IB Environmental systems and societies 4.4D Pollutants in Water Notes

Five pollutant types damage water in distinct ways, and fat-soluble POPs like PCBs magnify up the food chain to top predators

1. Water pollution occurs when harmful substances enter water bodies and disrupt aquatic ecosystems.
2. Pollutants fall into five types: organic matter, dissolved substances, persistent organic pollutants, plastics, and thermal pollution.
3. Their effects range from oxygen depletion and endocrine disruption to biomagnification up the food chain.

The five types of water pollutants

1. Organic matter: biological material such as sewage that decomposers break down.
2. Dissolved substances: toxic chemicals dissolved in water, such as tributyltin.
3. Persistent organic pollutants: long-lived chemicals that resist degradation, such as PCBs.
4. Plastics: synthetic polymers present as macroplastics and microplastics.
5. Thermal pollution: warm water discharged that raises the temperature of a water body.

Organic matter

1. Organic pollutants include sewage, food waste, and agricultural effluents containing biological material.
2. Decomposer bacteria break this material down and consume dissolved oxygen as they do so.
3. The resulting oxygen depletion causes fish kills and ecosystem collapse.
4. Organic load is measured indirectly by biochemical oxygen demand (BOD); see Water quality (4.4B) for how BOD works.

Dissolved substances: tributyltin (TBT)

1. TBT was used as an antifouling agent in ship paints to stop algae and barnacles growing on hulls.
2. It leaches slowly into water, settling in sediments or entering aquatic food chains.
3. It acts as an endocrine disruptor, altering hormonal balance in marine species.