I am 20 years old, healthy, never smoked cigarettes for more than a few months and only 1 cigarette a day or less, and have had blood work, EKG's, and a chest x-ray done and all came back fine. I have black specks in my sputum for the past few days, since I've had a sinus infection and sore throat. Is this anything to be worried about? Could it be anything serious/potentially fatal? Thanks.