IB Environmental systems and societies 4.4A Water Pollution Notes

Water Pollution: Point Sources Are Traceable, Non-Point Sources Are Diffuse

1. Water pollution occurs when harmful chemical, physical, or biological substances contaminate natural water bodies and degrade their quality.
2. It affects both marine and freshwater systems.
3. Point sources release pollutants from a single identifiable location, such as a factory discharge pipe or sewage outlet.
4. Non-point sources are diffuse and enter water over a wide area, such as agricultural runoff or urban stormwater.

Major Sources of Water Pollution

Sewage and Domestic Wastewater

1. Domestic sewage contains organic matter, pathogens, and nutrients such as nitrogen and phosphorus.
2. The nutrients in sewage trigger eutrophication, covered in depth in the Eutrophication article (4.4C).
3. Pathogens from human waste cause diseases such as cholera, typhoid, and dysentery.

Agricultural Runoff

1. Water running off farmland carries fertilisers, pesticides, animal waste, and sediments into nearby water bodies.
2. Fertiliser nitrates and phosphates trigger eutrophication, explained in the Eutrophication article (4.4C).
3. Pesticides can build up in the tissues of non-target organisms and pass into food chains.
4. Soil erosion adds sediments that raise turbidity and reduce light penetration and photosynthesis.

Industrial Effluent

1. Industries discharge toxic chemicals, heavy metals, and solvents into nearby water bodies.
2. Pollutants such as mercury, lead, cadmium, and arsenic disrupt aquatic ecosystems and contaminate drinking water.
3. Many industrial pollutants are carcinogenic and persistent, remaining in ecosystems for decades.