On Saturday, engineers plan to tow a gigantic floating boom out of San Francisco Bay, past Alcatraz prison, and to the open ocean. It is destined to begin cleaning up the mountains of plastic rubbish circulating in the Pacific. But is this the right way to do it?
The idea of the project, called , is to collect plastic passively. As waves lap against the boom, the buoyant rubbish fragments should collect against it. Any drifting animals such as jelly fish, should be washed underneath. The team then plans to send ships to collect the rubbish and bring it back to land.
The project leader Boyan Slat and his team have been refining and testing the concept for years, including testing a prototype in the North Sea in 2016. That has helped them answer important questions. For instance, some doubted the boom would clear up enough plastic to make it worthwhile, because most pieces of plastic in the ocean are microscopic and would wash underneath it. But a series of surveys from ships and aircraft have shown that about , and so should be large enough to collect.
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The boom, scheduled for launch today, will take on a curved shape in the water and plastic should collect in its centre. This means it will look a little like a giant pool noodle bent in the middle to take on the shape of a rubbish-gobbling Pac-Man. It is the first of a planned 60 similar systems. If all are deployed successfully by 2020 as the team plan, they should extract 14,000 tonnes of plastic in five years, or about half the mass of the plastic in the gyre. The team expects this to cost 鈥渟everal tens of millions of dollars per year鈥�. That sounds like a lot, but the UN Environment Programme has estimated the total cost of plastic rubbish to the marine environment as.
But other questions remain. For example, the team plans to collect the plastic by ship and ideally sell it so it can be recycled. But recycling plastic isn鈥檛 easy and there may not be a market for that much of it. Large amounts may end up in landfill.
Independent marine ecologist Andrew Thaler has said that the booms will, like any floating structure, attract fish and their predators. The rubbish gyre is mostly quite diffuse and by concentrating the plastic and attracting fish, the booms may expose animals to more concentrated toxins leaching from plastic.
On the other hand, some of the criticisms of the project seem ill-founded. For example, some reckon it is wrong to focus on clean up rather than prevention. But the team acknowledges the importance of both and says that there are plenty of existing ideas for picking rubbish from rivers before it gets into the oceans. These range from a barge-cum-vacuum cleaner called the M V Recylone, proposed by James Dyson, to a plastic-collecting water wheel in Baltimore harbour called 鈥淢r Trash Wheel鈥�. It has .
