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Are mussels the secret answer to cleaning polluted water?

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These tanks, filled with water from the same source, show how mussels can filter the water. The tank on the right has mussels. The tank on the left doesn't. Photo credit: Virginia Tech.
These tanks, filled with water from the same source, show how mussels can filter the water. The tank on the right has mussels. The tank on the left doesn’t. Photo credit: Virginia Tech.

By Valerie K Clark

Short answer: Yes, but should they be introduced to clean polluted water is another question.

Let’s start with some basic biology and history of mussels.

What is a mussel?

When you think of mussels, you might envision the ones served in fancy restaurants. While clams and oysters are related to mussels (they are all mollusks or bivalves), clams and oysters are NOT the kind of mussels I am talking about here (although, they clean polluted water, too). Just in case you love eating mussels, clams, and oysters, I promise not to ruin your appetite for them while reading this article.

Mollusks are bottom dwellers, meaning they live on the bottom of the lake or ocean. For food, they filter the water from above and consume plankton – phytoplankton and zooplankton, mostly. The zebra mussel is a key member of the mollusk family, an invasive species that has garnered a great deal of attention in the United States in recent decades.

The Zebra Mussel Invasion

Retrieval of zebra mussel-encrusted Vector Averaging Current Meter near Michigan City, IN. Lake Michigan, June 1999. Photo credit: NOAA/M. McCormick.
Retrieval of zebra mussel-encrusted Vector Averaging Current Meter near Michigan City, IN. Lake Michigan, June 1999. Photo credit: NOAA/M. McCormick.

The late 1980s and early 1990s marked the zebra mussel invasion in the Great Lakes. Zebra mussels were introduced in US waterways by ships traveling across the Atlantic from Western Europe. Today, zebra mussels, numbering in the hundreds, attach themselves to underwater surfaces of piers, rocks, and boats throughout the US, including the Ohio River and Mississippi River. Invasive species tend to have a negative effect on the native species.

“Invasive species have been documented in lakes since the early 1800s,”  said David Reid, director of NOAA’s National Center for Research on Aquatic Invasive Species. One negative effect of zebra mussels results from their ability to travel downstream. In the Great Lakes, zebra mussels clogged pipes for urban water systems and power plants.

Finally, a good use for mussels!

Mussels are amazing at cleaning dirty water. That means they inhale water full of plankton and algae, consume what they need, and exhale filtered water back into the environment. Scientists have done experiments to show the ability of mussels to clean dirty water. A single mussel filters about 2 liters of water per day.

To show the effect, there are dozens of experiments on the Internet including a time-lapse video on that you can see below.

The Mussel Theory

If mussels can clean a large tank of water, could they also clean a dirty lake? A group of researchers at Stanford University is testing this theory at Mountain Lake in San Francisco, a heavily polluted lake. That work has not been published yet, but the group is basing their theory on results of a prior study that used two species of mollusk – an invasive clam and a native mussel. Both species were equally sufficient in cleaning water in a flow-through tank. Two types of contaminants – triclocarban (TCC) and propranolol – were reduced in the water due to mussel activity. The contaminants were found in the tissues of mussels and as excretions from mussels. These researchers concluded that mussels can improve water quality in a natural setting, like a polluted lake; however, mussels appear to be somewhat selective about what they absorb. Also, it is unknown if the mussel theory could be applied to ocean waters.

More recently, a similar concept was tested in Sweden with mussels exposed to pharmaceuticals near a wastewater treatment plant outlet.[4] This study highlights some of the limitations mussels may have with increasing exposure to contaminants in water, such as limited growth rate, respiration, and consumption. Interestingly, the mussels’ ability to absorb toxins was not limited by higher exposure levels.

Clean water = healthy fish = good food for humans

Water pollution is a major concern for humans who eat fish, which is most of us. If the water is tainted with pollutants, the fish are also toxic. Fish containing high levels of mercury, pharmaceuticals, phosphorus, and nitrogen are unsafe for humans to eat. The need for a large-scale water filtration system is clear, but should mussels be used to improve water quality on a large scale?

Potential for harmful effects

Think about this:

  • Mussels are highly reproductive organisms, and history has shown how well they can invade urban waterways. See Zebra Mussel Invasion above.
  • More mussels means less plankton for fish to eat, so what else will fish eat? Is there enough plankton for all, or will fish turn to food sources with a reduced nutrient value?
  • Over time, could an increase in mussel excretion dirty the water again…with contaminants that are not re-absorbed by mussels?

Bottom line

Using mussels to clean polluted water should be done with extreme caution to avoid introducing an invasive species to an ecosystem. Perhaps future efforts can be directed to engineering a tiny bot that can mimic the natural water filtering power of mussels without causing harm to the ecosystem.

 

SOURCES: 

1. “The Zebra Mussel Invasion,” NOAA, noaa.gov/features/earthobs_0508/zebra.html. Accessed Oct 24, 2015.

2. Palermo, E, “Mussels and Clams Can Clean Up Polluted Water,” Discovery, published Aug 21, 2014, Accessed Oct 24, 2015. http://news.discovery.com/animals/mussels-and-clams-can-clean-up-polluted-water-140821.html

3. Ismail, NS, et al., “Uptake of Contaminants of Emerging Concern by the Bivalves Anodonta californiensis and Corbicula fluminea,” Environmental Science & Technology, Published online July 21, 2014, Accessed Oct 24, 2015. http://pubs.acs.org/doi/abs/10.1021/es5011576

4. Kumblad, L, et al., “Response and recovery of Baltic Sea blue mussels from exposure to pharmaceuticals,” Marine Ecology Progress Series, 526: 89-100 (2015).

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