The Agricultural Marketing Service of the U.S. Department of Agriculture has moved to tighten its oversight of the expanding organic food industry. Under a final rule published in the Federal Register on Nov. 8, beginning in 2013, accredited certifying agents of the A.M.S.’s National Organic Program will be required to visit annually no fewer than 5% of the farms and businesses they certified as organic to ensure products, production methods and premises remain free from residues of prohibited substances and in compliance with N.O.P. regulations.

Under the Organic Foods Production Act of 1990, as implemented by the N.O.P., which was established in 2000, farms and businesses seeking to market products as organic must be certified as meeting the program’s requirements by accredited certifying agents of the N.O.P. If approved, a farm or business becomes certified as an organic food producer or handler and may market its products as such.

As of January 2012, there were 17,281 organic farms and processing facilities in the United States that were certified as meeting U.S.D.A. organic standards and permitted to market their products accordingly. The U.S. organic industry achieved $31.4 billion in sales in 2011. Additionally, thousands of foreign producers and businesses have been approved as providers of certified organic products to the United States. Worldwide, as of January 2012, there were 28,386 U.S.D.A.-certified organic operations in 133 countries.

To certify the operations as organic, the A.M.S. enlists the services of more than 100 accredited agents (inspection companies) worldwide, with about 93 of the agents operating in the United States.

Once certified as organic producers, though, most approved farms and businesses weren’t likely to be visited by their certifying agent to ensure their products remained free from prohibited substances used in commercial farming and that the methods employed in producing their crops or livestock remained in accordance with U.S.D.A. organic regulations.

An audit of the N.O.P. conducted by the U.S.D.A. Office of the Inspector General in March 2010 revealed that none of four U.S.-based accredited certifying agents it visited conducted periodic residue testing at operations they initially certified as organic producers or businesses to the N.O.P. The inspector general’s office indicated the certifying agents noted they considered residue testing to be required by regulations only “under certain circumstances,” for instance, if there was a complaint.

The A.M.S. said it reviewed the issue and concluded under the Organic Food Production Act accredited certifying agents are required to conduct residue testing of organic products on a regular and reoccurring basis as well as when there is reason to believe contamination has occurred.

The A.M.S. in 2011 published for comment a proposed rule requiring periodic residue testing to be conducted at organic operations, and the proposed rule, with modifications, was the basis for the final rule issued in November.

The final rule requires accredited certifying agents to take samples and tests each year from a minimum of 5% of the operations they certified as organic operations to the N.O.P.

“Basing sampling on a percentage of the operations reduces the burden on the certifying agents by providing a clear and simple formula for how to comply with the regulations,” the A.M.S. said. “The 5% requirement satisfies the A.M.S.’s intent to discourage mislabeling of agricultural products and provides a means for monitoring compliance with the N.O.P.”

The A.M.S. indicated it considered alternatives to the 5% target, but proposals for testing 25% of operations or even 100% of the operations each year were considered too costly and beyond the aim of alerting certified organic producers they must continue to ensure they adhere to U.S.D.A. organic regulations.

“The objectives for periodic residue testing can be met by sampling a subset of operations annually, and, therefore, the additional costs that would be required to test all operations are unnecessary,” the A.M.S. said.

The A.M.S. said it would leave selection of operations to be inspected each year to the discretion of the agents.

“Certifying agents are knowledgeable about the risk factors affecting the operations they certify,” the A.M.S. said. “Therefore, it is appropriate for a certifying agent to determine what operations should be tested under this action.”

In a Nov. 8 letter to accredited certifying agents, Miles McEvoy, A.M.S. deputy director, said, “As long as you test at least 5% of the operations you certify to the U.S.D.A. organic regulations, you may establish your own criteria to determine which operations are subjected to testing. Possible selection criteria include: selecting operations at random, focusing on operations that produce more organic products, testing operations more likely to have residues of prohibited substances or methods, conducting testing as part of another investigation, and combining these or other selection criteria.”

Testing may include sampling soil, water, seed, plant tissue and other pre-harvest inputs as well as the organic products themselves.

The A.M.S. said certifying agents must retain test results for three years, and the results will be considered when the agent’s performance and compliance with the final rule is reviewed.

At the same time, the agency made clear it was not necessary to forward all results of testing to the A.M.S. Certifying agents would be required to report violations of Environmental Protection Agency or Food and Drug Administration regulations to the agencies and relevant state agencies, and would be required to report violations of N.O.P. regulations that would affect an operation’s certification as an organic producer. But the A.M.S. asserted it “does not intend to consolidate residue testing data from certifying agents and does not need reporting of residue testing results as the mechanism to ensure that certifying agents are meeting the required periodic residue testing.”

The Organic Trade Association issued a statement on the new final rule, saying, “This additional testing will help certifying agents identify and take enforcement action against farms and businesses intentionally using prohibited substances or methods.”

David Acheson, a partner in the law firm of Leavitt Partners, observed, “This is an indication that those producing organic food will be under more scrutiny. But in practice, I don’t anticipate this will drive a lot of change for the organic industry, although it may drive up costs.

“If one were to connect dots on this I think overall, it is indicative of the pressure on those claiming ‘organic’ or ‘natural’ products to pay more attention to ensuring that the products really do meet any standards that there are, which, for ‘natural’ is a challenge since the definitions are vague.”