B6 - Water Pollution

Question 1

How can humans pollute water?

Answer 1

• oil escapes from tankers and oil pipelines.
• treated sewage from sewage plants contains nitrates and bacteria
• acid rain contains acids. This falls into the water, lowering the pH
• PCBs are toxic waterproofing chemicals in paints used on boats
• farms use fertilisers and pesticides which wash into rivers and lakes
• detergents from our homes can reach the water via sewage plants

Question 2

Describe the process of eutrophication

Answer 2

• farmers use fertilisers
• rain falls
• minerals, including nitrates are washed into lakes and streams
• nitrates cause algae and plants to grow
• this blocks sunlight
• plants and algae die just below the surface because not enough light for photosynthesis
• bacteria digest the dead algae and plants, using up oxygen
• fish die due to lack of oxygen in water

Question 3

Why are industrial chemicals called PCBs, and the pesticide DDT harmful?

Answer 3

Both of these chemicals can build up in the bodies of whales over many years. The result is that some whales, such as killer whales, are among the most contaminated animals on Earth.

PCBs are known to suppress the immune systems of these animals. This may contribute to the decrease in their numbers.