A shipment of 36 million pounds of soybeans sailed late last year from Ukraine to Turkey to California. Along the way, it underwent a remarkable transformation.

The cargo began as ordinary soybeans, according to documents obtained by The Washington Post. Like ordinary soybeans, they were fumigated with a pesticide. They were priced like ordinary soybeans, too.

But by the time the 600-foot cargo ship carrying them to Stockton, Calif., arrived in December, the soybeans had been labeled “organic,” according to receipts, invoices and other shipping records. That switch — the addition of the “USDA Organic” designation — boosted their value by approximately $4 million, creating a windfall for at least one company in the supply chain.

After being contacted by The Post, the broker for the soybeans, Annapolis-based Global Natural, emailed a statement saying it may have been “provided with false certification documents” regarding some grain shipments from Eastern Europe. About 21 million pounds of the soybeans have already been distributed to customers.

The multimillion-dollar metamorphosis of the soybeans, as well as two other similar grain shipments in the past year examined by The Post, demonstrate weaknesses in the way that the United States ensures that what is sold as “USDA Organic” is really organic.

The three shipments, each involving millions of pounds of “organic” corn or soybeans, were large enough to constitute a meaningful proportion of the U.S. supply of those commodities. All three were presented as organic, despite evidence to the contrary. And all three hailed from Turkey, now one of the largest exporters of organic products to the United States, according to Foreign Agricultural Service statistics.