Soil Pollution

DDT

DDT (Dichloro Diphenyl Trichloroethane) was banned due to serious biomagnification issues. Step 1: DDT does not decompose easily and persists in the environment. Step 2: It accumulates in fatty tissues of organisms and concentrates up the food chain. Step 3: This biomagnification caused thinning of eggshells in birds like eagles and falcons. Step 4: Many bird species became endangered, leading to DDT being banned in most Western countries. Urea (B) and phosphate (D) are fertilizers, not pesticides. Potash (C) is also a fertilizer component.

Increase in chemical concentration up the food chain

Biomagnification refers to the increasing concentration of toxic chemicals as we move up the food chain. Step 1: Small organisms like phytoplankton absorb chemicals from their environment. Step 2: Small fish eat many phytoplankton, concentrating the chemicals in their bodies. Step 3: Larger fish eat many small fish, further concentrating the chemicals. Step 4: Top predators have the highest concentration of toxic chemicals. Option A is opposite to what actually happens. Option C suggests no change, which is incorrect. Option D suggests removal, which doesn't happen with persistent chemicals.

Earthworms

Earthworms are extremely beneficial soil organisms that improve soil health. Step 1: Earthworms burrow through soil, creating tunnels that allow air and water to penetrate. Step 2: Their tunneling activity helps in soil aeration, which is essential for root respiration. Step 3: They consume organic matter and produce nutrient-rich castings (excreta). Step 4: Their castings contain 5 times more nitrogen and 7 times more phosphate than normal soil. Options B, C, and D are non-living materials that pollute soil rather than help it.

Excessive use of fertilizers and pesticides

Excessive use of chemical fertilizers and pesticides is the primary agricultural cause of soil pollution. Step 1: Overuse of NPK fertilizers leads to accumulation of harmful chemicals in soil. Step 2: These chemicals reduce soil fertility over time and decrease crop quality. Step 3: Pesticides persist in soil and can biomagnify through food chains. Step 4: Heavy metals from fertilizers accumulate and become toxic to crops and soil organisms. Option A (planting trees) helps prevent soil pollution. Option C (watering) is essential for crops. Option D (crop rotation) is a beneficial practice.