Which of the following is a primary source of pollution in aquatic ecosystems?

Analyze the question The question asks which option is a primary source of pollution in aquatic (water) ecosystems. A primary source is one that directly introduces pollutants into the water body.

Explain the concept Water pollution sources are often grouped into:

• Point sources: pollutants enter water at an identifiable place, such as a pipe, drain, or factory outlet. Examples are industrial discharge and sewage outfalls.
• Non-point (indirect) sources: pollutants reach water indirectly, for example through runoff, erosion, or atmospheric deposition.

Step-by-step evaluation

• A. Soil erosion: It carries silt into rivers and causes siltation and turbidity. This is an indirect process, often a consequence of other activities like deforestation or farming.
• B. Industrial discharge: Factories release effluents directly into rivers, lagoons, and the sea. These contain heavy metals (lead, mercury), oil, acids, and chemicals. In Nigeria, an example is oil spills and industrial waste in the Niger Delta. This is a direct, major source.
• C. Air pollution: It affects water only secondarily, for example through acid rain. It is not a direct source.
• D. Deforestation: It is a land-use activity that leads to erosion and runoff. It is an indirect cause, not a direct pollutant source.

Answer Industrial discharge is the direct, primary source of aquatic pollution.

Exam tip When you see "primary" or "direct source" of water pollution, look for the option that puts waste straight into water, such as effluent, sewage, or oil spills. Options like erosion, deforestation, and air pollution usually act indirectly, so they are often distractors.