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Transfer of 137Cs to cow's milk: Investigations on dairy farms in Sweden
J. Environ. Radioactiviry, Vol. 28 No. 1. pp. l-15,
1995
Copyright 0 1995 Elsevia Science Limited Printed in Ireland. All rights reserved 0265-93 ELSEVIER
I X/95
$9.50 + 0.00
0265-931X(94)00070-0
Transfer of 13’Cs to Cow’s Milk: Investigations on Dairy Farms in Sweden
Gunnel Karl&n, Karl J. Johanson Department
of Radioecology, PO Box 7031, Swedish University of Agricultural S-750 07 Uppsala, Sweden
Sciences,
&
Jan Bertilsson Department
of Animal Nutrition and Management, PO Box 7024, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden (Received 22 December 1993; accepted 19 November 1994)
ABSTRACT Since 1986, the year of the nuclear accident at Chernobyl, 137Cs activity concentrations in cow’s milk on dairy farms were studied in Sweden. Transfer coefficients, F,, of ‘37Cs from pasture and fodder to cow’s milk were determined on farms in the counties of Uppsala, Gavleborg and Vastmanland in central Sweden for one month on winter-fodder, andfor the first month in 1987 and in 1988 on pasture. The average F, for all investigations (of 10 farms on winter-fodder and 11 farms on pasture in 1987 and 4 farms on pasture in 1988) south of Grivle was estimated to be 0.0055 with a range of 0.0039 to 0.0080. The 137Cs activity concentration in milk decreased with time. In summer 1992 and 1993, ‘37Cs in milk, on the farms still producing milk, was determined. On these farms, 137Cs activity concentration in milk was found to be < 2-21 Bq kg-‘. The effective ecological half-ltfe from 1987 was estimated to be 1.4 f 0.5 (sd) years for milk from IO farms with a range of 0.8-2.0 years. One farm where 137Cs in milk decreased at a slower rate, or not at all, used semi-natural and uncultivated pasture, forest meadows. On intensely managed farms, where potassium fertilizer was distributed, ploughing was performed and, in 1986, forage was cut at a higher stubbleheight, the decrease of ‘37Cs in milk was observed to be faster.
2
G. Karl& et al.
INTRODUCTION The accident at the Chernobyl nuclear power plant in the Ukraine occurred on 26 April 1986. In parts of central Sweden, radionuclides were wetdeposited in rain (Fig. 1). The 137Cswas deposited on the ground, forage crops and grass. Subsequently, ‘37Cs could be detected in milk of cows grazing on pasture or fed hay/silage harvested from the contaminated regions. In 1986 a gradient of ‘37Cs was found in the grass where the 137Cs activity concentration in the top portion of the grass was often found to be 10 times lower than that in the bottom (Karlen et al., 1991). During the following years, the ‘37Cs activity in grass was more homogeneously distributed, and studies of the transfer coefficient, F,, of 137Cs transfer from pasture to milk could be performed. The bioavailability of ‘37Cs from hay harvested in 1987 to goat’s milk was
I 0
Fig. 1. 13’Csground
deposition
I 50 km
(kBqm_‘) in Sweden two areas.
@GAB.
1986) and location
of the
Transfer of ‘37Cs to cow’s milk
3
suggested to be higher than from hay harvested in 1986 (Hansen & Hove, 1991). On pasture and when feeding green-cut forage, another suggestion for the observed variation of 13’Cs uptake in the gastro-intestinal tract was contamination of grass by different soil particles, e.g. clay, which strongly bind radiocaesium (Fredriksson et al., 1966; Bertilsson et al., 1988). The bioavailability of different forms of radiocaesium for transfer to animal products was also studied by Beresford et al. (1992) and Howard et al. (1989). Most farmers in the most contaminated areas of Sweden and using intensive management systems followed the recommendations in 1986, set by the Swedish Board of Agriculture to prevent radiocaesium entering the human food chain. The farmers were recommended to plough certain pastures and old ley fields, to fertilize with potassium and, in 1986, to cut hay/silage at a higher stubble height. In the most contaminated area, the cows were not released onto pasture until the end of June or about 1 month later than what would be normal time. On some semi-natural pastures, like forest pastures or mountain meadows, where extensive management was performed, the recommendations could not be followed to the same degree. Since 1986, dairy farms have been investigated in the counties of Uppsala, Vastmanland and Gavleborg (Karlin et al., 1991; Alskog, 1992). The transfer of 13’Cs from grass and fodder to milk was studied during the first month of 1987 and 1988 in which the cows were grazing on pasture, and a transfer coefficient, F,, was calculated for each farm and year. In the summers of 1992 and 1993, a study was performed on some of the dairy farms studied previously, where 13’Cs in milk, grass and fodder was determined and F,,, was estimated. The aims of the investigations were to determine the 13’Cs transfer coefficient, F,,,, from pasture and fodder to cow’s milk, to study timedependent changes in the 13’Cs transfer to cow’s milk and to estimate the effective ecological half-life of 13’Cs in milk.
MATERIAL
AND METHODS
Dairy farms located 3&50 km south (Area A) and 20 km north of Gavle (Area B) were studied. The i3’Cs ground deposition was 20-60 kBq m-* in Area A, and 100-200 kBq m-* in Area B (Fig. 1). The farms represented different soil types, different sizes of dairy herd in the range of 9-50 milking cows of mostly Swedish Red and White and Swedish Friesian dairy breeds and different pasture management systems. Hay or silage and concentrate were used as supplementary fodder. The different studies are described in Table 1. More information about the farms and the diets can be found in Karlen & Johanson (1987) and Alskog (1992).
G. Karl& et al.
4
TABLE 1 Study Periods, Areas and Farms in the Dairy Farm Studies Sampling series
4
5
Period
Area
Farms
Study
1986
A
2 farms
Sampling of milk and grass F,,, (winterfodder)
1987 April-May 1 month 1987 May-June 1 month 1987 June l-5 weeks 1988 May-June 1 month 1989
A
12 farms
A
11 farms
F,,, (pasture)
B
4 farms
F,,, (pasture)
A
5 farms including A,
F,,, (pasture)
A
A, = extensive
Sampling of milk
farm 1990 1992 One day 1993 One day
A A and B A and B
8 farms altogether 8 farms altogether
Estimated F, Sampling of milk
1986, Area A
In 1986, continuous farms in Area A.
sampling of grass and milk was performed
on two
1987 and 1988, Area A During the first month on pasture in 1987 and 1988, daily samples of milk and fodder were collected on the 11 farms south of Gavle, in Area A. The same 11 farms had previously been studied when feeding winter-fodder in 1987. The transfer coefficient, F,,,, for transfer of 137Cs from fodder to milk for the individual farm and for each period was calculated (Karlen et al., 1991). 1987, Area B Four farms north of Gavle, in area B, were investigated during the first l5 weeks on pasture in 1987 by Alskog (1992) in the same manner as in
Tram@
of ‘37Cs to cow’s milk
5
Area A, but milk samples were taken every second day. F, was calculated for each farm. 1992, Areas A and B In summer 1992, the ‘37Cs in milk, grass and fodder was determined. Eight farms from previous investigations where the milk production continued were included in this investigation. Samples of grass and fodder were taken one day in each month. Samples of milk were taken two days after each sampling of feed. The amount of supplementary fodder consumed was estimated by the farmer. 1993, Areas A and B Caesium-137 activity concentrations in milk on the remaining farms still producing milk were measured in summer 1993. Field data In all investigations, samples of pasture grass were taken from an area of 1 m2 in the field where the cows grazed. Milk samples were taken daily in Area A and every second day in Area B. Daily samples of supplementary fodder were taken from the feeding trough where the cows ate. All fodder was weighed twice a week in the more intensive investigations in 1987 and in 1988. The amount of milk produced at each farm was registered in the regular routines when milk was transported to the dairies with the addition of milk fed to the calves and used in the household. Radiometric and chemical analysis All ‘37Cs activity concentrations were measured using hyperpure Germanium detectors (ORTEC or PGT) placed in a low background laboratory at the Department of Radioecology, Uppsala. Chemical analyses of the fodder and pasture grass were performed by the Swedish National Laboratory for Agricultural Chemistry using standard methods. Intake of grass The average consumption of energy in pasture grass was calculated from Swedish standards for the cow’s need of metabolizable energy for maintenance and production, less the energy derived from the fodder (Eriksson et al., 1972; Spiirndly, 1989). Knowing the energy intake from
6
G. Karl& et al.
grass, the dry matter (DM) intake from grass (MJ) divided by MJ/kg protein in milk were obtained from recording, i.e. milk recording every (Bigs et al., 1987).
could be calculated as total energy DM grass. The contents of fat and the regular routines of official milk month and IR-analyses of the milk
The transfer coefficient, F,,,, for milk
The transfer coefficient, F,,, (d kg-‘), were calculated as outlined by Ward and Johnson (1986) Bq kg-’ milk/Bq intake per day
(at equilibrium)
As the density of cow’s milk is close to 1, the units litre and kg were considered to be equivalent, and 137Csactivity concentrations were determined on a weight basis. The aggregated transfer coefficient,
Tag
The aggregated transfer coefficient, Tag, is expressed as Tag = Bq kg-’ of food product/ground deposition (BqmP2) (Howard et al., 1994). The effective ecological half-life
The decrease in 137Cs activity concentration in cow’s milk sampled from cows grazing under similar conditions for several years can be described as the effective ecological half-life (Aarkrog, 1992; Howard et al., 1994) 1 _=-T4f
1
1
TPhYs+ T,,,
Teff = the effective ecological half-life, Tphys= the physical half-life, T,,, = the half-life of the stable elements in the studied ecosystem.
RESULTS 1986
The 137Cs activity concentration in milk during the summer of 1986 on two farms is shown in Fig. 2. At these farms the cows grazed outdoors throughout the pasture season. The aggregated transfer factor of 137Cs from pasture to milk was estimated to be 3.5 x low3 m2 kg-’ f 1.5 x lop3 (sd). No estimation of the F,,, could be made.
Transfer qf 13’Cs to COW’Smilk
,-* ,
10
20
30 40
50
60
70 80
’ I
:
1
:
:A1
90
loo
110
Days Fig. 2. ‘37Cs activity concentrations
Transfer coeffkients,
in milk from two farms in Area A, in 1986. Day 0 is about 15 May 1986.
F,
The ‘37Cs transfer coefficients, F,,for all the years are summarized in Table 2. In all the investigations from Area A (winter-fodder 1987, pasture 1987 and 1988) an average F, was estimated to be 0.0055 with a range of O-0039 to 0.0080. In 1992, an average F, was estimated to be O-006 in June, 0.007 in July and 0.01 in August in Areas A and B. TABLE 2 Average F,,, and Mean Errors in the Studies of Area A and B Study
Winter-fodder Pasture Pasture Pasture Pasture
Area
Year
A A B A A and B
1987 1987 1987 1988 1992 June July August
F,
Range
0.0048 f 0.002 (me) 0.0055 f 0.0016 0.01* 0.0071 & 0.0007 Estimation: 0.006 0.007 0.01
*Data from Alskog (1992) have been further calculated in the present work, to estimate mean F,,, and range.
G. Karlth et al.
8
The 137Csactivity transfer coefficient, F,, to milk on live farms on three occasions in the summer of 1992 are shown in Table 3. Caesium-137 in milk in 1992 and 1993
The 137Cs activity concentrations in milk ranged from < 2-11 Bq kg-’ in June, 2-15 Bqkg-’ in July and < 2-21 Bqkgg’ in August 1992. In 1993, the 137Csactivity concentrations in milk were 2-12 Bq kg-‘. The estimated F,, increased from 0.006 in June and 0.007 in July to 0.01 in August 1992. On three more farms (A5, A6 and B4), the ‘37Cs activity concentration in milk was considered too low to be used for F,,, determination in June 1992. In 1993, the ‘37Cs activity concentration in milk on the same farms and in milk from an additional two farms (A7 and A8) was measured to be within the same range as in June 1992. The effective ecological half-life
The changes in 137Cs activity concentration in milk with time on the intensively managed farms is shown in Fig. 3. The effective ecological halflife for milk from 10 farms was estimated to be 1.4 f 0.5 (sd) years from . 1987 to 1993, with a range of 0.8-2.0 years. On one extensively managed farm, A,, the effective ecological half-life could not be estimated. The average 137Cs activity concentration in milk was found to be about 300 Bq kg-’ in June 1988 and 170 Bq kg-’ in August 1988. In the following years there were large variations in the 137Csactivity in milk. During August in 1989 and 1990, the average 137Cs activity in milk was still comparatively high, 100 Bq kg-‘. Caesium-137
The ’37Cs activity concentration in grass (Table 4) on farm A 1 in 1986 was on average 28 000 Bq kg-’ dry weight (dry wt) in the bottom part of the grass ( < 5 cm), and 1600 Bq kg-’ dry wt in the top of the grass ( > 5 cm). In 1992, the 137Csactivity concentration of the whole grass was 40 Bq kg-’ dry wt on the farms Al and A4. In Area B, the average 137Csactivity concentration in grass was 1600 Bq kg-’ dry wt in 1987 and 50 Bq kg-’ dry wt in 1992.
DISCUSSION In 1986, the aggregated transfer factor (T& was estimated to be 3.5 x 10W3m* kg-’ f 1.5 x 10e3 (sd) on two farms south of Gavle, in Area A
Average
0.006
3
0.004
3 <2 <2 12
24 6
0.003 0.004 0.009
B3 B4 A5 A6 A7 A8
15
0.01
11
<2 2 6
Al
Cs activity (Bq kg-‘)
F,,,
July 1992
<2
oGO9
0.007
28 21
Cs activity (Bq kg-‘)
0,003 0.004 0.01
0.009
F,
August 1992
0.01
3 O-008
3 <2 <2 ‘E3
5 12
Cs activity (Bq kg-‘)
1993
0.008 0.016
F,
TABLE 3 in Milk in 1992 and 1993, and Estimated F,,, in June, July and August 1992
Cs activity (Bq kg-‘)
June 1992
A4 Bl B2
Farm
‘37Cs Activity Concentrations
W
k 3 s S Q 6 B d h3 g
2
Bq kg-’ 140 130
1986
1987
1988
Years (a) Bq kg-’ 130 120 110 100 90 80 70 60 50 40 30 20 10 0 1987
1992
Years (b) Fig. 3. (a) “‘Cs activity concentrations in milk from farms in Area A. Mean values for June 1986. and for the first four weeks on pasture in 1987 and 1988. One days milk sample in June 1992 and in June 1993. (b) “‘Cs activity concentrations in milk from farms in Area B. Mean values from the study period in June 1987. One days milk sample in June 1992 and in June 1993.
Al Al-Al 1 Al-A3, AS, A, Al,A4 Bl-B4* Bl-B3
1986 1987
1600 f 900 (sd)
500 f 500 (sd)
28 000 f 6 000 (sd)
Bottom (&5 cm)
50 f 60 (sd)
150 f 60 (sd) 40 f 30 (sd)
Combined
1300 * 1300 (sd)
I 600 f 1000 (sd) 400 f 400 (sd)
Top (5 cm)
Average 137Cs activity in grass (Bq kg-’ dry wt)
*Data from Alskog (1992) have been further calculated in this work, to estimate mean 13’Cs activity concentration the first four weeks on pasture.
1987 1992
1992
1988
Farms
Year
TABLE 4 13’Cs Activity Concentrations in Grass of Study Farms
in grass (dry wt) and sd,
4 30 10
20
40
3
Samples (N)
’
5 z? S 8 F *3
%
Y $ % TL
12
G. Karl& et al.
(Fig. 2). The average F,,, in all the initial more intensive investigations from Area A (Table 2) was 0.0055 with a range of 0~0039-0~0080, including the study when feeding winter-fodder. In the first month on pasture in 1987 the average F,,,was 0.0055 f 0.0016 (me) in Area A, and in 1988 0.0071 f 0.0007 (me). As a comparison an average F,,2of 0.0079 with a range of 0.001-0.027 was reviewed by IAEA (1994). The variations from year to year in F,,, and the variations of F,,, between different farms were rather small (Table 2). One reason for the variations of F,,, might be that the bioavailability of 13’Cs increased over the years, compared with the year of the fallout (Hansen & Hove, 1991; Hilton, 1992). Another explanation of the variations within each investigation might be that the fodder and pasture were contaminated by soil, which influences the transfer of 13’Cs across the gut, depending on the type of soil (Bertilsson et al., 1988; Desmet et al., 1991). Clay particles bind radiocaesium strongly, whereas peat binds it loosely (Eriksson, 1978). The soil intake of a cow on pasture might be up to 1 kg per day (Fries & Marrow, 1982), especially on well-frequented and used pasture (Burmann, 1968). Hansen and Hove (1991) reported also higher bioavailability of 13’Cs in mushrooms, which might be one reason for the tendency of increased F, observed in August 1992 compared to June 1992 (Table 3). In all investigations of F, on a farm level, it is essential to distinguish between an estimation of F,,, based on a few samples and a more rigorously calculated F,, where samples are taken regularly for a longer period (Hansen & Andersson, 1994) and the amount of fodder is weighed as in the present studies of 1987 and 1988 (Mayes, 1989). There is a variation in 13’Cs transfer from soil to grass depending on the type of soil, which was also observed after the Chernobyl fallout (Eriksson & Rosen, 1991). Transfer of 13’Cs from different types of soil to grass is described in Haak et al. (1973) and Eriksson (1978). The hay or silage used in the present investigations on pasture was usually harvested on the same farms, and mostly from the same region. In 1986, the 13’Cs activity concentration in the bottom of the grass was found to be higher than in the top of the grass. The recommended harvest methods (Hadders & Nilsson, 1987; Bertilsson et al., 1988) to take hay and silage at a higher stubble-height were followed by most of the farmers. The 13’Csactivity concentration in hay and silage was part of the 13’Csactivity concentration in total fodder. Crude fibre was found to bind radiocaesium (Johnson et al., 1968). Beresford et al. (1992) also found higher 13’Cs transfer across the gut of sheep for 13’Cs incorporated in grass than for r3’Cs incorporated in heather. The ‘37Cs activity concentration in milk on the farms decreased with time (Fig. 3). The effective ecological half-life for milk from 1987 to 1993 is estimated to be on average 1.4 f 0.5 (sd) years for 10 farms (Fig. 3) with
Transfer of 137Cs to cow’s milk
13
a range of 0.8-2.0 years. Most of the farms included in this study use an intensive management system, rather typical for the agricultural districts in Sweden, and the recommendations set by The Swedish Agricultural Board were followed. The farms where 13’Cs in milk decreased at a slower rate used some semi-natural pasture, sometimes in forest, where the cows had access to wild plants and mushrooms. The effective ecological half-life for ‘37Cs in milk in the study might also be shorter, since no sampling of milk was performed on these farms in 1989-1991. On the extensively managed farm, A,, using forest fields of peat soil, no effective ecological half-life could be estimated-or set to 30 years-since there were large temporal variations in i3’Cs in milk (Karlen et al., 1991). Also in Norway, the effective ecological half-life for one extensively managed farm in the mountain was estimated to be about 30 years based on studies from 1988 to 1992. On three other extensively managed farms in the same area in Norway, the effective ecological half-life for milk was estimated to be 4.8 years based on studies from 1989 to 1992, with a range of 2.7-6.7 years (Strand et al., 1992). An effective ecological half-life in Norway was estimated to be 2.3 years based on studies from 1987 to 1992 in milk of dairies in contaminated regions (Hansen & Andersson, 1994). In Denmark, an estimated effective half-life was reported to be 1.6 years, based on studies conducted in dairies from 1987 to 1991 (Aarkrog, 1992). In Sweden an effective ecological halflife of 13’Cs in milk of all dairies was estimated to be 1-Oyear, based on studies from 1986 to 1990. In the mountain areas of Sweden where uncultivated pasture was used, the effective ecological half-life of 13’Cs in milk of the dairies was estimated to be about 3 years (Suomela & Melin, 1992). The differences might be explained for example by differences in agricultural management system, as the farms in Norway and in Sweden are more extensively managed in the mountain areas than farms in the agricultural districts of Sweden or Denmark. It can be concluded that on semi-natural pasture, especially on peat soil, and where no ploughing was undertaken, nor any application of potassium, the 13’Cs in cow’s milk decreases at a much slower rate than on intensely managed and well-kept fields, which was reflected both in the present single farm investigations and studies of dairy statistics (Suomela & Melin, 1992; Hansen & Andersson, 1994).
ACKNOWLEDGEMENT This work was done with the financial support of The Swedish Radiation Protection Institute. The authors especially want to thank all the farmers
G. Karl&
14
et al.
participating in the studies. They are also grateful to all the technical staff at the Department of Radioecology.
REFERENCES A. (1992). d;kologiske Halveringstider i Ftiroske og Danske Landbrugsokosystemer. (In Danish.) (Effective Eecological Half-Lives in the Agricultural Ecosystems of Faroe islands and Denmark.) The Sixth Nordic Seminar of Radioecology, Torshavn, Faroe Islands, 1418 June 1992. Alskog, E. (1.992). Lokala Undersokningar i Jordbruket efter Tjernobylolyckan 1986, I. Overforing av Radiocesium frdn Betesmark till Mjolk i Gavleborgs Ian 1987. (In Swedish.) Rapport SLU-REK-69-SE, ISSN 0280-7963, Dept. of Aarkrog,
Radioecology, Swedish University of Agricultural Sciences, Uppsala, Sweden. Beresford, N. A., Mayes, R. W., Howard, B. J., Eayres, H. F., Lamb, C. S., Barnett, C. L. & Segal, M. G. (1992). The bioavailability of different forms of radiocesium for transfer across the gut of ruminants. Radiat. Prot. Dosim., 41,87-91.
Bertilsson, J., Andersson, I. & Johanson, K. J. (1988). Feeding green-cut forage contaminated by radioactive fallout to dairy cows. Health Phys., 55, 855-62. Bigs, D. A., Johnson, G. & Sjaunja, L.-O. (1987). Analyses of fat, proteins, lactose and total solids by infra-red absorption. Rapid indirect methods for measurements of the major components of milk. Znt. Dairy Fed., Bull., 208. Burmann, F. J. (1988). Influence of grazing intensity on Cs-137 levels in milk. J. Dairy Sci., 50, 1891-6.
Desmet, G. M., Van Loon, L. R. & Howard, B. (1991). Chemical speciation and bioavailability of elements in the environment and their relevance to radioecology. Sci. Total Environ., 100, 105-24. Eriksson, S., Sanne, S. & Thomke, S. (1972). Feeds (In Swedish.) LT Publishing Company, Sweden. Eriksson, A. (1978). Transport of Radioactive Fission Products from Arable Land and Pastures to Domestic Animals and Man. Swedish University of Agricultural Sciences, Dept. of Radiobiology, Report 46, Uppsala, Sweden. Eriksson, A. & Rosen, K. (1991). Transfer of caesium to hay grass and grain crops after Chernobyl. In The Chernobyl Fallout in Sweden, ed. L. Moberg. The Swedish Radiation Protection Institute, Stockholm, Sweden, pp. 291-304. Fredriksson, L., Garner, R. J. & Russell, R. S. (1966). Caesium-137, In Radioactivity and Human Diet, ed. R. Scott Russell. Pergamon Press, Oxford, pp. 3 17-52. Fries, G. F. & Marrow, G. S. (1982). Soil ingestion by dairy cattle. J. Dairy Sci., 6561
l-18.
Haak, E., Eriksson, A. & Karlstrom, F. (1973). Studies of Plant Accumulation Under Swedish Conditions. Entry of 90-Sr and 137-Cs into Herbage of Contrasting Types of Pasture. FOA-4, Rapport C 4525-A3, Fiirsvarets Forskningsanstalt, Sweden. Hadders, G. & Nilsson, E. (1987). Sk&d av Foder som Drabbats av Radioaktivt Nedfall. JTI-Report No. 87, Swedish Institute of Agricultural Engineering, Ultuna, Uppsala, Sweden (in Swedish).
Transfer of 137Cs to cow’s milk
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Hansen, S. H. & Andersson, I. (1944). Transfer of Chernobyl i3’Cs fallout to cow’s milk in the Nordic countries. Nordic Radioecology, Chapter 3.5, Reports from the RAD-programme. Hansen, S. H. & Hove, K. (1991). Radiocaesium bioavailability: Transfer of Chernobyl and tracer radiocaesium to goats milk. Health Phys., 64&5), 665-73. Hilton, J., Cambray, R. S. & Green, N. (1992). Chemical fractionation of radioactive caesium in airborne particles containing bomb fallout. Chernobyl fallout and atmospheric material from the Sellafield Site. J. Environ. Radioactvity, 15, 103-l 1. Howard, B. J., Mayes, R. W., Beresford, N. A. & Lamb, C. S. (1989). Transfer of radiocesium from different environmental sources to ewes and suckling lambs. Health Phys., 57, 579-86. Howard, B., Johanson, K. J., Linsley, G. S., Hove, K., Priihl, G. & Horyna, J. (1994). Transfer of Radionuclides by Terrestrial Food Products from SemiNatural Ecosystems. VAMP terrestrial working group. Part of the IAEA/ CEC Co-ordinated Research Programme on the Validation of Environmental Model Predictions (VAMP). IAEA (1984). Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Temperate Environments. IAEA, Vienna, Austria. Johnson, J. E., Ward, G. M., Firestone, E. & Knox, K. L. (1988). Metabolism of radioactive cesium (‘34Cs and 13’Cs) and potassium by dairy cattle as influenced by high and low forage diets. J. Nutr., 94, 282-8. Karlen, G. (1993). Transfer of 37Cs to Milk of Cow and Muscle of Roe Deer. Report SLU-REK-71, Dept. of Radioecology, Swedish University of Agriculture, Uppsala, Sweden. Karlen, G. & Johanson, K.-J. (1987). Betesvallens Radioekologi. SSI-Rapport (in Swedish). The Department of Radioecology, Swedish University of Agricultural Sciences, Uppsala, Sweden. Karlen, G., Johanson, K.-J. & Bertilsson, J. (1991). Transfer of cesium-137 from pasture to milk after Chernobyl. Investigations of dairy farms in Sweden, In The Chernobyl Fallout in Sweden, ed. L. Moberg, The Swedish Radiation Protection Institute, Stockholm, Sweden, pp. 343-60. Mayes, R. W. (1989). The quantification of dietary intake, digestion and metabolism in farm livestock and its relevance to the study of radionuclide uptake. Sci. Total Environ., 85, 29-51. SGAB (1986). Ground deposition of Cs- 137 in Sweden. Map, Swedish Geological Company, Uppsala, Sweden. Sporndly, R. (1989). Fodertabeller for Idisslare (in Swedish). Speciella Skrifter 39, Swedish University of Agriculture, Uppsala, Sweden. Strand, P., Amundsen, I. & Selnaes, T. (1992). Overvdkingsmalinger for Radiocesium in Norske Husdyrprodukter (in Norwegian). Interim Report of The Norwegian Radiation Protection Authority (Norska Statens Strblevarn), Osteras, Norway. Suomela, J. & Melin, J. (1992). Farekomsten av Cesium och Strontium-90 i Mejerimjiilk fiir Perioden 1955-1990 (in Swedish). SSI-Rapport 92-20. Statens Strilskyddsinstitut. The Swedish Radiation Protection Institute, Stockholm, Sweden. Ward, G. M. & Johnson, J. E. (1986). Validity of the term transfer coefficient. Health Phys., 50,41 I-14.
1995
Copyright 0 1995 Elsevia Science Limited Printed in Ireland. All rights reserved 0265-93 ELSEVIER
I X/95
$9.50 + 0.00
0265-931X(94)00070-0
Transfer of 13’Cs to Cow’s Milk: Investigations on Dairy Farms in Sweden
Gunnel Karl&n, Karl J. Johanson Department
of Radioecology, PO Box 7031, Swedish University of Agricultural S-750 07 Uppsala, Sweden
Sciences,
&
Jan Bertilsson Department
of Animal Nutrition and Management, PO Box 7024, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden (Received 22 December 1993; accepted 19 November 1994)
ABSTRACT Since 1986, the year of the nuclear accident at Chernobyl, 137Cs activity concentrations in cow’s milk on dairy farms were studied in Sweden. Transfer coefficients, F,, of ‘37Cs from pasture and fodder to cow’s milk were determined on farms in the counties of Uppsala, Gavleborg and Vastmanland in central Sweden for one month on winter-fodder, andfor the first month in 1987 and in 1988 on pasture. The average F, for all investigations (of 10 farms on winter-fodder and 11 farms on pasture in 1987 and 4 farms on pasture in 1988) south of Grivle was estimated to be 0.0055 with a range of 0.0039 to 0.0080. The 137Cs activity concentration in milk decreased with time. In summer 1992 and 1993, ‘37Cs in milk, on the farms still producing milk, was determined. On these farms, 137Cs activity concentration in milk was found to be < 2-21 Bq kg-‘. The effective ecological half-ltfe from 1987 was estimated to be 1.4 f 0.5 (sd) years for milk from IO farms with a range of 0.8-2.0 years. One farm where 137Cs in milk decreased at a slower rate, or not at all, used semi-natural and uncultivated pasture, forest meadows. On intensely managed farms, where potassium fertilizer was distributed, ploughing was performed and, in 1986, forage was cut at a higher stubbleheight, the decrease of ‘37Cs in milk was observed to be faster.
2
G. Karl& et al.
INTRODUCTION The accident at the Chernobyl nuclear power plant in the Ukraine occurred on 26 April 1986. In parts of central Sweden, radionuclides were wetdeposited in rain (Fig. 1). The 137Cswas deposited on the ground, forage crops and grass. Subsequently, ‘37Cs could be detected in milk of cows grazing on pasture or fed hay/silage harvested from the contaminated regions. In 1986 a gradient of ‘37Cs was found in the grass where the 137Cs activity concentration in the top portion of the grass was often found to be 10 times lower than that in the bottom (Karlen et al., 1991). During the following years, the ‘37Cs activity in grass was more homogeneously distributed, and studies of the transfer coefficient, F,, of 137Cs transfer from pasture to milk could be performed. The bioavailability of ‘37Cs from hay harvested in 1987 to goat’s milk was
I 0
Fig. 1. 13’Csground
deposition
I 50 km
(kBqm_‘) in Sweden two areas.
@GAB.
1986) and location
of the
Transfer of ‘37Cs to cow’s milk
3
suggested to be higher than from hay harvested in 1986 (Hansen & Hove, 1991). On pasture and when feeding green-cut forage, another suggestion for the observed variation of 13’Cs uptake in the gastro-intestinal tract was contamination of grass by different soil particles, e.g. clay, which strongly bind radiocaesium (Fredriksson et al., 1966; Bertilsson et al., 1988). The bioavailability of different forms of radiocaesium for transfer to animal products was also studied by Beresford et al. (1992) and Howard et al. (1989). Most farmers in the most contaminated areas of Sweden and using intensive management systems followed the recommendations in 1986, set by the Swedish Board of Agriculture to prevent radiocaesium entering the human food chain. The farmers were recommended to plough certain pastures and old ley fields, to fertilize with potassium and, in 1986, to cut hay/silage at a higher stubble height. In the most contaminated area, the cows were not released onto pasture until the end of June or about 1 month later than what would be normal time. On some semi-natural pastures, like forest pastures or mountain meadows, where extensive management was performed, the recommendations could not be followed to the same degree. Since 1986, dairy farms have been investigated in the counties of Uppsala, Vastmanland and Gavleborg (Karlin et al., 1991; Alskog, 1992). The transfer of 13’Cs from grass and fodder to milk was studied during the first month of 1987 and 1988 in which the cows were grazing on pasture, and a transfer coefficient, F,, was calculated for each farm and year. In the summers of 1992 and 1993, a study was performed on some of the dairy farms studied previously, where 13’Cs in milk, grass and fodder was determined and F,,, was estimated. The aims of the investigations were to determine the 13’Cs transfer coefficient, F,,,, from pasture and fodder to cow’s milk, to study timedependent changes in the 13’Cs transfer to cow’s milk and to estimate the effective ecological half-life of 13’Cs in milk.
MATERIAL
AND METHODS
Dairy farms located 3&50 km south (Area A) and 20 km north of Gavle (Area B) were studied. The i3’Cs ground deposition was 20-60 kBq m-* in Area A, and 100-200 kBq m-* in Area B (Fig. 1). The farms represented different soil types, different sizes of dairy herd in the range of 9-50 milking cows of mostly Swedish Red and White and Swedish Friesian dairy breeds and different pasture management systems. Hay or silage and concentrate were used as supplementary fodder. The different studies are described in Table 1. More information about the farms and the diets can be found in Karlen & Johanson (1987) and Alskog (1992).
G. Karl& et al.
4
TABLE 1 Study Periods, Areas and Farms in the Dairy Farm Studies Sampling series
4
5
Period
Area
Farms
Study
1986
A
2 farms
Sampling of milk and grass F,,, (winterfodder)
1987 April-May 1 month 1987 May-June 1 month 1987 June l-5 weeks 1988 May-June 1 month 1989
A
12 farms
A
11 farms
F,,, (pasture)
B
4 farms
F,,, (pasture)
A
5 farms including A,
F,,, (pasture)
A
A, = extensive
Sampling of milk
farm 1990 1992 One day 1993 One day
A A and B A and B
8 farms altogether 8 farms altogether
Estimated F, Sampling of milk
1986, Area A
In 1986, continuous farms in Area A.
sampling of grass and milk was performed
on two
1987 and 1988, Area A During the first month on pasture in 1987 and 1988, daily samples of milk and fodder were collected on the 11 farms south of Gavle, in Area A. The same 11 farms had previously been studied when feeding winter-fodder in 1987. The transfer coefficient, F,,,, for transfer of 137Cs from fodder to milk for the individual farm and for each period was calculated (Karlen et al., 1991). 1987, Area B Four farms north of Gavle, in area B, were investigated during the first l5 weeks on pasture in 1987 by Alskog (1992) in the same manner as in
Tram@
of ‘37Cs to cow’s milk
5
Area A, but milk samples were taken every second day. F, was calculated for each farm. 1992, Areas A and B In summer 1992, the ‘37Cs in milk, grass and fodder was determined. Eight farms from previous investigations where the milk production continued were included in this investigation. Samples of grass and fodder were taken one day in each month. Samples of milk were taken two days after each sampling of feed. The amount of supplementary fodder consumed was estimated by the farmer. 1993, Areas A and B Caesium-137 activity concentrations in milk on the remaining farms still producing milk were measured in summer 1993. Field data In all investigations, samples of pasture grass were taken from an area of 1 m2 in the field where the cows grazed. Milk samples were taken daily in Area A and every second day in Area B. Daily samples of supplementary fodder were taken from the feeding trough where the cows ate. All fodder was weighed twice a week in the more intensive investigations in 1987 and in 1988. The amount of milk produced at each farm was registered in the regular routines when milk was transported to the dairies with the addition of milk fed to the calves and used in the household. Radiometric and chemical analysis All ‘37Cs activity concentrations were measured using hyperpure Germanium detectors (ORTEC or PGT) placed in a low background laboratory at the Department of Radioecology, Uppsala. Chemical analyses of the fodder and pasture grass were performed by the Swedish National Laboratory for Agricultural Chemistry using standard methods. Intake of grass The average consumption of energy in pasture grass was calculated from Swedish standards for the cow’s need of metabolizable energy for maintenance and production, less the energy derived from the fodder (Eriksson et al., 1972; Spiirndly, 1989). Knowing the energy intake from
6
G. Karl& et al.
grass, the dry matter (DM) intake from grass (MJ) divided by MJ/kg protein in milk were obtained from recording, i.e. milk recording every (Bigs et al., 1987).
could be calculated as total energy DM grass. The contents of fat and the regular routines of official milk month and IR-analyses of the milk
The transfer coefficient, F,,,, for milk
The transfer coefficient, F,,, (d kg-‘), were calculated as outlined by Ward and Johnson (1986) Bq kg-’ milk/Bq intake per day
(at equilibrium)
As the density of cow’s milk is close to 1, the units litre and kg were considered to be equivalent, and 137Csactivity concentrations were determined on a weight basis. The aggregated transfer coefficient,
Tag
The aggregated transfer coefficient, Tag, is expressed as Tag = Bq kg-’ of food product/ground deposition (BqmP2) (Howard et al., 1994). The effective ecological half-life
The decrease in 137Cs activity concentration in cow’s milk sampled from cows grazing under similar conditions for several years can be described as the effective ecological half-life (Aarkrog, 1992; Howard et al., 1994) 1 _=-T4f
1
1
TPhYs+ T,,,
Teff = the effective ecological half-life, Tphys= the physical half-life, T,,, = the half-life of the stable elements in the studied ecosystem.
RESULTS 1986
The 137Cs activity concentration in milk during the summer of 1986 on two farms is shown in Fig. 2. At these farms the cows grazed outdoors throughout the pasture season. The aggregated transfer factor of 137Cs from pasture to milk was estimated to be 3.5 x low3 m2 kg-’ f 1.5 x lop3 (sd). No estimation of the F,,, could be made.
Transfer qf 13’Cs to COW’Smilk
,-* ,
10
20
30 40
50
60
70 80
’ I
:
1
:
:A1
90
loo
110
Days Fig. 2. ‘37Cs activity concentrations
Transfer coeffkients,
in milk from two farms in Area A, in 1986. Day 0 is about 15 May 1986.
F,
The ‘37Cs transfer coefficients, F,,for all the years are summarized in Table 2. In all the investigations from Area A (winter-fodder 1987, pasture 1987 and 1988) an average F, was estimated to be 0.0055 with a range of O-0039 to 0.0080. In 1992, an average F, was estimated to be O-006 in June, 0.007 in July and 0.01 in August in Areas A and B. TABLE 2 Average F,,, and Mean Errors in the Studies of Area A and B Study
Winter-fodder Pasture Pasture Pasture Pasture
Area
Year
A A B A A and B
1987 1987 1987 1988 1992 June July August
F,
Range
0.0048 f 0.002 (me) 0.0055 f 0.0016 0.01* 0.0071 & 0.0007 Estimation: 0.006 0.007 0.01
*Data from Alskog (1992) have been further calculated in the present work, to estimate mean F,,, and range.
G. Karlth et al.
8
The 137Csactivity transfer coefficient, F,, to milk on live farms on three occasions in the summer of 1992 are shown in Table 3. Caesium-137 in milk in 1992 and 1993
The 137Cs activity concentrations in milk ranged from < 2-11 Bq kg-’ in June, 2-15 Bqkg-’ in July and < 2-21 Bqkgg’ in August 1992. In 1993, the 137Csactivity concentrations in milk were 2-12 Bq kg-‘. The estimated F,, increased from 0.006 in June and 0.007 in July to 0.01 in August 1992. On three more farms (A5, A6 and B4), the ‘37Cs activity concentration in milk was considered too low to be used for F,,, determination in June 1992. In 1993, the ‘37Cs activity concentration in milk on the same farms and in milk from an additional two farms (A7 and A8) was measured to be within the same range as in June 1992. The effective ecological half-life
The changes in 137Cs activity concentration in milk with time on the intensively managed farms is shown in Fig. 3. The effective ecological halflife for milk from 10 farms was estimated to be 1.4 f 0.5 (sd) years from . 1987 to 1993, with a range of 0.8-2.0 years. On one extensively managed farm, A,, the effective ecological half-life could not be estimated. The average 137Cs activity concentration in milk was found to be about 300 Bq kg-’ in June 1988 and 170 Bq kg-’ in August 1988. In the following years there were large variations in the 137Csactivity in milk. During August in 1989 and 1990, the average 137Cs activity in milk was still comparatively high, 100 Bq kg-‘. Caesium-137
The ’37Cs activity concentration in grass (Table 4) on farm A 1 in 1986 was on average 28 000 Bq kg-’ dry weight (dry wt) in the bottom part of the grass ( < 5 cm), and 1600 Bq kg-’ dry wt in the top of the grass ( > 5 cm). In 1992, the 137Csactivity concentration of the whole grass was 40 Bq kg-’ dry wt on the farms Al and A4. In Area B, the average 137Csactivity concentration in grass was 1600 Bq kg-’ dry wt in 1987 and 50 Bq kg-’ dry wt in 1992.
DISCUSSION In 1986, the aggregated transfer factor (T& was estimated to be 3.5 x 10W3m* kg-’ f 1.5 x 10e3 (sd) on two farms south of Gavle, in Area A
Average
0.006
3
0.004
3 <2 <2 12
24 6
0.003 0.004 0.009
B3 B4 A5 A6 A7 A8
15
0.01
11
<2 2 6
Al
Cs activity (Bq kg-‘)
F,,,
July 1992
<2
oGO9
0.007
28 21
Cs activity (Bq kg-‘)
0,003 0.004 0.01
0.009
F,
August 1992
0.01
3 O-008
3 <2 <2 ‘E3
5 12
Cs activity (Bq kg-‘)
1993
0.008 0.016
F,
TABLE 3 in Milk in 1992 and 1993, and Estimated F,,, in June, July and August 1992
Cs activity (Bq kg-‘)
June 1992
A4 Bl B2
Farm
‘37Cs Activity Concentrations
W
k 3 s S Q 6 B d h3 g
2
Bq kg-’ 140 130
1986
1987
1988
Years (a) Bq kg-’ 130 120 110 100 90 80 70 60 50 40 30 20 10 0 1987
1992
Years (b) Fig. 3. (a) “‘Cs activity concentrations in milk from farms in Area A. Mean values for June 1986. and for the first four weeks on pasture in 1987 and 1988. One days milk sample in June 1992 and in June 1993. (b) “‘Cs activity concentrations in milk from farms in Area B. Mean values from the study period in June 1987. One days milk sample in June 1992 and in June 1993.
Al Al-Al 1 Al-A3, AS, A, Al,A4 Bl-B4* Bl-B3
1986 1987
1600 f 900 (sd)
500 f 500 (sd)
28 000 f 6 000 (sd)
Bottom (&5 cm)
50 f 60 (sd)
150 f 60 (sd) 40 f 30 (sd)
Combined
1300 * 1300 (sd)
I 600 f 1000 (sd) 400 f 400 (sd)
Top (5 cm)
Average 137Cs activity in grass (Bq kg-’ dry wt)
*Data from Alskog (1992) have been further calculated in this work, to estimate mean 13’Cs activity concentration the first four weeks on pasture.
1987 1992
1992
1988
Farms
Year
TABLE 4 13’Cs Activity Concentrations in Grass of Study Farms
in grass (dry wt) and sd,
4 30 10
20
40
3
Samples (N)
’
5 z? S 8 F *3
%
Y $ % TL
12
G. Karl& et al.
(Fig. 2). The average F,,, in all the initial more intensive investigations from Area A (Table 2) was 0.0055 with a range of 0~0039-0~0080, including the study when feeding winter-fodder. In the first month on pasture in 1987 the average F,,,was 0.0055 f 0.0016 (me) in Area A, and in 1988 0.0071 f 0.0007 (me). As a comparison an average F,,2of 0.0079 with a range of 0.001-0.027 was reviewed by IAEA (1994). The variations from year to year in F,,, and the variations of F,,, between different farms were rather small (Table 2). One reason for the variations of F,,, might be that the bioavailability of 13’Cs increased over the years, compared with the year of the fallout (Hansen & Hove, 1991; Hilton, 1992). Another explanation of the variations within each investigation might be that the fodder and pasture were contaminated by soil, which influences the transfer of 13’Cs across the gut, depending on the type of soil (Bertilsson et al., 1988; Desmet et al., 1991). Clay particles bind radiocaesium strongly, whereas peat binds it loosely (Eriksson, 1978). The soil intake of a cow on pasture might be up to 1 kg per day (Fries & Marrow, 1982), especially on well-frequented and used pasture (Burmann, 1968). Hansen and Hove (1991) reported also higher bioavailability of 13’Cs in mushrooms, which might be one reason for the tendency of increased F, observed in August 1992 compared to June 1992 (Table 3). In all investigations of F, on a farm level, it is essential to distinguish between an estimation of F,,, based on a few samples and a more rigorously calculated F,, where samples are taken regularly for a longer period (Hansen & Andersson, 1994) and the amount of fodder is weighed as in the present studies of 1987 and 1988 (Mayes, 1989). There is a variation in 13’Cs transfer from soil to grass depending on the type of soil, which was also observed after the Chernobyl fallout (Eriksson & Rosen, 1991). Transfer of 13’Cs from different types of soil to grass is described in Haak et al. (1973) and Eriksson (1978). The hay or silage used in the present investigations on pasture was usually harvested on the same farms, and mostly from the same region. In 1986, the 13’Cs activity concentration in the bottom of the grass was found to be higher than in the top of the grass. The recommended harvest methods (Hadders & Nilsson, 1987; Bertilsson et al., 1988) to take hay and silage at a higher stubble-height were followed by most of the farmers. The 13’Csactivity concentration in hay and silage was part of the 13’Csactivity concentration in total fodder. Crude fibre was found to bind radiocaesium (Johnson et al., 1968). Beresford et al. (1992) also found higher 13’Cs transfer across the gut of sheep for 13’Cs incorporated in grass than for r3’Cs incorporated in heather. The ‘37Cs activity concentration in milk on the farms decreased with time (Fig. 3). The effective ecological half-life for milk from 1987 to 1993 is estimated to be on average 1.4 f 0.5 (sd) years for 10 farms (Fig. 3) with
Transfer of 137Cs to cow’s milk
13
a range of 0.8-2.0 years. Most of the farms included in this study use an intensive management system, rather typical for the agricultural districts in Sweden, and the recommendations set by The Swedish Agricultural Board were followed. The farms where 13’Cs in milk decreased at a slower rate used some semi-natural pasture, sometimes in forest, where the cows had access to wild plants and mushrooms. The effective ecological half-life for ‘37Cs in milk in the study might also be shorter, since no sampling of milk was performed on these farms in 1989-1991. On the extensively managed farm, A,, using forest fields of peat soil, no effective ecological half-life could be estimated-or set to 30 years-since there were large temporal variations in i3’Cs in milk (Karlen et al., 1991). Also in Norway, the effective ecological half-life for one extensively managed farm in the mountain was estimated to be about 30 years based on studies from 1988 to 1992. On three other extensively managed farms in the same area in Norway, the effective ecological half-life for milk was estimated to be 4.8 years based on studies from 1989 to 1992, with a range of 2.7-6.7 years (Strand et al., 1992). An effective ecological half-life in Norway was estimated to be 2.3 years based on studies from 1987 to 1992 in milk of dairies in contaminated regions (Hansen & Andersson, 1994). In Denmark, an estimated effective half-life was reported to be 1.6 years, based on studies conducted in dairies from 1987 to 1991 (Aarkrog, 1992). In Sweden an effective ecological halflife of 13’Cs in milk of all dairies was estimated to be 1-Oyear, based on studies from 1986 to 1990. In the mountain areas of Sweden where uncultivated pasture was used, the effective ecological half-life of 13’Cs in milk of the dairies was estimated to be about 3 years (Suomela & Melin, 1992). The differences might be explained for example by differences in agricultural management system, as the farms in Norway and in Sweden are more extensively managed in the mountain areas than farms in the agricultural districts of Sweden or Denmark. It can be concluded that on semi-natural pasture, especially on peat soil, and where no ploughing was undertaken, nor any application of potassium, the 13’Cs in cow’s milk decreases at a much slower rate than on intensely managed and well-kept fields, which was reflected both in the present single farm investigations and studies of dairy statistics (Suomela & Melin, 1992; Hansen & Andersson, 1994).
ACKNOWLEDGEMENT This work was done with the financial support of The Swedish Radiation Protection Institute. The authors especially want to thank all the farmers
G. Karl&
14
et al.
participating in the studies. They are also grateful to all the technical staff at the Department of Radioecology.
REFERENCES A. (1992). d;kologiske Halveringstider i Ftiroske og Danske Landbrugsokosystemer. (In Danish.) (Effective Eecological Half-Lives in the Agricultural Ecosystems of Faroe islands and Denmark.) The Sixth Nordic Seminar of Radioecology, Torshavn, Faroe Islands, 1418 June 1992. Alskog, E. (1.992). Lokala Undersokningar i Jordbruket efter Tjernobylolyckan 1986, I. Overforing av Radiocesium frdn Betesmark till Mjolk i Gavleborgs Ian 1987. (In Swedish.) Rapport SLU-REK-69-SE, ISSN 0280-7963, Dept. of Aarkrog,
Radioecology, Swedish University of Agricultural Sciences, Uppsala, Sweden. Beresford, N. A., Mayes, R. W., Howard, B. J., Eayres, H. F., Lamb, C. S., Barnett, C. L. & Segal, M. G. (1992). The bioavailability of different forms of radiocesium for transfer across the gut of ruminants. Radiat. Prot. Dosim., 41,87-91.
Bertilsson, J., Andersson, I. & Johanson, K. J. (1988). Feeding green-cut forage contaminated by radioactive fallout to dairy cows. Health Phys., 55, 855-62. Bigs, D. A., Johnson, G. & Sjaunja, L.-O. (1987). Analyses of fat, proteins, lactose and total solids by infra-red absorption. Rapid indirect methods for measurements of the major components of milk. Znt. Dairy Fed., Bull., 208. Burmann, F. J. (1988). Influence of grazing intensity on Cs-137 levels in milk. J. Dairy Sci., 50, 1891-6.
Desmet, G. M., Van Loon, L. R. & Howard, B. (1991). Chemical speciation and bioavailability of elements in the environment and their relevance to radioecology. Sci. Total Environ., 100, 105-24. Eriksson, S., Sanne, S. & Thomke, S. (1972). Feeds (In Swedish.) LT Publishing Company, Sweden. Eriksson, A. (1978). Transport of Radioactive Fission Products from Arable Land and Pastures to Domestic Animals and Man. Swedish University of Agricultural Sciences, Dept. of Radiobiology, Report 46, Uppsala, Sweden. Eriksson, A. & Rosen, K. (1991). Transfer of caesium to hay grass and grain crops after Chernobyl. In The Chernobyl Fallout in Sweden, ed. L. Moberg. The Swedish Radiation Protection Institute, Stockholm, Sweden, pp. 291-304. Fredriksson, L., Garner, R. J. & Russell, R. S. (1966). Caesium-137, In Radioactivity and Human Diet, ed. R. Scott Russell. Pergamon Press, Oxford, pp. 3 17-52. Fries, G. F. & Marrow, G. S. (1982). Soil ingestion by dairy cattle. J. Dairy Sci., 6561
l-18.
Haak, E., Eriksson, A. & Karlstrom, F. (1973). Studies of Plant Accumulation Under Swedish Conditions. Entry of 90-Sr and 137-Cs into Herbage of Contrasting Types of Pasture. FOA-4, Rapport C 4525-A3, Fiirsvarets Forskningsanstalt, Sweden. Hadders, G. & Nilsson, E. (1987). Sk&d av Foder som Drabbats av Radioaktivt Nedfall. JTI-Report No. 87, Swedish Institute of Agricultural Engineering, Ultuna, Uppsala, Sweden (in Swedish).
Transfer of 137Cs to cow’s milk
15
Hansen, S. H. & Andersson, I. (1944). Transfer of Chernobyl i3’Cs fallout to cow’s milk in the Nordic countries. Nordic Radioecology, Chapter 3.5, Reports from the RAD-programme. Hansen, S. H. & Hove, K. (1991). Radiocaesium bioavailability: Transfer of Chernobyl and tracer radiocaesium to goats milk. Health Phys., 64&5), 665-73. Hilton, J., Cambray, R. S. & Green, N. (1992). Chemical fractionation of radioactive caesium in airborne particles containing bomb fallout. Chernobyl fallout and atmospheric material from the Sellafield Site. J. Environ. Radioactvity, 15, 103-l 1. Howard, B. J., Mayes, R. W., Beresford, N. A. & Lamb, C. S. (1989). Transfer of radiocesium from different environmental sources to ewes and suckling lambs. Health Phys., 57, 579-86. Howard, B., Johanson, K. J., Linsley, G. S., Hove, K., Priihl, G. & Horyna, J. (1994). Transfer of Radionuclides by Terrestrial Food Products from SemiNatural Ecosystems. VAMP terrestrial working group. Part of the IAEA/ CEC Co-ordinated Research Programme on the Validation of Environmental Model Predictions (VAMP). IAEA (1984). Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Temperate Environments. IAEA, Vienna, Austria. Johnson, J. E., Ward, G. M., Firestone, E. & Knox, K. L. (1988). Metabolism of radioactive cesium (‘34Cs and 13’Cs) and potassium by dairy cattle as influenced by high and low forage diets. J. Nutr., 94, 282-8. Karlen, G. (1993). Transfer of 37Cs to Milk of Cow and Muscle of Roe Deer. Report SLU-REK-71, Dept. of Radioecology, Swedish University of Agriculture, Uppsala, Sweden. Karlen, G. & Johanson, K.-J. (1987). Betesvallens Radioekologi. SSI-Rapport (in Swedish). The Department of Radioecology, Swedish University of Agricultural Sciences, Uppsala, Sweden. Karlen, G., Johanson, K.-J. & Bertilsson, J. (1991). Transfer of cesium-137 from pasture to milk after Chernobyl. Investigations of dairy farms in Sweden, In The Chernobyl Fallout in Sweden, ed. L. Moberg, The Swedish Radiation Protection Institute, Stockholm, Sweden, pp. 343-60. Mayes, R. W. (1989). The quantification of dietary intake, digestion and metabolism in farm livestock and its relevance to the study of radionuclide uptake. Sci. Total Environ., 85, 29-51. SGAB (1986). Ground deposition of Cs- 137 in Sweden. Map, Swedish Geological Company, Uppsala, Sweden. Sporndly, R. (1989). Fodertabeller for Idisslare (in Swedish). Speciella Skrifter 39, Swedish University of Agriculture, Uppsala, Sweden. Strand, P., Amundsen, I. & Selnaes, T. (1992). Overvdkingsmalinger for Radiocesium in Norske Husdyrprodukter (in Norwegian). Interim Report of The Norwegian Radiation Protection Authority (Norska Statens Strblevarn), Osteras, Norway. Suomela, J. & Melin, J. (1992). Farekomsten av Cesium och Strontium-90 i Mejerimjiilk fiir Perioden 1955-1990 (in Swedish). SSI-Rapport 92-20. Statens Strilskyddsinstitut. The Swedish Radiation Protection Institute, Stockholm, Sweden. Ward, G. M. & Johnson, J. E. (1986). Validity of the term transfer coefficient. Health Phys., 50,41 I-14.