Transfer of Chernobyl radiocaesium (134Cs and 137Cs) from grass silage to milk in dairy cows

J. Environ. Radioactivity 13 (1991) 125-140

Transfer of Chernobyl Radiocaesium (t34Cs and from Grass Silage to Milk in Dairy Cows

137Cs)

P. I. Voors & A. W. van Weers Radiobiology and Radioecology. Department of Physics. Netherlands Energy Research Foundation (ECN). PO Box 1, 1755 ZG Petten (NH), The Netherlands (Received 12 October 1989; revised version received 19 February 1990; accepted 6 March 1990)

A BSTRA CT The transfer of Chernobyl radiocaesium dlrough the sihtge--cow-milk path way has been in vestigated under normal farming conditions. A period bt which grass silage with a relatively high level of radiocaesium was fed was preceded attd followed by periods of low-level contanzinated feeds. A n average tran.,fer coefficient from feed to milk, Fro, of 0.25% d liter- t has been derived for radiocaesium. A simph, two-compartmental model has been applied to predict the radiocaesium concentration in milk from the intake with feed. An estimate of three model parameters, F (fractional digestibility of radiocaesium in feed and the fraction secreted in both urine and milk), m attd u (tran.sfer rates from the body fluids to milk and urine) was made on the basis of a sampling and measurement programme on the urine, faeces and milk of two cows during a 48h period. With the derived F-vahte of O.13 and a u/m-ratio of Sl liter d -t, the model appeared to predict a 1.5-fold lower concentration of radiocaesium b~ milk than wtts, actually measured. This discrepancy was consistent with the observed rather low total excretion of radiocaesium. With an F-vahte of 0.19, acceptable agreement between predicted and measured radiocaesium concentrations in milk was reached.

INTRODUCTION As a result of the Chernobyl nuclear accident (26 April 1986), radioactive fallout c o n t a m i n a t e d pastures and o t h e r vegetation used as animal or 19_5 J. Environ. Radioactivity 0265-931X/90/$03.50 ~ 1991) Elsevier Science Publishers Ltd. England. Printed in Great Britain

126

P. 1. Voors. A . W. van Weers

human foods throughout Europe. These radionuclides reach man via contaminated (fresh or stored) crops and animal products (e.g. meat, milk). The long-lived fallout radionuclides, e.g. t34Cs and 137Cs. will be detectable in the environment for many years in locations where initial contamination levels were relatively high. As a result, radiocaesium isotopes were still easily measurable in grass silage harvested in June 1986 but used as fodder for dairy cows in 1988. To predict the concentration of radiocaesium which reaches man through the silage-cow-milk pathway, transfer coefficients from feed to milk have been investigated here. In addition, the study aimed to test a simple two-compartmental model. The study was carried out under normal farming conditions in the period March-May 1988 and was supported by the Dutch Ministry of Agriculture and Fisheries.

MATERIALS AND METttODS

Feeding periods The transfer of Chernobyl t34Cs and t37Cs in the silage- cow-milk pathway was investigated under normal farming conditions with a herd of twenty-one dairy cows in varying stages of the lactation cycle. During this period, feeds with different contamination levels of the Chcrnobyi radionuclides t~4Cs and I'WCs were available to the herd. The herd was fed grass silage (or hay and pasture grass) as a bulk feed supplemented with potatoes and concentrate. The grass silage fed till 5 March was harvested in June 1987 and contained a relatively low level of Chernobyl radioactivity (silage-1987). in the following period till 13 April, the herd was fed grass silage harvested in June 1986, which contained a relatively high level of Chcrnobyl radioactivity (silage-1986). Towards the end of the silage1986 feeding period, two dairy cows in the second week of the lactation cycle were isolated from the herd for 48 h and milk, urine and faeces were sampled. Between 13 April and 13 May, the herd was grazing and returned to the cowshed at night. During the night, the herd was fed grass silage (till 27 April) harvested in July 1987, which contained a relatively low level of Chernobyl radioactivity, and subsequently hay harvested in July 1986. From 13 May, the herd stayed permanently on pasture except for milking.

~mple collectionand trmdment Single or multiple samples were taken from each lot of grass silage, hay, potatoes and concentrate. During 23 January-15 April 1987 (about a year

127

Transfer o f radiocaesium from silage to milk in dai~ cows

before this study), nine silage-1986 samples were obtained by vertical coring through the clamp to determine whether contamination was homogeneous. During feeding of the silage-1986, eight samples were obtained (with time intervals of about 4 d) by taking samples from the front of the clamp. The silage-1987 samples were also obtained by taking samples from the front of the clamp. Hay samples were collected from the sides of the bales. All samples of grass silage and hay were dried overnight at 100°C and subsequently cut into small pieces. Hay harvested during the pasturing periods was used to derive the concentrations of l~Cs, 137Csand 4°K in pasture grass. The potatoes were sliced and subsequently freezedried. Concentrate samples were collected from the lots and were not treated further. The milk produced by the herd was collected in a cooling tank, from which 5-liter samples were collected. The milk from the two isolated dairy cows was sampled before mixing occurred in the cooling tank. All milk samples were prcscrved with formaldehyde. The sampling scheme is given in Table 1. The fced intake was registered :rod the urinc and faeces produced by the two dairy cows were collected for 48 h. The urine and faeces were stored in 10-1itcr bottles and buckets, respcctively. The daily-produced faeces of each cow were mixed to obtain two st, bsamplcs, which were freeze-dried. Thymol was added to the urine as a preservative.

TABLE I Milk Sampling Scheme Period

1x Daily

2x Daily

I x 2 Daily

! x Weekly

tterd o f dairy cows

29 Feb. 1988-5 Mar. 1988 6 Mar. 1988--9Mar. 1988 I0 Mar. 1988-23 Mar. 1988 24 Mar. 1988-12 Apr. 1988 13 Apr. 1988-15 Apr. 1988 16 Apr. 1988-20 Apr. 1988 21 Apr. 1988-311Apr. 1988 1 May 1988-311May 1988 Two dairy, cows

6 Apr. 1988-8 Apr. 1988 (Time 6:30) (Time 6:30)

×

×

128

P. 1. Voors, A . W. van Weers

Analysis The activities of ~34Cs, ta7Cs and 4°K in all samples (counting time 50 000 s) were d e t e ~ n e d with High Purity Germanium detectors. A quantity of 200--400g dry matter of grass silage, hay, potatoes or concentrate was counted in a l-liter Marinelli beaker. Milk and urine samples were measured in a 3-3-liter Marineili beaker, which is standard at ECN for measurements of radionuclides in water samples (density of I kg liter-~). Counting efficiencies of 0.2 and 0.4 kg liter "l were determined using sawdust and a commercial dried animal feed labelled with a 10 g standard solution (No. 87-679, Physikalisch,Technische Bundesanstalt, Braunschweig, Germany) of 7Be, 54Mn, 57Co, 6SZn. SSy, 133Ba" 137Csand t39Ce" Estimates of daily intake As the study was carried out under normal farming conditions, accurate determinations of the herd's daily intakes of activity with feed were not possible. Estimates of the daily dry matter intake were made by calculating the theoretical energy requirements of the dairy cows using milk production data, dairy cow body weights and milk fat percentages (Central Office of ttusbandry-feed in The Netherlands, 1986; Voors & van Weers, 1989). The average body weight of the dairy cows was about 500 kg. The number of dairy cows, average daily milk production, fat percentages in milk and the estimated daily ration of grass silage and the total daily ration supplied in 11 periods (distinguished on the basis of the number of dairy cows and feed lots) are given in Table 2. The estimated daily intakes of the bulk feeds, grass silage and pasture grass (or hay) were obtained by subtracting the amounts of potatoes (1400 kg fresh weight per week) and concentrate (1 kg per 5 liter milk produced) from the theoretical energy requirement. Conversion of VEM-units (VEM = fodder unit lactation: 1 VEM ~ ! 1-5 kJ metabolic energy) to dry matter (DM) was based on VEM-values 1044. 1090, 766 and 937 for concentrate, potatoes, grass silage (or hay) and pasture grass, respectively. The calculated rations for the two isolated dairy cows are in good agreement (less than 10%) with the measured rations. It should be noted that uncertainties in the calculated bulk feed rations in the latter three periods (15 April to 30 May) are directly related to uncertainties in the average VEM-values used and the assumption that during pasturing 20% more energy is required (Central Office of Husbandry-Feed in The Netherlands, 1986; Voors & van Weers, 1989). In Fig. 1, the composition of the calculated daily rations of the herd is shown.

1 Mar. 5 Mar. 14 Mar. 30 Mar. 6 Apr. 8 Apr. 9 Apr. 13 Apr. 15 Apr. 27 Apr. 13 May

6 Apr. 1988-8 Apr. 1988

Cow-2

1

1

19 19 19 21 19 21 21 21 21 21 22

( ' 0 W$

Dairy

29-5

27-5

16.9 16-5 17.1 17-4 18-2 19.2 19.3 18.6 21.6 22-8 24-4

Prod. (l/d)

Milk

4.46

4.46

4.32 4.37 4.38 4.39 4.46 4.46 4.46 4.46 4.42 4.13 4-118

Fat (%)

"Supplied to the dairy cows; 22.9 +_8-3% and 23.3 + 4.7%. bSupplied to the dairy cows; 16.3 + 11.3('f- and 16-4 _+6-05~, .

6 Apr. 1988-8 Apr. 1988

1988-4 Mar. 1988 1988-13 Mar. 1988 1988--29 Mar. 1988 1988-5 Apr. 1988 1988--8 Apr. 1988 1988-8 Apr. 1988 1988--12 Apr. 1988 1988--14 Apr. 1988 1988--26 Apr. 1988 1988--12 May 1988 1988-311 May 1988

Cow-I

Two dairy cows

! 2 3 4 5 6 7 8 9 10 I1

tlerd of dairy cows

Perio,l

Silage

ttay

Grass

18.5 (19.4 19.5 (19.8

12.7 12-5 12.8 13-0 13.5 14.0 14.1 13-7 16-1 16.3 17.0 21.5 22-9)" 22.8 23.3)"

14.9 14.7 15.1 15.2 15-8 16-4 16-5 16.(I 17-5 17.7 17.4 11-6 (12-5 12.3 (12-6

8.1 8-0 8-2 8.1 8-4 8.8 8.8 8-6 4.3

15.1 16-3)b 16.(I 16.4) h

10.6 10.5 111.7 10.5 11-0 11-5 11-5 11.2 5-6 4.3

5-6

6.11 6.0 111.8

6.5 ~.5 11.5

Energy DM Energy DM Energy DM Energy DM fkVEMJ (kg/d) (kVEAI) (kg/d) (kVEM) (kg/d) (kVEM) (kg/d)

Total intake

TABLE 2 Number of Dairy Cows, Average Daily Milk Production, Fat Percentage in Produced Milk, Calculated Total Intake and Daily Rations of Bulk Feeds Supplied in Different Periods

t~

q:

"-t

130

P. !. Voors, A. W. van Weers 100

potatoes 80

concentrate L

II

60

pasture grass 40

silage

grass

>.

20

hay

O

.

0

•

I0

~

i

20

•

i

30

*

t

.

40

,.

I

I]

,~0

60

70

•

I

80

go

Oeys

Fig. I. The composition of the daily rations supplied commencing on I March 1988(Day 0).

Modeling The model used to predict the concentrations of radiocaesium in the milk of dairy cows is described by Peiletier & Voilleqtie (1971). It in turn describes radiocaesium metabolism in terms of its transfer to milk and urine from two compartments, the body fluids and muscles. The model assumes that no endogenous radiocaesium is excreted via the faeces and that the transfer rates are constant with time. Furthermore, it is assumed that the concentration of radiocaesium in urine is directly proportional to that in the body fluids. The model is expressed in its differential form by two equations: d Q h l d t = F x C x l + b, x Q m - ( k d Q . . / d t = b,, x Q . - (b, + ~t)Q.,

+ m X Vm + u + b.,)Qh

(1) (2)

where Qb and Q,. = the quantities of the radiocaesium isotopes in the body fluids and muscles, respectively (Bq); F = the fractional digestibility of the caesium isotopes in feed and secreted in both urine and milk; C = the average concentrations of the caesium isotopes in feed (Bq kg-m dry weight); 1 = the average daily intake (kg dry weight d - l ) ; bi and bo = the transfer rates into the body fluids from the muscles and out of the body fluids into the muscles, respectively (d-t); m and u = the transfer rates from the body fluids to milk (liter -t) and urine (d-m); V,. = the average milk production (liter d - t ) ; ~ = the physical decay constant of a radiocaesium isotope (d-I).

Transfer ofl radiocaesium from silage to milk b~ dairy cows

13t

RESULTS AND DISCUSSION Activities in feed, milk, urine and faeces

The results of the radionuclide analyses of the different lots of feeds are presented in Table 3. Silage-1986 contained relatively high levels of Chernobyl t34Cs and n37Cs, whereas silage-1987 was moderately contaminated. Supplementary feeds contained much lower levels of t37Cs, whereas 134Cs was only detectable in hay. The concentrations of both caesium isotopes in pasture grass were derived from hay harvested in 1988. Here it should be noted that continuous grazing could influence the radiocaesium concentration in pasture grass. However, it was expected that the effect of this potential source of uncertainty in the estimate of the total radiocaesium intake was small, because, two years after the deposition of Chernobyl fallout, the radiocaesium level in grass was, in relation to silage-1986, already very low. The potassium isotope, 4°K, was measured in all feeds in concentrations in the ranges 34(b-437 Bq kg(concentrate) and 710-1127 Bq kg-t (grass silage and pasture grass). in addition, the average concentrations of t3~Cs, 1~7Cs and ~q'K in milk are given in Table 3 for sevcn periods corresponding to different bulk feeds. The concentrations of 134Cs, n37Cs and 4°K in milk samples taken from the cooling tank are presented as a function of time in Fig. 2. The low concentrations of both caesium isotopes till Day 4 are the result of low-level contaminated feeds. A marked increase in the concentrations of both caesium isotopes occurred when feeding with silage- 1986 was started. Conversely, the concentrations of both caesium isotopes in the milk decreascd after Day 43 when feeding with silage-1986 was ended and was changed to feeds with relatively low levels of both caesium isotopes. The potassium content in milk was not markedly influenced by the composition of the daily intake and ranged from 0.125 to 0-170% (w/v) and from 0-155 to 0.162% (w/v), which is in good agreement with the published range 0.120-0.189% (w/v) (Ward, 1956; Dennis & Hemken, 1978, Larson, 1985). The differences between the two isolated dairy cows with respect to 4°K concentrations in excretion products were not significant, whereas the l~Cs and t37Cs concentrations in milk, urine and faeces produced by Cow- 1 were respectively about 43%, 38% and 21% higher than for Cow-2 (Table 4). The daily intakes by both dairy cows were the same (Table 2). The percentages of daily radiocaesium intake secreted in milk, urine and faeces of Cow-I (and Cow-2) were 5(3)%, 8(5)% and 42(32)%, respectively (Table 4).

TABLE 3

1 Mar. 1988--4 Mar. 1988 5 Mar. 1988-12 May 19'88 13 May 1988-29 May 1988

5 Mar. 1988-12 Apr, 1988 ! Mar. 1988-4 Mar. 1988 13 Apt, 1988-26 Apr, 1988

9 A p r . 1988-12 May 1988 13 May 1988-29 May 1988

1988-29 Mar. 1988 1988-12 Apr. 1988 1988-14 Apr. 1988 1988-26 Apr. 1988 1988.-12 May 1988

0.1 0.8 1.2 1-4 1-3 0.5 0.2

10.1 2-1

b b b ~'

b

b

b

49.9 2"3 1.9

"Derived from hay activities. fMarked increase or decline of radiocaesium concentration.

CCotmling uncertainty. aAverage activities of the concentrate 1-3.

bNot detectable.

"Number of samples analysed.

14 Mar. 30Mar. 13 Apr. 15 Apr. 27 Apr.

5 Mar, 1988-13 Mar. 1988

1 Mar, 1988-4 Mar. 1988

Afiik (cooling lank j

-1986 27 Apr. 1988-12 May 1988 Pasture" 15 Apr. 1988-.'I,0 May 1988

Ha)' July

-3 -4

Concentral¢ -i 1 Mar. 1988-13 Mar, 1988 -2 14 Mar. 1988-8 Apr. 1988

-I -2 -3

Potatoes

-1986 -1987

Grass silage

45.1 42-8t 15-0 I 1-3 12-2 42.1 -t 24.0

35-2 22.6

13-1 36.7 20-3

0,4 2'6 4-1 4.7 4.3 1-8 0.9

37.4 7-6

0-7 1" I 0.7 0.8

~ 0.4 b

171-8 8-2 9.2

tJ'Cs s.d. tJvCs (Bq kg -t or Bq liter -t) ¢%) (Bq kg -t or Bq liter -t)

14-1 45.0 ¢ 12"2 8'4 11"6 42-6/ 14.4

40.6 5-2

22-3" 15-2" 19.0" a

53-6c

13.4 7.8 12.5

45-8 48,6 50.7 47-6 48-5 46-6 46-0

605.9 i 126.6

437-0 340-0 393.0 390-0

670.0 508.11 794.0

910-4 710.0 1028.0

s.d. *OK (%) (Bq kg -t or Bq liter -t)

4.5 3.8 3.4 4.3 2.9 3.0

I0'I

18-5 3-7

I. 1" 1.5" 1"2" a

1.4¢ 1.7' 1.4'

7.1 21.1 9.7

s.d. ¢%)

4 13 13 4 4 10 6

10 5

a

1

1 I

1 l

I

17 2 3

N~

The Average n-UCs,I-~TCsand *~K Concentrations in Milk (Bq liter -I) and Different Lots of Feed (Bq kg -t dry matter)

e~

e,

,,,..

Transfer o[ radiocaesium from silage to milk in dairy cows

133

60

7

si;age--1986

]

6

50

5

;1" "

",li

'"" .................................

T 40

4

.c_ (J

30 3

2O 2

10

1 J

0

0 0

10

20

30

40

50

60

70

80

90

Days Fig. 2. The concentrations of 'UCs ( - - - - ) , 1~7Cs ( . ) and "U'K(. - • ) as a function of time starting on 1 March 1988 (Day 0).

The radiocaesium bahmce data do show, on the one hand, the phcnomcm~n of a predominant excretion in faeces, as observed by Stewart et al. (1965), Johnson et al. (1968) and Stcinwcndcr et al. (1988). On the other hand, they also show that, after feeding silage-1986 for 33 days, about 4(t--55% of the daily radiocaesium intake was excreted daily. This could indicate that a true equilibrium between uptake and excretion of radiocacsium was not yet obtained as a result of the slow turnover of caesium in certain body compartments, e.g. soft tissues, llowevcr, short-term studies with '37Cs-contaminated hay (7-14 days) (Stewart etal., 1965; Johnson et al., 1968) and with 134CsCI ( v a n den tlock, 198(I) have shown that 93.2%, 99-8% and 92-95%, respectively, were excreted. A five-week study with radiocaesium-contaminated hay and grass silage has also shown that 90.4-99% was excreted (Steinwender et al., 1988). The percentages of the daily ~K intakes of both dairy cows secreted in milk and faeces, of 8% and 8-9% respectively, are in good agreement with the values, of about 7%, given by Johnson et al. (1968) and Stcinwcnder et al. (1988). As a result of the dominance of the urinary excretion of 4~K, a high standard deviation on the average a°K concentration does strongly influence the outcome of the "inK-balance (Table 4). As the uncertainties in the intake figures are only of minor significance, it seems that the 48-h observation period was too short to eliminate the effect of metabolic fluctuations on the balance between intake and excretion.

TABLE 4

29.5 33-3 31.1

Milk Urine" Faeces b

0-05 0-08 0-42 0.55

0-03 0-05 0.32 0.40

f~n, /-,mac f~,~-, ~otaj

f

fmitk fu,~m: ff~.ces ftotal

Average excretion fraction

27-5 41-3 42-3

Production rawa

Milk Urine* Faeces h

Product

IJ4Cs

14.0 13-7 13.3 10-7

13-9 17.4 13"2 10.5

s.d. (%)

0.94 1' 22 51.3

1.34 ! .65 60-7

tJJCs (Bq liter -t)

6-8 7-3 2:5

5.9 10.8 4.7

s.d. {%)

0.04 0.05 0.32 0-41

0.05 0.09 0-43 0.56

f

tJTCs

3-39 4.33 182.1

4.80 5.95 219-8

tJTfs (Bq liter -t)

13-7 15.0 14.6 11.7

14-1 17-8 13.5 10-6

s.d. (%)

3-4 6.5 5.5

4-4 11.7 3.5

s.d. (%)

0-08 0.50 0-08 0.66

0.08 0-65 0-09 0.82

f

5(I-7 262-1 278.4

49.9 27(I-0 261.5

aJK

4°K (Bq liter -t )

6.2 17.2 7.1 13-0

6.6 26.8 6.4 21.4

s.d. (%)

2-8 16.9 5.6

3.2 24.5 5.2

s.d. (%)

OBq kg-~ urine. bBq kg -I dry matter. ~Counting uncertainty. aMilk (kg d-t); urine (kg d-t); faeces (kg wet d-t). The dry matter contents in faeces of Cow-I and Cow-2 is 13 and 16-°r'~,/~,respcctiwqy.

Cow

Cow

The Average Concentrations and Excretion Fractions of I~tCs, t3~Cs and *'K in btilk, Urine and Faeces of Two Dairy Cows

Transfer of radiocaesium from silage to milk in dais" cows

135

Calculation of transfer coefficients

The equilibrium coefficient for transfer of radionuclides from feed to milk, Fro, is defined as the fraction of the daily intake of a radionuclide which is excreted per kilogram (or liter) of milk produced (d kg-t or d liter-~) or as a percentage of the daily intake excreted per kg milk (% d kg -~ or % d liter-l). The contribution of grass silage to the average intake concentrations of radiocaesium is 99-8% or more in the periods of interest (between 5 March and 12 April 1988) (Table 5). As a result of feeding silage-1986 as a bulk feed in both experiments, the average intake concentrations of both caesium isotopes are relatively high. Consequently, standard deviations of 13.1% and 13-4% for t34Cs and 137Csin silage-1986 and 11-3-15-0% and 8-4-12.2% for 134Cs and 137Csin milk (Table 3) were relatively small when equilibrium between uptake and secretion in milk was reached for both caesium isotopes. Therefore, the precision of the calculated F,, is best at the end of feeding silage- 1986 (Period 4 in Table 3 and Pcriod 4-7 in Table 5). The average/;~ value was 0.25% d liter -I, for both caesium isotopes; in agreement with the range of 0-1-4)-4% d litcr -~ published in rcccnt post-Chcrnobyl studies (Staatlichc Lchr- und Vcrsuchanstalt fiir Vichhaltung Aulcndorf, 1986; Bradley & Wilkins, 1989; Pcarce et al., 1989; Voors & van Weers, 1989). For the two isolated dairy cows, the average transfer coefficient, Fro, was 11.15% d liter- t for both caesium isotopes; signilicantly lower than the average value, of 0.25% d liter -~, for the herd. Nevertheless, this lower F,,, value is still within thc range of published l~,, data from recent studies on Chernobyl radiocaesium. The average Fm value for 4~JKvaried from {I.47 to 0.29% liter d - i (Table 5). There was no evidence that milk production and daily intake data influenced the Fm value markedly. Model The 137Csconcentrations were corrected for dilution in the cooling tank and fitted by the model (Fig. 3). This correction was only important in the periods when there was a rapid increase (or decrease) in the concentrations of the caesium isotopes in the milk. In these periods, two milk samples were collected daily from the cooling tank after morning and evening milking, respectively (Table 1). It was therefore possible to derive the concentration of radiocaesium in each separate milk production on the basis of the amounts of milk produced and the measured or calculated concentrations of radiocaesium from previous productions. Some of the model parameter values used (Table 6) were obtained from the uptake and

TABLE 5

8 Apr.

9 Apr. 13 Apr. 15 Apr. 27 Apr.

13 May

6

7 8 9 10

11

Cow-I Cow-2

1988-4 Mar. 1988 1988-13 Mar. 1988 1988--29 Mar. 1988 1988-5 A p r . 1988 1988-8 Apr. 1988 1988-8 Apr. 1988 1988-12 Apr. 1988 1988-14 Apr. 1988 1988-26 Apr. 1988 1988-12 May 1988 1988-30 May 1988

6 Apr. 1988-8 Apr. 1988 6 Apr. 1988-8 Apr. 1988

Two dairy cows

1 Mar. 5 Mar. 14 Mar. 30 Mar, 6 Apr.

1 2 3 4 5

Herd of dairy con,s

Period

1~TCs

~°K

34.2 34-3

1.6 35-9 35.5 34.3 34.3 34-3 34.2 1.3 1-4 3.9 1.4 100.0 10041

100.0 100.0 100-0 100.0 100-0 100-0 100.0 100.0 44.2 --0.18 0.12

0-45 0.15 0.23 0.25 0-24 0.24 0.26 4.61 1.73 0-37 0.92 119.4 119-9

5.9 122.2 122-2 119.4 ! 19-8 119.8 119.6 6-7 6-0 14.8 5.3 99.8 99.8

97.7 99.9 99.8 99,8 99.8 99-8 99-8 97-2 49-7 --0-19 0.12

0.47 0-15 0'22 (I.25 0,25 0-25 0.27 3.18 1.41 0-36 0-87

748.8 749.1

650.7 793.8 773-6 752.6 753-4 753-(i 764-1 846-2 878.3 737.9 912.8

84.4 84.7

77.3 81.4 83.6 83-9 84. ! 84-2 83.(I 84-6 37.6 ---

0.31 0.30

0'47 0,41 0.44 0.43 0.39 0-36 0.37 0.35 0-30 0.35 0.29

Average Grass Fm Average Grass Fm Average Grass F,,, cone. silage (% d liter -z) cone. silage (% d liter -t) cone. silage (% d liter -t) (Bq kg -t) (%) (Bq kg -t) (%) (Bq kg -~) (%)

t34Cs

The Average Intake Concentrations of 134Cs. 137Cs and ~ K and the Contribution of Grass Silage to the Average Daily Intake (Bq k g i l)ry Matter)

(Bq kg )) (Bq) (Bq)

(kg d -t ) (liter d - i )

(d-t) (d-i) (d-~) (d- ~) (d- e) (liter- ~)

5-9 80 360

0-0198 0.30 0.066 0.026 11.170 0.1 X ) 3 4 0.13 14.9 16.9

0--4,4

Da;'

122.2-119-6 57-938 166-1258

0-0198 0.30 0.066 0.026 0.171-0.164 0.1X13.4--0-0033 O. 13 14-7-16-4 16.5-19.3

4.4-43,4

5 Mar. 1988 I(9 13 Apr. 1988

6.3 979--570 1414.- 1444

0.0198 0.30 0.066 0-026 0.16,5-41.159 0.(X)33-O.IX)32 0-13 16.0-17.5 18.6--21-6

43.4-55

13 Apr. 1988 to 27 Apr. 1988

14.8 182 1270

0.0198 0-30 0.(~6 0.026 0- ! 56 11.(X)31 O. 13 17.7 22-8

55-71

27 Apr. 1988 to 13 Afay 1988

5-3 213 1020

0.(1198 0.311 0.066 ().021) 0.153 ().(X)31 l). 13 17-4 24.4

71-89

13 May 1988 to 30 May 1988

rl is the secretion rate from the long-lived compartments, r~, is the secretion rate from the short-lived com|)artment, (.)~, is the estimated quantity of t~TCs in body lluids at the start of a period and Qmo is the estimated quantity of i-~7Cs in muscles at the start of a Period.

C Q~ Qmo

t ~7Cs:

Vm

F I

m

rt r: bo b, u

Parameter

1 Afar. 1988 to 5 Afar. 1988

Period

TABLE 6

Parameters Used in the Model

-.-..I

S

r,

?,

138

P+ 1. I/oors. A . W. van Weers

5

T

o}

4

3

2

1

0 0

10

20

30

40

50

60

70

80

90

Dsys

Fig. 3. The concentration of ~+TCs corrected for dilution ( ) and the: predicted concentrations using F = II. 13 ( - - - - ) and F = I). I t~ ( - - - - - ) , respectively, with a u / m rati() of 51 liter d '

secretion data (F, u and m) l+orthe two dairy cows and from the studies by Pelletier & Voilleqfie (1971) and Voors ~: van Weers (1989) (r,, r2, b i and bo). An F value of 0-13 (s.d. 10-8%) and a u/m-ratio of 51 liter d - i (s.d. 17%), obtained from the excretion pattern of Cow-1, were used because the ~+TCsconcentration in this cow's milk happened to correspond to the level measured in the cooling tank milk. ltowever, Cow-I was in the second week of the lactation cycle and the herd consisted of cows in varying stages of lactation. The F-value and u / m - r a t i o for Cow-2 were 0,08 (s.d. 10.9%) and 43 liter d - ' (9%), respectively. The discrepancy between the measured and predicted 137Cs concentrations in milk is a factor of about 1.5. This factor corresponds to the discrepancy between the total excretion measured in the present study and those of Stewart et al. (1965), Johnson et al. (1968) and van den Hoek (1980). This discrepancy, which leads to a low derived F value of 0-13, might bc related to the early lactation stage of Cow-1 with an associated temporary imbalance between radiocaesium intake and excretion. In conclusion, it is obvious that the predicted 137Cs concentration is very sensitive to F. A value of 0.19 does fit the measured and predicted concentrations for herd milk much better (Fig. 3). This value is in good agreement with the figure of 0.20 calculated by Pelletier & Voiileqfie (197 !) for hay and with the Fvalue for grass silage calculated in our earlier study for a u / m ratio smaller than 73 liter d - ' (Voors & van Weers, 1989).

Transfer off radiocaesium from silage to milk in dai~ cows

139

CONCLUSIONS Average transfer coefficients of Chernobyl ~-~Cs and 137Cs from a diet c o m p o s e d of grass silage (70%), concentrate (20%) and potatoes (10%) to milk in dairy cows were calculated to be 0-25% d liter -~ for a herd of twenty-one cows. This value is within the range of values published for Chernobyl radiocaesium and falls at the lower end of the range of pre-Chernobyl observations. The model used here to predict the concentration of caesium in milk after feeding with grass silage contaminated with Chernobyl fallout strongly d e p e n d s on the p a r a m e t e r F. The measured low total excretion of radiocaesium by two isolated dairy cows after thirty-three days of feeding silage-1986 produced a calculated F value of (I-13, too small to fit the m e a s u r e d and predicted concentrations. A combination of the calculated u / m ratio of 5 ! liter d - t and an Fvalue of(l. 19 will best fit the measured and predicted concentrations.

ACKNOWLEDGMENTS The authors wish to thank R. J. Bas and t I. J. Collc-Veldhuizcn for sample collection and sample trcatment, and R. E. J. Groothuis and G. (iul for analysis of the samples by gamma-spectroscopy.

REFERENCES Bradley, E. J. & Wilkins, B. T. (1989). Influence of husbandry on the transfer of radiocaesium from feed to milk during the winter that billowed the Chernobyl reactor accident. Sci. Total Environ., 85, 119-28. Central Office of tlusbandry-Fced in The Netherlands (1986). Abstracts of feed standards for husbandry and feed-values of cattle-feed, Lelystad, The Netherlands (in Dutch). Dennis, R. J. & tlemken, R. W. (1978). Potassium requirement of dairy cows in early and midlactation. J. Dairy. Sci., 61,757-61. llock, J. van den (1980). The influence of bentonite on cesium absorption and metabolism in the lactating cow, Z. Tierphysiol. Tiernahrg. u. Futtermittelkde., 43, 101-9. Johnson, J. E., Ward, G. M., Firestone, E. & Knox, K. L. (1968). Metabolism of radioactive cesium (t34Cs and 137Cs) and potassium by dairy cattle as influenced by high and low forage diets. J. Nutrition, 94, 282-8. Larson, B. L. (1985). Lactation. The Iowa State University Press, Ames, p. 138. Pearce, J., McMurray, C. H., Unsworth, E. F., Moss, B. W. & Gordon, F. J. (1989). Studies of the transfer of dietary radiocaesium from silage to milk in dairy cows. Sci. Total Environ., 85, 267-78,

140

P. L Voors. A. W. van Weers

Pelletier, C. A. & Voilleqtie, P. G. (1971). The behavior of Cs-137 and other fallout radionuclides on a Michigan dairy farm. Health Physics, 21,777-92. Staatliche Lehr- und Versuchanstatt ftir Viehhaitung Aulendorf (1986). 2. Tierversuch zur bestirnmung der radioactivitat in Milch und Fleisch (Winterfiitterung). Aulendorf, Germany. Bericht no. 3, 1-31. Steinwender. R., Lettner, F., Gruber, L., Uray, G. & Kapp, A. (t988). Experimental studies about the relationship between caesium concentration and yield in the milk of dairy cows. Die Bodenkultur, 39, 269-80. Stewart, H. F., Ward, G. M. & Johnson, J. E. (1965). Availability of fallout 137Cs to dairy cattle from different types of feed. J. Dairy Sci., 4@, 709-13. Voors, P. !. & Weers, A. W. van (I989). Transfer of Chernobyl t~Cs and 137Csin cows from silage to milk. Sci. Total Environ., 85, 179-88. Ward, G. M, (1956). Calcium balances and changes of some blood and urinary constituents as related to parturient paresis in dairy cows. Ann. N.Y. Acad. Sci., 64, 361-9.