Chapter 15 Section 8 What causes water pollution? Objective: Describe the major sources of water pollution.

Water Pollution Water pollution occurs when harmful substances enter water sources. Some pollutants dissolve in the water. Others float. Many lakes and rivers were once used for drinking and swimming. Today, many of these are polluted. Not even fish can live in some of these waters.

EXPLAIN: Why are many lakes and rivers not used for drinking water today?

Sewage Wastes that usually are flushed away in water, such as biological wastes, are called sewage. Sewage is a source of water pollution. Bacteria and other disease-causing organisms live in sewage. Sewage also contains soaps and chemicals.

2. DESCRIBE: What harmful things are in sewage?

Chemical Pollutants Many different chemicals pollute the water. Fertilizers are chemicals that help plants to grow. Pesticides are used to kill animal pests and weeds. Farmers use fertilizers and pesticides on their food crops.

Chemical Pollutants Many of the chemicals that make up fertilizers and pesticides are poisonous to living things. They can be washed off of farm fields and seep into the groundwater. This water is then carried to lakes and rivers. The chemicals in the water may harm organisms that live in the water.

Chemical Pollutants Chemical pollutants also come from industry. Some industries illegally bury their wastes in barrels, or metal drums, in the ground. If the drums rust or break apart, the wastes can leak into the groundwater.

Chemical Pollutants Industries also dump chemical wastes directly into water. These wastes are harmful to fish living in the water. They are also harmful to the people who eat the fish.

Chemical Pollutants Mercury is a poisonous element that is sometimes found in polluted water. Many fish cannot be eaten because they contain mercury.

FRESHWATER POLLUTANTS Kinds of Pollutants Examples Sources Disease-causing organisms Giardia, Cryptosporidium, bacteria Human wastes, runoff from livestock pens Pesticides and fertilizers DDT, nitrates, phosphates Runoff from farm fields, golf courses Industrial chemicals PCBs, carbon tetrachloride, dioxin Factories, industrial waste, disposal sites Metals Lead, mercury, copper Factories, waste disposal sites Radioactive wastes Uranium, Carbon-14 Medical and scientific disposal sites, nuclear power plants Petroleum products Oil, gasoline Road runoff, leaking underground storage tanks

3. NAME: What are two sources of chemical pollutants?

Protecting the Water Sewage treatment plants have been built in many cities and towns. These plants change sewage into less harmful materials. Laws also help to fight water pollution. These laws require industries to clean their wastes before dumping them into lakes and rivers. Laws have also banned the use of certain pesticides and soaps.

4. EXPLAIN: What happens to sewage at sewage treatment plants?

15-8 Classwork CHECKING CONCEPTS What are pesticides used for? What causes water pollution? What happens when metal drums storing industrial wastes rust? Where do fertilizers and pesticides that seep into groundwater end up? Why is sewage potentially harmful?

15-8 Classwork THINKING CRITICALLY 6. EXPLAIN: How could you help stop water pollution? 7. PREDICT: What might happen if drums containing harmful chemicals were buried on a beach? Explain your answer.