4.4D Pollutants in water (HL) Notes

1. Water pollution occurs when harmful substances enter water bodies, disrupting aquatic ecosystems and threatening human health.
2. Pollutants can be organic (e.g., sewage), chemical (e.g., persistent organic pollutants), plastic-based, or thermal (heat pollution).
3. These contaminants have varying effects, including eutrophication, endocrine disruption, biomagnification, and ecosystem degradation.

Types of Water Pollutants

1. Water pollutants can be grouped into five main types:
   1. Organic matter (e.g., sewage)
   2. Dissolved substances (e.g., tributyltin)
   3. Persistent organic chemicals (e.g., PCBs)
   4. Plastics (macro and microplastics)
   5. Heat energy (thermal pollution)
2. Each type affects ecosystems differently but often acts synergistically, compounding the overall environmental impact.

Organic Matter

1. Organic pollutants include sewage, food waste, and agricultural effluents containing biological material.
2. As decomposers (bacteria) break down the organic matter, they consume dissolved oxygen.
3. This leads to oxygen depletion, fish kills, and ecosystem collapse.
4. The process is closely linked to biochemical oxygen demand (BOD).

Dissolved Substances

1. These are chemicals dissolved in water that may interfere with biological or physiological processes in organisms.
2. A well-known example is tributyltin (TBT), a toxic organotin compound.

Tributyltin (TBT)

1. Used as an antifouling agent in ship paints to prevent biofouling (growth of algae and barnacles).
2. Slowly leaches into water, settling in sediments or entering aquatic food chains.
3. Acts as an endocrine disruptor, altering hormonal balance in marine species.
4. The effects are:
   1. Causes imposex (female mollusks developing male organs) in oysters and snails.
   2. Leads to immune suppression in dolphins and hearing loss in toothed whales.
   3. Humans exposed to TBT may experience fatigue, respiratory issues, and liver/kidney damage.

Persistent Organic Pollutants (POPs)

1. Persistent organic pollutants (POPs) resist degradation, remaining in the environment for decades.
2. They accumulate in fatty tissues and increase in concentration up the food chain (biomagnification).

Polychlorinated Biphenyls (PCBs)

1. Source: Used in transformers, paints, sealants, and electrical equipment.
2. Characteristics: Stable, non-reactive, lipid-soluble, making them persistent and bioaccumulative.
3. Environmental Fate:
   1. Leak from industrial sites or landfills into rivers and oceans.
   2. Settle in sediments and enter food webs.
4. Effects:
   1. Cause immune suppression, cancer, and reproductive failure in humans and animals.
   2. Accumulate in top predators like polar bears, seals, and tuna.

Plastics and Microplastics

1. Plastics are synthetic polymers derived from petroleum.
2. They are non-biodegradable and persist for hundreds of years in aquatic ecosystems.

Macroplastics

1. Include bottles, bags, fishing nets, and packaging materials.
2. Cause entanglement, injury, and ingestion hazards for marine animals.
3. Large plastics break down into microplastics through UV radiation and abrasion.

Microplastics

1. Particles <5 mm in size, originating from degraded plastics or personal care products.
2. Can be ingested by fish and plankton, entering the food web.
3. Act as vectors for toxic chemicals like PCBs, DDT, and heavy metals by adsorbing them on their surfaces.

Heat Energy (Thermal Pollution)

Thermal pollution occurs when industrial facilities, such as power plants or factories, discharge warm water into rivers or seas.

Sources

1. Cooling water from power stations.
2. Discharge from industrial plants.
3. Removal of riparian vegetation allowing direct sunlight to heat the water.

Effects

1. Reduces dissolved oxygen (warmer water holds less O₂).
2. Alters species distribution as cold-water fish like trout die, while warm-tolerant species dominate.
3. Increases metabolic rate in aquatic organisms, shortening lifespan.
4. Can trigger thermal eutrophication by accelerating algal growth.