WASHINGTON — The Environmental Protection Agency hit a 30-year low in 2018 in the number of pollution cases it referred for criminal prosecution, Justice Department data show. EPA said in a statement that it is directing “its resources to the most significant and impactful cases.” But the 166 cases referred for prosecution in the last fiscal year is the lowest number since 1988, when Ronald Reagan was president and 151 cases were referred, according to Justice Department data obtained by the nonprofit Public Employees for Environmental Responsibility advocacy group and released Tuesday. “You don’t get closer to the core of EPA’s mission than enforcing the law,” Jeff Ruch, PEER’s executive director, told The Associated Press.