A. Shoumkova, V. Stoyanova. "TRACE ELEMENTS IN FLY ASHES FROM “VARNA”, “BOBOV DOL”, “MARITZA IZTOK I”, “MARITZA ІІІ”, „REPUBLIKA” AND “ROUSSE IZTOK” POWER PLANTS, BULGARIA." 6th International Scientific Conference - SGEM, 2006, pp. 349-358.