NEW YORK (AP) — Doctors traced an Arkansas man's kidney failure to an unusual cause — his habit of drinking a gallon of iced tea each day. Black tea has a chemical known to cause kidney stones or even kidney failure in excessive amounts. The man is on dialysis, perhaps for the rest of his life, Ghaffar said. Besides black tea, oxalate is found in spinach, rhubarb, nuts, wheat bran and chocolate.