Which statement about environmental pollution's effects on oral health is true?

Leukoplakia is characterized by white patches that form on the mucous membranes of the oral cavity, and it is often associated with irritation, potentially leading to more serious conditions, including oral cancer. While there are various environmental factors that can influence oral health, research has not established a direct correlation between mercury exposure and the development of leukoplakia. Thus, stating that leukoplakia is not a result of mercury exposure aligns with current understanding and the evidence available.

Other statements in the question present misconceptions regarding the connections between environmental pollution, smoking, and oral health. For instance, air pollution can have an adverse effect on oral health by exacerbating conditions like periodontal disease and impacting overall systemic health, which can, in turn, affect oral health. Similarly, smoking is widely accepted to have detrimental effects on oral health, including increased risk of periodontal disease, oral cancer, and delayed healing following dental procedures.