Contrary to the above findings, a study on surface coal workers, underground coal workers without pneumoconiosis, and underground coal workers with simple pneumoconiosis showed no significant difference in antioxidant enzyme activities (SOD, CAT, and GSH-Px) between surface workers and underground workers without pneumoconiosis, no significant difference in Cu2+/Zn2+ SOD activities between underground workers with simple pneumoconiosis and underground workers without pneumoconiosis (74). Here, CAT is linked to pneumoconiosis.