The U.S. EPA has issued new requirements for cleansing ballast water dumped from ships, which scientists believe has brought invasive species that damage ecosystems and cost the economy billions of dollars. A general permit will apply to commercial vessels longer than 79 feet. It requires them to meet international standards for treating ballast water. The U.S. Coast Guard adopted similar requirements last year. Ships could meet the standards by installing equipment that cleanses the water with chemicals or uses other methods to kill organisms. Environmental groups say the standards are too weak to prevent more invasive species from entering the Great Lakes and coastal waterways.