Science

Shell-mounted motion sensors turn mussels into pollution detectors

Shell-mounted motion sensors t...
Each sensor is made up of two linked IMUs – one on either side of the shell
Each sensor is made up of two linked IMUs – one on either side of the shell
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Each sensor is made up of two linked IMUs – one on either side of the shell
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Each sensor is made up of two linked IMUs – one on either side of the shell
Two of the wired-up mussels in a test tank
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Two of the wired-up mussels in a test tank

When toxins are present in a waterway, freshwater mussels are one of the first creatures to react. A new mussel-mounted sensor has been designed with this in mind, as a means of catching water pollution early.

Mussels feed by opening up their shells, then filtering tiny organisms out of the water. And even though the molluscs typically live in groups (aka beds), the members of those groups aren't usually all feeding at once.

This means that typically, they're opening and closing their shells independently of one another. That said, if a harmful waterborne substance flows through a group of mussels, they will all suddenly close their shells at the same time. And that's where the new sensor comes in.

Designed by a team at North Carolina State University, it's made up of two linked inertial measurement units (IMUs). One IMU is adhered to one side of the mussel's shell, and the other is adhered to the other side. Each one contains an accelerometer and a magnetometer.

When the mussel shuts its shell, the two IMUs detect the action, as the angles of both sides of the shell suddenly change. Therefore, if multiple mussels in a single bed are equipped with the sensors, it's possible to tell if they all close their shells simultaneously.

All of the sensors for one group could be hard-wired to a solar-powered processor mounted on a stake within a stream. That unit would in turn continuously transmit data via a cellular network. If a group shell-shutting was detected, then authorities could immediately begin looking for the source of the toxin that presumably caused it.

Two of the wired-up mussels in a test tank
Two of the wired-up mussels in a test tank

When tested on freshwater mussels in fish tanks, the sensors consistently detected shell movements as small as less than one degree. And while the devices have so far been used on four mussels simultaneously, the technology could conceivably keep track of dozens at once.

"Our aim is to establish an 'internet-of-mussels' and monitor their individual and collective behavior," says Prof. Alper Bozkurt, who is leading the study along with Prof. Jay Levine. "This will ultimately enable us to use them as environmental sensors or sentinels."

A paper on the research was recently published in the journal IEEE Sensors Letters. Readers may also be interested in research carried out at Northwestern University, in which mussel-shaped "robomussel" sensors were created to track the effects of climate change on the marine environment.

Source: North Carolina State University

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