Impact of water pollution Revision Notes

Water pollution varies worldwide due to differences in sewage and water treatment infrastructure. In many developed countries, sewage is treated to remove harmful pathogens and chemicals before being released into water bodies. Conversely, in some developing regions, untreated or partially treated sewage is discharged directly into rivers and lakes. This contamination introduces pathogens and organic matter that degrade water quality and pose health risks.

For example, in rural areas without sewage treatment plants, human waste may enter local streams, contaminating drinking water sources. This disparity means that populations in poorly served areas face higher exposure to waterborne diseases and environmental degradation.

• Sewage treatment removes pathogens and organic pollutants before discharge.
• Lack of treatment leads to direct contamination of water bodies.
• Developing regions often have inadequate sewage infrastructure.
• Contaminated water sources increase health risks and environmental damage.

Untreated sewage contains bacteria, viruses and parasites that cause infectious diseases. Typhoid and cholera are two serious illnesses transmitted through contaminated water. Typhoid fever is caused by the bacterium Salmonella typhi, while cholera is caused by Vibrio cholerae. Both diseases spread when people consume or come into contact with water polluted by human faeces.

For instance, during floods or in slum areas with poor sanitation, contaminated water can lead to outbreaks of cholera. Symptoms include severe diarrhoea and dehydration, which can be fatal without treatment. Preventing these diseases requires effective sewage treatment and access to clean drinking water.

• Untreated sewage contains pathogens causing diseases.
• Typhoid and cholera spread via contaminated water.
• Outbreaks occur where sanitation is poor or during floods.
• Clean water and sewage treatment reduce disease risk.

Industrial activities release toxic substances such as heavy metals (e.g., mercury, lead) and chemicals (e.g., pesticides, PCBs) into lakes and rivers. These toxins persist in the environment and accumulate in aquatic organisms. Small organisms absorb toxins, which then concentrate in larger predators through the food chain, a process called bioaccumulation.

For example, mercury released from mining can accumulate in fish. Humans eating contaminated fish may suffer neurological damage. This magnification means even low environmental concentrations can become harmful at higher trophic levels.

Bioaccumulation threatens biodiversity and human health, highlighting the need for industrial waste regulation and monitoring.

• Industries discharge toxic substances into water bodies.
• Toxins accumulate in aquatic organisms and magnify up food chains.
• Bioaccumulation can harm wildlife and humans consuming contaminated organisms.
• Regulation is essential to control industrial pollution.

Acid rain forms when sulfur dioxide (SO2) and nitrogen oxides (NOx) from burning fossil fuels react with water vapour in the atmosphere, producing acidic precipitation. When acid rain falls into lakes and rivers, it lowers the pH of the water, making it more acidic.

Aquatic organisms such as fish and invertebrates are sensitive to pH changes. Acidic water can damage gills, reduce reproductive success, and cause mortality. For example, trout populations decline in acidified lakes due to disrupted breeding and increased toxicity of metals released from sediments.

Acid rain thus disrupts aquatic ecosystems and reduces biodiversity, emphasizing the importance of controlling air pollution sources.

• Acid rain results from atmospheric SO2 and NOx forming acids.
• It lowers water pH, increasing acidity in lakes and rivers.
• Acidic water harms fish and aquatic invertebrates, affecting survival and reproduction.
• Reducing fossil fuel emissions helps prevent acid rain.

Nutrient enrichment occurs when excess nutrients, mainly nitrogen and phosphorus from fertilisers, sewage, and detergents, enter water bodies. These nutrients stimulate excessive growth of algae and aquatic plants, a process called eutrophication.

Dense algal blooms block sunlight, reducing photosynthesis in submerged plants. When algae die, their decomposition consumes dissolved oxygen, leading to hypoxic (low oxygen) conditions. Fish and other aerobic organisms may suffocate and die, causing ecosystem collapse.

For example, fertiliser runoff into a lake can cause algal blooms in summer, followed by fish kills due to oxygen depletion. Managing nutrient inputs is crucial to prevent eutrophication and protect aquatic life.

• Excess nitrogen and phosphorus cause nutrient enrichment.
• This leads to algal blooms and dense aquatic plant growth.
• Decomposition of algae depletes oxygen, causing hypoxia.
• Hypoxia kills fish and disrupts aquatic ecosystems.
• Controlling nutrient runoff prevents eutrophication.