Environmental health – Fluorosis due to air contaminants: Fluorosis is a bone disease observed in communities exposed to high concentrations of which contaminant in the ambient air?

Introduction / Context:
Fluorosis is a public-health problem linked to excessive fluoride exposure. While groundwater with high fluoride is a common source, certain industrial emissions also contribute. Understanding which air pollutant causes skeletal and dental fluorosis is essential in environmental engineering and occupational hygiene.

Given Data / Assumptions:

• The question concerns atmospheric exposure pathways.
• Bone disease (skeletal fluorosis) is explicitly referenced.
• Candidate pollutants include acidic gases and typical urban/industrial species.

Concept / Approach:
Fluoride ions accumulate in calcified tissues. In air, the relevant species is gaseous hydrogen fluoride (HF) or particulate fluorides emitted from aluminum smelters, phosphate processing, brick/ceramic kilns, and glass manufacture. Chronic exposure can lead to dental mottling progressing to skeletal fluorosis marked by bone thickening and joint stiffness.

Step-by-Step Solution:
Identify pollutant that contains fluorine capable of yielding fluoride ions in the body: hydrogen fluoride.Link exposure to health endpoint: HF inhalation leads to systemic fluoride burden and fluorosis with chronic exposure.Exclude other listed pollutants whose toxicology does not include fluorosis.

Verification / Alternative check:
Industrial hygiene references list fluoride compounds (HF, particulate fluorides) as causes of fluorosis; NO2 and H2S cause respiratory and neurological effects respectively, not fluorosis.

Why Other Options Are Wrong:

• Nitrogen dioxide: primarily causes airway inflammation and contributes to photochemical smog; no fluorosis.
• Hydrogen sulfide: neurotoxic at high doses; no link to fluoride-related bone changes.
• Unburned hydrocarbons: participate in smog formation; not fluoride.
• Sulfur dioxide: respiratory irritant and acid rain precursor; does not cause fluorosis.

Common Pitfalls:
Confusing HF with HCl or SO2 because they are all acid gases; only HF provides fluoride ions that accumulate in bone.

Final Answer:
Hydrogen fluoride (HF)