Pesky Purifiers

In the mid-1980’s, a thumbnail-size mollusk called the zebra mussel was inadvertently introduced into the Great Lakes of North America in the ballast water of freighters from Europe. Maclean’s, a Canadian newsmagazine, says that the shellfish has “become the poster creature for invasive aquatic species.” Why?

A single female can produce 500,000 eggs a year. Moreover, these mussels attach themselves in colonies to any hard surface. As many as 600,000 can occupy one square yard [700,000 per sq m]. As a result, they clog intake pipes that draw water into water treatment plants and generating stations. They are also a costly problem for boat and dock owners.

Yet, there is a positive side to this much-maligned creature. Zebra mussels may soon be at work protecting our health. Environmental scientists, who have for a long time studied the creature’s design and function, know that the zebra mussel is also a hardy water purifier. Parasitologist Thaddeus K. Graczyk, of Johns Hopkins University in Baltimore, and Environment Canada research scientist Yves de Lafontaine, of Montreal, have collaborated in their study of this shellfish. Maclean’s reports that the zebra mussel is able to ingest “suspended particles containing everything from tributyltin, a toxic ingredient in marine paint, to the lethal Cryptosporidium parasite and the E. coli bug.”

Cryptosporidium is the size of a human red blood cell and is difficult to remove from drinking water. It is immune to most common forms of disinfectant, such as chlorine and ozone. “Zebra mussels, however, can handily filter out particles that size,” says Maclean’s. In fact, researchers say that “during the warm months, each adult mussel can filter a litre [about a quart] of water a day, removing algae, mineral particles, pollutants and other potentially life-threatening pathogens and bacteria.” They estimate that a square-yard colony could digest ten million [sq m colony; 13,000,000] of such parasites in about two hours.

Indeed, what science is learning about the cleaning capacity of this mollusk is a marvelous testimony to the perfect balance of all of God’s creative works.

[Picture Credit Lines on page 31]

Fingers holding zebra mussel: U.S. Geological Survey; all other mussels: © Rob and Ann Simpson/Visuals Unlimited; Cryptosporidium: H.D.A. Lindquist, U.S. EPA