Why is oil considered an environmental pollutant in aquatic systems?

• A. It is highly toxic to animals and can be carcinogenic.
• B. It evaporates quickly and leaves no residues.
• C. It reduces oxygen levels and harms aquatic life.
• D. It disperses nutrients in the water.

Answer: (A)

Oil in aquatic systems brings toxic, and many times carcinogenic, hydrocarbons into the water. These substances can injure or kill a wide range of organisms, and some components, like PAHs, are known to be carcinogenic. When oil forms a slick, it coats surfaces and animals, blocks light, and hinders gas exchange, which disrupts photosynthesis and respiration. As microbes break down the oil, they consume dissolved oxygen, potentially lowering oxygen levels and stressing aquatic life. Many fractions of oil persist in water and sediments, leading to longer-term contamination and bioaccumulation up the food chain.

The idea that oil evaporates quickly and leaves no residues isn’t accurate because residues can remain in the water and on sediments. While reduced oxygen can occur as a consequence of degradation, the primary reason oil is viewed as a pollutant is its toxicity and persistence, not the notion of nutrient dispersion.