Which one of the following is the well known example of bioindicator of air pollution?

The answer is A) Lichens. Lichens are a symbiosis of a fungus and an alga, and they have no roots or protective waxy cuticle. They absorb gases and dissolved matter directly from the air and rain through their thallus. That makes them very sensitive to sulphur dioxide, so they disappear first from polluted areas. Field studies use their presence, absence and species diversity to map pollution levels, which is why they are the textbook bioindicator of air quality.

• B) Methyl mercury is a toxic pollutant, not an indicator. It is an organomercury compound linked to Minamata disease, and it bioaccumulates in fish.
• C) Rose plant shows visible leaf injury from some pollutants, but it is not the established reference bioindicator for air pollution.
• D) Sunflower is known for uptake of heavy metals and radionuclides after the Chernobyl accident, which makes it a phytoremediation example, not an air pollution bioindicator.

This sits under Environment and Ecology, in the topics on bioindicators and pollution monitoring. In Mains GS-III, it links to air quality monitoring and the use of ecological indicators in impact assessment.

Trap: Candidates confuse a bioindicator with a bioaccumulator or phytoremediator, and pick sunflower or methyl mercury because they are associated with pollution or metal uptake.