Which are toxic elements that are not easily degraded?

• A. Dissolved Oxygen Levels
• B. Heavy Metals
• C. Fracking
• D. Decomposing Bacteria

Answer: (B)

Toxic elements that resist degradation in the environment are persistent contaminants. Heavy metals like lead, mercury, cadmium, and arsenic fit this pattern because they do not biodegrade; they remain in water and soil for long periods and can accumulate in organisms, often increasing in concentration up the food chain. Their persistence means they can cause chronic toxicity even at low concentrations, which is why they are a major concern for water quality and ecological health. The other options aren’t elements that persist as toxins: dissolved oxygen is a condition, not a toxic substance; fracking is a extraction process, not a toxic element itself; and decomposing bacteria are organisms that break down organic pollutants, not persistent toxic elements.