Environmental Chemistry - Water and Soil Pollution

Water Pollution: Presence of undesirable substances such as pathogens, organic wastes, and chemical pollutants (heavy metals like $Pb^{2+}$, $Hg^{2+}$, and $Cd^{2+}$) in water bodies.

Dissolved Oxygen (DO): The amount of oxygen dissolved in water, essential for aquatic life. The concentration of DO in cold water can reach up to $10\text{ ppm}$. If it drops below $6\text{ ppm}$, the growth of fish is inhibited.

Biochemical Oxygen Demand (BOD): The amount of oxygen required by bacteria to break down the organic matter in a certain volume of a water sample over five days. Clean water has a BOD value of less than $5\text{ ppm}$, whereas highly polluted water can have a BOD of $17\text{ ppm}$ or more.

Chemical Oxygen Demand (COD): A measure of the oxygen required to oxidize all organic matter (biodegradable and non-biodegradable) in water using a strong oxidizing agent like acidified $K_2Cr_2O_7$.

Eutrophication: The process where water bodies receive excess nutrients, specifically phosphates ($PO_4^{3-}$) and nitrates ($NO_3^-$), leading to dense plant growth (algal blooms) and depletion of dissolved oxygen.

Soil Pollution: Contamination caused by the excessive use of synthetic fertilizers, pesticides (insecticides like $DDT$, herbicides like $NaClO_3$), and industrial effluents containing heavy metals.

Biomagnification: The increase in the concentration of non-biodegradable toxic substances (e.g., Mercury or $DDT$) as they move up the food chain.

Pesticides and Herbicides: Chemicals like Organochlorines (e.g., $DDT$), Organophosphates, and herbicides like Sodium chlorate ($NaClO_3$) and Sodium arsentite ($Na_3AsO_3$).