The prolonged exposure to the toxic chemicals had a ____________ effect on the workers' health, leading to severe chronic illnesses.
Correct: C
The phrase 'leading to severe chronic illnesses' clearly indicates a harmful effect. 'Deleterious' means causing harm or damage. This is the most appropriate word. 'Salutary' means producing good effects; beneficial. 'Benign' means gentle and kind; not harmful in effect. 'Innocuous' means not harmful or offensive.