The answer given by WHO is that these residues are at very low levels. Some work has been done on the effect of irradiation on packaging materials and the US Food and Drug Administration have issued a list of approved materials, but there must be concerns about how well other countries are able to observe any conditions. Furthermore, it is one thing to show that carefully monitored doses under laboratory conditions have no deleterious effects, it may be a different matter where large quantities of foods are treated in industrial plants and dosage levels are much more difficult to control. Irradiation can be used to prolong storage and shelf life. This may well provide greater choice but given the high costs of irradiation treatment this will almost certainly be only of benefit to consumers in the developed and wealthier countries.
Irradiation can treat raw foods.
There are certain foods like certain raw fish products, sushi for example, where irradiation is the only method that can be used. However, raw fish need not and should not be contaminated at source. The consumer movement has achieved a major victory over the issue of labelling irradiated foods. Standards for the labelling of foodstuffs are set by the Codex Alimentarius. Codex has a special committee that deals with food labelling and the original proposals to the committee from the proponents of irradiation were that a flower-like symbol should be used on any food that had been irradiated.