The USDA's Animal and Plant Health Inspection Service (APHIS) this week issued 'emergency action notifications' to inform distributors of the seed, which had been scheduled for planting this spring, that it must be held until the agency concludes its investigation.
Developed by chemicals company BASF, Clearfield CL 131 was not developed as a genetically engineered product. However, the firm's own testing revealed that the variety may have been contaminated with a genetically modified strain. BASF last week notified the USDA of its findings, which are now due to be verified by further tests conducted by APHIS.
The regulatory agency will also conduct an investigation into the circumstances surrounding the release and whether any violations of USDA regulations occurred.
BASF Agricultural Products said that it is removing all Clearfield CL 131 rice seed from the market.
"BASF notified the USDA immediately after becoming aware of the laboratory findings and we continue to work cooperatively with USDA on this situation," said Andy Lee, a director with the firm.
This is not the first detection of genetically engineered material in Clearfield CL131 rice seed. Last week, APHIS announced that trace levels of a previously deregulated genetically engineered trait had been identified in Clearfield CL131.
However, the genetic material currently in question is regulated - which means that it has not been approved for commercial use.
The US rice industry already suffered a major disruption last year, after Bayer Crop Sciences in July notified the USDA that it had discovered trace amounts of an unapproved GM rice in samples of commercial rice seed.
The GM contamination - involving the GMO LL Rice 601 variety - sparked a flow of reactions against the firm and the US rice export market. Such limits on rice exports had an immediate impact on US farmers, who retaliated with a flood of lawsuits against Bayer.