North-east Irish Sea Research Articles

Radionuclides and large particles in estuarine sediments

Radionuclides, released into the north-east Irish Sea from the British Nuclear Fuels plc uranium reprocessing plant at Sellafield, Cumbria, UK and which are present in sediments of the Esk estuary, Cumbria, are initially associated with large (i.e. >0.5 mm) rather than fine grained (i.e. <63 μm) particles. I call these macro particles organoliths. They consist of an agglomerate of sediment grains held together with an organic iron rich matrix; their surfaces are coated with a patina of iron and manganese oxides with which the radionuclides are associated. Concentration factors (Kd's) for plutonium, americium, and other radionuclides, together with various stable elements in the patina are orders of magnitude greater than those found in bulk sediments. Some implications concerning the radionuclide content of organoliths are discussed in relation to geochemical process, pollution studies and the requirements of radiological protection.

Radionuclides in shoreline waters of the Northeast Irish sea

The shoreline waters of the Irish Sea along the Cumbrian coast near the British Nuclear Fuels plc works at Sellafield have been sampled at three locations over a 3 1 2 year period from December 1980. The particulate content was analysed for 238Pu, 239+240Pu, 241Am, 137Cs and stable Al. In some cases the radionuclide concentrations in filtered seawater were also determined. The results showed that the suspended particulate loads were high (typically about 100 mg l −1) and variable, and that they contained about 65 mg g −1 of aluminium. The isotopic ratio 238Pu/ 239+240Pu, which can indicate the chronology of the discharge, was about 0.26, which suggested that the Sellafield discharges over at least 5 years contributed to the observed concentrations. The 239+240Pu and 241Am annual average concentrations in the particulate material were in the ranges 3.0–5.1 and 3.3–5.2 Bq g −1, respectively. The individual values were very variable in time, but highly correlated with each other. No significant downward trends in the concentrations could be identified over this period. This is consistent with the behaviour of a reservoir (the northeast Irish Sea) where Pu and Am, which are available for suspension in particulate material, are fed by the Sellafield discharges and are subject to a mean removal time of several years. Thus the effects of the large reduction in the Sellafield discharges which occurred over this period should only be observable over a longer time interval. The concentrations in the dissolved fractions in seawater were negligible compared with the particulate fraction concentrations, in sharp contrast with the situation in offshore seawater. For 137Cs, the annual average concentration in filtered seawater was in the range 7.6–12.0 Bq l −1, which was 87–90% of the total concentration in seawater, proportions rather lower than some results reported in the 1970s, possibly reflecting a residual effect of the higher discharges. In general, the work showed that measurements of shoreline seawater are necessary in order to interpret littoral effects such as the sea-to-land transfer of radionuclides and the uptake of radionuclides by molluscs, in the environment of the Irish Sea.

Observed and predicted concentrations of caesium-137 in seawater of the Irish Sea 1970–1985

The results of the MAFF programme to monitor the concentrations in seawater of 137Cs discharged to the northeast Irish Sea from the BNFL fuel reprocessing plant at Sellafield in Cumbria are presented. A box model of coastal waters in northern Europe is constructed and tuned so that there is good agreement between sampling observations from the monitoring programme and model predictions. Two sets of flow conditions are necessary to adequately match the model with measurements. They include a net flow rate through the Irish Sea of 2·2 km 3 day −1 up to September 1976 and 4·4 km 3 day −1 thereafter. These flow rates fall within the previously reported range of 2–8 km 3 day −1.

Mechanisms for northwards dispersal of Sellafield waste

Almost all of the plutonium and americium discharged as liquid effluent from Sellafield is retained in the sediments of the north east Irish Sea1–5, whereas the waste radiocaesium shows relatively conservative behaviour in seawater and is mostly dispersed into more distant waters with only a small fraction being retained in Irish Sea sediment6–12. Sellafield discharges13,14 considered in the light of radionuclide geochemistry and radioactive decay and grow-in15 imply that, by the end of 1984, the sediments of the north-east Irish Sea contained about 6 x 102 TBq each of 239,240Pu and 241Am and of the order of 103TBq of 137Cs. This contamination, of globally significant magnitude16,17, is largely concentrated in restricted areas of fine sediment off the Cumbrian coast close to Sellafield3,4,18 so it is important to identify processes which could lead to the dispersal of these nuclides to areas of potential human contact (such as intertidal sediments) over the long time scales appropriate to the half lives of 241AM Am (458 yr), 239Pu (2.44 x 104 yr) and 240Pu (6.58 x 103 yr). Because no significant return of these actinides to solution in seawater is likely19,20, most concern must be centred upon physical dispersal processes affecting the contaminated sediment. These are ill-defined, although Hunt21 contends that actinides incorporated in intertidal sediments near Sellafield are subject to mixing with previously discharged waste and to dispersal, with removal from the surface sediments within one or two decades. Here we present the results of a study of radionuclide concentrations in surface (<0.5cm depth) intertidal sediments collected during 1984–85 which provide the basis for an estimate of the extent of northwards dispersal of the contaminated sediment and an assessment of the importance of this process relative to transport of radionuclides in solution.

Water transport from the North-east Irish Sea to western Scottish coastal waters: Further observations from time-trend matching of Sellafield radiocaesium

Radiocaesium isotopes, discharged into the North-east Irish Sea from the Sellafield (formerly Windscale) nuclear fuel reprocessing plant in Cumbria, have been employed as flow monitors to update and extend the record of coastal water movement from the Irish Sea to the Clyde Sea area and, further north, to Loch Etive. The temporal trends in radiocaesium levels have been used to determine the extent of water mixing en route and to define mean advection rates. Flow conditions from the Irish Sea have changed considerably since the mid-1970s, the residence time of northern Irish Sea waters being ∼12 months during 1978–1980 inclusive. Average transport times of four and six months are estimated for the Sellafield to Clyde and Sellafield to Etive transects respectively. Sellafield 137Cs levels in seawater were diluted by factors of 27 and 50 respectively during current movement to the Clyde and Etive areas. The decrease in salinity-corrected 137Cs concentrations between the Clyde and Etive suggests that dilution by Atlantic water occurs, the latter mainly entering the Firth of Lorne from the west. The majority (∼94%) of the radiocaesium supply to Loch Etive enters the Firth of Lorne via the portion of the coastal current circulating west of Islay, only ∼6% arriving via the Sound of Jura.

Growth rate of Raia clavata in the Northeast Irish Sea

Growth rate of Raia clavata in the Northeast Irish Sea

Inhibitions to pollutant dissipation in the north-east Irish Sea

Observations on the surface and sub-surface density fields in the north-east Irish Sea have been made during frequent cruises over a number of years. Data are presented to show that considerations of the presence and persistence of both lateral and vertical density discontinuities are important to the water quality management problems of this sea area.

The use of reprocessing effluent radionuclides in the geochronology of recent sediments

Over the last three decades, artificial radionuclides have been introduced into the environment from the nuclear industry. This paper discusses the use of such radionuclides for interpreting the geochronology of recent sedimentary deposits. The discharges into the northeast Irish Sea from the Windscale reprocessing plant (U.K.) provide a useful opportunity to study the transport and geochronology of sediments in this area. A variety of different methods have been developed to study the behaviour of the local sediments, and a number of examples are discussed, illustrating the techniques used for “dating” the sediment deposits. These involve the use of fission-product radionuclides ( 134Cs, 137Cs, 106Ru and 144Ce), transuranics ( 239+240Pu and 238Pu), and the application of radionuclide concentration ratios in cores and surface samples. The radionuclide activity profiles of the sediment cores and the concentration ratios of the surface samples were interpreted by comparison with the known discharge histories. This provided information on net sedimentation rates, apparent diffusion coefficients and lag-times of transport. The studies showed that post-depositional redistribution of Cs and especially Pu nuclides within a sediment column are small (apparent D < 10 −8 cm 2 s −1). Net sedimentation rates varied in the range 16–71 mm yr. −1 and lag-times 0–0.75 yr. From samples taken along a mud bank salt marsh transect correlations were shown between activities and sedimentary environment.

The identification of critical groups and its application to fish and shellfish consumers in the coastal area of the North-East Irish Sea.

Control of radioactive waste disposal to the environment, based on the recommendations of the International Commission on Radiological Protection (ICRP), necessitates an identification of the critical group of members of the public exposed from a given practice. Criteria for identification of critical groups based mainly on ICRP recommendations are discussed. Methods existing up to 1974 are briefly reviewed in the light of these criteria. Two more recent methods are described and compared on the basis of previous data; these methods, which are complementary, are based on homogeneity considerations and satisfy the criteria generally rather better than do the earlier methods. The application of the newer techniques to recent surveys of fish and shellfish consumption in the coastal area of the North-East Irish Sea is described, in relation to discharges from the Windscale reprocessing plant. The results of this survey are presented, and estimates are given of the effective dose equivalent to members of these critical groups in recent years, to show the effect of liquid discharges from Windscale in terms of public radiation exposure.

Further studies on the distribution of 137Cs in British coastal waters—I. Irish Sea

The concentrations of 137Cs, discharged to the northeast Irish Sea from the British Nuclear Fuels Limited (BNFL) Windscale Works, Cumbria, have been measured in the Irish Sea and its approaches during 1970 to 1978. Seawater labelled by 137Cs has been used to study the variability of local and distant dispersion and to estimate residence times and volume transports. In the immediate vicinity of the outfall a release rate of 1 Ci d −1 produces a mean annual concentration of 4.2 pCi l −1 (2.6 to 6.3 pCi l −1) with an approximate 30-fold reduction to 0.15 pCi l −1 in the northern exit to the Irish Sea and at least a 300-fold reduction at the southern entrance. The release rate ranged from 60 to 400 Ci d −1 (annual average) during the study period. The main flow patterns are deduced and show a substantial change before and after 1976. Using estimated inventories of the radionuclide in various areas, the rate of input into the system, and a simple exponential model, the residence ‘half time’ of water east of a line south from Scotland through the Isle of Man to Anglesey is estimated to be 200 days. The estimate for the whole northern Irish Sea was 1 year between 1970 and 1976, with a sharp reduction thereafter. The change is confirmed by estimating the volume transport through the North Channel from data from the Stranraer-Larne, Fishguard-Rosslare, and Swansea-Cork ferries. The mean flow through the Irish Sea for the period October 1971 to May 1978 was 5 km 3 d −1 with mean flows of 3.4 km 3 d −1 prior to January 1976 and 7.9 km 3 d −1 thereafter to May 1978. Transit times from the discharge point to the North Channel have also been estimated from the change in concentration of the radionuclides 137 Cs( t 1 2 = 30.1 y) and 134 Cs( t 1 2 = 2.1 y) and from serial correlation of rates of discharge and concentrations of 137Cs at distance.

α-Particle radioactivity of hot particles from the Esk estuary

Transuranium radionuclides (Pu, Am and Cm) present in effluents discharged into the north-east Irish Sea by British Nuclear Fuels Limited, Windscale, Cumbria, UK, are found in sediment and biota of the Esk estuary ∼10 km to the south. The site of the present investigation was at Newbiggin and the materials examined were suspended particulate debris samples at the sea surface, bottom sediments and some forms of biota collected in September 1977. It is shown here that hot particles (defined as small volumes of material emitting a particles recorded in a dielectric detector as dense clusters of tracks from a common origin) found in the estuary are likely to be original effluent debris derived from the processing of Magnox uranium fuel elements and not formed in situ as a result of natural processes common to the estuary.

Marine disposal of radioactive wastes

In a general sense, the main attraction of the marine environment as a repository for the wastes generated by human activities lies in the degree of dispersion and dilution which is readily attainable. However, the capacity of the oceans to receive wastes without unacceptable consequences is clearly finite and this is even more true of localized marine environments such as estuaries, coastal waters and semi-enclosed seas. Radionuclides have always been present in the marine environment and marine organisms and humans consuming marine foodstuffs have always been exposed, to some degree, to radiation from this source. The hazard associated with ionizing radiations is dependent upon the absorption of energy from the radiation field within some biological entity. Thus any disposal of radioactive wastes into the marine environment has consequences, the acceptability of which must be assessed in terms of the possible resultant increase in radiation exposure of human and aquatic populations. In the United Kingdom the primary consideration has been and remains the safe-guarding of public health. The control procedures are therefore designed to minimize as far as practicable the degree of human exposure within the overall limits recommended as acceptable by the International Commission on Radiological Protection. There are several approaches through which control could be exercised and the strengths and weaknesses of each are considered. In this review the detailed application of the critical path technique to the control of the discharge into the north-east Irish Sea from the fuel reprocessing plant at Windscale is given as a practical example. It will be further demonstrated that when human exposure is controlled in this way no significant risk attaches to the increased radiation exposure experienced by populations of marine organisms in the area.

The radiation dose received by plaice (Pleuronectes platessa) from the waste discharged into the north-east Irish Sea from the fuel reprocessing plant at Windscale.

Abstract A large proportion of the radioactive waste discharged into the north-east Irish Sea from the nuclear fuel reprocessing plant at Windscale is reconcentrated on to the seabed silt and sediment in the vicinity of the outfall. This results in an extensive environment in which benthic and demersal organisms receive a radiation dose rate significantly greater than the natural background. Calculations based on seabed radioactivity measurements made during routine environmental monitoring surveys indicated that the dose rate to the plaice (Pleuronectes platessa), a commercially important species in the area, could range up to 5 mrad hr−1 from beta- and gamma-radiation. In situ measurements of the dose rate regime experienced by the plaice have been made with lithium fluoride dosimeters combined with the “Petersen disc” tag normally used for fish population surveys. The results show substantial agreement with the calculated dose rates and the data have been used to derive an estimate of the mean dose rate to the plaice gonad. It is concluded that the increased radiation exposure experienced by the plaice will not have any discernible effect at either the individual or population level.

Distribution of caesium-137 in British coastal waters

The safe discharge of wastes into the sea depends upon achieving adequate dilution of the effluent, otherwise inshore biological reserves may be damaged. Water in the north-east Irish Sea can be identified because of its content of radioactive caesium emanating from the Windscale nuclear fuel processing plant. A survey shows how closely this water hugs the coasts as it travels across the Irish Sea and along the west and north coasts of Scotland. Inshore waters receive almost all our effluents and this report suggests that the dilution capacity of the sea may be far less than is supposed.

On the occurrence of lymphocystis, with notes on other pathological conditions, in the flatfish stocks of the north-east Irish Sea

On the occurrence of lymphocystis, with notes on other pathological conditions, in the flatfish stocks of the north-east Irish Sea

Epidermal Lesions in Irish Sea Flatfish

PERKINS et al.1 suggest that the apparent increase of epidermal lesions in the flatfish of the north-east Irish Sea during 1971 may be associated with pollutants, particularly polychlorinated biphenyls (PCBs). They suggest that the simultaneous increase of lymphocystis, fin damage and ulcers represents an abnormal situation that may have resulted from the increased dumping operations carried out in the Irish Sea over the past few years.

Incidence of Epidermal Lesions in Fish of the North-East Irish Sea Area, 1971

THE fish of the North-East Irish Sea (Fig. 1) and Solway Firth area have been surveyed continuously by ourselves and others since 1959 at least. During the period until the end of 1970, epithelial lesions were not observed to a significant degree. In March 1971, however, concurrent with observations made by fishermen, a marked incidence of such disease was noted in plaice(Pleuronectes platessa) and dab(Limanda limanda)(Fig. 2). A confirmed occurrence off the coasts of Cumberland, Kirkcudbrightshire, as well as unconfirmed reports from Luce Bay, Wigtownshire, and Bahama Bank, Isle of Man, indicate that fish from some 1,500 square miles of sea were affected.

Recent Geological Investigations in the Irish Sea

AN area of Carboniferous rocks between the Isle of Man and Anglesey has been found during a recent geological and geophysical survey by the Institute of Geological Sciences in the north-east Irish Sea. Echo sounder records from this area indicate a notably uneven sea bed, which locally has a relief of up to about 40 feet and probably consists of outcrops of solid rock surrounded by boulder clay or gravel. Rock samples were recovered with a gravity corer at fifteen localities and it seems likely that they were cored from outcrops rather than from boulders in boulder clay. The samples have been identified as follows (see Fig. 1 for localities): three cores of Manx Slates (close to the Isle of Man), three cores of rocks from the Mona Complex (close to Anglesey), four cores of Carboniferous (Westphalian) mudstones and siltstones, one core of Ordovician mudstone, and four cores of mudstone and siltstone of undetermined age. These have yielded no Carboniferous spores but are currently being examined for any other microfauna. They may be of Lower Palaeozoic age.