Police, health and education authorities in both Dorset and Wiltshire have been alerted after the failure to recover 11 of the necklaces sold to a young couple who planned to hide them in the garden as a game for a children's party.
Oxfam renewed appeals yesterday for the return of 1,150 of the necklaces which are made from castor seeds containing ricin, a deadly poison. Ricin was used to kill Georgi Markov, the Bulgarian dissident, who died in 1978 after a poisoned pellet was shot into his leg from the tip of an umbrella.
Doctors warn that children could be killed through swallowing just one of the seeds - about the size of a broad bean.
Oxfam said the public had begun to return many of the necklaces after widespread publicity, but it is unable to say how many of those sold remain untraced. More than 7,000 of the necklaces, made in Guatemala, were distributed to 346 Oxfam shops between 8 June and 17 June.
'The shops have been returning all their stock to us but we can't differentiate between those not sold and those sold and then brought back,' John McGrath, of Oxfam, said.
The charity believes it will be the end of the week before a more accurate total of necklaces outstanding can be calculated. It is worried that the small value of the necklaces will mean people will not bother to return them. All customers are being urged to notify shops even if they have destroyed the beads.
Necklaces were sold in every part of the country, but Oxfam is most worried by those purchased in Shaftesbury as it is known they were intended for use by children. Volunteer staff who run the charity's shop in the town said a woman in her early thirties first purchased 10 necklaces. A day later, her husband bought another one.
The danger was first identified by a customer in Birmingham, who had visited South America and recognised the seeds. She contacted the local trading standards office, which alerted Oxfam.Reuse content