Five samples were found to be irradiated in a survey carried out in early 2005 by the Food Safety Authority of Ireland and four of these were previously identified in a survey last year.
This reveals a continuing lack of traceability in the herbal supply chain, already revealed in 2004. That year, a survey found that more than half of 26 herbal supplements tested in 2003 had been either wholly irradiated or had a component that was irradiated.
Under current laws, the only foods with EU authorisation for irradiation are dried aromatic herbs, spices and vegetable seasonings. A number of other products are also authorised under individual Member States' national legislation but these do not include herbal supplements.
Irradiation does not present an immediate food safety concern, said FSAI, but implicated batches are being removed from sale.
The Irish Health Trade Association (IHTA), the Irish Association of Health Stores and the Irish Pharmaceuticals Association have been advised of the results and will inform their members.
Last year the IHTA, which represents 33 supplement companies, mainly distributors, in Ireland, said it did not recommend the use of irradiation, as "there is little or no consumer confidence in the process, in our experience".
There are also questions about the long-term safety of the practice and some evidence to suggest that irradiation may adversely affect micronutrients and the active principles of plants.
"The modern practice of irradiation has no place in these ancient traditions [of herbal medicine] and therefore herbal products which have been irradiated can no longer be considered as bone fide natural health products," said a statement from the group.