-grass, except that the final contamination levels were: 1.474 kBqg-’ dry soil for treatments l-5, 1.773 kBqg_’ dry soil for treatment 6 and 1.723 kBqg-’ dry soil for treatment 7. Clover was harvested every fifth week (8 harvests over 9.5 months). After each harvest, the pots were fertilized as for the rye-grass experiment.

All data were analysed using SAS statistical software (General Linear Models (GLM), Duncan tests for differences). Statistical analysis for differences between treatments for each harvest has been performed, but the reporting of the data would have hindered the readability and clarity. Therefore, differences between treatments were considered over the whole time course of the experiment, although DW and TF fluctuated with time because of seasonality. With this approach, the overall effect of AFCF addition and ploughing on radiocaesium TF is envisaged.

RESULTS

Rye-grass

Neither the addition of AFCF nor homogenous mixing (simulating ploughing) influenced plant dry weight production (Table 3). Within each individual treatment, variations of DW production were correlated with the observed TF. Overall (all treatments, all cuts) a Pearson correlation coefficient of r = -0.246 (P < 0.0001) was obtained.

The TF obtained for the control [O-l 17 f O-012 (Bq g-’ plant)/(Bq g-’ soil)] (Table 4) is in perfect agreement with TF recorded in separate studies for rye-grass on loamy soil under field conditions [O-l 14 f 0*080 (IUR, 1989)]. Only AFCF additions of 3 g m-* and higher resulted in any significant TF decrease: with 3 and log AFCF m-*, TF was decreased with 28% and 64%, respectively (Table 4). Homogeneous mixing was similarly effective in reducing the transfer factor as was 10 g AFCF m-*.

Radiocaesium transfer from loamy soil to rye-grass and clover 197

TABLE 3 Effect of AFCF Application on Biomass Production of Rye-grass and Clover

Treatment AFCF Plant dry weight (rye-grass)

(g mm2)

Plant dry weight (clover) (mean f SD for I4 cuts) (mean f SD,for eight cuts)

1 0 I.19 l 0.09” 147 f 0.06” 2 0.3 1.16 f 0.08” 1.65 f 0.08” 3 1 1.07 * 0.09” 1.56 k 0.02” 4 3 1.03 It 0.09” 1.68 + 0.05” 5 10 1.11 50.09” 0.78 It 0.10” 6 1 1.19 It 0.09” 1.86 zt 0.05” 7 1 1.10f0~10” 1.57 f 0.06”

Dry weights with a different letter are significantly different at the 5% level.

TABLE 4 Effect of AFCF Application on 134 Cs Transfer to Rye-grass and Clover

Treatment AFCF

(g m-‘)

Transfer factors (rye-grass) (mean f SD for 14 cuts)

Transfer factors (clover) (mean f SD for eight cuts)

1 0 0~117f0~012” 0.143 f 0.007” 2 0.3 0.124 f 0.012” 0.159 =k 0.008” 3 1 0.111 f 0.009” 0.160 f 0.010” 4 3 0.084 III 0.005’ 0.15 1 f 0.007” 5 10 0.042 I!Z 0.003’ 0.058 f 0.006’ 6 1 0.042 f 0.003’ 0.043 * 0.003h 7 1 0.027 k 0.002’ 0.038 f 0.00 1 b

Transfer factors with a different letter are significantly different at the 5% level.

Applying AFCF superficially or mixing it with the soil, when radio- caesium is distributed homogeneously in the profile (treatments 6 and 7) did not affect transfer (all treatments used in analysis). When comparing treatments 3 and 6 (both 1 g AFCF m-* and radiocaesium, respectively, superficially applied or mixed in the profile), the effect of homogenous mixing on the transfer factor can be estimated. In our experimental conditions (rye-grass grown on loamy soil), ploughing reduced TF with 62%.

When the Duncan statistical test for differences is performed only on treatments 6 and 7 (radiocaesium mixed in profile and AFCF superficially applied or mixed), transfer is significantly more reduced when AFCF is mixed together with the radiocaesium in the protile than when AFCF is superficially applied. This difference in transfer reduction between both treatments is explained by the more intimate mixing between radiocaesium and AFCF.

198 H. Vandenhove et al.

Clover

The growth of clover appeared to be more affected than for rye-grass by elevated AFCF additions: addition of log AFCF m-*, reduced the yield by a factor of 2 (Table 3). The growth reduction was predominantly caused by a decreased emergence. Once the plants passed this stage, their growth was not hindered and one might expect the TF to be unaffected by these circumstances. A correlation between the standing biomass and the TF, as done for rye-grass, might not be valid since the number of plants involved varies between individual experiments.

The TF of the control, 0.143 f O-007 (Table 4) is in agreement with the TFs for clover grown on loamy soil, reported in the literature [O.ll (Nishita et al., 1960); 0.22 f 0.11 (IUR, 1989)]. Only the highest AFCF addition rate (10 g m-*) significantly reduced transfer, by 60%, compared to the control. Mixing was equally effective in reducing transfer. No difference in transfer reduction between superficially added or mixed AFCF (treatment 6 and 7, respectively) was found, neither when analysed separately, as was done for rye-grass.

CONCLUSIONS

The application of AFCF on loamy soil as a countermeasure for radio- caesium uptake by rye-grass resulted in significant reductions in TF when at least 3 g AFCF m-* was applied, this without affecting growth. For clover, only 10 g AFCF m-* significantly reduced TF, and this was to the same extent as for rye-grass. It remains unclear as to why no effect was obtained with 3 g AFCF m-*, as was found for rye-grass. The transfer reduction with AFCF application is, however, far less spectacular than what was found for rye-grass grown on sandy soil: here, AFCF concentrations of 1, 10 and lOOgm_* resulted, respectively, in a four-, 25- and 225-fold decrease in transfer (Vandenhove et al., 1997). The higher radiocaesium fixation on a loamy soil, as a result of the presence of micaceous clay minerals (Sawhney, 1970; Cremers et al., 1988), is partly responsible for the lesser effectiveness of AFCF. The higher caesium retention of a loamy soil compared to a sandy soil is reflected in a significantly lower TF for the control treatment of the former, 0.117 (Bqg-’ plant/Bqg-’ soil) compared to 1.869 (Bqg-’ plant/ Bqg-’ soil) for the sandy soil. This difference in radiocaesium TF for radiocaesium with a factor of 20 between both soil types is also reported by Mascanzoni (1988) [in Lembrechts (1993)].

Given that homogeneous mixing (simulating ploughing) was as effective in reducing the TF as AFCF additions of 10 gm-*, and given the extra

Radiocaesium transfer from loamy soil to rye-grass and clover 199

cost involved in AFCF application ($60 kg-r, resulting in $6000 ha-’ at 10 g m-l), makes it unlikely that AFCF can be recommended as a coun- termeasure for radiocaesium uptake on loamy soil. The negative influence of elevated AFCF concentrations on emergence of clover, when grown on loamy soil, means that AFCF would not be advisable as a countermeasure on loamy soil. This negative influence of elevated AFCF concentrations on emergence of clover must be particularly linked to loamy soil since, on sandy soil, this negative influence was not recorded (results to be published). The reason for this difference in harmful effect of elevated AFCF concentrations with soil type is, so far, not clear. Liberation of CN-, as a result of the decomposition of AFCF, which is reported to be favoured by the presence of clay minerals (Meeussen, 1992) might explain this difference.

Although AFCF can be recommended as a rather cheap, easy, safe and effective countermeasure for radiocaesium uptake on sandy soil (Vanden- hove et al., 1996), for a loamy soil, ploughing should be recommended rather than AFCF application, because the former is as effective and less costly. It should be emphasized, however, that ploughing might not be practical, if, for example, as a result, grazing land is to be taken out of use for several months or years.

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Cremers, A., Elsen, A., De Preter, P. and Maes, A. (1988) Quantitative analysis of radiocaesium retention in soils. Nature 335, 247-249.

Giese, W. W. (1988) Ammonium-ferric-cyano-ferrate(I1) (AFCF) as an effective antidote against radiocaesium burdens in domestic animals and animal derived foods. British Veterinary Journal 144, 363-369.

International Union of Radioecologists (1989) Vth Report of the working group soil-to-plant transfer factors. Report of the Working Group Meeting in Guttannen, Grimselpass, Switzerland, 24-26 May, RIVM, Bilthoven, The Netherlands, pp. 215.

Lembrechts, J. (1993) A review of literature on the effectiveness of chemical amendments in reducing the soil-to-plant transfer of radiostrontium and radiocaesium. Science of the Total Environment 137, 81-88.

Madshus, K., Stromme, A., Bohne, F. and Nigrovic, V. (1966) Diminution of radiocaesium body-burden in dogs and human beings by Prussian Blue. International Journal of Radiation Biology 10, 5 19-520.

Meeussen, J. C. L. (1992) Chemical speciation and behaviour of cyanide in contaminated soils. Ph.D. thesis, Agricultural University, Wageningen, The Netherlands.

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Nigrovic, V. (1963) Enhancement of the excretion of radiocaesium in rats by ferric cyanoferrate(I1). International Journal of Radiation Biology 7, 307-309.

Nigrovic, V. (1965) Retention of radiocaesium by the rat as influenced by Prus- sian Blue and other compounds. Physical and Medical Biology 10, 8 1-91.

Nishita, H., Romney, E. M., Alexander, G. V. and Larson, K. H. (1960) Influence of K and Cs on release of Cs 137 from three soils. Soil Science 89, 167-176.

Sawhney, B. L. (1970) Potassium and caesium ion electivity in relation to clay mineral structure. Clays and Clay Minerals 18,47-52.

Vandenhove, H., Van Hees, M., De Brouwer, S. and Vandecasteele, C. M. (1997) Transfer of radiocaesium from podzol to ryegrass as affected by AFCF concentration. Science of the Total Environment, in press.