Which of the following pollutants cannot be degraded by natural process?

The correct answer is All of the above.

To understand why none of these pollutants can be degraded by natural processes, let us look at each option in detail:

1. Heavy metals:
Heavy metals such as lead, mercury, cadmium, and arsenic are basic chemical elements. Unlike complex organic molecules, elements cannot be broken down or decomposed into simpler, non-toxic substances by microorganisms (like bacteria or fungi) or environmental factors. They persist indefinitely in the environment and can only change their chemical form or accumulate in living organisms.

2. DDT (Dichlorodiphenyltrichloroethane):
DDT is a synthetic organochlorine pesticide. Its chemical structure is highly stable and resistant to biological, chemical, and physical degradation. Because decomposers lack the specific enzymes required to break down its strong carbon-chlorine bonds, DDT remains in the soil and water for decades, leading to biomagnification in the food chain.

3. Nuclear waste:
Nuclear waste contains radioactive isotopes (such as uranium, plutonium, and cesium) that decay by emitting radiation over spans of thousands or even millions of years. This radioactive decay is a nuclear process determined solely by the physics of the atomic nuclei, and it cannot be accelerated or altered by any natural biological decomposers or chemical processes on Earth.

Since heavy metals, DDT, and nuclear waste are all non-biodegradable substances that resist natural decomposition, they all fall under the category of pollutants that cannot be degraded by natural processes.