Page 167 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

lead, mercury, sulphur, asbestos, nitrates, etc., into water bodies, without filtering or

treating water to remove toxins from the waste. This dumped waste contaminates
the water.

Oil spills: When oil or liquid petroleum spills occur in water bodies due to human
activities or oil container accidents, it is termed as an oil spill. It is harmful for marine

life, such as fish and various sea animals. The spilled oil coats the skin of the aquatic
animals and makes it difficult for them to breathe.

Plants growing near or underwater are also harmed due to oil spills. The layer of oil
on water blocks the sunlight from reaching the plants due to which plants cannot

perform photosynthesis and will eventually die.
Agricultural effluents: Multiple farming activities as livestock breeding, pesticide

use, fertilisation and unsustainable land use lead to water pollution. Agricultural
practices also damage aquatic ecosystems and river beds. Some pollutants that are

added to the soil are nitrates, phosphorus, pesticide, soil sediment and salt.
Sewage: Sewage is released untreated into rivers and streams throughout the

world. At home, wastewater includes the water used for activities, such as bathing,
washing, cleaning etc. It also includes the rainwater that flows into the drains during

heavy rainfall. When sewage is dumped into water bodies, it not only pollutes them
but also contaminates the groundwater which is consumed in households, causing

diseases, such as cholera, diarrhoea and typhoid.

8. List a few ways to control sewage generation.
Ans: A few ways to control sewage generation are:

• Encourage others to use less water in daily activities to reduce sewage
production.

• Install systems to separate different types of waste to make treatment easier.

• Teach people how to correctly dispose of waste & protect water sources.
• Regularly check & fix sewage systems to prevent problems & pollution.

• Encourage water saving at home, school & everywhere to lover sewage

production.
9. Name and write about any three alternative sewage disposal.

Ans: Septic tank: A septic tank is often installed under the ground in houses or buildings,

such as hospitals. It allows decomposition of sewage by the action of anaerobic
bacteria.

Chemical toilet: Chemical toilet has a separate compartment that treats human
waste with chemicals and decreases odour.

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