[article] (CNN) -- On any day, between 5 million and 6 million containers are on the high seas, carrying everything from potato chips to refrigerators. But not all of them make it to their destination, as the crew of the Svendborg Maersk have just found out. Their Danish-flagged ship was in the Bay of Biscay last week as hurricane-force winds battered the Atlantic coast of Europe. Amid waves of 30 feet and winds of 60 knots, the Svendborg began losing containers off northern France. After the ship arrived in the Spanish port of Malaga this week, Maersk discovered that about 520 containers were unaccounted for. Stacks of others had collapsed. It's the biggest recorded loss of containers overboard in a single incident. As repairs are made to the Svendborg in Malaga, Palle Laursen, Maersk's vice president of operations, says the company is examining its procedures "to avoid similar incidents in the future." The company told CNN that the extreme weather had an unexpectedly forceful impact on the ship's movements. It said 85% of the lost containers were empty and others included such dry goods as frozen meat. None contained dangerous goods. Maersk is now contacting customers to tell them that their shipments are at the bottom of the ocean. The Svendborg, which was on its way from Rotterdam in the Netherlands to Colombo in Sri Lanka via the Suez Canal, warned French maritime authorities that vessels should look out for floating containers, but most sank quickly in the mountainous seas.Thirteen have now been recovered, according to French officials. The French environmental group Robin des Bois said Friday it would sue Maersk for failing to disclose the full extent of the loss when it occurred, putting the lives of others in danger, causing pollution and abandoning waste at sea. The group claimed the containers were a lasting danger to fishing vessels and the environment. Most containers won't float for long, especially in heavy seas. But one that is refrigerated may be buoyed by its insulation, and the use of polystyrene as packaging for goods also aids flotation. New Zealand marine insurer Vero Marine says a 20-foot container can float for up to two months, and a 40-foot container might float more than three times as long.