MOBILE, Ala. (AP) — Scientists with Auburn University and the Dauphin Island Sea Lab say there are limits to how much pollution oysters can clean up.

Adult oysters are known to filter about 50 gallons of water daily. The Mobile Press-Register reports (http://bit.ly/NuL1aO) after 10 years of study, scientists figured out a way to measure how much nitrogen an oyster can remove each day as it pumps water through its body. Nitrogen is one of the key nutrients responsible for the creation of the dead zone that builds in Mobile Bay each year.