Cumulative deposition of 137Cs, 238Pu, 239+240Pu and 241Am from global fallout in soils from forest, grassland and arable land in Bavaria (FRG)

J Envtron. Radtoactwtty 8 (1988) 1-14

Cumulative Deposition of "~Cs, ~Pu, 239+240puand ~'Am from Global Fallout in Soils from Forest, Grassland and Arable Land in Bavaria (FRG) K. B u n z l & W. Kracke Gesellschaft fur Strahlen- und Umweltforschung Munchen, InstltUt fur Strahlenschutz, D-8042 Neuherberg, FRG (Recewed 12 October 1987; accepted 23 December 1987)

A B S T R A CT The cumulattve deposinon of "T Cs, 238pu, 239+24°puand 241Am/rom global nuclear weapons fallout to the end of 1984 was determined m sods at 25 sttes in southern Bavaria. A t each locatton, sod samples were taken Jrom forest, arable and grassland and these samples were analysed separately. On average, the accumulated deposztton of these radtonuclides per square metre was sigmficantly htgher (30%) m the forest (old spruce) than m the grassland sods. No difference was observable between the depostts on pasture and arable sods. A slgmficant correlaaon was found between the accumulated depostttons of these radlonuchdes and mean annual prectpitation at each stte The regresston hnes obtained for thts assoctatlon show the same slope for grass and forest sods but are displaced against each other by 800 Bq m -2 The data indicate that the long-term mean drv deposmon velocity of t37Cs is higher in the forest by about a factor oJ 9, relattve to that on grassland. A contour map for the spattal dtstrlbutton O) 137Cs lS presented. The mean observed ratios, relative to 137Cs, for the other radtonuclides in the cumulative depositton were. 238pu, 0"000 68 +_0.000 12, 239+24°pU,0.018 +_0-0024, and 241Am, 0-0053 + 0 0016

INTRODUCTION

For many years ~3VCs, 23Sptl and 239+2~pu from above-ground nuclear weapon tests were injected mto the atmosphere and distributed subsequently in the environment. Up to 1978, 960 PBq of 137Cs, 0-79 PBq of 23Spu ( f r o m which 0"51 PBq was released from the bum-up of the nuclear 1 © 1988 Gesellschaft fur Strahlen- und Umweltforschung mbH Munchen (GSF)

2

K. Bunzl, W Kracke

powered satellite SNAP-9A in 1964) and 13 PBq of 239+24°pu w e r e produced in this way (Bennett, 1978; Perkins & Thomas, 1980; UNSCEAR, 1982). The radionuclide 241Am IS also, like 23Spu and 239+24°pu, a long-lived alpha-emitter, resulting essentially from the decay of fallout 241pu (betaemitter; tl/2 = 14.4 years). By this route, 3.1 PBq of 241Am had been produced by 1978 and eventually 5-5 PBq will be formed (Bennett, 1978) Because of their deposition and long half-lives, the above radionuclides are still present m sods and, as the rates of vertical migration of Cs, Pu and Am are very slow, more than 95% of their activities are still present m the 0-20 cm layers of most undisturbed soils (Bachhuber et al., 1982; Schlmmack et al., in press). The aims of the present study were. (l), to determine the spatial distributions of the accumulated depositions of 137Cs, 238pu, 239+24°puand ~-41Am from global nuclear weapons fallout in the soils of southern Bavaria (FRG) to provide 'baseline' information, by which to assess any addmonai inputs to the terrestrial environment as a result of emissions from the nuclear industry, as e.g. from the reactor accident at Chernobyl; 0i), to evaluate a possible correlation between the cumulative deposition and the mean annual precipitation at the sites; and (fii), to determine whether there are any observable effects of vegetational cover or of soil management on radionuclide deposition. For the above reasons we collected, at each site, soils from comferous forest, grass and arable land. Differences m the inventories of radionuclides in soils from woodland and nearby grassland can be expected, e.g. as a result of interception of the forest canopy during dry deposition or of enhanced run-off or erosion during heavy rain in hilly grassland relative to woodland soils. To minimize this latter effect only sites on level ground were selected. A difference can arise between the concentratmns of a fallout radionuclide in the 0-20 cm layer in undisturbed grassland sod and in the ploughed layer of arable land (usually the upper 20-30 cm) because, for several years after deposition, the effect of ploughing will cause an addltmnal leaching of the radionucllde from the ploughed layer into the deeper soil horizons. However, after longer periods of time, ploughing results in a retarded leaching of radionuchdes relative to that in undisturbed soils (Schimmack & Bunzl, 1986).

MATERIALS AND METHODS Sites

The soil samples were collected from 25 sites in southern Bavarm, extending from the foothills of the Alps (south) to the river Danube

Cumulatwe deposmon o f Z37Cs, 23Spu, 239+24°pu and 241Am m Bavarta

10" I

11 ° I

12 °

13 °

I

, so km ~

I

3

14" I

, , ~

49 °- N

./,90

~

/, 8*-

.48*

47*

47*

lq °

1'2"

;3 °

I 'F

Fig. 1. Isopleths for the distribution of the cumulative deposition of 137Cs (in kBq m :) from global fallout to the end of 1984 in grassland soil in South Bavaria, FRG To obtain the corresponding deposmons of 238pu, 239+24°pu and 24lAin the values shown in the figure should be multiplied by 0 000 68, 0-018 and 0-0053 respectively Samphng sites (&) and the geographical location of the area are also shown

(north) and from Memmingen (west) to the Austrian border (east), as shown in Fig. 1. Because we expected the cumulative depositions of the fallout radionuclides to be correlated with average annual rainfall (Cawse, 1983), we planned the samphng grid according to the long-term distribution of precipitation in Bavaria. In general, the mean annual preo p i t a t i o n increases rapidly from north to south as one approaches the Alps. F o r this reason, five sites were located along each of five transects running from north to south along mean distances of about 50 km. H o w e v e r , the between-site d~stance along each of these transects was progresswely shortened from north to south, m sympathy with the o b s e r v e d increase of rainfall in this direction. The elevations of the sites were b e t w e e n 410 and 840 m above sea level, and are shown in Table 1 As near as possible to, and within 1 km of, each of these sites, locations were selected at which fields on level ground under permanent grass or forest (in every case spruce, at least 40 years old) or ploughed arable land were present. The areas of these fields were at least several thousand square metres. In a few places it was tmposs~ble to find all three of these field types in such close proxLmity and, at these places, samples were collected from only two fields. There were no nuclear installations near the selected sites

4

K_ Bunzl, W Kracke

TABLE 1 Accumulated 137Cs Depositions and Concentrahons in Sods from Global Fallout in South Bavaria Untd the End of 1984 at 25 Sites Exhlbmng Different Types of Vegetation (F = forest, G = grassland, A = arable land), and Other Environmental Data. Samphng Depth. Forest and Grassland, Circa 20cm, Arable Land, Tdled Sod Layer

RamJall ( m m y ~)

Altitude m

1

1 300

630

2

1 300

510

3

1 3(.10

570

4

1 300

840

Stte

5

1 200

780

6

1 150

750

7

1 100

620

8

1 0(O

490

9

1 000

680

10

1 000

530

11

950

650

12

900

570

13

850

490

Type oJ vegetation

pH oJ sod (CaCl2)

F G A F G A F G A F G

3 6 6-0 5-8 4-9 6-3 7-1 4-0 6-2 5-7 3 7 6-1

137Cs Bqkg ~ 20 28 25 41 22 20 18 14 14 19 13

7 6 7 6 7 3 7 2 0 7 2

Bqm 2 4 4 3 5 4 3 4 3 4 3 2

640 090 190 670 450 250 (~)0 420 120 420 780

A

a

a

a

F G A

3 7 5 3 o

40-7 29-4 .

3 750 4 600 a

F G A F G A F G A F G A F G A F G A F G A F G A F

34 4 8 a 37 7 2 6 1 -5 9 6 1 4-3 5-6 6-2 3 3 6-0 5-4 3 4 52 a 3 6 5 5 6 1 -7-2 7 4 3 4

24 5 14 3 a 1%2 9.16 10-2 57 3 23 1 24 6 24 4 14 6 7 72 24 3 15 5 9 40 22 8 15-4 a 12"8 11-6 3-80 37 2 18 3 15 1 34-6

4 (170 3 01(I a 3 96(t 1 760 2 35(1 2 060 2 500 1 930 4 300 1 6411 1 640 4 130 3 270 2 611) 3 970 3 0511 a 2 570 2 780 1 100 3 190 2 340 1 840 4 09(I

-t

o

C~.

C~

t~

.f-~ ~,i~ L.~ t ~

I~

I~

~--~ I ~

L.~ t ~

~

~--

t~

t-~

I~

t~

t-,~ t ~

t~

I~-~ L.~ - -

t ~-~ I ~

~+-~ -t,-~ t ~

t~-~

A..,

%

+

m

c~

c~

L~

K. Bunzl, W Kracke

Table 1---contd. Type of vegetauon

Average accumulated deposttton (Bq m-2 )

Mean

F G A

3 580 2 820 2680

Standard deviation

F G A

790 840 910

Site

Ramfall (mmy -1)

Altttude m

a Not existing at the s~te

Soil sampling Soil sampling was carried out in autumn, 1984. In each field, 5 to 10 soil samples were taken with a core sampler (4-5 cm in diameter) within an area of circa 50 m × 50 m to a depth of circa 20 cm, with the exception of the arable soil samples, for which the core length always corresponded to the depth of the ploughed soil layer (usually 20-30 cm). For grassland samples, the organic mat layer was included and the litter layer was also m c o r p o r a t e d in the woodland soils. However, twigs, but not needles, were r e m o v e d from the woodland soils before sampling. The arable soils had already been harvested by the time of sampling. Several preliminary experiments on grassland and woodland soils showed that a sampling depth of 20 cm is sufficient to account for more than 95% of the depostted activities of Cs, Pu and A m from global fallout. At a few sites (nos 1, 8 and 13) it was evident that peat was present. However, no attempt was made to classify exactly the soils collected at each site. Nevertheless, soil p H was d e t e r m i n e d at each site (0-001 M CaCl2) and the data are shown in Table 1. As expected, the forest soils always exhibited lower pH values than those from grass or arable land. As a result of partial diversion of precipitation by tree branches, one cannot necessarily expect radionuclide deposition on forest soil surfaces to be uniform. Therefore, soil samples in forest areas were not collected from the immediate vicinity of tree trunks.

Preparation and analysis T h e soil samples from each field were air-dried, crushed to pass a 2 mm diameter sieve, carefully mixed and weighed. Larger stones were removed and weighed separately.

Cumulattve deposttion o f

137C$, 238pu, 239+240pu

and 241Am tn Bavarta

7

137Cs was determined by direct gamma-spectrometry by counting weighed amounts (circa 150 g) on a Ge-detector linked to a multichannel . . analyser. For the determination of 23~pu, 239+240pu and 2 4 1 A m ' 200 g soil samples were first ashed at 550°C in a muffle furnace and subsequently, after addition of tracers (z42pu, Z43Am), digested with HF and HCIO4 until a clear solution was obtained. Pu and Am were then separated from the solution by radiochemmal procedures (Bunzl & Kracke, 1983; 1987a) and determined by alpha-spectrometry after electrodeposmon on stainless steel discs. The overall chemical ymlds were, for Pu, 50-80% and, for Am, 30-50%. The spectrometric resolution was 40-60 keV (full width at half maximum). The one-sigma percentage counting error depended slightly on the activity concentration of each sample and was, on average, 3% for 137Cs a n d 239+24°pu and 7% for 238pu and 241Am.

RESULTS AND DISCUSSION

Cumulative deposition of 137Cs With the exception of the arable land profiles, the vertical distributions of Cs, Pu and A m in the top soils will not be uniform. The observed activity concentrations (in Bq kg -1) of these radlonuclides in the soils thus depend critically on the lengths of the soil cores. To eliminate this effect, the core lengths were always selected to be sufficiently long to assess the total deposited activity (in Bq m -2) of each radionuclide. The measured activity concentrations of 137Cs in the soil samples at each site are presented in Table 1. From these values, the weights of the soil samples and the area of the core sampler, the total deposited activity of this nuclide can be obtained (see Table 1). If, m addition, the length of each soil core is known exactly, the soil bulk density can be obtained. In the present study, however, as a result of the considerable lengths of the sod cores, compression of the soil during sampling was observed in several cases. Hence no attempt was made to calculate the soil bulk densities. If the values from all sampling points are combined, the average total depositions of 137Cs on soils from forest, grass and arable land can be obtained (Table 1). By applying the chi-squared 'goodness-of-fit' test at the 5% level, we observe that the frequency distributions of the values are log-normal, even though this test shows that a normal distribution describes the values almost equally well. For this reason the averages of the values in Table 1 are characterised by the median and its 95% confidence limits (because compared to the geometric mean this quantity is less sensitive to the presence of outliers), as well as by the mean and the standard devmtion. As can be seen, the data indicate that the average

8

K. Bunzl, W Kracke

accumulated 137Cs deposition on the forest soils (3580 Bq m-'-) is higher than that for both grassland (2720 Bq m -2) and arable land (2620 Bq m-2). The M a n n - W h i t n e y U-test for the comparison b f medians (Sachs, 1976) shows that the difference between 137Csdeposition on forest soils and those on grassland and arable soils is significant at the 99% level (two-tailed), while the corresponding difference between grassland and arable soils is not statistically significant ( < 90%). To test whether a correlation exists between the total 137Cs depositions m forest and grassland soils, the S p e a r m a n correlation coefficient was calculated, reveahng that thin correlation is statistically significant at the 99.9% level (two-tailed), i.e. that at sites where Cs deposition m the forest is higher (or lower), the Cs deposition on the adjacent grassland is also higher (or lower). Thus it is justifiable to calculate, for each site, the ratio of the Cs deposition on the forest soil to that on the adjacent grassland soil. The resulting median ratio for all sites was 1-27, with a 95% confidence limit of 1.17-1-35. Therefore, on average, the total 137Csdeposmon from global fallout on forest soil was about 30% higher than on adjacent grassland soil. This finding may be explained by the lnterceptlve function of woodland canopies and confirms the observations, by Schreiber & Woerner (1979), who measured fallout 9°Sr in soils from grassland and the Black Forest in Germany. The deposition of this latter nuclide on forest soils was also about 30% higher than on comparable grasslands. On the other hand, no sigmficant difference between the cumulatwe depositions of 137Cs and plutomum m woodland and grassland soils was observed m a British survey by Cawse (1983). However, In this latter study, deciduous woodland sites were selected and at these the interception of airborne fallout by woodland canopies will occur only during the vegetative growth period. In a regional survey near Sellafield, Cawse also reports that more plutonium Is deposited on coniferous woodland than on grassland (Cawse, 1983). The Spearman correlation test was also used to investigate a possible correlation between total 137Cs deposition in soils and mean annual precipitation The significance levels obtained were 99-9% for the forest soil, 99.9% for the grassland soil and < 90% for the arable soil. The fact that no significant correlation was detected for arable soils does not imply that such an association does not exist. Most probably, because of the rather m h o m o g e n e o u s structure of a ploughed field, the small diameter of the core sampler will cause comparatively large errors in the estimates of the accumulated 137Cs depositions on an areal (m 2) basis. The spatial variability of the cumulative activity concentrations of this nuclide in 100 samples of arable soil was studied recently (Bachhuber et a l , 1987); the coefficient of variation was 20% If these activity concentrations are c o n v e r t e d to deposition values on an areal basis, the resulting coefficient of

Cumulattve deposttton 0f137Cs, 238pu, 239+240pbland 241Am m Bavarta

9

variation will substantially increase. As a result, the correlatmn between 137Cs deposition and mean annual precipitatmn is no longer detectable, unless the n u m b e r of samples is increased considerably. Calculation of the linear regression line yielded for the forest soft:

137Cs (Bq/m 2) = 1800 + 1-94 × mean annual precipitation (mm) and for the grassland sod: t 3 7 C s ( B q / m 2 ) = 660 + 2.33 × mean annual preopitatlon (mm)

The hnear correlatmn coeffictent for these assocmtions was s~gnificant at the 99% level (two-tailed). Extrapolation of the corresponding regression lines to zero precipitation (see Fig. 2) indicates the deposttlon resulting from dry deposition only (,including the deposition due to fog). However, calculation of the standard deviatmn, Sa, of the Intercepts of the regression lines on the y-ax~s shows that the uncertainty is very large: for the forest soil 570 Bq m -2 and for the grassland soil 600 Bq m -2. Therefore, in the present study, it is not possible to derive from these intercepts useful values for the dry deposition of 137Cs. T h e extent of the accumulatmn of actwlty from dry deposition of fallout ~37Cs on a grassland sod can be estimated more accurately by multiplying the integral 137Cs concentration in air during the fallout period w~th the average deposition velooty for this radmnuclide. The 137Cs concentrations m air in G e r m a n y and Milford Haven, UK, were very stmdar (Hotzl et al., 1976). Therefore, using the mean annual concentrations of this nuchde m ground-level air from 1954 to 1984 at Milford Haven (Cambray et a l , 1987), a value of 4-74 mBq m 3 year-1 is obtamed for the integral air concentration for th~s period, after correction for radmacttve decay to 1984. For the deposition velocity of 137Cs on the grass, a value of about 1 m m s -~ can be assumed (Schwarz, 1985; Roed, in press). However, considering that during winter in South G e r m a n y the grass either will be covered w~th snow or at least does not stand upright, a value of 0.7 mm s -L seems more appropriate. The value obtained in th~s way for the mean long-term dry deposition of global fallout 137Cs Is about 100 Bq m -2. This value is not in contradiction with the corresponding value obtained from the intercept of the regression line given above for grassland (660 Bq m 2), in view of the large standard devmtion associated with the latter While the absolute values for dry deposition cannot be obtained w~th reasonable accuracy by extrapolating total deposition values to zero p r e o p i t a t l o n , the difference between the dry deposition on grass and woodland can be evaluated more accurately. For this purpose, we have calculated, for each of the 24 sites, the difference in the total 137Cs

10

K_ Bunzl, W Kracke

deposition on grass and forest land. This difference did not depend, in a statistically significant way, on the mean annual precipttation at the sites, as was shown by calculating the Spearman correlation coefficient (p < 90%). This observation is in agreement with the fact that the slopes of the two regression lines for the association between cumulative deposttion and m e a n annual precipitation (see previously) also do not differ from each o t h e r in a statistically significant way (for this purpose, the residual variation of the regression was calculated and a test for the comparison of two regression coefficients at the 95% level was apphed (Sachs, 1976)) The average (median) difference estimated in this way for the accumulated deposition on the forest and grassland was 800 Bq m -2, with a 95% confidence limit (cl) of 580-920 Bq m -2. Therefore, if we assume that 100 Bq m -2 (see above) is a good estimate for the average dry deposition of 137Cs on grassland, we can estimate that the deposition velocity of this nuclide in coniferous woodland is about (100 + 800)/100 = 9 (95% confidence limit 7-10) times greater than that in grassland. To assess the sensitivity of this value to the assumed deposition velocity v~ for grassland, let us assume that vd may vary between 0.4 and 1 m m s -1. On this basis, we find, for the accumulated dry deposition of global fallout, 60 and 150 Bq m 2 respectively and, for the difference between dry deposition on coniferous woodland and grassland, a factor of 14 (95% cl 11-16) and 6 (95% cl 5-7) respectively. Finally, the observed values for the cumulative deposition of 137Cs were used m the construction of an isopleth map, in which the contour lines give a graphical representation of this radionuchde in south Bavaria (Fig. 1). The increasing values for the inventories of 137Cs as one approaches the Alps are clearly wsible and are the result of increasing precipitation from north to south.

Deposition of 23apu, 239+24°puand U~Am Because the fallout radlonuclides considered here are attached to aerosol particles, a fractionation between Cs and Pu or A m during the deposition process is unlikely. For this reason, plutonium and americium were d e t e r m i n e d only in grassland and forest soil samples from four sites to obtain the ratios 239+24°pu/137Cs,241Am/137Csand 23Spu/E39+24°pu.Even though the m e a n annual precipitation at these sites was quite different (700, 800, 1000 and 1200 ram), a dependence of this ratio on the mean annual precipitation was not detectable. Because the mean ratios of 239+24°pu/137Cs In grassland and forest soil did not differ significantly (t-test, p -- 95%, two-tailed), the average of all ratios (n -- 8) was calculated. The resulting value was 239+24°pu/137Cs = 0-018 +_ 0-0024, which is very similar to the

Cumulative deposition of l37Cs, 238pu, 239+24°pu and 241Am m Bavaria 6000 hE o" IZl tJ

-

'4-

FOREST SOIL

5000

++ +:t

¢000

+4. j

3000 2000

11

s

s

~

+

"~ +

~

"~ 4÷

1ooo

6000 ~E O"

GRASSLAND

5000

m

3000

¢J

2000

SOIL 4

~000

1000

0

i

i

250

500

10'00,2 0

,500

PRECIPITATION, mm Fig. 2. Cumulative deposition of 137Csfrom global fallout to the end of 1984 m forest and grassland sods from South Bavaria, F R G , as a function of mean annual prectpitatlon

0.0178 ratio observed m Great Britain (Cawse, 1983). Usmg the above ratto and the deposition values for ~37Cs (Table 1), the average deposttlon o f 239+a4°pu In south Bavaria can be obtained at 0-018 × 2720 = 49 Bq m -2 for grassland soil and 0.018 × 3580 = 64 Bq m -2 for forest soil. These data confirm the value reported in U N S C E A R (1982) in which the total integrated deposition density of 239+24°pu w a s estimated at 58 Bq m -2 for the north temperate zone (40-50°). A value of 110 Bq m-: for 239+24°pu deposition was also given recently by Cigna et al. (1987). However, this value was obtained only from measured activity concentrations in sotls and an estimated soil bulk density for all soil types found in the region (Piemonte, north-west Italy, 25 400 km:). The cumulative deposition of 239+a4°pu as a function of mean annual precipitation can be obtained by multiplying the right-hand terms of the regression equations given above for 1~7Cs, in grassland and forest soils, by 0.018. The ratio of 238pu/239+24°pu was also determined in the 8 grassland and forest soil samples from the 4 sites. Again, no significant difference b e t w e e n grassland and forest soils was detectable nor did this ratio depend on m e a n annual precipitation. The mean observed 23Spuff39÷24°pu r a t i o was

12

K Bunzl. W Kracke

0.037_+ 0-0033, a value which is characteristic of fallout from nuclear w e a p o n s testing and is similar to values observed previously in Bavarm: 0-036 ( H a r d y et al., 1973) and 0-028 _+ 0-017 (Bunzl & Kracke, 1987b). The mean value obtained for the ratio 23Spu/13~Cs is 0.000 68 _+ 0-000 12. F o r 241Am, there was again neither an observable correlation of the ratio 241Am/Z37Cs with mean annual precipitation nor a statistically sigmficant difference m the ratio between grassland and forest soil. For this reason the mean ratio 241Amf37Cs was calculated from all 8 measurements, yielding a value of 0-0055 + 0-0016 Using this ratio and the observed z37Cs deposition (Table 1), the average accumulated deposition of 24tAm In south Bavaria is assessed at 15 and 20 Bq m -z for grassland and forest soil respectively The depositions of 24~Am on grassland and forest soils as a function of mean annual precipitation can be estimated by multiplying the right sides of the regression equation given previously for ~37Cs by 0.0055 Experimental values for the accumulated deposition of this rad~onuclide on an areal basis are rare U N S C E A R (1982) estimates the integrated deposition density in the north temperate zone (40-50 °) at 25 Bq m -2, which is similar to our measurements. The ratio 24~Am/239+24°pu in soft has b e e n determined more frequently. Cawse & Baker (1985) report 0 30 + 0.06 as a mean for several softs m Great Britain, while Bunzl & Kracke (1987b) observed a value of 0.28 _+ 0.02 in several arable soils. In this present mvestigauon, the value found for the rauo ~s qmte s i m d a r 0 30 _+ 0.07. The contour maps for the spatml dmtnbutlons of 239+24°pu and 241Am m south Bavaria are essentmlly identical to those shown for 137Cs In Fzg. l, except that the cesium values should be multiplied by 0-0185 and 0-0055 to derive values for 239+24°puand 24tAm respectively. The depositions reported here for Cs in forest, grassland and arable land as a function of mean annual preclpitat~on can be used as basehnes to assess the additional Chernobyl-derived deposition of 137Cs. By contrast, depositions of Pu and A m isotopes from the Chernobyl accident were negligible in most countries relative to their inventories from weapons testing (HOtzl et al., 1987). The basehne values reported here for these actinldes can thus be used to assess the significance of possible releases a r o u n d nuclear installations.

ACKNOWLEDGEMENTS The authors would like to thank Dr P. Jacob for stimulating discussions and to M. Haimerl, C. Lapomte, W. Schultz and V. TschOpp for technical assistance.

Cumulattve deposttton of 137Cs, 238pu, 239+ 24Op1l a n d 241Am m Bavarta

13

REFERENCES Bachhuber, H , Bunzl, K. & Schlmmack, W. (1982). The migration of 137Csand 9°Sr in multilayered soils results from batch, column, and fallout investigations_ Nucl. Technol., 59,291-301 Bachhuber, H , Bunzl, K. & Schimmack, W (1987) Spattal variability of fallout 137Cs In the soil of a cultivated field Envtronm. Momtor and Assessment, 8, 93-101 Bennett, B G_ (1978). Environmental Aspects of Amertcmm, Environmental Measurements Lab., Department of Energy, EML-348, New York, USA Bunzl, K. & Kracke, W. (1983). Fallout 239+24°pu and 238pu In human tissues from the Federal Republic of Germany Health Phys., 44 (Suppl. 1), 441-51 Bunzl, K & Kracke, W (1987a). Simultaneous determination of plutomum and americium in biological and environmental samples J Radtoanal & Nucl Chem., 115, 13-21 Bunzl, K. & Kracke, W (1987b) Soil to plant transfer of 239+24°pu, 238pu, 241Am, 137Cs and 9°Sr from global fallout m flour and bran from wheat, rye, barley and oats, as obtained by field measurements. Sct Tot Envlronm , 63, 1 11-24 Cambray, R. S , Cawse, P A , Garland, J A , Gibson, J A_ B., Johnson, P_, Lewis, G N. J , Newton, D , Salmon, L. & Wade, B. O. (1987) Observations on radioactivity from the Chernobyl accident, Nucl. Energy, 26, 77-101_ Cawse, P. A. (1983) The accumulation of 137Cs and z39+24°pu in soils of Great Britain, and transfer to vegetation. In Ecologtcal Aspects o] Radtonuchde Release, ed P. J Coughtrey, 47-62, Blackwell Scientific Pubhcatlons, Oxford. Cawse, P A. & Baker, S. J (1985). Soil to plant transfer factors for 241Am and additional data for 137Cs and z39+24°pu, determined by field measurements m G r e a t Britain, International Union of Radloecologists IV Report of the working group on soil-to-plant factors. Bllthofen, The Netherlands, pp. 28-50 Cigna, A. A., Rossi, L. C , Sgorbmi, S. & Zurhni, G. (1987) Enwronmental study of fallout plutonium from the Plemonte region (north-west Italy), J. Envtron Radtoacttwty, 5, 71~81 Hardy, E P., Krey, P W & Volchok, H L. (1973). Global inventory and distribution of fallout plutonium. Nature (London), 241, 4 Ao 6 Hotzl, H , Rosner, G & Winkler, R. (1976). Kunsthche Radtoaktlvitat der bodennahen Luft und des Niederschlages in Munchen-Neuherberg. Report S-413, Gesellschaft fur Strahlen- und Umweltforschung, Neuherberg, FRG Hotzl, H., Rosner, G. & Wlnkler, R (1987) Ground depositions and air concentrations of Chernobyl fallout radionuchdes at Munlch-Neuherberg. Radtochtm Acta, 41,181-90 Perkins, R. W. & Thomas, C W. (1980) Worldwide fallout. In Transurantc elements m the Environment, ed. W. C_ Hanson, 5 3 ~ 4 , US Department of Energy, Springfield, Rep DOE/TIC-22800 Roed, J. (in press). Dry deposition m rural and urban areas Radtat Prot Dosimetrv Sachs, L (1976). Angewandte Stausttk, Springer Verlag, Berlin Schlmmack, W & Bunzl, K. (1986) Migration of solutes m a cultwated soft: effects of ploughing Geoderma, 38, 155-63 Schimmack, W , Bunzl, K. & Zelles, L (in press). Initial rates of migration of radionuchdes from the Chernobyl fallout m undisturbed sods. Geoderma_

14

K Bunzl, W. Kracke

Schreiber, H & Woemer, F. (1979). Die zeltliche Entwmklung der Verteilung yon 9°St in land- und forstwirtschaftlich genutzten Boden. Landw. Forschung, 32, 55-62. Schwarz, G (1985). Deposition and post-deposition radionuchde behavlour in urban environments. In Proc Workshop on Methods for Assessing the Off-site Radiologtcal Consequences of Nuclear Accidents, eds F Luykx and J. Smnaeve, 533-58, Commission of the European Communitms, Luxembourg, EUR 10397 EN. UNSCEAR (1982). lontzing Radiation Sources and Biological Effects. United Nations Scmnt~fic Committee on the Effects of Atomic Radiation, New York, Umted Nations