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With the cessation of sea disposal of sewage sludge at the end of 1998, the amounts of sewage sludge applied to agricultural land may increase. This sludge may contain radionuclides as a result of authorised discharges of liquid radioactive wastes to the sewer system. These radionuclides may be transferred from the sludge into food crops and animal products produced on the land to which the sludge has been applied.
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Before authorisations to discharge radioactive waste into the sewage systems are granted, the Environment Agencies consult the Food Standards Agency (FSA). The FSA carries out dose assessments on the impact on the public of these discharges with specific emphasis on the food chain. To do this, the FSA requires a model that allows calculation of the concentration of radioactivity in crops to which the sludge is applied.
Two models have been developed. One deals with tritium and carbon-14, and the second deals with other radionuclides. The models are based on an extensive review of the relevant primary and secondary literature also produced for the FSA under this project. Detailed technical accounts of the implementation and application of both the general and special models are also available.
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These models are currently being used to evaluate the potential radiological impacts of existing radioactive effluent discharges, and to provide guidance to the Environment Agencies in the establishment of authorisations for the discharge of radioactive effluents into sewage systems.
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Although the models are generally well supported by data, there are deficiencies that could usefully be overcome by further research. In particular, the partitioning of radionuclides between sewage sludge, liquid effluents and volatilisation at wastewater treatment works is deserving of further study.
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Furthermore, it would be useful to confirm the conclusion, based largely on stable element data, that radionuclides added to soil-plant systems in sewage sludge behave similarly to radionuclides entering such systems by other routes, such as atmospheric deposition.
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Find more about this project and other FSA food safety-related projects at the <a href="http://www.food.gov.uk/science/research/" target="_blank">Food Standards Agency Research webpage</a>.