Americium in intertidal sediments from the coastal environs of Windscale

Volume 12/Number

5/May

1981

sea and estuaries from 1980. The collection of data within the London Dumping Convention has been patchier but on the other hand, it adopted comprehensive measures to control incineration at sea very quickly. In terms of progress 'on the ground' (or 'in the sea') the Conventions have certainly stopped some dumping practices that were causing concern in the early 1970s (e.g. dumping of vinyl chloride process residues), and have encouraged the effective legal and administrative control of dumping and incineration from many countries, thus reducing the potential for abuse of these disposal outlets. One can also point to progress in reducing the quantities of Annex I substances being dumped as 'traces' in wastes such as sewage sludge. At the same time, however, the total quantities of wastes actually dumped have tended to rise

MarinePollutionBulletin,Vol. 12, No. 5. pp.

rather than fall. One can argue therefore that considerable progress has been made towards the stated aim of preventing pollution by dumping although not towards the goal of some States of reducing or eliminating dumping itself. One of the reasons for this has been the willingness of the decision-makers in the Oslo Commission and the LDC Consultative Meeting to allow matters to be thoroughly aired at a scientific and technical level, and to proceeed on the basis of a consensus even if this takes time to achieve. Thus the devisive and often counterproductive arguments that can result from scientific considerations being too politically inspired or overtaken too soon by political negotiation have largely been avoided in the dumping Conventions. In this respect, their relative success may hold a lesson for other areas of international regulatory activity.

149-153, 1981

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Americium in Intertidal Sediments from the Coastal Environs of Windscale S. R. ASTON* and D. A. STANNERS f

Department of Environmental Sciences, University of Lancaster, Lancaster LA1 4YQ, England *Present address: T Present address:

International Laboratory o f Marine Radioactivity, Mus~e Oc~anographique, Monaco. Chemistry Division, J.R.C. lspra, 21020 Varese, Italy.

The distribution of americium in surface intertidal sediments from a coastal environment near the Windscale nuclear fuel reprocessing plant has been investigated. The study includes data on the broadscale distribution of UlAm in Northwest England, but focuses on the sediments of the Ravenglass estuary 10 km south of Windscale. The results indicate that americium concentrations in the inner estuary sediments are up to seven times higher than those from the Irish Sea itself. Americium distribution on silt banks is rather constant on a small scale, but varies considerably between adjacent silt bank and salt marsh areas.

Americium is quantitatively the next most important transuranic element to plutonium in the release of man-made radioactivity to the marine environment. The principal isotope in such releases is 241Am (t,/2= 485 y) which decays with alpha emissions at 5.48, 5.43 MeV. Several studies of americium in the marine environment have been made recently (see e.g. Livingston & Bowen, 1976, 1977; Pentreath & Lovett, 1976; Murray & Kautsky, 1977), and it is now known that this transuranic is rapidly and effectively removed from sea water to sediments (Hetherington et al., 1976; Livingston & Bowen, 1977).

In view of the importance of sediments in the removal of americium from sea water, and its consequent accumulation in sediments, the present study examines the activities of 2~lAm in the sediments of a coastal environment contaminated by nuclear fuel reprocessing effluents. The coast is that of Cumbria and Lancashire, Northwest England (eastern Irish Sea) where there is a controlled release of low-level liquid effluents from the Windscale nuclear fuel reprocessing facility (Fig. 1). The annual direct releases of total alpha activity and 241Am to the Irish Sea from Windscale are shown in Table 1. The decay of 241pu (t,/2= 13.5 y) in the effluents also contributes to the ingrowth of 241Am in the marine environment. The data in Table 1 demonstrate that in some years, e.g. 1973 and 1974, the direct release of 241Amis the dominant release of transuranic alpha activity from Windscale, the remaining activity being due to 239+24°pu, 238pu and minor quantities of neptunium and curium. During the period 1968-1978 the annual 241Am releases directly to the Irish Sea have accounted for between 8 and 70% of the alpha activity of effluents from Windscale. The total direct release over this period was about 125 000 Ci 241Am. Clearly, the fate of Z41Amin the sediments of the region is an important aspect of transuranic dispersion into 149

Marine Pollution Bulletin this marine environment. Intertidal sediments were sampled because: (1) they are a m o n g the potential sources o f exposure (e.g. resuspension/inhalation) to the h u m a n population; and (2) they allow for simple and rapid sampling c o m p a r e d to off-shore deposits; a n d (3) little published d a t a is available on this topic.

Solway_, Firth

i

TABLE 1

Annual discharges (Ciy-1) of total alpha activity and 241Am from the Windscale pipeline to the Irish Sea. Year

Total alpha activity

241Amactivity

1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978

1416 1356 1656 2688 3864 4896 4560 2350 1614 1241 1837

576 396 540 1020 2172 2952 3192 980 323 99 214

Data from Hetherington et al. (1976) and B.N.F.L. (1978, 1979).

CUMBRIA

TABLE 2

241Am activities (pCi g-l, dry wt.) in surface intertidal sediments collected from the Northwest coast of England.

Windscale

~

Ravenglass Duddon

Easlern

Irish Se8

Bay

LANCASHIRE

scale

1: 500000

Sample No. AS- 1 AS-2 AS-3 AS-4 AS-5 AS-6 AS-7 AS-8 AS-9 AS-10

Location (see Fig. 1) Maryport Harbour Workington Harbour Whitehaven shore Esksmeals, Ravenglass R. Duddon estuary R. Lune estuary R. Lune estuary R. Wyre estuary R. Wyre estuary R. Wyre estuary

Muds, mean activity = 28.8. Silts, mean activity = 6.1.

241AmActivity Sediment (pCi g - l, dry wt.) type 4.0 _+0.12 silt 31.3 _+1.6 mud 28.6 _+1.5 mud 41.9 -2_2.2 mud 60.0 _ 3.2 mud 7.2 _+0.4 mud 8.6 -+0.5 silt 18.5 +_1.1 mud 5,4 _+0.3 silt 14.3 _+0.8 mud

All other sands, < 3 pCi g - 1.

Fig. 1 The Northwest Coast of England and the location of Windscale

(54° 27'N 3° 32' W) and the Ravenglass estuary (54° 22' N 3° 24' W).

All sediments were sampled in 1978 b y carefully removing the u p p e r m o s t 0.5 cm over an area o f a p p r o x i m a t e l y 1 m 2 at each location. The samples were stored in polythene bags at a b o u t 4°C, dried at 60°C and compressed into cylindrical pellets in polythene petri dishes for analysis. The 241Am activities in individual samples were measured by the technique o f Stanners & A s t o n (1980). This involves the detection and measurement o f the 241Am p h o t o n emission at 59.5 KeV by a NaI(TI) detector and a g a m m a spectrometer. A correction is m a d e for the iodine K X-ray escape in the NaI(TI) detector after the elimination o f the interfering 26 KeV p h o t o p e a k with a silica absorber. This r a p i d and non-destructive m e t h o d has a c o m p a r a b l e precision a n d accuracy with the long and complicated a l p h a counting a p p r o a c h (Stanners & Aston, 1980). All errors shown refer to + 1 o counting statistics.

activities is f r o m < 3 pCi g - l for beach sands (not shown as individual samples in Table 2) up to 60.0 pCi g - 1in a sample from the R. D u d d o n estuary. The ranges and arithmetic means o f activities in muds (7.2-60.0 pCi g-~, mean 28.8 pCi g - i ) and silts (4.0-8.6 pCi g ~, mean 6.1 pCi g - l ) presumably reflect the dependence o f americium activity on the grain-size characteristics o f the sediments. The p r i m a r y interest in this study was not centred on the general coast o f Northwest England, but on the Ravenglass estuary (Fig. 1) which lies a b o u t 10 k m south o f the Windscale facility. The estuary is o f interest because it is an intertidal site o f fine grained sediment accumulation (Aston & Stanners, 1979) closest to the source o f the radioactive effluent. Various publications (e.g. Hetherington & Jefferies, 1974; Hetherington et al., 1976; Mitchell, 1978; Hunt, 1979) have reported the general levels o f activities o f radionuclides in various sediments and biota o f this locality. However, the present d a t a provide a m o r e comprehensive evaluation o f 2alAn] activities in surface sediments and their relation to sedimentary features.

Results and Discussion

Broadscale features o f 24tAm distributions

Table 2 shows the activities o f 241Am (pCi g-~) in intertidal sediments collected f r o m the open coast and embayments o f Northwest England. The range o f 24~Am

Figures 2 and 3 illustrate the 24~Am activities (pCi g - ~, dry weight) o f surface sediments collected from the intertidal reaches o f the estuaries o f the Rivers Irt and Esk

Sampling and Analysis

150

Volume 12/Number5/May 1981

241Am

and the consequent accumulation of the finest grain size sediments (Stanners, 1980). Hetherington et al. (1976) have reported the analysis of surface sediments from the bed of the north-eastern Irish Sea for 24JAm. At distances comparable to that of Ravenglass from the Windscale pipeline, i.e. ~ l0 km, they report activities of 15--47 pCi gdry weight. Clearly, the surface sediments of the Ravenglass inlet are, for the most part, enriched in Z41Am relative to those from the Irish Sea itself. The inner estuary sediments contain 24~Am concentrations up to seven fold the mean ~lAm concentration in the samples collected from the Irish Sea at equivalent distances from the Windscale outfall. Such comparisons are difficult to interpret due to the asymetrical distribution of radionuclides around the source, and differences in sediment types.

N

R. Irt

1:25000

35e 13o

\

\ \

Ounes

Small scale f e a t u r e s of 2~~A m distributions Beach

\ Irish

I

Sea

I I I \

Dunes

Fig. 2 The distribution of 241Am(pCi g - l, dry wt.) in surfaceintertidal sediments from the estuaryof the Riverlrt, Ravenglass.

respectively. These two estuaries (and the lesser River Mite) constitute a tidal inlet adjacent to the village of Ravenglass. The overall range of 241Am activities in the Ravenglass sediments is 10-191 pCi g-1, with an arithmetic mean of 65 pCi g- 1. The sediments of the estuary of the River Esk are, on average, slightly more contaminated with 241Am (69 pCi g- l) compared to those of the estuary of the River Irt (60 pCi g- t). The higher ~tAm activities are found in sediments from the inner sections of the two estuaries, and correspond to the regions of low energy flow regimes during tidal excursions

241Am

11

The results discussed above refer to the general distribution of 241Am in the Ravenglass inlet, and to supplement these two specific aspects of 241Amdistributions in relation to small scale sedimentary features have been investigated. These features are the variations of 241Am activities in surface sediments from a small area (10 m x 10 m) of an intertidal silt bank, and the variations along a transect through salt marsh, intertidal bank and associated tidal-stream channel features. Figure 4 illustrates the two sampling localities at the Newbiggin site on the River Esk estuary. The 24~Amactivities of 25 sediment samples equally spaced on the l0 m x l0 m grid are plotted in Fig. 5 as computer interpolated contours. The range of activities is 31.2 + 1.8-40.7 + 2.5 pCi g- 1, with an arithmetic mean of 35.4 pCi g- i. The maximum percentage variation from the mean is 26%, illustrating a rather constant activity of 241Am on this small scale sediment area. The per cent < 50/am grainsize of each sample was determined, and showed no significant correlation with 241Anl activity over the limited range of 30.3--40.1 per cent < 50/am grain size. The factor or factors giving rise to the small degree of variation in the 241Am in these sediments has not been established, but it appears that monitoring on a fairly broad basis is adequate

JR. Mite

Fig. 3 The distribution of 241Am(pCi g-l, dry wt.) in surface intertidal sedimentsfrom the estuaryof the RiverEsk, Ravenglass. 151

Marine Pollution Bulletin

I

and 65.6 + 18.7 pCi g-I respectively. These results can be explained by two possible processes which may lead to 241Am enrichment on the salt marshes. First, these marshes are only covered by spring tides at high water and this results in the deposition of very fine material which has not settled out of suspension at an earlier stage in the tidal cycle. Second, because the marshes are only occasionally covered the rate of sediment accumulation is slow. This may lead to the gradual ingrowth of 241Amfrom 2"lPu even in the surface layers of sediment. For some (unknown) reason the left hand salt marsh is particularly enriched in 241Aln relative to its adjacent silt bank.

Main channel

flat

,

It jl

sall /

}

marsh

, , / . ::. i ~l ~ I z

salt ma r sh

flat 200 ¸

fi

Newbiggin

Inlet

~'Am pC~g-~

100

/

i/

×-section of transect

1

NEWBIGGIN

Fig. 4 The locations of a small-scale sampling grid (silt bank) and transect for surface intertidal sediments at Newbiggin, River Esk estuary.

for intertidal silt banks since localized variations are not important. In contrast to the rather uniform distribution of 241Am over the silt bank, the transect of samples (T1 to T30) taken through the salt marsh, silt bank and channel section (see Figs 5 and 6) showed a dramatic variation of 241Amactivities in the surface sediments. The overall range of 241Am activities is 46.9___2.4-195.8_+10.9 pCi g-l. The mean activities on the salt marsh and silt bank were 102.8_+39.6

241Am 0

• /

•

pC g- 1 •

•

i 34 • Sample sites Fig. 5 Contours of 241Am distribution (pCi g 1, dry wt.) over a silt bank sampling grid at Newbiggin.

152

.~OIt rr~rsh I

silt bank

[ salt marsh

Fig. 6 The activity profile for 241Am (pCi g - l , dry wt.) for surface sediments along a transect (55 m) at Newbiggin, TI (left side) to T30 (right side).

General Conclusions The surface sediments of the coast and inlets of Northwest England are contaminated to varying degrees with 24~Am. The range of activities found was < 3-191 pCi g-l, the greatest activities being those in the fine grained sediments from the inner sections of the Ravenglass estuary about 10 km south of Windscale. In these environments the sediments of 241Amconcentrations are up to seven fold those reported for some Irish Sea surface sediments. The variability of 241Am over small areas of intertidal silt banks of uniform grain size distribution is small, but salt marshes immediately adjacent to silt banks and tidal channels are enriched in 241Am.

We are grateful to Mr. S. Benner for technical assistance. This work received financial support from the Natural Environment Research Council (U.K.).

Aston, S. R. & Stanners, D. A. (1979). The determination of estuarine sedimentation rates by 134Cs/]37Cs and other artificial radionuclide profiles. Estuar. CoastaI Mar. Sci., 9, 529-541. B.N.F.L. 0978). Annual Report of Radioactive Discharges and Monitoring of the Environment. British Nuclear Fuels Ltd., Risley, England, 64 p. B.N.F.L (1979). Annual Report o f Radioactive Discharges and Monitoring o f the Environment. British Nuclear Fuels Ltd., Risley, England, 64 p. Hetherington, J. A. & Jefferies, D. F. (1974). The distribution of some fission product radionuclides in sea and estuarine sediments. Neth. J. Sea Res., 8,319-338.

Volume 12/Number 5/May 1981 Hetherington, J. A., Jefferies, D. F., Mitchell, N. T., Pentreath, R. J. and Woodhead, D. S. (1976). Environmental and public health consequences of the controlled disposal of transuranic elements to the marine environment. In I.A.E.A. Symp. Proc. Transuranic Nuclides in the Marine Environment, Vienna, pp. 138-154. Hunt, G. J. (1979). Radioactivity in Surface and Coastal Waters of the British Isles, 1977. M.A.F.F. Aquatic Environment Monitoring Rept. No. 3, Lowestoft, 36 pp. Livingston, H. D. & Bowen, V. T. (1976). Americium in the marine environment- relationships to plutonium. In: Environmental Toxicity of Aquatic Radionuclides--Models and Mechanisms. (Miller, M. W. & Stannard, J. N., eds.), pp. 107-121. Ann Arbor Science, Michigan. Livingston, H. D. & Bowen, V. T. (1977). Windscale effluents in the waters and sediments of the Minch. Nature, Lond., 269, 586-588.

Mitchell, N. T. (1978). Radioactivity in Surface and Coastal Waters of the British Isles, Part 1: The Irish Sea and its Environs. M.A.EE Tech. Rept. FRLI3, Lowestoft, 16 p. Murray, C. N. & Kautsky, H. (1977). Plutonium and americium activities in the North Sea and German coastal regions. Estuar. Coastal Mar. Sci., 5,319-338. Pentreath, R. J. & Lovett, M. B. (1976). Occurrence of plutonium and americium in plaice from the north-eastern Irish Sea. Nature, Lond., 262, 814-816. Stanners, D. A. (1980). Transport and Deposition of Radiocaesium and other Radionuclides in Irish Sea Intertidal Sediments. Ph.D. Thesis, University of Lancaster, Lancaster, 435 pp. Stanners, D. A. & Aston, S. R. (1980). The rapid determination of americium in sediments by NaI(TI) gamma spectroscopy. Envirn. Tech. Len., 1,333-338.

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Hydrocarbon Concentrations in Water and Sediments from UK Marine Waters, Determined by Fluorescence Spectroscopy R. J. L A W Ministry o f Agriculture, Fisheries a n d Food, Directorate o f Fisheries Research, Fisheries Laboratory, B u r n h a m - o n - C r o u c h , E s s e x CMO 8 H A , U K

Between January 1978 and September 1979 samples of subsurface (1 m) water and surface sediment were collected from sites in the North Sea, English Channel, Irish Sea and a number of estuarine areas. These have been analysed by fluorescence spectroscopy (UVF) in order to provide information on the levels of hydrocarbons generally present in UK marine waters. Total hydrocarbon concentrations (THCs) of water samples ranged from 1.1-74 tag I. 1 Ekofisk crude oil equivalents, all values greater than 3.5 tag i. 1 occurring inshore. In offshore areas the mean THCs were: 1.3 tag I. 1 in the northern North Sea, 1.5 tag I. 1in the western Channel, 2.5 ~g I. 1 in the eastern Channel and southern North Sea, and 2.6 ~g I. j in the Irish Sea. THCs of sediment samples ranged from 0.27-340 pg g-I dry weight Ekofisk crude oil equivalents, the highest concentration being in the Queen's Channel, the main entrance to the River Mersey. H y d r o c a r b o n s enter the marine environment f r o m a number o f sources, e.g. land r u n - o f f via rivers, refinery and sewage discharges, accidental shipping loss, d u m p i n g o f wastes at sea, and in connection with oil exploration and exploitation. In a recent study, Read & B l a c k m a n (1980) have estimated the input o f oil to the waters a r o u n d England a n d Wales. They believe the input from the quantifiable sources mentioned above to be 94 000 tonnes per a n n u m , the m a j o r i t y o f which enters the near coastal

waters. In addition, unquantifiable inputs exist from both normal operational shipping loss, a n d from the rain-out o f hydrocarbons from the atmosphere (e.g. f r o m the burning o f fossil fuels). The authors believe that the former o f these, although occasionally, locally and variably significant, is unlikely to form m o r e than a m i n o r addition to the figure quoted, but that atmospheric input could be very large, perhaps o f the order o f tens o f thousands o f tonnes per annum. Little i n f o r m a t i o n is available on the resulting total h y d r o c a r b o n concentrations (THCs) o f water and sediments in U K waters, although considerable w o r k has been done on the n-alkane content ( H a r d y et al., 1977; Mackie et al., 1974). Ultraviolet fluorescence (UVF) analyses o f subsurface (1 m) water samples collected near Ekofisk 2 V2 months after the blow-out resulted in T H C s o f < 0.2-4.0/ag 1_1Ekofisk crude oil equivalents (Mackie et al., 1978). M o r e d a t a are available for C a n a d i a n waters and these show a mean T H C offshore o f 0.8 tag 1-1 Venezuelan crude oil equivalents at 1 m depth ( G o r d o n et al., 1974). Two metre samples from the Scotian Shelf and the St Lawrence Estuary ranged from 0.2-1.1 tag 1_1, with T H C s in the Bedford Basin ranging f r o m 1.6-9.3 tag 1_ 1 (Keizer et al., 1977), a n d averaging 2.5 tag 1_1 ( G o r d o n et al., 1978) (all G u a n i p a crude oil equivalents). F o r sediment samples, T H C s from 1 - 4 ~g g-] d r y sediment have been quoted in deep water samples (> 3000 m), whereas over 1000/ag g J has been found in samples taken from polluted inshore 153