Starting in 2017, it will be illegal for shippers to dump oil, oily waste or noxious materials into Arctic or Antarctic waters.
Friday's action, which followed the approval in November of a set of marine safety standards for ships sailing in polar waters, cements what is now a comprehensive International Code for Ships Operating in Polar Waters -- commonly known as the Polar Code.
Other provisions in the environmental standards approved by the IMO include a requirement for barriers to separate fuel tanks from ships' outer hulls, a limit on discharge of sewage and a prohibition of trash disposal within close proximity to land or sea ice.
Those add to the standards that were approved in November, which range from ship design rules to a requirement that mariners avoid marine mammals.
The result of the year-long process is a major improvement for ship and environmental safety in the vulnerable and icy waters near the globe's two poles, said Kevin Harun, Arctic program director for the conservation group Pacific Environment.
"We had a really good win on some things," said Harun, who has been working on Polar Code issues and attended this and other IMO meetings in London.
Still, the code falls short of what Harun and other environmentalists and Northerners wanted.
Chief among the omissions, many observers say, is the failure to address ships' use of heavy fuel oil in the Arctic. The heavy type of fuel used by many vessels, when burned in engines, emits soot, also known as black carbon. Black carbon is an issue of major concern in the Arctic, largely because its dark particles, when they settle out of the atmosphere, hasten the melt of ice and snow and contribute to the region's climate warming. The eight-nation Arctic Council has created a task force to try to find ways to reduce the amount of black carbon reaching the far North.
Use of heavy fuel oil by ships traveling in Arctic waters is concerning for another reason, Harun said -- the damage such fuel would cause if spilled in maritime accidents.
"The Arctic Council has said the biggest threat to the Arctic is a heavy fuel oil spill," he said.
Shippers already have access to alternative fuels that would leave a lighter touch on the environment, he said.
"Distillates would evaporate," he said. "LNG would be a good fuel."
Another gap in the code is a lax definition of ships permitted to sail in the Arctic, Harun said.
"It allows many non-ice-class ships into Arctic waters," he said.
Friends of the Earth, another environmental group that has been monitoring the Polar Code process, faulted the IMO for some other omissions in the new standards, including the lack of mandatory provisions to prevent introduction of invasive species, failure to restrict discharges of graywater and failure to address underwater noise.
Creating the Polar Code, a project several years in the making, has been a complex process. Different IMO committees have overseen environmental and marine safety standards. The IMO, as an agency of the United Nations, operates on a consensus model, requiring agreement from all parties before action is taken. And nations and constituencies around the world, with varying and sometimes clashing interests, sometimes prevent easy agreement.
Harun said the indigenous peoples of the North have yet to be properly represented in the IMO's Polar Code proceedings. Shipping representatives from other nations have had difficulty comprehending the marine-based subsistence lifestyles of indigenous peoples from Alaska, Canada and parts of Russia, where sometimes 70 percent to 80 percent of communities' food comes from the sea, he said.
"That's the refrigerator," Harun said. "You're going to be dumping stuff in it?"
The IMO structure has no indigenous representatives, even though the UN normally requires indigenous input, he said.