The type and amount of chemicals released into the air when microwave popcorn is popped or opened are being studied by the U.S. Environmental Protection Agency. A rare lung disease contracted by popcorn factory workers in four states has been linked to exposure to vapors from butter flavoring in microwave popcorn, the Associated Press reports. Mike in BrazilBut health officials say the popcorn poses no health threat to consumers who pop popcorn in their microwaves. The National Institute for Occupational Health and Safety has said it suspects the workers' health problems were caused by the chemical diacetyl. The EPA plans to study about 50 brands, batches and flavors of microwave popcorn. 8th street latinas The U.S. Food and Drug Administration said it considers butter popcorn flavoring to be safe for consumers.