The “Clean-up mussel” – A nasty-tasting shellfish could be just the job for cleaning rivers – Filtering out the pollutants The Economist December 9th 2018

Its traditional to have a “spoof” paper in the Christmas edition of some professional magazines. I was not sure if this was or was not a spoof, but the thought that Rick Stein, Jamie Oliver or Nadia Hussein could be drafted in to make these mussels edible seems rather attractive. Many of us love mussels….. It would be at the risk of bringing in another invasive species, but presumably, if the levels of nitrates and other pollutants fell it would not thrive so well? Further research needed?

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This problem—and another, of excess nitrogen that can cause poisonous algal blooms—might be mitigated by shellfish that people don’t eat, reckon Eve Galimany and Julie Rose at the National Oceanic and Atmospheric Administration at Milford Laboratory in Connecticut. As they report in Environmental Science & Technology, their chosen candidate for the job is the ribbed mussel, more formally known as Geukensia demissa.

The ribbed mussel is edible, but it tastes terrible and so has no commercial value. This means growing the mussels in tainted waters is unlikely to tempt anyone into harvesting them. Previous studies have shown that the ribbed mussel is both hardy and adept at collecting a range of troublesome materials from its environment. Dr Galimany and Dr Rose thought it would be ideal to help clean up the Bronx River Estuary in New York. With an industrial waterfront and wastewater run-offs from a dense urban environment, the estuary has a long history of suffering from harmful bacteria and high levels of nitrogen.

With a group of colleagues they moored a six-square-metre commercial mussel-growing raft in the estuary and populated it with ribbed mussels. They closely monitored the health of the mussels over six months and, using a flow-through device, also analysed the chemistry of the water both before and after the mussels had done their filtering. The results were impressive.

The researchers found that not only did the mussels thrive in the polluted waters of the Bronx River Estuary, but they also collected a lot of pollutants. More specifically, a fully stocked raft of mussels cleared an average of 12m litres of water daily, removing 160 kilograms of particulate matter, of which 12 kilograms was absorbed by the mussels’ digestive systems and integrated into their bodies. The remainder was excreted as waste, which drops down and is ultimately buried in the river sediment. The material filtered out by the mussels included nitrogen, bacteria, relatively harmless trace metals like aluminium, copper and iron, as well as toxic metals like mercury, lead and arsenic. Five groups of organic contaminants, including the insecticides chlordane and DDT, also ended up accumulating in the mussels.

Based upon these numbers, the team estimates an annual harvest of a single raft of mussels would remove more than 62 kilograms of nitrogen waste alone by sequestering it into the tissues and shells of the animals. But what can be done with the mussels once harvested? The researchers hope they can be treated and recycled instead of ending up in landfill. Provided the levels of contaminants are not too high, the mussels could be used as animal feed or fertiliser. What they will not do, though, is end up on someone’s plate.

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