Bivalves retain nanoparticles in marine snow

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Scientists have found that oysters and mussels retain significant amounts of manufactured nanoparticles from seawater in clumps of so-called “marine snow.”

Manufactured nanomaterials can be found in such diverse applications as electronics, cosmetics, paints, and even medicines, but their effects on the environment remain largely unknown.

Nanoparticles are tiny versions of common materials that have a diameter of less than 100 nanometres, or about four millionths of an inch.

Their minute size gives them properties that normal-sized particles don't have: for example, their large surface area for their size makes them stronger, lighter, and more reflective, making them ideal for reinforcing metals, increasing the SPF in your sunscreen, and producing paint that improves your home's energy efficiency.

Some scientists, however, are concerned that these very properties could also make manufactured nanoparticles dangerous.

When products break down in landfills, nanoparticles can wash away into soils, waterways, and the ocean, potentially creating hazards to animals and plants.

Nano, nano
Some materials that one would assume are safe can in fact cause damage to cells in their "nano" form.

Studies of the environmental physiology of oysters, mussels, and their relatives, which use their gills as specialized filters to take up food from ocean water.

Although nanoparticles themselves are too small to be captured in large amounts, Ward's study focused on how the bivalves' feeding ecology affected their rate of uptake.

Materials rarely exist as individual particles in the ocean, instead ocean currents bind up particles and sticky organic matter into aggregates known as "marine snow." These aggregates then sink to the bottom, where filter feeders like bivalves ingest them.

Labelled nanoparticles
In a paper, published in Marine Environmental Research, Professor Evan Ward and co-author Dustin Kach used natural seawater to produce marine snow that contained fluorescently labelled polystyrene nanoparticles. They then exposed oysters and mussels to this snow-filled seawater.

The researchers found that nanoparticles were taken up in much higher amounts when the bivalves were exposed to marine snow. But they also found that when filtered from marine snow, nanoparticles remained in the bivalves' bodies for a much longer time than would be expected for non-nutritive materials: up to three days.

Ward suspects that the particles are being treated as food by the animals, and are being taken up into their digestive cells. This could be particularly dangerous, he says, since small nanoparticles can circumvent living cellsí natural defences.

"Because of their high surface area, manufactured nanoparticles can strip off electrons from other compounds and create free radicals," he says. "Particles like these can cause havoc in cells."

Ward sees his work as a first step in understanding the potential issues associated with manufactured nanoparticles. He emphasizes that further work is needed to determine the amounts of manufactured nanoparticles in seawater and their levels of toxicity to living things.