12.1.3 Disadvantages of Natural Substances Found in Water

This topic explains the harmful effects of natural and human-introduced substances found in water.

Main Idea

Natural water contains many dissolved substances. While some are beneficial, others are harmful to human health, aquatic life, and the environment.

The book lists seven categories of harmful substances:

• Dissolved oxygen (can be harmful in excess or when depleted)
• Metal compounds (toxic ones)
• Plastics
• Wastewater
• Harmful microbes
• Nitrates from fertilizers
• Phosphates from fertilizers and detergents

Simple explanation: Natural water can contain substances that are harmful to health and the environment.

Core Concept

Detailed Explanation

1. Dissolved Oxygen

Where do fish and other marine life get their oxygen? Water contains dissolved oxygen. This oxygen is responsible for the survival of aquatic organisms.

Simple explanation: Dissolved oxygen is essential for aquatic life. If oxygen levels drop too low (due to pollution), fish and other organisms die.

Disadvantage: When oxygen levels are depleted (e.g., due to pollution or eutrophication), aquatic life cannot survive.

2. Metal Compounds

Natural water can contain metals such as iron, sodium, potassium, magnesium, calcium, manganese, zinc, and copper. Some of these metals are necessary for life.

• Long-term neurological problems
• Kidney diseases
• Nausea
• Dizziness
• Cancer

Simple explanation: Some metals in water are essential, but others are toxic and can cause serious health problems.

3. Plastics

Plastic waste can pollute water bodies. This is a serious threat to aquatic life and ecosystem.

• Aquatic animals can eat plastic and die.
• Plastics can entangle fish and other animals.
• Plastics break down into microplastics, which enter the food chain.
• Plastics can block waterways and cause flooding.

Simple explanation: Plastics harm and kill aquatic animals and damage entire ecosystems.

4. Wastewater

Wastewater can enter natural water supplies. Wastewater carries pathogens, bacteria, viruses and other harmful substances. These pollutants pose a serious threat to humans and aquatic life.

• Spreads waterborne diseases.
• Harms aquatic life.
• Pollutes drinking water sources.
• Causes bad odour and poor water quality.

Simple explanation: Wastewater carries disease-causing organisms and pollutes water bodies.

5. Harmful Microbes

Natural water sources can contain harmful microbes such as bacteria, viruses and parasites that can cause waterborne diseases such as diarrhea, dysentery, cholera and stomach upsets.

• Cause waterborne diseases.
• Can lead to dehydration and even death (especially in children).
• Spread quickly through contaminated water.

Simple explanation: Harmful microbes in water cause diseases like cholera, dysentery, and diarrhea.

6. Nitrates from Fertilizers

Fertilizers add nitrates to water bodies through agricultural runoff. High concentrations of nitrates in drinking water cause health risks, especially for young children.

• Can cause blue baby syndrome (methemoglobinemia) in infants.
• Can cause health problems in adults.
• Contributes to eutrophication (algae blooms, oxygen depletion).

Simple explanation: Nitrates from fertilizers can make water unsafe to drink, especially for babies.

7. Phosphates from Fertilizers and Detergents

Phosphates in fertilizers and detergents can enter water bodies through runoff. High concentrations of phosphate can cause eutrophication. This can cause harmful algae blooms and oxygen caps in water bodies. Detergents used in water systems can destroy the outer mucous membranes that protect fish from bacteria and parasites. In addition, detergents can also damage their gills.

• Causes eutrophication (excess nutrients).
• Leads to harmful algae blooms.
• Causes oxygen depletion in water bodies.
• Detergents destroy the outer mucous membranes of fish.
• Detergents damage fish gills.
• Makes fish vulnerable to bacteria and parasites.

Simple explanation: Phosphates cause algae blooms that use up oxygen, and detergents directly harm fish.

Intermediate Level

Why Each Substance Is Harmful

• When oxygen levels drop, fish and other aquatic organisms suffocate.
• Caused by pollution, eutrophication, and high temperatures.

• Lead, arsenic, mercury, and chromium can cause:
• Neurological damage
• Kidney disease
• Cancer
• They accumulate in the body over time (bioaccumulation).

• Animals mistake plastic for food → blockage of digestive system.
• Animals get entangled in plastic → injury or death.
• Plastics break into microplastics → enter food chain.

• Contains pathogens (bacteria, viruses, parasites).
• Carries organic matter that depletes oxygen.
• Contains chemicals from households and industries.

• Cause waterborne diseases:
• Diarrhea
• Dysentery
• Cholera
• Typhoid
• Hepatitis
• Can cause death if untreated.

• Cause methemoglobinemia (blue baby syndrome) in infants.
• Can cause cancer in adults (with long-term exposure).
• Contribute to eutrophication.

• Cause eutrophication → algae blooms → oxygen depletion → fish kills.
• Detergents damage fish mucous membranes and gills.
• Fish become vulnerable to bacteria and parasites.

Eutrophication — In Detail

Eutrophication is the process where a water body becomes enriched with nutrients (especially nitrates and phosphates).

• Nutrients enter the water (from fertilizers, detergents).
• Algae grow rapidly (algae bloom).
• Algae die and decompose.
• Decomposition uses up oxygen in the water.
• Oxygen depletion kills fish and other aquatic life.

Simple explanation: Too many nutrients → algae bloom → oxygen depletion → fish die.

Bioaccumulation

Bioaccumulation is the build-up of harmful substances (like toxic metals) in the body over time.

• Small amounts of toxic metals enter the water.
• Small organisms absorb them.
• Larger organisms eat the small ones → metals accumulate.
• Top predators (including humans) get the highest concentration.

Simple explanation: Toxic metals build up in the food chain — the higher you are, the more you get.

Important Points

• - Dissolved oxygen depletion → harms aquatic life.
• - Toxic metal compounds → poisonous; cause long-term health problems.
• - Plastics → threat to aquatic life and ecosystems.
• - Wastewater → carries pathogens, bacteria, viruses.
• - Harmful microbes → cause waterborne diseases (diarrhea, dysentery, cholera, stomach upsets).
• - Nitrates from fertilizers → health risks, especially for young children.
• - Phosphates from fertilizers and detergents → cause eutrophication, algae blooms, oxygen depletion; detergents damage fish mucous membranes and gills.

Remember

• - Oxygen depletion → fish die.
• - Toxic metals → poison.
• - Plastics → harm aquatic life.
• - Wastewater → disease.
• - Microbes → waterborne diseases.
• - Nitrates → blue baby syndrome.
• - Phosphates → eutrophication, harm fish.

Common Mistakes

• 1. Thinking dissolved oxygen is always harmful. It is essential for aquatic life. Depletion of oxygen is the problem.
• 2. Thinking all metals in water are harmful. Some are essential (iron, zinc); others are toxic (lead, arsenic).
• 3. Thinking plastics only affect large animals. Plastics break into microplastics that enter the food chain.
• 4. Forgetting that wastewater carries diseases. Wastewater contains pathogens, bacteria, and viruses.
• 5. Confusing the effects of nitrates and phosphates. Nitrates → health risks; phosphates → eutrophication.
• 6. Thinking eutrophication is a natural process. It is accelerated by human activities (fertilizers, detergents).

Quick Revision

• Dissolved oxygen depletion: harmful to aquatic life; oxygen is essential for aquatic organisms.
• Toxic metal compounds: poisonous to humans and animals; can cause long-term health problems.
• Plastics: serious threat to aquatic life and ecosystems.
• Wastewater: carries pathogens, bacteria, viruses; serious threat to humans and aquatic life.
• Harmful microbes: cause waterborne diseases such as diarrhea, dysentery, cholera, and stomach upsets.
• Nitrates from fertilizers: high concentrations in drinking water cause health risks, especially for young children.
• Phosphates from fertilizers and detergents: cause eutrophication, harmful algae blooms, and oxygen depletion; detergents destroy fish mucous membranes and damage gills.

60-Second Revision

• Oxygen depletion → fish die.
• Toxic metals → poison.
• Plastics → harm aquatic life.
• Wastewater → disease.
• Microbes → waterborne diseases.
• Nitrates → blue baby syndrome.
• Phosphates → eutrophication.
• Warning: natural water contains many harmful substances that require water treatment.