The radiation dose to man from the marine environment is dominated by the consumption of fishery products. The radionuclide 210Po plays an important part in this. 210Po (half life 138 days) is a daughter of 210Pb (half life 21 years). Both these natural radionuclides belong to the 238U series which has several other daughters amongst which is 226Ra. Locally, large quantities of these radionuclides are released into the coastal environment by nonnuclear industries (eg in phosphogypsum effluents of phosphorus industries). In contrast to the knowledge of artificial radionuclides and of 226Ra, little is known about the behaviour of 210Po and 210Pb in marine ecosystems.
This study has the general aim of obtaining an insight into the effects of such industries on the activity levels and distribution of 210Po and 210Pb in abiotic components and bioindicators, both in adjacent estuaries and in nearby coastal areas. An additional aim is to apply the obtained insight to the development of a model to predict 210Po and 210Pb distribution and levels.
The four participants of the contract cover a wide geographical range. Depending on the situation and expertise each participant directs his research to certain parts of the chain : emission, dissolution and absorption, distribution and accumulation in the abiotic environment, coupled with modelling and with the effects on potential bioindicators. Doing this in a coordinated joint study will yield a more complete insight into the chain from emission to effect and into geographical differences.
Samples of phosphogypsum effluent (polonium-210 and lead-210) emitted into the Nieuwe Waterweg by 2 fertilizer plants near Rotterdam have been obtained. The effluents from the 2 different plants were very similar; the dissolved polonium-210 concentrations ranged from 0.4 to 32 Bequerels per cubic metre. Samples were also obtained from a thermoprocess plant near Vlissingen in the waterschelde. At the point of discharge the offgas filter water contained 4000 Bequerels per cubic metre of polonium-210.
An inventory of generic estuary models was completed and 3 models studied in detail. Models of the Westerschelde were constructed and predicted lead-210 concentration were compared to sampled data.
In the Seine estuary and the nearby Channel coast a detailed study was made of the polonium-210 levels in the mussel Mytilus eclulis and in the brown algae Fucus vesiculosus to characterize their potential as bioindicators. Several collecting sites were chosen in the estuary and beyond. Phosphatic gypsum is released into the Seine estuary by Norsk Hydro Azote (NHA).
In the estuary, at Le Havre, the activity of filtered seawater fluctuates between 0.5 and 1 MBq per litre. Polonium-210 levels fell off between June and October 1990. Activities are higher in non filtered seawater and are correlated with turbidity. For M edulis, activity levels lie in the range 90 to 100 Bq per kg dry weight. The levels show seasonal variation. Polonium-210 activity levels are lower in F vesiculersus, ranging from 3 to 22 Bq per kg dry weight. Seasonal flutuations are apparent but are different from those if M edulis.
The evolution of polonium-210 levels are difficult to explain, since the discharge from the NHA plant varies only very slightly with time. Other inputs to the estuary system must be involved.
Samples were taken in order to study sources, sinks and the dynamics of the distribution of polonium-210 and lead-210 in the Westerscheldt. Some preliminary conclusions can be drawn. It seems that the Westerscheldt estuary, unlike the Nieuwe Waterweg, does not cut as a sink for polonium-210. The concentrations in the sediment are those of the natural background, except in the Sloehaven and near the BASF plant. Polonium-210 concentrations in suspended matter are around 150 Bq/kg, which is higher than that of the North Sea.
The Mira river estuary in Portugal was studied to establish the natural background levels of polonium-210 in the absence of any industrial emissions. In the Tagus estuary, the distribution of polonium-210 and lead-210 discharged by the phosphorus industry was measured. The emphasis was on abiotic materials rather than bioindicators.
The study encompasses the Westerschelde estuary in the Netherlands, the Seine estuary in France and the Tagus estuary in Portugal. A link will be established to the data obtained in 1989 on the Rhine estuary (CEC project BI6A 0328ANL). In each of these estuaries large quantities of 210Po and 210Pb are emitted by local phosphate industries. In addition, natural levels will be studied in a Portuguese river and estuary free from industrial 210Po emissions.
The effluents of the Dutch phosphate industries will be studied in laboratory experiments, in order to identify the characteristics determining the behaviour of 210Po and 210Pb after emission (RIVM). A sampling programme of water and bottom sediment of the Westerschelde and the adjacent North Sea coast with analyses of 210Po and 210Pb will be executed. Particular attention will be given to possible distribution pathways of industrial effluents and to seasonal, hydrological and biological effects (NIOZ). The data and information obtained will be used to develop a model to predict 210Po and 210Pb levels in the Westerschelde (RIVM).
In the Seine estuary and the nearby Northern coast, a detailed study will be made of the 210Po and 210Pb levels in the mussel Mytilus edulis to characterize its potential use as a bioindicator. Special attention will be given to the geographical and seasonal variation in these waters and to bottom sediments. Laboratory experiments will be executed with M. edulis to study the evolution of its 210Po level in correlation with sudden or regular contamination of water and/or suspended matter, with the quality of seawater, and to determine the characteristics of Po and Pb metabolism by M. edulis (CEA).
In Portugal a river and estuary on which no industrial 210Po emissions take place, will be studied to establish the natural background levels of this environment and their variation. In the Tagus estuary and the adjacent coast the focus will be on the distribution of 210Po and 210Pb discharged by the phosphorus industry. The major emphasis will be on abiotic materials and to a lesser extend on bioindicators (LNETI).
Conclusions of general applicability will be drawn and location specific differences will be identified from the data and the conclusions of the five estuaries. This will give new inputs both to future generic and location specific modelling, as to the direction of future research (RIVM, NIOZ, CEA, LNETI).
By coordinating these studies, a more complete insight in the total chain will be obtained and geographical differences will be identified. General characteristics of Po and Pb behaviour and the effects of industrial emissions will be identified from the research data of the five estuaries. Attention will be given to location specific differences in the behaviour of Po and Pb. All this will give new inputs to future generic and location specific modelling, and to the direction of future research. (RIVM, NIOZ, CEA, LNETI).
Funding SchemeCSC - Cost-sharing contracts
1790 AB Texel, Den Burg