Distribution of 210Pb, 210Po, stable lead and fallout 137Cs in soil, plants and moorland sheep of a heath

The Science of the Total Environment, 39 (1984) 143--159 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

143

D I S T R I B U T I O N O F 21°pb, 21°p0, S T A B L E L E A D A N D F A L L O U T 137 Cs IN SOIL, PLANTS AND MOORLAND SHEEP OF A HEATH

K U R T B U N Z L and W. K R A C K E Gesellschaft ff~rStrahlen- und Umweltforschung m b H M~nchen, Institutff~r Strahlenschutz, 8042 Neuherberg (Federal Republic of Germany)

(Received February 7th, 1984; accepted April 15th, 1984)

ABSTRACT

The concentrations of 21°pb, 21°Po, 137Csand stable lead (Pb) were determined in soil, and various vegetation samples from the heath, and in the liver and kidneys (137Cs, Pb and K also in meat) of LSneburg heath sheep. The concentrations of 21°Pb, 21°po, 1~7Cs and Pb in the soil are within the range of what is presently observed in other largely unpolluted areas of West Germany. While this is also true for the samples of vegetation with regard to 21°pb, 21°po and Pb, parts of heather and bilberry plants accumulate 137Cs. The behaviour of Pb, Po, 137Cs, Pb and K in the meat, liver and kidneys of the sheep is complex: depending on the tissue and the radionuclide or element considered, significant differences between male and female animals and/or a dependence of the concentration on the age exist. Compared to other animals, the concentration of 137Cs in tissues of the heath sheep is unusually high. Most likely this is because for most of the year they feed on heather. A significant correlation between 13~Cs and K in the tissues was not observed. The concentrations of Pb found in the livers and kidneys of the animals are comparatively high. A considerable fraction of these samples exhibits Pb concentrations which are above the "Guidance Values '79" of the Federal Health Office~for the concentration of this element in livers. Concentration factors for the transfer of 2mPb, 2mPo, 137Cs and Pb from the feed to the animal tissues are estimated. INTRODUCTION I n r e c e n t investigations o n f a l l o u t r a d i o n u c l i d e s in h o n e y o f d i f f e r e n t origins (Bunzl a n d K r a c k e , 1 9 8 1 ) a n d in a n i m a l livers (Bunzl a n d K r a c k e , 1 9 8 4 ) , we o b s e r v e d t h a t 137Cs was a l w a y s p r e s e n t in u n u s u a l l y high c o n c e n t r a t i o n s if t h e s a m p l e s w e r e c o l l e c t e d f r o m a h e a t h . Because t h e deposit i o n o f 137Cs f r o m t h e w o r l d - w i d e f a l l o u t o f earlier w e a p o n t e s t i n g is c o m p a r a t i v e l y u n i f o r m w i t h i n West G e r m a n y ( H a r d y , 1 9 7 3 ) a n d since n o o t h e r s o u r c e o f 137Cs p o l l u t i o n is p r e s e n t , this suggests t h a t t h e e n r i c h m e n t o f this r a d i o n u c l i d e in t h e h e a t h is d u e t o t h e special s t r u c t u r e o f this e c o s y s t e m . T o o b t a i n m o r e d e t a i l e d i n f o r m a t i o n a b o u t t h e d i s t r i b u t i o n o f 137Cs in t h e h e a t h we d e t e r m i n e d t h e a c t i v i t y c o n c e n t r a t i o n s in t h e soil, in v e g e t a t i o n s a m p l e s (grass, leaves, f l o w e r s , s t e m a n d r o o t s o f h e a t h e r , b r o o m , j u n i p e r a n d 0048-9697/84/$03.00

©1984 Elsevier Science Publishers B.V.

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bilberry) as well as in the meat, livers and kidneys of a large group of heath sheep as a function o f their sex and age. These animals are still maintained in herds and feed mainly on heather; their meat and livers are sold as delicacies. To find o u t whether or not the distribution of 137Cs in the organs of the heath sheep is correlated with that of other alkali metals, the concentration o f potassium in these samples was also determined. Because we cannot exclude the possibility that the distribution of other elements or radionuclides in the heath is also unusual, in the samples we. also determined the activity concentrations of two important naturally occuring radionuclides, 21°Pb and 21°po, for which sufficient data from other animal tissues and vegetation are available for comparison (Bunzl et al., 1979, 1983a; Glabasnia, 1978). Finally, stable lead was included in the present study as the representative of a toxic heavy metal, which is known to accumulate in the kidneys and livers of animals, and also to determine the extent to which the distribution of lead is correlated with that of 21opb.

MATERIALS AND METHODS

Site The heath ("Liineburgerheide") is the oldest wild-life reserve in West Germany (established in 1921) and covers 20 000 hectares, located ~ 40 km south of Hamburg. A b o u t 4800 hectares are covered with heather; the rest consists o f forests, fens and grassland; the mean annual temperature for the area is 8.0°C. The annual precipitation near the sampling site is "~ 720 mm, the m a x i m u m occurring in July and August, the minimum from February t o April. The relative humidity is, on average, 80--82%. A detailed description o f the climate o f this area has been given b y Horst (1962). The area where the samples o f soil and vegetation were taken and where t h e heath sheep sampled in this study were grazing was in the southern part o f the heath, a few kilometres north-west of the small village of Bispingen. Moderately dry, slightly loamy, sandy soils with a pH of 3.4--3.9 are present, covered with heather, grass, firs, birch trees, juniper, brooms and other typical plants, as described by Grupe (1979). The older heath sheep graze outside, on the heather throughout the year; the lambs from May to October.

Sampling In May and October, soft samples were taken from the upper ( 1 5 c m ) layer, immediately adjacent to heather plants or from grassland. Each sample consisted of four subsamples, collected a b o u t 1 - - 2 m apart and weighing ~" 10kg. All subsamples were transported in plastic bags to the laboratory, air dried in plastic trays, sieved to 2 r a m diameter, mixed carefully and stored in polyethylene bottles (ACS, 1980). Grass samples were taken in May 1981, at which time young green leaves as well as grey, dead plant material from the previous year were collected

145 separately, and again in October 1981, at which time only fresh grass samples were taken. Samples of heather (CaUuna vulgaris) were also collected in May and October 1981 both as whole plants and segmented into leaves, flowers, stems and roots; the plants were ~ 10 y old. In May 1981, samples of shoots from juniper (Juniperus communis) and b r o o m (Sarothamnus scoparius) were taken, as well as from bilberry (Vaccihum myrtillus), and were separated into leaves and stems. The 40 Liineburg heath sheep (graue, gehSrnte Heidschnucke), sampled in the autumn o f 1981, lived in the same area from which soil and vegetation samples were collected. Only those animals were taken whose exact age and sex was known. Because male heath sheep are slaughtered and sold at an age o f 6--8 months, o f the older animals only female sheep were available. From each animal the whole liver, both kidneys and 150 g of meat from the neck was removed for analysis.

Procedures Meat and organs. A 100 g portion of meat or liver or ~ 40--60 g o f kidneys were cut into small pieces, and after addition of 2°Spo as a tracer and 20 mg o f Cs carrier, were wet-ashed with HNO3/H202 as previously described (Bunzl et al., 1979). A few millilitres of the solution were used to determine stable potassium b y flame atomic absorption, and stable lead according to the m e t h o d o f Sansoni et al. (1972). In this procedure lead is enriched by precipitation and the chemical yield is determined by addition of carrier-free 212Pb. Finally, Pb is determined by flameless atomic absorption spectrometry in a graphite tube. To the remaining part of the solution lead, bismuth and lanthanum are added as carriers and 21°pb and 21°Po precipitated as sulphides b y passing H2S into the solution. After filtration 137Cs was determined in the supernatant b y direct gamma~spectrometry while 2~°pb and 21Opo were determined in the precipitate as previously reported (Bunzl et al., 1979). Vegetation. After drying to constant weight at 105°C the samples were disintegrated first by grinding, and 137Cs was determined b y direct gammaspectrometry, using ~ 1 0 g aliquots. Subsequently, 5 g samples were wetashed and 21°pb, 21Opo and stable lead were determined as described above for meat. Soil. Soil samples (10g) were first heated under reflux conditions with concentrated nitric acid, then silica was removed by fuming with hydrofluoric acid. The residue was fumed with perchloric acid and the sample was finally taken up in HNO3. 2°Spo was again added as a tracer as in the beginning. In an aliquot o f the solution, stable lead was determined b y flame atomic absorption spectroscopy, subsequent to an enrichment procedure b y

146 an extraction process using ammonium pyrrolidinedithiocarbamate/methylisobutylketone (Schmidt and Dietl, 1980). In the remaining solution 21°pb and 2'°po were separated and determined as described above. Details of this procedure can be found in Bunzl et al. (1983b). 137Cs was determined by direct gamma-spectroscopy of 50 g soil samples, using a Ge(Li) detector. The standard deviation (2~sigma) in the above analyses was ~ 5% for the determination of stable lead and potassium (obtained from four replicate measurements of each sample by atomic absorption spectrometry) and 10% for the determination of 21°pb, 21°po and 137Cs (calculated from the counting statistics). The absence of systematic errors was tested by analysing samples with known amounts of the above radionuclides and elements. All samples were analysed within six months after sample collection. If the time interval between sampling and analysis exceeded about one month and the measured concentrations of 2'°pb and 2'°po differed substantially, corrections for the ingrowth of 21°po and 21°pb and for decay of 21°po were applied.

RESULTS AND DISCUSSION Soil

In Tables 1 and 2 are given the mean concentrations, standard deviations and ranges of concentrations of 21°pb, :l°Po, 137Cs and stable lead in the soil samples. On average, 14 Bq/kg 21°pb were found and 16 Bq/kg 21Opo. This confirms earlier observations, where the ratio 21°Pb/21°Po was found to be close to unity (Parvenov, 1974). In the soil, 21°po is obviously in radioactive equilibrium with 21°pb. The absolute values for the concentrations of 21opb and 21°po in soils vary widely, 8--220 Bq/kg being reported, depending on the type of soil and the location (Parvenov, 1974). In West Germany 10--40 Bq/kg axe found in general (Bundesministerium des Innern, 1980; Bunzl et al., 1984). The concentrations measured by us in the soil samples from the heath are, therefore, well within the range of what is generally observed in this country. On average, 15Bq/kg laTCs were found, the values ranging from 3 to 37 Bq/kg. These values are usually observed in the soils of West Germany as a result of the world-wide fallout from nuclear weapons testing programmes. For a similar soil in northern Germany (also in Lower Saxony) an average concentration of 15.5 Bq/kg laTCs was observed in 1978, the values ranging from 5 to 59 Bq/kg (Bundesministerium des Innern, 1980). The average concentration of stable lead observed in the soil was 20 mg/kg, the lowest single value being 10 and the highest 70mg/kg. These values are comparable with concentrations of lead in other largely unpolluted soils of West Germany. By investigating 35 soils from grassland (Balks, 1961; Matthess, 1972) an average of 33.7 (11.5--79.3) mg Pb/kg was found. In general, for temperate regions, values between 10 and 80mg Pb/kg are

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149 reported (Aubert and Pinta, 1979). The Umweltbundesamt of West Germany considers values between 10 and 20mg Pb/kg as "normal" concentrations for unpolluted softs (Umweltbundesamt, 1976). Compared to these values, the Pb concentrations in the soil samples from the heath are still within the range observed for uncontaminated soils. Therefore, neither of the radionuclides investigated, nor stable lead is present in the soil samples from the heath at a concentration above that usually observed in largely unpolluted areas.

Vegetation The concentrations in the various vegetation samples of 21°pb and 21°Po, as well as of 137Cs and stable lead, are given in Tables 1 and 2, respectively. The concentrations of 21°Pb and 2~°Po in samples of grass, heather, juniper, broom and bilberry plants are between 10 and 150 Bq/kg dry weight, which is well within the usual range reported (Parvenov, 1974). The lowest concentrations were found in the leaves and stem of bilberries and in the flowers of heather, the highest values being found in old dry leaves of grass, which on average contained about three times as much 2~°Po and 2mPb than young green leaves, both sampled in May from the same plant. This is in agreement with observations by Holtzman (1966) and is most likely the result of a constant average rate of 2~°Pb fallout onto the plant surface: While the quantity of grass also increases during the growing season, 21°Pb is accumulated on the surface of the grass leaf when it is dormant or dead. Grass sampled in October from the same location and from the same plant showed, as expected, 2~°Pb and 2mPo concentrations between those observed for the dry leaves and young shoots sampled in May. For the perennial heather plant no differences between the samples collected in May and October were observed; the highest concentrations of 2t°pb and 2~°po were observed in the leaves and the stem of the plant and the lowest in the flowers. Again, this seems to be because of the fact that the flowers grow relatively fast during a short period of time while the leaves and the stem grow slower, thereby making an accumulation of 2t°pb from atmospheric fallout possible at the plant surface over a longer time. The bilberry also belongs to the Ericaceae family and is also a perennial plant which (in contrast to heather) sheds its leaves in winter. For this reason we observed significantly lower concentrations of 2'°pb and 21°Po in the leaves as compared to the stem (see Table 1). From the values given in Table 1 the ratio of 2'°pb/2t°po for the various vegetation samples is seen to be "~ 1 for the perennial plant parts (heather, stem of bilberry) and the older parts of grass. The ratio is, however, > 1 for the young grass leaves and the leaves of bilberry, where a value of 1.5 was observed. This supports similar observations reported for grass by Holtzman (1966). The distribution of stable lead in the plants (see Table 2) is in some respects similar to that of 21opb and 2mPo. Again, one finds that the older leaves of the grass show higher Pb concentrations than the young shoots

150 (28 versus 9.1 mgPb/kg dry weight). The concentration of Pb in grass, growing in places without Pb pollution, is in general between 3 and 10 mgPb/kg dry weight (Leh, 1972). Even though the Pb concentrations observed by us in the grass of the heath are slightly higher in some samples, they are certainly not in a range where one could speak of "contaminated" grass. Again, in heather, the flowers show the lowest Pb concentrations (4.9 mg Pb/kg dry weight). Pb concentrations in broom and juniper samples were similar to grass (9.4 and 19mgPb/kg dry weight); those in the leaves and stem of blueberries were comparatively low (5 mg Pb/kg dry weight). Using the values given for the concentrations of 2]°Pb and stable Pb in Tables 1 and 2 it is possible to calculate the ratio 21°pb/Pb in the various samples. In this way one obtains ratios for the three grass samples between 4.7 and 5.0 Bq/mg Pb, even though in these samples the absolute concentrations of 21°Pb and Pb vary more than a factor of three. Similar behaviour is observed for the leaves, flowers and stem of the heather plant, where the ratio 21opb/Pb is 5.9, 4.9 and 4.6, respectively, even though here also the absolute concentrations of 21°Pb and Pb for these plant parts vary considerably. On the other hand, for the bilberry, the 21opb/Pb ratios observed in leaves and stem are significantly different (2.8 and 6.8 Bq/mg, respectively). The lowest 2'°Pb/Pb ratios were found for juniper shoots and heather shoots (1.5 and 1.9 Bq/mg, respectively), therefore even within a small area from plant to plant and sometimes even within the same plant, differences in the ratio occur and most likely they reflect the proportion of lead isotopes that are derived from deposition of airborne particulates and from root uptake. The distribution of 'STCs in the vegetation samples is different from that observed for 2mPb, 21°Po and Pb. Table 2 shows that significant concentrations of this radionuclide were found in the two perennial plants, heather (400--500 Bq/kg dry weight) and bilberry (~ 200 Bq/kg), while those in grass, broom and juniper were below our detection limits (20--70 Bq/kg, depending on the specific weight of the samples), even though the two latter plants are also perennial. It can be seen that within the heather plants the flowers and the leaves both have high '37Cs concentrations, while the stem exhibits the lowest. In the bilberry plant the stem contains about twice the amount of ~37Cs as that found in the leaves, in contrast to the observations for 2]°pb, 2mpo and Pb, where the opposite was observed. While it is not surprising that the distribution of the monovalent alkali metal ion Cs is different from that of the heavy metal ions Pb and Po, it is interesting to note that ~37Cs accumulates in the heather and to a smaller extent also in bilberries. In other areas of West Germany, where the deposition of 137Cs from fallout is comparable, the present concentration of this radionuclide in the grass crop is b e t w e e n ~ 0.5 and 10Bq/kg dry weight (Bundesministerium des Innern, 1980). This is similar to what we observed on the heath for grass, juniper and broom shoots. Considering that the concentration of 137Cs in the soil is not higher than that observed in other areas of West Germany, the comparatively high concentrations of this radionuclide in heather and bilberry seem to be the result of the slow growth of these plants and possibly

151

also of specific accumulation processes. In this laboratory the possibility of also using other plants from the family Vaccinium as bioindicators for certain radionuclides and elements is presently under investigation.

Heath sheep The concentrations o f 21°pb, 21°Po, t37Cs, Pb and K in the livers, kidneys and meat of heath sheep are given in Table 3. Due to the comparatively large number of animals available, it was possible also to determine the frequency distributions of the radionuclide concentrations in the organs by applying the chi~quare goodness-of-fit test. In this way we found that in many cases normal distributions or log-normal distributions were present; in some cases, however, none of these distributions was observed. As a result, we show in Table 3 the average concentration of a radionuclide, or a stable element, not only by the arithmetic mean and standard deviation, but also b y the median and its 95% confidence limit. If the frequency distribution is normal, the mean and the median coincide; Table 3 lists the range of concentrations observed for each radionuclide and element and the number of samples investigated. Because male and female animals, whose ages were also known exactly, were available it was possible to evaluate whether, at a constant age, male and female animals exhibited different concentrations of a given radionuclide or element and whether an age dependence of these concentrations was observed. Since, however, male sheep are always slaughtered at an age of ~ 1 y, the age dependence could only be evaluated for female sheep. Because not all frequency distributions are normal, nonparametric tests (U-tests by Mann--Whitney and Spearmans rank correlation coefficient) are used for the data evaluation. As can be seen in the following, in several cases statistically significant differences were observed between the radionuclide (or element) concentrations in male and female and young and old animals; possible reasons will, however, n o t be discussed in the present work. For 21°Pb we observed that, in the age group of animals ~ 1 y old, livers o f male sheep always had smaller concentrations than female sheep (1.82 versus 2.59 Bq/kg wet weight) and in kidneys (1.68 versus 2.38 Bq/kg wet weight); see Table 3. These differences were shown to be significant with the help o f the U-test at the 95% level (two-tailed). Also, for the livers it was observed that 21°pb concentrations decreases with increasing age of the animal. Compared to female sheep ~ 1 y old, with 2.6 Bq21°Pb/kg wet weight, the older animals (1--7.5 y) had, on average, only 1.6 Bq 21°Pb/kg wet weight in this tissue. The Spearman correlation coefficient (rs = --0.5380, n = 26) for this age dependence was significant at the 99% level (two-tailed). The corresponding linear regression line for livers was 21°pb (Bq/kg wet weight) = 2.59 -- 0.0127 x age (months) In the kidneys an age dependence for 21opb was not observed ( ~ 95% significance level). For this reason the average concentration of this radionuclide in this tissue was obtained b y pooling all female sheep (0.5--7 y old),

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153 see Table 3. These values for 21°pb may be compared with corresponding values obtained for cattle in an area of West Germany with little traffic or industry (Bunzl et al., 1979). The median concentrations observed there were rather similar: 0.66 Bq 21°Pb/kg wet weight in the livers and 1.63 Bq 21°Pb/kg wet weight in the kidneys. In the case of 21Opo in livers and kidneys of the heath sheep no difference between male and female animals was observed (U-test, ( 9 0 % level); no dependence of the concentration of this radionuclide on the age of the animals was observed ( ( 9 5 % level, Spearman correlation coefficient). Therefore, in order to obtain the average quantities the pooled 21°po concentrations for all animals, independent of age or sex (see Table 3) were used. laTCs was determined not only in the livers and kidneys but also in the meat, because this radionuclide is known to be present in this tissue in comparatively high concentrations. Application of the U-test and calculations of the Spearman correlation coefficient showed that in meat no correlation of the laTCs-concentrations with the age of the animals was present ( ~ 95% level, two-tailed). However, a significant difference between the concentration of this radionuclide in male and female sheep was observable (99% level, two-tailed), the male sheep exhibiting higher laTCs-concentrations than the female sheep (182vs. 118 Bq/kg wet weight). For this reason the average 1arCs in meat was obtained by pooling all male sheep separately from the female sheep, but independent of age (see Table 3). In livers and kidneys the opposite behaviour was observed. A significant difference between the laTCs-concentrations in male and female animals was not observable ( ~ 90% level, two-tailed) but an age dependance was present (99.9% level, two-tailed); the concentration of this radionuclide decreasing with increasing age in these tissues. Regression analysis yielded for the livers 137Cs (Bq/kg wet weight) = 86.3 -- 0.368 x age (months) and for the kidneys: 1arCs (Bq/kg wet weight) = 172 -- 0.811 x age (months) As a result the average concentrations of laTCs in livers and kidneys in Table 3 are given separately for the age group ~ 1 y, where male and female animals were pooled and for the age group 1--7.5y, where only female animals were available. A comparison of the 1arCs-concentrations in the different tissues then shows that the highest concentrations are present in the kidneys and in meat (between 118 and 182 Bq/kg wet weight, depending on age) and the lowest in livers (61--82 Bq/kg wet weight). These values may be compared with corresponding ones in the meat of other animals in West Germany (Bundesministerium des Innern, 1980). While for beef and pork, on average, 0.74 and 1.2Bq/kg wet weight, respectively are reported, 1.5 and 1.9 Bq/kg wet weight are found for sheep and goats, respectively. At present the highest 1arcs concentrations observed in meat are in deer (13 BqlaTCs/kg wet weight) and wild boars

154 (17 Bq laTCs/kg wet weight). Thus, even when comparing heath sheep with these other animals, the laTCs concentrations in their meat are higher b y an order of magnitude. Most likely, this is the result of the comparatively high concentrati(~ns of 137Cs in heather (see Table 2), the major fodder plant of these sheep. This confirms earlier observations which show that a slow growing, mat-like vegetation on nutrient-poor, thin soils, such as is found on alpine meadows or tundras, acts as a fallout trap, enhancing the uptake of radionuclides by native animals (Odum, 1971; Russell, 1965). As similarities between caesium and potassium in metabolic processes o f animals are well known (Davis, 1963), the concentrations of K in meat, livers and kidneys of the heath sheep were also determined (see Table 3). First, by application of the U-test to animals of the same age, we found no significant difference whether the samples came from male or female animals ( ~ 90% level). The K concentration in meat, however, was highly correlated with the age of the animals (99.9% level, two-tailed, Spearman correlation coefficient), the older animals exhibiting higher concentrations than the younger ones. Regression analysis yielded, for meat K (g/kg wet weight) = 3.08 + 0.00393 × age (months) In the kidneys an age dependence was also observed (99.9% level); the K concentration, however, decreased with illcreasing age. For the regression analysis, the following relation was obtained K (g/kg wet weight) = 2.28 -- 0.00312 × age (months) In the livers an age dependence of the K concentration was not observed ( ~ 95% level). As a result, we calculated (see Table 3) the average K concentration in meat for animals ~ 1 y old (males and females pooled) and, for comparison, also for animals 1 - - 7 . 5 y old (female animals only, because males of this age were not available). In the case of the livers all animals, independent of age and sex, were pooled and the kidneys were evaluated, as for the meat samples. As is evident from Table 3, the highest K concentrations were observed in meat (3.06g K/kg wet weight for animals ~ 1 y old), somewhat smaller for the livers ( 2 . 6 9 g K / k g wet weight) and the smallest for kidneys (2.28 g K/kg wet weight). Even though these differences are small, they are statistically significant (95% level, U-test), because the 95% confidence limit of the corresponding medians is so small (see Table 3). This sequence is, however, not identical with that of laTCs, where the lowest concentrations were found in the livers. It was also tested by calculating the Spearman correlation coefficient to determine whether or not in any of these tissues a correlation exists between ~aTCs and K. This was, however, not the case. For each tissue the significance level of a possible correlation was < 95%. Finally, in Table 3, the concentration of stable lead in the animal tissues are also given. Differences between the concentrations of Pb in tissues for male and female animals were observed for livers and kidneys (U-test, 99%

155 level, two-tailed), b u t not for meat ( < 90%). An age dependence was observed for kidneys only (95% level, Spearman correlation coefficient), where the concentration decreased with increasing age according to Pb (mg/kg wet weight) = 0.756 -- 0,00305 × age (months) For this reason we calculated the average Pb concentrations in meat for all animals (males and females, independent of age), in the case of the livers, separately for all male and female animals, and in the case of the kidneys, separately for the males and females, where they were separated into age groups o f ~ 1 y and 1--7.5 y of age. The data show that the lowest concentrations are observed in the meat (median: 0 . 0 6 m g P b / k g wet weight). Comparing this value to the Pb concentration in the liver, the latter is higher b y a b o u t one order of magnitude (0.7 and 0.9 mg Pb/kg wet weight for males and females, respectively). In kidneys the highest values were f o u n d in young female animals (0.8 mg Pb/kg wet weight) and the smallest for young male animals (0.3 mg Pb/kg wet weight). Because the meat and livers of heath sheep are consumed as food these values may be compared with the present "Guidance Values '79" of the Federal Health Office for t h e concentrations of Pb in meat ( 0 . 3 m g P b / k g wet weight) and livers ( 0 . 8 m g P b / k g wet weight) in West Germany (ZEBS, 1979). Nevertheless, while all Pb concentrations observed for meat were below this limit, 8% of t h e livers from male heath sheep and 70% of the livers from female sheep were above this limit; for kidneys no guidance values are available at present in West Germany. If we also assume, in this case, 0.8 m g P b / k g wet weight as the upper r e c o m m e n d e d concentration, we find that 15% of the male kidneys and 35% of the female kidneys are above this limit. On average 1 5 6 g of meat and 9 g of offal are consumed per day by an adult living in West Germany (Deutsche Gesellschaft fur Ern~ihrung, 1976). Assuming that for persons living on the heath that their only source of meat is the heath sheep and that the offal consists only of livers from male animals < 1 y old, a total intake of 0.11 mg Pb per week can be calculated b y using t h e values given in Table 3. If we take as a basis the recommendations of the FAO/WHO Expert committee, which proposes as a maximum weekly ingestion o f 3 mg Pb per person, we find that as a result of the consumption o f meat and offal of heath sheep only ~ 4% of this limit are taken up b y an adult consumer. At present, no explanation for these relatively high Pb concentrations, especially in the livers of the animals, can be given. The concentrations of this metal in the fodder plants of the sheep (heather and grass) are, if higher at all, only slightly above the normal Pb concentrations for vegetation (see Table 2). Uptake of Pb with the soil, though possible for sheep (Thornton and Abrahams, 1983), can not be responsible, because the concentration of Pb in the soils of this area is also low (see Table 2). No other sources of possible lead contamination were detected. The rather complex behaviour of 21°Pb, 21°Po, 137Cs, Pb and K in meat,

156

male

0 0 t-.

tN tD I"-

[~ female

0

I"-

0

e

o cO

o

tO ~ ~ei r.ei

i

0 o

m

Pb

21°Pb

21°po

laTCs

@

o

o

i~

Fig. 1. Median concentrations of 21°Pb, 21°Po and laTCs (in Bq/kg wet weight), Pb (in mg/kg wet weight) and K (in g/kg wet weight) found in meat, livers and kidneys of moorland sheep < 1 y old. For female sheep, sufficient animals older than 1 y were available in order to test the age dependence of the above concentrations in the various tissues: o, no dependence on age; e , concentration decreases with age; e, concentration increases with age.

liver and kidneys of the heath sheep is summarized in Fig. 1, where the differences in the concentrations of these radi0nuclides as a function o f the sex or the age of the animals for the different tissues can easily be seen. It is interesting to compare the behaviour of stable lead and its radioactive isotope 21°pb in the livers and kidneys of the heath sheep. As shown before, we observed in the major fodder plants of these animals (heather and grass) a 21°pb/Pb ratio of around 5 Bq/mg. If we calculate this ratio for the kidney of each animal we obtain for male animals ( < 1 y old), a median value of 5.0 Bq/mg and for the females (also < 1 y old) a value of 4.2 Bq/mg. These values are very close to those observed in the vegetation, but are different from the corresponding ones in liver, where for the male sheep a ratio o f 2.9 and for the female sheep 2.6 Bq/mg was observed. Therefore, the ratio 21opb/Pb in the fodder of the animals cannot be constant, b u t obviously varies to some extent; for cows, such behaviour was n o t observed (Bunzl et al., 1979).

Transfer of 21°pb, 21°po, laTcs and Pb from feed to tissue No precise data for the feeding habits of the Liineburg heath sheep are

157 available. It can be estimated, (Hecht, 1984), that the daily intake of these animals when feeding, as in our case, almost exclusively on heather, amounts to ~ 4--5 kg dry weight for adult animals. One-year old animals will consume 3--4 kg and 6-month old animals 2--2.5 kg heather/day, respectively. Using the concentrations of the above radionuclides and also Pb, found in the heather shoots (see Tables 1 and 2), one can estimate the following daffy intakes for the older sheep

137Cs: 1000--1300 Bq/d; 21°po:

160-- 200 Bq/d;

21°pb: 160--200 Bq/d Pb: 30-- 4 0 m g / d

An estimate for the transfer o f a radionuclide, or an element, from the feed to a given animal tissue can be obtained by calculating the corresponding concentration factor, i.e. the ratio o f the concentrations of a radionuclide or element in the tissue and in the feed. If we take as a basis the wet weight of the samples and consider that the dry weight of heather is 50% of its wet weight, we obtain the following concentration factors (male sheep ~ I y old). Liver/feed:

137Cs: 0.6;

21°pb: 0.09;

21°po:0.05;

Pb: 0.2

Kidney/feed:

137Cs: 1.3;

21°Pb: 0.08;

21°Po:0.5;

Pb: 0.07

Meat/feed:

137Cs: 1.4;

-

-

-

-

Pb: 0.01

These values show that in general only 137Cs shows a small enrichment (concentration factors ~ 1 ) in the meat and kidney of the young animals with respect to their feed, while the other concentration factors are always, 1. The lowest concentration factor observed was for the transfer of Pb from feed to meat. Similar results are obtained for the older animals.

CONCLUSIONS The concentrations o f the 21°pb, 21°p0, 137Cs and stable lead in the soil of the heath are within the range of what is presently observed in other, largely unpolluted areas of West Germany. Also within the usual range are the concentrations of 21opb, 21°p0 and stable lead in the vegetation samples; higher concentrations were always found in the older parts of the plants (old leaves of grass or leaves and stem from heather, compared to young grass shoots or flowers from heather}. 137Cs, on the other hand, is considerably enriched in heather and bilberry, at concentrations higher than one order of magnitude compared to the other vegetation samples. Within heather, the highest concentrations were observed in flowers and leaves and the lowest in stems and roots. The behaviour of 21°pb, 21°po, 137Cs, lead and K in meat, livers and kidneys of heath sheep is complex. Depending on the tissue and radionuclide or element considered, statistically significant differences between male and female animals and/or dependence of the concentration on age will

158 be observed. The concentrations of 21°pb and 21°po are within the range observed for m a n y other animals, but the enrichment of 2~°Po in the kidneys o f the heath sheep, by a factor o f nine with respect to the livers, is remarkably high. The concentration of ~aTCs in tissues o f heath sheep also is unusually high. Even when compared to game, which exhibit generally higher concentrations of this radionuclide than other animals, the concentrations in meat and kidneys are higher by one order of magnitude. Most likely this reflects the fact that heath sheep for most of the year feed on heather, a perennial plant which accumulates laTCs. A statistically significant correlation between laTCs and potassium was not observed. Even though the concentration of laTCs in meat and kidneys of heath sheep is high when compared to other food, health hazards resulting from the consumption cannot be expected. The concentrations of stable lead observed in the kidneys and especially in the livers o f heath sheep are comparatively high. A considerable fraction of these tissues has Pb concentrations above the "Guidance Values '79" for the concentration of Pb in livers.

ACKNOWLEDGEMENTS The authors would like to thank Mrs V. TschSpp, Mr B. Chatterjee, Mr F. Dietl and Mr W. Schultz for valuable help, Dr Hecht (Bundesanstalt fiir Fleischforschung), Professor Kreuzer (University of Giessen), and Dr Seefeld (Heath Sheep Breeding Association) for their kind assistance in obtaining the samples as well as "Peroxid-Chemie-HSllriegelskreuth" for supplying the hydrogen peroxide.

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