4.4A Water pollution Notes

1. Water pollution occurs when harmful substances, chemical, physical, or biological, contaminate natural water bodies, degrading their quality and harming organisms.
2. It affects both marine and freshwater systems through multiple sources such as sewage, agriculture, industries, and urban runoff.
3. Pollutants may come from point sources (e.g., factory discharges, sewage outlets) or non-point sources (e.g., agricultural runoff, urban stormwater).

Major Sources of Water Pollution

1. Sewage and Domestic Wastewater

1. Domestic sewage contains organic matter, pathogens, and nutrients such as nitrogen and phosphorus.
2. When untreated sewage enters rivers or lakes, bacteria decompose organic matter, consuming dissolved oxygen (DO) and leading to oxygen depletion.
3. Low oxygen levels cause fish kills and loss of aquatic biodiversity.
4. Pathogens from human waste cause diseases such as cholera, typhoid, and dysentery.

2. Agricultural Runoff

1. Water running off agricultural land carries fertilizers, pesticides, animal waste, and sediments into nearby water bodies.
2. Fertilizers rich in nitrates and phosphates promote algal blooms, which decompose and cause oxygen depletion (eutrophication).
3. Pesticides accumulate in the tissues of non-target organisms (bioaccumulation) and increase in concentration up the food chain (biomagnification).
4. Soil erosion contributes sediments that increase turbidity, reducing light penetration and photosynthesis.

3. Industrial Effluent

1. Industries discharge toxic chemicals, heavy metals, and solvents into nearby water bodies.
2. Pollutants like 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.

4. Urban Runoff

1. During rainfall, water flowing through cities carries oil, fuel, litter, pet waste, detergents, and metals from roads and rooftops.
2. Urban storm drains often lead directly to rivers and oceans without treatment.
3. Pollutants in runoff cause oxygen depletion, algal blooms, and contamination of groundwater sources.

5. Solid Waste Disposal and Leachate

• Open dumps and poorly managed landfills release leachate, a contaminated liquid formed when rainwater percolates through waste.
• Leachate contains toxic chemicals, organic matter, and pathogens, contaminating groundwater.
• Properly engineered sanitary landfills use impermeable liners to collect and treat leachate safely.

6. Oil Spills

1. Occur during oil extraction, transport, or accidents involving pipelines and tankers.
2. Oil forms a surface layer that blocks sunlight and oxygen exchange, killing fish and marine plants.
3. Birds and mammals become coated with oil, losing insulation and buoyancy.

Plastic Pollution

1. Over 14 million tonnes of plastic enter the oceans each year, mostly from land-based sources.
2. Plastics are non-biodegradable; they undergo photodegradation into micro- and nanoplastics.
3. Ocean currents form gyres, large circular systems that trap floating debris.
4. The Great Pacific Garbage Patch is the largest, containing up to 1.8 trillion plastic fragments.

How Plastic Accumulates in Oceans

1. Ocean currents form gyres, large rotating systems that trap floating debris.
2. The Great Pacific Garbage Patch, the largest, covers 700,000 to 15 million km².
3. Plastic is transported by wind and rivers, becoming concentrated in central gyres over time.

Environmental Impacts of Plastic Pollution

1. Entanglement and Ingestion

1. Marine animals (e.g., turtles, dolphins, seabirds) become trapped in fishing nets or plastic rings.
2. Many species mistake plastic for prey (e.g., turtles mistake plastic bags for jellyfish).
3. Leads to starvation, suffocation, or mobility loss.

2. Microplastics in the Food Chain

1. Microplastics are consumed by plankton and filter-feeders.
2. Undergo bioaccumulation and biomagnification, passing toxins up the food web.
3. Toxic chemicals (e.g., PCBs, BPA, pesticides) adhere to plastics and disrupt hormonal balance in animals and humans.

3. Ecosystem and Economic Effects

1. Plastics damage coral reefs, reducing biodiversity.
2. Polluted beaches deter tourists, reducing local income.
3. Cleaning operations and coastal restoration are costly and only partially effective.
4. Floating plastics also act as vectors for invasive species, altering native ecosystems.

Management and Solutions

1. Reduction Strategies

1. Bans on single-use plastics (e.g., straws, bags).
2. Economic incentives for biodegradable alternatives.
3. Promoting a circular economy - reuse, recycle, and redesign plastic products.

2. Waste Management and Cleanup

1. Improvement in recycling infrastructure and waste segregation.
2. Global initiatives like The Ocean Cleanup Project use floating barriers to collect debris from gyres.
3. Bioremediation using bacteria and fungi to degrade plastics is under research.