R01061: Tritium concentrations in crops fertilised with contaminated sewage sludge
Monday 7 April 2008
Study Duration: April 2005 to October 2007
Contractor: Health Protection Agency - Radiological Protection Division
Background
Authorised discharges of radionuclides into sewers can result in contamination of sewage sludge, which can be used as a soil conditioner. A review of published information, carried out by the Health Protection Agency (HPA) indicated that specific data on the uptake of radionuclides from treated land into crops was scarce. Discharges from a radiopharmaceutical plant in Wales were routed to a waste water treatment works, and have resulted in elevated concentration in sewage sludge pellets. This provided the opportunity to generate specific data on crop uptake.
Research Approach
The project made use of the contractor's existing lysimeter facility to generate realistic uptake data for selected crops grown in three soil types. This was augmented by smaller scale studies on a wider range of crops that generated relative values for uptake parameter values applicable to the Agency's predictive models. Losses via transpiration are an important area of uncertainty, and experiments to measure the extent of these losses were also undertaken.
Results and findings
Concentrations of tritium in treated soil decreased throughout the period of the experiment, and measured values in the soil itself displayed considerable variability, although this variability decreased with time.
On the basis of the results obtained, for risk assessment purposes it would be reasonable to assume that the proportion of tritium transferred into crops from soil treated with sewage sludge would be small.