Radioecological studies of activation products released from a nuclear power plant into the marine...

Marine Environmental Research 12 (1984) 225-242

Radioecological Studies of Activation Products Released from a Nuclear Power Plant into the Marine Environment

Mats Ni lsson, S6ren Ma t t s son & Elis H o l m

Radiation Physics Department, University of Lund, Lasarettet, S-221 85 Lund, Sweden

(Received: 24 February, 1984)

ABSTRACT

The seaweeds Fucus vesiculosus, Fucus serratus, Ascophyllum nodosum and Cladophora glomerata and crustaceans of the Idothea and Gammarus families have proven to be excellent bioindicators for radioactive corrosion products released from a nuclear power plant into the marine environment. These bioindicators have been used to map the spatial and temporal distribution of the released radioactivity. The activity has been followed up to 150km from the power plant, and the decrease in activity concentration C(z) in the bioindicators with distance z can be expressed by a power function C(z) = ~t. z- 1.4 where ~ is a constant.

The variation with time of activity concentration very well reflects the amount of activity discharged from the power plant, with surprisingly good resolution in time.

The bioindicators exhibit different uptake patterns of the radionuclides detected, and variations from summer to winter for the crustaceans Idothea, when compared to Fucus, have been found.

I N T R O D U C T I O N

The handling and processing of nuclear fuel and waste give rise throughout the fuel cycle to releases of radioactive substances into the environment. An important source at present, and probably the most

225 Marine Environ. Res. 0141-1136/84/$03.00 © Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain

2 2 6 Mats Nilsson, S6ren Mattsson, Elis Holm

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Nuclear power plant in the marine environment 227

important in the future, for the irradiation of man is the marine environment.

We have therefore considered it of great importance to study the transport of radionuclides released under controlled conditions from a nuclear power plant into the marine environment. This applies to both the radionuclide content in water and its concentration along food-chains of interest with respect to estimating the dose commitment to the exposed population.

The discharged radioactivity is, however, dispersed into enormous volumes of water. It is therefore desirable to find a bioindicator which concentrates the substances but still, to a certain degree, describes the radionuclide concentration in its immediate surroundings. We have found species of the brown seaweed Fucus to be very suitable bioindicators for such studies (Mattsson et al., 1982).

The source of the discharged radioactivity is the Barseb/ick nuclear power plant which is located on the Oresund sound between Denmark and Sweden. It consists of two boiling water reactors, each of 1700 MW thermal effect. The first reactor (B 1) became operational in 1975, and the second (B2) in 1977 (cf. Fig. 1). The release of radionuclides, mainly activation products, is, during normal operation, due to high filtering and waste containment capacity, quite low. During the summer period, when annual overhaul and partial refuelling take place, the discharge is much higher. This gives a pulsed pattern of released radionuclides, which is fortunate for our studies since it simplifies the interpretation and mathematical treatment of data regarding the time variations of concentration, uptake and retention of the radionuclides.

Our studies of the radionuclide content in Fucus started in 1967, being, at that time, mainly studies of the long-term variation of 137Cs activity concentration. These studies were carried out at a considerable distance (140 km north) from the power plant. In the summer of 1976 we, for the first time, found traces of 6°Co in Fucus from this collecting station. From that time on, we expanded our programme to regular collection at eight sampling stations.

MATERIAL AND METHODS

Samples of Fucus vesiculosus, F. serratus, Ascophyllum nodosum and Cladophora glomerata, firmly rooted on heavy stones, were collected

228 Mats Nilsson, S6ren Mattsson, Elis Holm

from water depths between 0.5 and 1 m along the coast. Samples of the crustaceans Idothea, I. baltica, I. viridis and I. granulosa, as well as Gammarus found on the Fucus plants, were sorted out for analysis. A number of samples of the mussel, Mytilus edulis, as well as a limited number of sediment profiles, were also taken. After drying in air at room temperature for 2-3 days the samples were ground and packed in plastic containers of 5- or 180-ml volume. The measurements were carried out using Ge(Li)-detectors of 46-100cm 3 volume with a counting time of between 5 and 100 h. The detector efficiencies were determined carefully using samples of different densities containing accurately known activities of 152Eu, 57Co and 22Na.

Water samples with volumes between 80 and 170 liters were taken at the Fucus fields 2.9 km NNE of the power plant. 57Co was added as a yield determinator and NaOH was then added to pH 12. The precipitate ( _ 5 liters) was dissolved the next day in HCl and co-precipitated with 200 mg Fe as carrier. The pH was adjusted to 12 with ammonia. This precipitation was centrifuged and dried before measurement.

RESULTS AND DISCUSSION

Activation products in Fucus

The location where collection has most frequently been made is situated 2.9 km north of the discharge pipe. Figure 1 gives the activity concentrations (dry weight) for 6°Co (T1/z = 5-26 years), 5SCo (71.3 days), 54Mn (303 days) and 65Zn (245 days) in F. vesiculosus collected at this location between 1976 and 1980. On the abscissae, different operational data for the plant are given. We have also, on occasion, detected ~ l°Agm (255 days), 57Co (270 days), 51Cr (27.8 days) and 1311 (8.05 days).

The activation products shown in Fig. 1 all follow a similar pattern and clearly reflect the increase in discharged activity during the overhaul periods.

From these results, we could establish that the increase in activity concentration in F. vesiculosus per unit activity released from the power plant was about the same for these radionuclides (Mattsson et al., 1980). Furthermore, from the very frequent collection in May-June, 1978 we could determine the biological half-life for these nuclides to be (60 + 15) days (Mattsson et al., 1980). For this purpose we were supplied with data


on released activity by the staff of the power plant (Sydkraft, 1980), The half-lives for the cobalt isotopes are in good agreement with laboratory experiments (Nakahara et al., 1975). For 65Zn, however, our results indicate a lower retention than found in laboratory experiments (Gutknecht, 1975; Young, 1975).

In Fig. 2 the annual discharge rates (from 1975 until November, 1980) of the activation products are shown. In 1975 and 1976, when the first reactor was tested and started and 6°Co, due to its long half-life, had not reached high activity values, 5aCo dominated the discharges. After 1976, the radionuclides can be ranked, in terms of activity discharge, as: 6 ° C o > 58Co > 6SZn > S4Mn > 11°Agm. This order has also been found in the Fucus plants (cf. Fig. 1).

The yearly activity discharge rate has, for all nuclides studied, a marked maximum in 1978, which is also reflected by the Fucus plants. In 1980, however, the 6°Co activity discharges again increased. The Fucus plants again responded to the increased discharge rate, as can be seen in Fig. 1. The activity content of the Fucus plants of the other activation products

Activity released GBq. a-1

100 -- Left to right: S°Co, 5SCo, 54Mn,65Zn,11°Agm

1975

i

°J

10

1976 1977

z l

/ I - _ A A

/ "~,/I /

/ /

/VV / ,'JHH /

1978 1979

/ A-~ / / _

/i P /

/I V /

,,/I/V /

/I/I / f / I - -

St;F / i / I / / _ / I / I / / /N//,,S

1980 (- nov)

I

J

i e Fig. 2. Annual discharge rates of activation products from Barseb/ick nuclear power plant into the (~resund. The shaded parts correspond to activity that can be absorbed on a

45 #m MiUipore filter.

230 Mats Nilsson, Siiren Mattsson, Elis Holm

also increased in the autumn of 1980, due to the fact that most of the activity is discharged during the second half of the year. The reason for the increased activities was probably (P.-A. Bliselius, pers, comm.) that a valve in a system for flushing the magnetite filters in reactor 1 was leaking. The general tendency, except for this incident, was towards a reduction in the activity being discharged after 1978. This has been accomplished by using a waste handling system giving more efficient filtering and evaporation of the liquid waste, thus reducing the volumes that are to be stored in the waste tanks (P.-A. Bliselius, pers. comm.).

It must be pointed out that the activity being discharged to the environment is extremely low compared with the limits allowed by Swedish regulations. In 1980, the activity released was, for beta + gamma emitters, about 0.5 ~o of allowed limits. (The absolute activity values were 60GBq compared with the allowed limit of 11 100GBq.)

We have also followed the ratio of 58Co/6°Co activity concentrations in F. vesiculosus at the same sampling station 2.9km north of the discharge pipe. This is presented in Fig. 3. From this Figure it is obvious

- - a c t i v i t y r a t i o soco

0.1

Fucus vesicuiosus

• 2.9 krn N 2.7 km SE

1 J ! J I

I l

! /

Fig. 3. Time variation of 5SCo/6°Co ratio in F. vesiculosus.


that the power plant releases S8Co and other activation products mainly during the overhaul periods. This Figure also clearly shows that the 5SCo/6°Co activity ratio is an excellent indicator of an increased discharge rate from the plant. The resolution in time is remarkably good although the interval between the two shutdowns in 1978 was only 3 weeks. The activity ratio still shows a decrease between the shutdowns.

For comparison, the s 8Co/6OCo ratio in samples collected 2.7 km south east of the discharge pipe is also shown in Fig. 3 (triangles). The agreement is good, illustrating the stability of the distribution in time of the direction of the water current. This is in agreement with hydrological data (SMHI, 1978 and 1979).

In Fig. 4, the same ratio (5SCo/6°Co) in the liquid discharges is given. Surprisingly, the curve initially seems to follow that for F. vesiculosus 2.9 km north of the discharge pipe. Linear regression of this ratio in discharge (x) and F. vesiculosus (y), however, gives the equation:

y = 0.77x - 0.005 (r = 0.94) (1)

The calculated factor of 0.77 is mainly conducted by the ratio (of S8Co/6°Co) Fucus/discharge for the highest SSCo/6°Co ratios. However,

SeC° activity ratio eOco

0.1

Fig. 4.

B1 1976 1977 1978 1979 1980

Time variation of SSCo/~°Co ratio in the liquid discharge.


58Co is mainly produced in the reaction 58Ni(n, p)58Co and 6°C0 in the reaction 59Co(n, V)6°Co. These cobalt isotopes could then be in different chemical states, thus initially giving them different chemical properties. The highest 58C0/6°Co ratios are found in connection with the overhaul periods, and a major part of the SSCo activity then released is recently produced. During the rest of the year, the ratio 58C0/6oc0, both in the discharge and in F. vesiculosus is lower and the 58Co activity released has, for some months (P.-A. Bliselius, pers. comm.) been stored in the waste tanks, where a change in chemical state and other chemical properties has perhaps taken place.

This assumption regarding 58Co is supported by Fig. 5, where the 58Co/6°Co ratio in the reactor water is shown. This ratio is, during normal operation, about 6, which is about 10-20 times higher than in the releases and in F. vesiculosus. Here this considerable difference could only be explained by the differential chemical behaviour of 58Co and 6°Co in the ion-exchangers in the reactor water purification systems, indicating that their different origin is the explanation of their different behaviour.

The results from Figs 3 and 4 also confirm the effect of the improved

58C° activity ratio 60Co

I

B2 Reactor water i

10,

, A

Fig. 5. Time variation of 5SCo/~°Co ratio in reactor water,


waste handling system. The 5SCo/6°Co ratio consistently decreases with time, which is in accordance with the reduced waste volumes and longer mean residence time in the waste tanks mentioned previously.

The more distant spread of activity has been investigated at eight collecting stations for F. vesiculosus along the Swedish west coast. In Fig. 6, the variations with distance of the activity concentrations in F. vesiculosus for 6°Co, SSCo, 54Mn, 65Zn, 11°Agm and SVCo, all activation products, are given. This figure is based on a collection made the same day in December, 1978.

As discussed in a previous paper (Mattsson et al., 1980) it is clear that

Fig. 6.

Activity concentration Activity concentration Bq .kg -1 (d. wt.) nCi .kg =1 (d. wt)

60C0 o ~

1000 -

100 -

1 0

~ l J l [

O.1

SaCo q~ eSZn ~ ~

54Mn ~

v 110Agm 1311

1 10 100 Distance (north) from Barsebick

100

10

0.1

0.01

km

Variation in activity concentration in F. vesiculosus by distance northwards in December. 1978.

2 3 4 Mats Nilsson, S6ren Mattsson, Elis Holm

this distance dependence of the activity concentration gives a good fit to a power function of the form:

C(z) = ~ . z - ~ (2)

where C(z)= activity concentration at distance, z, and ~ and // are constants.

The time variation of the constants ~ and/~ is shown in Figs 7 and 8. The variation of the constant ~ for the different radionuclides is similar to the variation of the activity concentrations at 2-9 km north of the discharge pipe (cf. Fig. 1), thus indicating that the activity concentration in Fucus is, at all sampling stations, closely connected to the discharge rate from the plant. This assumption is supported by the similarity between Figs 2 and 7. In Fig. 8, the time variation of the constant/~ is given for the activation products. The value of this constant, as shown in Fig. 8, is nearly the same for all radionuclides, except t l°Agm, which has a value of about 50 ~o

o Bq • kg -1

10 0 0 0 . . . . . . . . . . . . . . . .

1 0 0 0

100

0 / \ o

,/ / / / /

' / ,

/ 0\ / . . . . . . \ / o~q o ~] --\0// ",,

J f" ~ '/ '\ I / J/ ~, ", /

6OCo o ~ . . . . . . o / /,/// , \ / ! .~

¢- 5880 d I ' ' \ EJ . . . . . . 0 .

, / , ~ , --- '--4

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/ / " -n/ ~

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ta21 ,'//~ I ~ ' - ..~\\" -.~\\\'I I ~\\\\ i

1 9 7 7 1 9 7 8 1 9 7 9 1 9 8 0

Fig. 7. Time variation of the constant a (eqn 2).

6°Co | . . . . . . . . . . i ~ - - s :V I

" C o ½ . . . . . . . . . ?" - -

_ _ . _ . . . . . .

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i i


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Fig. 8. Time variation of the constant fl (eqn 2).

Y e a r

lower. The reason for this is probably that the silver released to the Oresund, due to its chemical properties, is behaving differently in the water compared with the other radionuclides, Differences in the uptake in Fucus have previously been reported (Mattsson et al., 1980).

In Fig. 8, a tendency can be seen for the E-values of the other four radionuclides to show a similar time variation. Furthermore, the highest E-values seem to occur in connection with periods with high discharge rates. Since the current situation in the Oresund is very stable, this/~-value pattern could be linked to the discharge rate. The slight variations of the fl constant could accordingly be explained by there being a considerable time delay between the discharge and established equilibrium conditions between water, sediments and Fucus.

236 Mats Nilsson, SOren Mattsson, Elis Holm

Studies of activation products in Idothea

Detectable concentrations of 6 ° C o w e r e found in several samples of ldothea. Because of the limited sample weights (0.2-1 g dry weight) the analysis had normally to be restricted to 6°Co. Figure 9 shows a comparison of the 6°Co activity concentration in I. baltica and F. t~esiculosus in December, 1978 at various distances from Barseb~ick. The activity concentration in I. baltica reflects well the concentration in F. z~esiculosus, presumably due to the fact that ldothea is grazing on the seaweed plants. The ratio between the 6°Co activity concentration in I. baltica and F. vesiculosus was 0.16 + 0.04 at that time. Considerably higher ratios, 0.93 + 0.10, are found in the summer. This is illustrated in Fig. 10. The explanation for this seasonal variation may be the decreased metabolic activity of Idothea during the winter period.

In 1979 a very large sample of Idothea was taken at a location 1.2km north of the discharge pipe. Over 3000 animals were separated, giving

Activity concentration Activity concentration

B q . k g - 1 (d . w t . ) n C i . k g -1 (d . w t . )

1 0 0 0 0 _ 1 1 I I i I I t ] t ~ r I ! ]

1 • ---_...._.. •

--- v e s i c u l o s u s I - - ~ 100

tO0 1 5 10

Distance (north) from B a r l w b i i e k k m

Fig. 9. Variation in 6°Co activity concentration m F. ~'esi¢~losus and ldothea baltica by distance northwards in December 1978.


Fig. 10.

Activity concentration in Idothell

1000

100

k ' k g ' ~ (d. wt.)

1 . . . . r ' ' ' r ' ' " J [ f I [ I I I I

o

/ °

I t J I J l 1 I I I , i ~ t l J I i I I l J J ~

lOO 1o0o 1o0o0

Activity concentration in Fucus vesicuiolul Bq.kg -1 (d. wt.)

Relationship between 6°Co activity concentrations in I. baltica and F. vesiculosus in summer (squares) and winter (circles).

separate samples of I. baltica, I. viridis and I. granulosa. Due to the large samples and the proximity to the power plant, it was possible to make an analysis of other radionuclides. The results from this analysis are shown in Fig. 11, where the activity concentration is given as it relates to L baltiea It is evident that I. viridis, for all radionuclides, shows a higher uptake than I. baltica. The opposite result applies to I. granulosa. It is a well known fact (L.-E. Persson, pers. comm.) that these three species of the Idothea family behave differently. For instance, I. viridis can usually be found in the most still waters near the shore and I. granulosa in more turbulent areas. Idothea baltica are present in areas 'in between'. This difference cannot explain the differences shown in Fig. 11 but it still indicates that other differences could exist, for instance, with regard to their feeding habits. This will hopefully be the subject of further studies.

Comparative studies of activity concentrations in different algae and crustaceans

The activity concentration in some algae and crustaceans relative to that of Fucus is given in Fig. 12. All concentrations are given on a dry weight


Activity relative to Idotheo Baltica

10

0.1

60C0

V

i

I

i

Fig. 11. Activity

SeCo S4Mn 65Zn lloAgm

B

v V

I ._) V 1 ~ m.~

Q r B B B 3.~r

!-7 i

i i I

i I I i concentrations, relative to I. baBica, for actwation products in I.

viridis and L granulosa.

basis. It is interesting to note the differences in activity concentration in I. baltica and Gammarus living side by side in Fucus plants. For the cobalt isotopes the concentration in I. baltica is a factor of 4 higher than in Gammarus. This may indicate a difference in their feeding habits. The highest activity concentrations of 54Mn, 6°'58'57Co, 65Zn and 131I are found in Fucus while crustaceans for these nuclides show an activity concentration of 4-40 % compared with Fucus, For x lOAgm ' the activity concentrations in Idothea and Gammarus are a factor of 9 and 6, respectively, higher than in the Fucus plants in which they live. This finding indicates an active uptake of silver in these crustaceans. Because Idothea and Gammarus are eaten by various fish species, these findings may be of considerable importance for the transport of radioactive substances to man.

S t u d i e s u s i n g Mytilus edulis

A limited number of samples of the common blue mussel, Mytilus edulis, were taken at some of the Fucus fields. The separate analysis of the shell


Activity concentration (d.wt.) relative to Fucus

10~

03

~- 54Mn

0.01

, IJ]

59Fe

o=

60, 58, 57C0

J

10 ~ 110Ag m , 65Zn I 1311 -~

I i . . . . . .

0 . 1 . . . . . . . . I! I [~ - i j 11

0,01 i ~ la ! Fig. 12. Relative content, per dry weight unit, in different algae and crustaceans of radionuclides released from Barsebiick in August-November 1979. Dry/wet weight ratios: Fucus, 0.2; Ascophyllum, 0.2; Cladophora, 0.05; Idothea, 0.19; and

Gammarus, O. 18.

and the muscle (body) of the mussel gave the muscle/shell activity ratios shown in Table 1 (based on dry weight). (The weight/wet weight ratio for Mytilus (muscle) is -~0.2.)

The differences between cobalt, manganese and zinc are in agreement with those found by Dahlgaard (1980). The considerable accumulation of 65Zn in the soft parts should be stressed because of the radiological importance of the mussel as part of important food-chains which finally lead to man.

TABLE 1 Muscle/Shell Activity Ratio

6OCo SaCo S,,Mn 6 5 Z n llO,/gm 4o K

2"4+0'1 2"8+0"7 0'82+0'30 12"9+2'9 1"9+2'0 21+6


TABLE 2 Activity Ratio Mytilus (muscle)/ Fucus

6OCo 58Co Sa Mn 6 5 Zn ~o K

0.08_+0.01 0.07_+0'02 0.05+_0.01 0.18_+0-02 0.55±0"05

In Table 2, a comparison between Mytilus edulis and Fucus is made. The ratio of activity concentrations on a dry weight basis is given.

The results clearly indicate that Fucus is superior to Mytilus for the purpose of mapping the geographical spread of activation products.

6°Co in water and sediment

The 6°Co activity concentration in unfiltered seawater 2.9km north- northwest of the power plant was determined as 5.4mBq/liter (1978- 06-15), 4.1 and 5.1 mBq/liter (1978-09-22) and 1.3 mBq/liter (1979-04- 11). Our results indicate that the concentration factor for Fucus (dry weight) is as high as (2+ 1). 105, corresponding to a wet weight concentration factor of (4 + 2). 104. This value is considerably higher than those computed by Fukai & Murray (1973) or measured in aquariums by Nakahara et al. (1975). It is interesting to note that the concentration factors for actinides in this area have also been found to be unusually high (Holm et al., 1980). Measurable concentrations of 6°Co have been found in sediments from sampling stations north-west of the power plant, 1-7-2.5 km offshore. The total area content of 6°Co was found to be 190 Bq/m 2 at 4.1 km from the plant, 76 Bq/m: at 6.4km and 560 Bq/m z at 11 km. Around 70 ~o of the 6°Co activity was found in the upper 25 mm of the sediment layer and the rest in the next 25 mm.

SUMMARY AND CONCLUSIONS

The macroalgae Fucus vesiculosus has, in comparison with other common algae, proved to be a very suitable and sensitive bioindicator for mapping the release of activation and fission products from a nuclear power plant into the marine environment. The activity concentration in Fucus along the coast can be expressed using a power function (cjl eqn (2)). It has been shown that the constant a reflects the discharge rate pattern well,


indicating that Fucus is a suitable indicator with regard to the activity concentration in the surrounding water. The small variations of the constant fl with time and between most radionuclides indicate that the spreading pattern is extremely constant in time, which makes the Oresund area suitable for radioecological studies.

Studies of the crustaceans Idothea have shown that the activity concentration of 6°Co varies between winter and summer. Within the Idothea family, the ability to concentrate activation products differs remarkably between species. The mussel Mytilus edulis generally shows lower activity concentration values than Fucus. The high accumulation of 65Zn in the soft parts should be noted. Because Idothea, as well as Mytilus, are eaten by various fish species, these findings may be of importance for the transport of radioactive substances to man.

ACKNOWLEDGEMENTS

Thanks are due to Lena Carlsson and Lars-Eric Persson, Department of Marine Botany, for valuable help with the collection and identification of samples.

This study was supported by grants from the Nordic Liaison Committee for Atomic Energy and the Swedish Natural Science Research Council.

REFERENCES

Dahlgaard, H. (1980). Loss of 51Cr, 54Mn, 57C0, 59Fe, 65Zn, and 134Cs by the mussel Mytilus edulis. In: Proc. of lnternational Symposium on the Impacts of Radionuclide Releases into the Marine Environment, Vienna, 6-10 October.

Fukai, R. & Murray, C. N. (1973). In: Environmental behaviour ofradionuclides released in the nuclear industry, IAEA, Vienna, 217.

Gutknecht, J. (1975). Uptake and retention of cesium-137 and zinc-65 by seaweeds. Limnology and Oceanography, 10, 58-66.

Holm, E. Persson, B. & Mattsson, S. (1980). 5th International Congress oJ IRPA, Jerusalem, Israel, lOth-14th March.

Mattsson, S., Finck, R. & Nilsson, M. (1980). Distribution of activation products from Barseb/ick Nuclear Power Plant (Sweden) in the marine environment. Temporal and spatial variations as established by seaweed. Environmental Pollution (Series B), 1, 105-15.


Nakahara, M., Koyanagi, T. & Saiki, M. (1975). Concentration of radioactive cobalt by seaweed in the food chain. Impacts of Nuclear Releases into Aquatic Environment. (Proc. Syrup. Otaniemi 30 June-4 July, 1975) IAEA, Vienna, 301-12.

SMHI (1978 and 1979). Oceanografiska kontrollunders6kningar utanfSr Barsebdcks kdrnkraftstation 1977 och 1978. SMHI. (In Swedish.)

Sydkraft (South Swedish Power Board) (1980). Monthly report over liquid releases from Barsebiick, May 1975-November 1980 (In Swedish.)

Young, M. L. (1975). The transfer of 65Zn and 59Fe along a Fucus serratus (L.)-Littorina obtusata (L.) food chain. J. mar. bioL Ass. UK, 55, 583-610.

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