Research and analysis

Tritium in crops: contaminated sewage sludge fertiliser

This report (HPA-RPD-038) describes a study to assess the transfer of tritium to crops from soil treated with contaminated sewage sludge.

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Discharge from a radiopharmaceutical facility to a waste water treatment works in Cardiff contributed to the dried sludge pellets used as a soil conditioner. The uptake of tritium from the treated soil into crops was investigated.

In 2005, a pilot study was performed to determine whether uptake was measurable and decide whether tritium was being lost rapidly from the soil. This was outside the constraints of the Sludge (use in agriculture) Regulations.

In 2006 the study was repeated without further addition of sewage sludge which provided conditions that did conform to the regulations. The tritium concentration in soil fell throughout the study. The changes in concentrations of tritium in soil over the growing seasons and the low concentrations measured in crops meant that it was not possible to quantify individual soil to crop transfer in terms of conventional concentration ratios. However it was possible to determine an aggregated transfer quotient relating the concentration in the edible part of the crop.

The observed values are likely to depend on factors such as temperature, rainfall and any artificial irrigation so these are not necessarily applicable in general radiological assessments. However, on the basis of these indicative values it would be reasonable to assume that the proportion of tritium transferred into crops from soil treated with sludge would be small.