Harmful substances from industrial and household sources belong to which category?

• A. Major Water Pollutants
• B. Toxic Chemicals
• C. Biodegradable Wastes
• D. Thermal Pollution

Answer: (B)

Harmful substances from industrial and household sources are best described as toxic chemicals because toxicity defines their ability to cause adverse health effects in humans and aquatic life, even at low concentrations. These contaminants come from a wide range of products and processes—heavy metals like lead and mercury, solvents, pesticides, cleaning agents, and pharmaceutical residues—that can persist in water, bioaccumulate, and travel through ecosystems, making them a central focus of toxic contamination.

Biodegradable wastes, by contrast, are organic matters that microorganisms can break down; they often affect water quality by consuming oxygen during decomposition, leading to low dissolved oxygen and odor, but they aren’t primarily defined by chemical toxicity. Thermal pollution refers to changes in water temperature from heat discharge, which affects dissolved oxygen dynamics and aquatic life but involves heat, not toxic chemicals. Major water pollutants is a broad term that encompasses many contaminant types, but the specific harmful chemical contaminants from everyday and industrial sources are best captured by the label toxic chemicals.