According to experts who planned the project, an oyster (along with other shellfish) is ideally designed for the job. During the feeding process, the mollusk sucks in water, retaining filth and polluted particulates along with its food, and releases clean water, with a turnover of 50 gallons of water a day.
Serving as water purification filters, these oysters are clearly not fit for human consumption. The toxins they contain make them very dangerous for human health (Verena Dobnik, "New York's New Environmental 'Hero'—the Oyster," Associated Press, Sept. 2, 2012).
But we should realize that oysters provide such filtration in general. And, in fact, the Creator God Himself commanded us not to eat mollusks and other shellfish, labeling them as "unclean"—not designed for human consumption. To learn more about this vital aspect of God's design for human health, read the online Bible study aid What Does the Bible Teach About Clean and Unclean Meats?.