Study of polonium and lead in shellfish (Mytilus Edulis) from NORM discharge area of Aberdeen Bay and Ythan Estuary of Scotland and radiological impact to the local people and environment

Introduction The problem of NORM in the oil and gas industry is a result of deposits of radioactive (Ra,BaSO4) scale within pipelines and processing equipment. The build-up of the scale has a significant impact on the activities of the operating company involved and is therefore a costly problem. The pipes and other equipment must therefore be cleaned on a regular basis or disposed of and replaced. Once the LSA scale has been removed from oil processing equipment the main route of disposal is into the sea. This scale contains mainly radium, lead and its daughter products, which have a long half-lives and high radiotoxicity. The volume of NORM waste produced by the petroleum industry is quite impressive. There are 230 oil and gas producing platforms in UK waters together with around 40 onshore oil and gas producing wells. All are involved in NORM production and discharging the NORM contaminated waste to the North Sea. Discharge of radioactive scale waste from offshore platforms into the surface waters of sea has been a matter of concern due to possible environmental effects of radioelements contained in such waters. Subject to certain conditions this is allowed under the UK Radioactive Substances Act 1993 which controls the release of radioactive materials into the environment. In the case for North sea oil and gas field waste, waste from the cleaning of contaminated plant and equipment is either discharged to sea off shore, discharged to sea from a pipeline in Aberdeen or stored at the Dounraey nuclear facility. Although allowed since 1981 no one has ascertained if these conditions are ensuring full protection of fish consumers. Furthermore, the disposal of large amounts of contaminated wastes resulting from the various stages of oil processing can pose an environmental problem due to its content of long lived radionuclides (226Ra t1/2 = 1600 y and 210Pb t1/2 = 22 years). In order that an accurate estimate of the contribution of polonium from NORM discharges can be made it is essential that the release rates of the nuclides from the discharges are known. If polonium becomes available in the marine environment from these discharges they will contribute to the impact on the environment. In order to evaluate the possible radiological impact to the local people and the environment, a comprehensive study was set up in order to determine the full extent of TENORM and NORM outputs and the impact that these radionuclides were having on the environment. The main aim of this study concerned the quantification of the levels of 210Po and 210Pb in shellfish species and other environmental samples taken from around Aberdeen, and use them as bio-indicators for the analysis of Polonium-210 and Lead-210 with particular emphasis on the seasonal variation in Mytilus edulis at one site of Ythan estuary. There was a supplementary programme undertaken to some dose assessment work relevant to human consumption of shellfish. Additionally, the study of the distribution of 210Pb and 210Pb between the filtered, particulate phases, sediment and mussels can provide interesting in formation about their behaviour in this aquatic system. Experimental Radiochemical separation and α Spectrometer with Dual surface barrier detector was used to count the polonium a particles. A Perspex disc holder for polonium deposition was specially designed to be held in a stirrer and to fit inside a 150-200 ml breaker. The holder provides positive protection to one face of the silver disc. Silver disc with a thickness of 0.2 mm and 25 mm in diameter was used for 210Po spontaneous deposition. Results: The measured 210Po and 210Pb concentrations and 210Po/210Pb activity ratio in filtrate water, sediment, particulate matter and mussel samples are reported. Some results are presented in Figure 1 and Table 1. Correlations between 210Po and 210Pb concentrations in mussel and related environmental samples, mussel wet weight and size are presented. The Condition Index (relationship between dry weight of tissue and shell length) of these mussels varied from 3.7 up to 7.2. The highest 210Po was found in the shell length of 60-70 mm length size, the activity of 210Po per mussel varied from 0.55 Bq per mussel in 40-50 mm size to a maximum of 0.43 Bq per mussel in 60-70 mm size. The results obtained show that levels of 210Po are well in excess of the levels of 210Pb in shellfish tissue, with the activity of the two nuclides comparable in water and particulate matter samples. This suggests that preferential uptake of 210Po is taking place by shellfish around Aberdeen, Scotland with sometimes as much as sixty five times the concentration of 210Po as there is 210Pb, The disequilibrium conditions which exist between the two nuclides in shellfish result in a significant dose from 210Po to any animal which may consume them, It is therefore apparent that certain groups who eat large numbers of shellfish are at risk from increased radiation doses. Dose rate work indicates that the variation in the activity of 210Po and 210Pb per mussel leads to large variations in the numbers of shellfish that would have to be consumed in order to exceed certain constraint doses.