The transfer of l!7Cs through the soil-plant-sheep food chain in different pasture ecosystems Arja Paasikallio Agricultural Research Centre ofFinland, Institute ofSoils and Environment, FIN-31600 Jokioinen, Finland, e-mail: arja.paasikallio@mtt.fi Riitta Sormunen-Cristian Agricultural Research Centre ofFinland, Institute ofAnimal Production, FIN-31600 Jokioinen, Finland A grazing experiment with sheep was carried out in 1990-1993 on natural, semi-natural and cultivat- ed pasture on clay soil. The pastures were located in Southern Finland and were moderately contam- inated with l37 Cs by Chernobyl fallout. Natural pasture refers to forest pasture and serai-natural pas- ture to set-aside field pasture, the latter having been under cultivation about 15 years ago. The trans- fer of l37Cs to sheep was clearly higher from forest pasture than from the other two pastures and it was lowest from cultivated pasture. The transfer was higher to muscle and kidney than to liver and heart. The transfer of l37Cs to plants and to meat varied with years. Seasonal variation in the plant l37 Cs was followed-up on forest and set-aside field pasture; the activity concentration of plants reached a maximum in June, a lesser increase occurred later in the autumn. In 1993, which was considered an average year with respect to l37Cs transfer to plants, the mean soil-plant transfer factors of l37 Cs for forest, set-aside field and cultivated pastures were 1.78, 0.36 and 0.09, and soil-meat aggregated transfer factors 11.0, 0.28 and 0,03, respectively. Key words: radiocesium, Chernobyl, transfer factor, concentration factor, forest, set-aside field, cul- tivated pasture ntroduction The l37 Cs activity concentration in sheep graz- ing on natural or semi-natural ecosystems has been elevated since the Chernobyl reactor acci- dent in 1986, and it has decreased more slowly than predicted (Mayes 1988, Salt et al. 1992). Sheep farmers in Great Britain, Norway and Sweden have had problems with the high activ- ity level of radiocesium found in sheep grazing on natural grasslands (Mayes 1988, Hove et al. 1994). It is known that natural or semi-natural pastures of poor vegetation facilitate the long- term transfer ofradiocesium from soil via vege- tation to sheep (Coughtrey et al. 1989, Howard et al. 1990,Livens et al. 1991, Melin et al. 1994). In Finland, sheep are mainly grazed on cultivat- © Agricultural and Food Science in Finland Manuscript received April 1996 577 Vol. 5 (1996): 577-591. AGRICULTURAL AND FOOD SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=NOnd9Cp1YHesLXgG.aRIvqtR4yUraKR_KlS8LRw.Y9vhwvEhCWa1QYSiIoUktmCJXKOKUyqJ_ZcqIEJtlRhEgpkY-gz5rdAJ6K2CcLE4v45DnpLXjHNlDbLFq-0VRfFGGakyYLk5Xk18YO2aU49joYLruJvJIIqeU_lRizTLm74ICWDUdlkfg56mc1_P3u6u-eH5sQ_45MAS8DlcikjdRfwB-g_iBCJrYoqTeHiebcrxSKMVi1-pWERWMUNxzU1IFAKoA2XiE-x3AkY19OMqa1kECmTFuZM69Rs3Y0Fd6doDSn8bwqu5Chuxwlr_yLDmHl-9T48MWGnBk9rH7pa1 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Paasikallio, A. & Sormunen-Cristian, R. Transfer of 137Cs through soil-plant-sheep food chain ed pastures in southern areas, where Cs-fixing clay soils dominate. Both the cultivated pasture with high soil K status and the soil clay fraction are considered to contribute to the low transfer of radiocesium to plants. However, interest in the restoration of natural and ecological values in the countryside and, consequently, grazing on natural and semi-natural ecosystems have grown in recent years. Further, the importance of sheep husbandry has increased in eastern and northern parts of the country and especially in areas too sparse for cultivation. The aim of this study was to get more information about the problem of sheep grazing on natural and semi-natural pas- tures compared to cultivatedpastures in case of a severe nuclear fallout. Material and methods Grasslands Natural, semi-natural and cultivated pastures were situated on heavy clay soil in Southern Fin- land in Jokioinen (60.9 °N, 23.5 °E) belonging to the Chernobyl fallout category 3 with an esti- mated surface activity of l37Cs of 11-23 kßq nr2 in 1987 (Arvela et al. 1987). The area of natural and semi-natural pasture was about 2 hectares. Half of it was forest pasture (natural pasture) with Table 1. Dominant plant species or genera of grasslands. Forest pasture Ranunculus acris Cirsium paluslre Trifolium repens Ruhus arcticus Anemone nemorosa Geranium sylvaticum Cultivated pasture & ley Dactylis glomerata Lolium perenne Phleum pratense Festuca pratensis Meadow-2 Agrostis capillaris Poa pratensis Achillea millefolium Anthriscus sylvestris Trifolium repens Veronica chamaedrys junipers, small birches, herbs and grass and the other halfset-aside fieldpasture (semi-natural pas- ture) with grass vegetation (Table 1). The latter pasture had been under cultivation about 15 years’ ago. The area had been used for sheep grazing in the 1980’s. Soil and plant samples of these pastures were taken during 1990-1994. Meteor- ological data are given for this period (Table 2). Agrostis capillaris Deschampsia cespitosa D. flexuosa Festuca ovina Achillea spp. Lathyrus pratensis Galium spp. Set-aside field pasture Deschampsia cespitosa Festuca rubra F. pratensis Agrostis capillaris Phleum pratense Meadow-1 Trifolium pratense Achillea millefolium Agrostis capillaris Table 2. Meteorological data from Jokioinen in May-September 1990-1994. Month Mean temperature a Precipitation a Evaporation b (Class A) ( ° C) (mm/month) (mm/month) 1990 1991 1992 1993 1994 1990 1991 1992 1993 1994 1990 1991 1992 1993 1994 May 9.3 7.2 11.4 13.6 7.8 22 29 7 1 34 114 88 141 155 108 June 14.4 12.1 15.7 11.4 12.1 20 69 25 56 66 159 86 178 99 104 July 15.2 16.6 16.0 15.6 19.0 85 55 47 107 I 112 123 146 122 186 Aug 15.0 16.2 14.3 12.9 15.1 90 92 107 136 54 85 81 72 59 93 Sept 8.0 9.1 11.3 5.7 10.0 62 80 59 13 105 31 41 24 35 36 “Monthly Reports of Finnish Meteorological Institute. b Hydrological Yearbooks of National Board of Waters and the Environment. 578 Vol. 5 (1996): 577-591. Table 3. Mean weight, mean growth rate, age and grazing period of sheep grazing on different types of pastures in 1990-1993. Combined pasture Forest Set-aside pasture field pasture 1990 1991 1992 1993 Live weight 1(kg) 22.1 26.0 22.4 21.5 21.9 Live weight2 (kg) 40.2 42.7 40.1 33.5 35.5 Carcass weight (kg) 15.7 16.9 15.5 11.5 13.1 Growth rate (g d ') 160 151 145 115 131 Age 1 (d) 71 71 73 70 69 Grazing period (d) 112 109 122 104 104 (Number of sheep) (10) (10) (10) (6) (6) Cultivated pasture 1990 1991 1992 1993 Live weight 1(kg) 19.0 28.8 26.2 24.5 Live weight2 (kg) 38.8 47.0 58.1 50.2 Carcass weight (kg) 16.6 19,6 26.2 20.5 Growth rate (g d 1) 180 166 262 247 Age 1(d) 63 72 74 66 Grazing period (d) 112 109 122 104 (Number of sheep) (10) (10) (10) (12) lin the beginning, 2 at the end of grazing period The cultivated pasture used in 1990 had not been ploughed after the Chernobyl accident and was partly on Carex peat soil and partly on clay soil. Since 1991, the cultivated pasture was moved to a nearby pasture on clay soil ploughed at least twice after the deposition. The pastures were fertilized normally (125 kg N, 50kg K and 25 kg P ha-1 ) during the growing season. Soil to plant transfer of 137Cs was studied also on cultivated ley and on two semi-natural mead- ows in 1990-1992. The ley on Carex peat soil was located near the cultivated pastures in Jo- kioinen and had been tilled once after the depo- sition and fertilized and harvested yearly. The two meadows were located in Pälkäne (61.3 °N, 24.2 °E) on fine sand soil. They had not been fertilized for 10-15 years but had been harvested yearly. The area belonged to the 137Cs fallout cate- gory 4 (23—45 kßq nr2). During the experiment, no agricultural practices were done on the ley and meadows. Meadow-1 was ploughed in 1991 and the sampling site was moved in 1992to the near- by similar meadow established after the Cher- nobyl fallout. The same grass species dominated on ley as on cultivated pasture (Table 1). Only few species grew on meadow-1, while on mead- ow-2 several species were found. Animals Five pure-bred and five cross-bred Finnsheep ewe lambs grazed on the combined forest and set-aside field pasture in 1990-1992 and on cul- tivatedpasture in 1990.Ten ram lambs were kept on the cultivated pasture in 1991-1992 (Table 3). In 1993,after dividing the combined pasture into two parts, six Finnsheep ewe lambs (four pure- bred and two cross-bred) grazed on forest pas- ture, six ewe lambs on set-aside pasture and 12 ram lambs on cultivated pasture. The lambs were supplemented with barley grain, 0.3 kg per head 579 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Paasikallio, A. & Sormunen-Cristian, R. Transfer of 137Cs through soil-plant-sheep food chain Table 4. Grassland soil characteristics. Soil depth 0-10 cm. Grassland Bulk Clay Humus pH K Ca Mg P (soil type) density (Hfi) (Acid AAc-extractable) (gem 3 ) (%) (%) (mg I' of soil) Forest pasture 0.83 52 11.6 5.1 184 700 262 3.3 (sandy clay) Set-aside field pasture 0.92 63 7.6 5.7 292 1970 464 1.2 (heavy clay) Cultivated pasture 1.01 62 7.6 5.8 407 1850 748 1.6 (heavy clay) Ley 0.61 34.9 5.6 152 3190 503 4.2 (Carex peat) Meadow-1 1.12 3 4.8 6.0 88 1020 43 2.0 (medium sand) Meadow-2 1.12 5 4.0 5.5 165 780 43 3.1 (medium sand) per day during the first ten grazing days. No other supplemental feeds except salt and minerals were given. Soil and plant sampling For studying soil to plant transfer of 137Cs four random squares of 0.25 m 2 each were taken. The vegetation was cut at the height of 2 cm. There- after four soil samples were taken from each of the squares with the aid of a soil cylinder 10cm high and 5 cm in diameter. Samples were col- lected in the beginning of September. For stud- ying the vertical distribution of l37Cs in the soil cores, three of the four soil samples were divid- ed horizontally into seven fractions in 1990; during the subsequent years the soil samples were divided into two fractions (0-5 and 5-10 cm). The fourth sample of a square was kept in- tact (0-10 cm). In addition, soil samples of un- ploughed (1990) and ploughed meadow (1992) were taken with a soil cylinder of 18 x 5 cm and divided into seven fractions. For studying the seasonal variation of l37Cs in pasture vegetation four random squares were taken in 1992-1994. For studying the 137Cs level of certain plant spe- cies of forest and set-aside field pastures single species were collected at different sites of pas- tures in July and combined for 137Cs measure- ment. Moss and lichen samples were taken from forest pasture in 1994. Sample analysis and measurement of activity Soil samples were air-dried, ground and passed through a 2-mm sieve. Soil potassium, calcium and magnesium were extracted with acid ammo- nium acetate (AAc, pH 4.65), pH was determined in soil-water suspension, organic carbon by dry combustion, clay fraction by dry and wet siev- ing and by the pipette method (Table 4) (MTT 1986). Plant samples were dried at 60° C and milled. The plant activity concentration of 40K was used instead of K. (The amount of 40K in the natural potassium is constant.) Samples of the neck muscle, heart, liver and kidney of the sheep were taken the day after slaughter. Visi- ble fat was removed from the meat samples. Activity measurements were performed using a low-background semiconductor spectrometer with a high purity germanium detector placed in a 13 cm lead background shield. The gamma spectra were analyzed with a computer pro- 580 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Voi 5(1996):577-591. gramme. The l37 Cs activity concentrations were decay-corrected to 1990. The plant and soil ac- tivity concentrations are presented in dry matter (DM) and that of meat in fresh weight (FW). Calculation of l37 Cs transfer and concentration factors Transfer factors (TF), aggregated transfer fac- tors (T ) and concentrationfactors (CF) of l37Cs were calculated as follows: TF (soil-plant) =Bqkgl DM of plant per kßq m-2 DM of soil T, (soil-meat) =Bqkg 1 FW of meat per kßq nr2 DM of soil CF (soil-plant) =Bqkgl DM of plant per Bq kg 1 DM of soil CF (plant-meat) = Bq kg 1 FW of meat per Bq kg 1 DM of plant Soil samples were taken from the depth of 0- 10cm. TF and T f values for grasslands ploughed after the fallout might be too high due to the soil sampling depth of 10 cm. In this case, CF val- ues are more reliable provided that l37 Cs was dis- tributed rather evenly in the plough layer. Statistical methods The effect of year and pasture type on the 137Cs activity concentration of plants was investigat- ed by using the standard two-way analysis of variance. Differences between years were test- ed by means of trend contrasts. The effect of year on the l37Cs activity concentrationof tissues was investigated using the analysis on a univariate repeated measures model similar to the split-plot model (Crowder and Hand 1990) where year was the between subject factor and tissue type was the within subject factor. Differences between muscle and other tissues were tested by contrasts. All the 137Cs activity concentrations were log- transformed. The data were analyzed with the SAS MIXED procedure. Results Soil l37 Cs In 1990, the 0-2 cm soil layer of forest pasture and other unploughed grasslands contained 80- 90% of l37 Cs and that of tilled ley about 50% (Fig. 1 a,b). In unploughed meadow, over 90% and in ploughed meadow, about 35% of 137Cs was found in the soil layer of 0-3 cm (Fig. 1 c,d). The distribution of l37Cs in the undisturbed pas- ture soils between the layers of 0-5 and 5-10 cm (Table 5) remained rather constant during the experimental years. The l34 Cs/l37 Cs ratio of pas- ture soils, decay-corrected to 1986, was 0.5. Plant l37 Cs Activity concentration The l37Cs activity concentrationof plants on for- est pasture was clearly higher than that on the other pastures, and it fluctuated with years. The plant 137Cs of set-aside field pasture was signif- icantly higher than that ofcultivated pasture, and the activity levels differed between years. When investigating the trend of the plant l37 Cs for the two pastures over years using orthogonal poly- nomials the quadratic polynomial proved to be the best approximation to this trend (Table 6). On forest pasture there were differences in the 137Cs concentration between plant species (Table 7). There was no correlation between the plant 137Cs and 40K (Fig. 2). Lichens had much higher and mosses mostly higher 137Cs concen- trations than vascular plants. The average 137Cs activity concentration was 180 in the mosses Aulacomnium palustre and Climacium den- droides, 370 in Hylocomium splendens and Pol- ytrichum spp., 610 in Pleurozium Schreberi, 750 581 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Paasikallio, A. & Sormunen-Cristian, R. Transfer of 137Cs through soil-plant-sheep food chain in Sphagnum spp. and 4880 Bq kg”1 in Grimmia spp. In the lichen genera Cladonia and Stereo- caulon the activity concentration was 490 and 5360 Bq kg' 1, respectively, and in the mushroom Lactarius torminosus 2240 Bq kg” 1 . Sheep were not found to feed on mosses and lichens. Table 5. Activity concentration of 137Cs of soil layer 0-5 cm as a percentage of that of layer 0-10 cm. Grassland l37Cs in soil (%) 1990 1991 1992 1993 Mean SD Forest pasture 96,6 96.7 93.7 95.1 95.5 1.4 Set-aside field pasture 91.3 91.4 90.8 89.6 90.8 0.8 Cultivated pasture* - 72.2 51.7 77.6 67.2 13.7 Meadow-1 97,3 97.3 (54.5*) 97.3 0 Meadow-2 96.0 95.5 92.7 94.7 1.8 Ley** 74.7 73.9 68.1 72.2 3.6 * = ploughed, ** = tilled, SD = standard deviation Fig. 1.Vertical distribution of 137Cs in soils of (a) forest pasture, (b) tilled ley, (c) umploughed meadow-1 and (d) ploughed meadow. 582 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Table 6. Results of analysis of variance for logarithmic plant activity concentration of 157Cs of set-aside field pasture and cultivated pasture in 1991-1993. Source of variation df F-value p-value Pasture I 6.06 0.02 Year 2 7.66 <0.005 Linear trend I 4.31 0.05 Quadratic trend I 11.02 < 0.005 Pasture x year 2 0.18 0.84 Error mean square = 1.78 (df = 18). Transfer factor The behaviour of the soil-plant transfer factors of 137Cs resembled in general those of the plant concentration of 137Cs in regard to pasture type and year (Table 8). The transfer factor of 137Cs for cultivated ley was rather low compared to that for meadows. The soil-plant transfer factor for semi-natural meadows on finesand soil was higher than that for semi-natural (set-aside field) pasture on clay soil. For meadow-1 the transfer factor was higher and soil K lower than those for meadow-2. Seasonal variation The l37Cs activity level of vegetation on forest and set-aside field pasture fluctuated during the growing season. The highest activity concentra- tion was found at the timeof vigorous growth in the early summer followed by a decrease in the middle of the summer and a slight increase in the autumn (Fig. 3). The second increase in growth was relatively more prominent on set- aside field pasture. Potassium 40 in vegetation decreased during the growing season on both pastures from about 800 to 320 Bq kg -1 and plant dry weight (%) on forest pasture increased from 25 to 50% and on set-aside pasture from 30 to 43% (1993). Table 7. Activity concentration of l37Cs of some plant species or genera of forest pasture (f) and set-aside field pasture (s). Each sample is a mixture of several subsamples. Species 137Cs in plant (Bq kg 1 DM) 1990 1991 1993 1994 f f s f f s Grasses, sedges Festuca ovina 103 321 36 Phleum pratense 233 3 15 2 Agmstis capillaris 37 6 Poa pratensis 16 4 Deschampsia cespitosa 24 13 1 D.flexuosa 176 354 Carex spp. 207 95 Juncus spp. 19 14 Herbs Anemone nemorosa 113 33 80 Ranunculus acris 41 12 9 Filipendula uimaria 36 11 Galium spp. 10 4 12 AnthriscusSylvester 28 165 23 5 7 3 Vida cracca 145 8 30 3 Lathyrus pratensis 74 9 33 24 1 Achillea millefolium 16 35 4 583 Vol. 5 (1996): 577-591. AGRICULTURAL AND FOOD SCIENCE IN FINLAND Paasikallio, A. & Sormunen-Cristian, R. Transfer of 137Cs through soil-plant-sheep food chain Sheep l37 Cs Activity concentration When the l37Cs activity concentration of tissues ofsheep on combined pasture in 1991-1992 was tested by the analysis of variance, the effects of year, tissue type and their interaction were highly significant (p < 0.001). Practically, the 137Cs ac- tivity level between muscle and kidney and be- tween liver and heart was of the same order of magnitude (Table 9). The mean and standard deviation (in parentheses) of l37 Cs activity con- centration of muscle, kidney, liver and heart of 6 sheep grazing on forest pasture in 1993 was 254 (70), 185 (57), 134 (35) and 126 (47) Bq kg-1 and on set-aside field pasture 4.0 (0.9), 2.7 (1.4), 1.3 (1.1) and 1.9 (0.8) Bq kg-1 , respec- tively. Transfer and concentration factors The soil-meat aggregated transfer factor of l37Cs for combined and cultivated pasture fluctuated by year and was clearly highest in 1991 (Table 10). The differences between forest, set- aside field and cultivated pasture were obvious (Table 11). The meat/plant concentration factor was not calculated for combined pasture in 1990- 1992 due to considerable differences in the plant concentration of 137Cs of the two sampling sites. After dividing the pasture in 1993, the mean and the standard deviation (in parentheses) of the meat/plant concentration factor of l37Cs for for- Fig. 2. Activity concentration of l37Cs and 40K of some vascular plant (1991, 1994) and moss spe- cies (1994) on forestpasture. Each sample is a mixture ofseveral sub- samples. 584 AGRICULTURAL AND FOOD SCIENCE IN FINLAND AGRICULTURAL AND FOOD SCIENCE IN FINLAND Vol. 5 (1996): 577-591. Table 8. Soil-plant transfer and concentration factors of l37Cs for different pastures by years. Year l37Cs (soil-plant) Transfer factor Concentration factor Mean SD Range Mean SD Forest pasture 1990 1.83 0.98 0.95-3.20 0.151 0.081 1991 8.24 2.66 5.59-10.62 0.684 0.221 1992 0.87 0.24 0.54-1.04 0.072 0.020 1993 1.78 1.92 0.33-4.56 0.149 0.159 1994 2.72 2.75 0.61-6.74 0.225 0.226 Set-aside field pasture 1990 0,39 0.14 0,31-0.60 0.036 0.013 1991 0.56 0.34 0.25-1.00 0.052 0.031 1992 0.07 0.06 < 0.01-0.12 0.006 0.005 1993 0.36 0.31