Which option correctly pairs two indoor air pollutants with one health effect and two outdoor pollutants with one health effect?

• A. Indoor: Radon—lung cancer; Mold spores—eye irritation; Outdoor: PM2.5—cardiovascular disease; Ozone—respiratory irritation.
• B. Indoor: Radon—lung cancer; Mold spores—respiratory irritation; Outdoor: PM2.5—cardiovascular disease; Ozone—respiratory irritation.
• C. Indoor: Radon—lung cancer; Mold spores—allergic/respiratory; Outdoor: PM2.5—cardiovascular disease; Ozone—respiratory irritation.
• D. Indoor: Radon—lung cancer; Mold spores—allergic/respiratory; Outdoor: PM2.5—diabetes; Ozone—respiratory irritation.

Answer: (C)

Understanding how indoor and outdoor pollutants affect health comes down to pairing each pollutant with the most well-supported health outcome from exposure. Radon is a radioactive gas that accumulates indoors, especially in basements, and long-term exposure is a major risk factor for lung cancer. Mold spores, when inhaled, are a common trigger for allergic reactions and respiratory symptoms—think allergic rhinitis, asthma flares, and coughing. Outdoors, fine PM (PM2.5) penetrates deep into the lungs and bloodstream and is strongly linked to cardiovascular problems such as heart attacks and strokes. Ozone, a powerful oxidant at ground level, irritates the airways and can cause coughing, throat irritation, and worsened asthma.

So the best pairing assigns indoor radon to lung cancer, indoor mold spores to allergic/respiratory effects, outdoor PM2.5 to cardiovascular disease, and outdoor ozone to respiratory irritation. The other options mix in less representative effects (for example, mold spores linked to eye irritation, or PM2.5 linked to diabetes), which don’t align as cleanly with established health outcomes for these pollutants.