POLLUTION Name(s) Many of the changes that occur on the earth are caused by human intervention. While some of these changes are beneficial to humans and other life forms, others are not. Pollution refers to any product that is introduced to an environment and which adversely affects the living or nonliving organisms found in the environment. Although not all pollution is the result of human activity, most of the focus in this section will be on pollution that is from this source. Chemical Pollutants When most people hear the word pollution, they think of chemical pollution. Chemical pollution occurs when the chemical by-products of human activities enter the environment in the air, water or soil. Sometimes the chemicals introduced are themselves dangerous, as is the case with ozone. Other times the chemicals themselves are not immediately harmful, but later they react with other molecules in the environment to cause harmful side effects. Such is the case with excess carbon dioxide (CO 2 ) a greenhouse gas. Another example of this is the production of acid rain, described in the Unit 5 section Erosion. If you did not do the activity associated with acid rain at that time, you may wish to do it now. Greenhouse Effect Carbon dioxide (CO 2 ) is commonly produced during burning when oxygen (O 2 ) in the air combines with carbon in the burning substance. Carbon dioxide is not harmful to humans in small amounts. In fact, carbon dioxide gas is necessary for our survival, because plants utilize it for photosynthesis. Large amounts of carbon dioxide can cause suffocation in humans, but this is not the primary concern of an overabundance of CO 2 in the air. A greater concern is that an overabundance of CO 2 in the atmosphere may cause the average temperature of the earth to increase. Just a small increase in average global temperature (of a few degrees) would have a profound effect on the life on earth. Polar ice caps would begin to melt, causing worldwide flooding, and climates could become drastically altered as wind patterns change. Whether or not global warming is a likelihood given the present rate at which CO 2 is released into the atmosphere remains unclear. However, the process by which CO 2 increases temperatures on the earth is well understood. A) Cut off the tops of two clear 2-liter plastic bottles. B) Place some soil to a depth of about 4 inches in each bottle. C) Rest thermometers at the bottom of both bottles in such a way that you can read the temperature in each bottle. D) Place plastic wrap across the top of one of the bottles, and secure the wrap with a rubber band. E) Shine two identical heat lamps or two bright lamps on the bottles and monitor the temperatures inside. A diagram of the set-up is shown on the next page.2 is released into the atmosphere remains unclear. However, the process by which CO2 increases temperatures on the earth is well understood. UNIT 5 INTERACTIONS AND CHANGE V - 19 CALVIN COLLEGE
1. One of the bottles will heat up more quickly than the other one. Which one is it? 2. Why do you think this bottle became warmer that the other bottle? 3. How is this demonstration similar to what happens inside a car on a sunny day when the windows are closed? Consider a car parked in the bright sunshine. The window glass is almost completely transparent to visible light, and so this light passes quite easily through the windows and into the car. Once inside, the light is absorbed by the seats, the floor, and the dashboard of the car. As these objects begin to heat up, they begin to warm the air in the car by giving off radiation (light) with frequencies too long for your eye to see. This low frequency light does not pass back out through the windows very easily, since glass is not very transparent to these frequencies of light. Instead, this light continues to reflect off the objects in the car and from the windows until the air in the car eventually absorbs the energy as heat. (Please note, the air in the car will also become much hotter with the windows closed than when they are opened because cool air is not able to get in and replace the hot air (via convection currents) because the hot air is not able to escape out through the top of the car. Carbon dioxide in the atmosphere has properties similar to the glass in a car when it comes to light. Visible light passes through CO 2 very easily. However, once the surface of the earth is warmed and it begins to radiate lower frequencies of light, this light does not pass through the CO 2. Therefore, much of this light is trapped within the atmosphere (instead of being transmitted back into outer space), and thus much more of the solar energy gets turned into thermal energy This leads to an increased temperature of the earth. UNIT 5 INTERACTIONS AND CHANGE V - 20 CALVIN COLLEGE
Ozone Ozone is a molecule made up of a combination of three oxygen atoms (O 3 ). It is poisonous to humans. The oxygen molecules we need to breathe are made of two oxygen atoms (O 2 ). Visible light passes through ozone very easily, but ultraviolet light is blocked by it. Since the sun gives off a lot of ultraviolet (UV) light, and since an overabundance of UV light is harmful to humans, it is fortuitous that ozone is produced naturally at very high altitudes. High above the earth, the ozone protects us from harmful photons from the sun, but it is far enough away that we do not have to breathe it. Unfortunately, certain human made chemicals, especially those containing of fluorocarbons, destroy ozone. As they amount of ozone decreases in the atmosphere (called ozone depletion), plants and animals are exposed to increasingly dangerous levels of UV light. A worldwide ban on the use of fluorocarbons in most instances is now in place in order to protect the ozone layer around the earth. One of the great ironies of ozone depletion is that there is often an overabundance of ozone at lower altitudes. This ozone is often created with the use and burning of gasoline products. Breathing ozone can be particularly dangerous if an individual has respiratory problems. 1. Consider the atomic makeup of ozone (O 3 ), nitrogen (N 2 ), and oxygen gas (O 2 ). Why does the ozone created near the surface of the earth remain at lower altitudes, where it is harmful to humans, instead of moving up to higher altitudes? Water Pollution Water pollution can occur due to a variety of causes. Sometimes it occurs directly when factories, people, or even animals discharge their waste into rivers, lakes, or oceans. Other times it happens indirectly, such as when pesticides or herbicides run off farmland or gardens and into water supplies. Sometimes it even falls from the sky in the form of acid rain. Insuring a clean water supply for human needs is an important worldwide endeavor. The activities below present a few of the methods used by water filtration plants for this purpose. Part 1 Sedimentation Think about the dirtiest water you have ever seen. How would you begin to make that water fit to drink? The first step would be to do nothing at all! A) Fill two small, clear cups about one-fifth full each with equal amounts of pebbles, gravel, large grained sand, and dirt. B) Add water to the cups until they are both about 2/3 full. C) Stir the contents of the cups so that the materials inside are completely mixed. D) Pour about one teaspoon of alum into one of the cups, and stir it a little bit more. Mark this cup so that you can tell it from the other one. E) Place the cups in a position where they will not be disturbed, and answer the questions below. UNIT 5 INTERACTIONS AND CHANGE V - 21 CALVIN COLLEGE
1. What do you expect to see happen to the contents of the cups over time? (If you think layering will occur, predict the order in which the layers will occur and explain why. If you do not predict that layering will occur, explain why not.) 2. What types of rocks are formed through the same type of process you are beginning to see occur before you now? 3. Heavy Metals (such as mercury and lead) are atoms that are particularly hazardous to human consumption. Where do you think the heavy metals will end up when the settling is complete? Why? 4. How long do you think it will take before sedimentation is complete? Sedimentation is the first and very important stage in water treatment plants. This stage allows much of the dirt and debris in the water to settle out before the water is passed through filters. Since sedimentation can take a long time, chemicals are often added to the water to speed the process. Alum is one such chemical that can be used. Dirt particles in the water tend to cling to the alum, forming larger, heavier clumps of dirt that settle more quickly. Over time you should be able to observe that sedimentation is taking place more rapidly in the cup in which you added alum. [While you wait for sedimentation to take place, you can skip over Part 2 and begin working on Thermal Pollution on page V 25] UNIT 5 INTERACTIONS AND CHANGE V - 22 CALVIN COLLEGE
Part 2 Making a Water Filter A) Use a thumbtack to poke about 15 small holes into the bottom of a large plastic cup. B) Put a layer are two of small, clean rocks in the bottom of the cup. C) Now fill the cup so that it is about 1/2 full by adding clean, white sand. Note: some of the sand may fall through the holes of the cup. Just discard this bit. D) Add more small, clean rocks until the cup is 2/3 to 3/4 full. E) Pour some clean water into the cup, and wait for it to come out the bottom. This will allow for a cleaning of your filter, and it will also wash out a bit more of the sand. Catch the water runoff in another container. If this water is full of sand, do not discard it down the drain. You may wish to pour it outside on the lawn instead. F) You may now carefully pour the dirty water solution you created in Part 1 into your filter, assuming it has had sufficient time to settle. Use the water that does not contain alum, as this water should be dirtier, and thus better able to display the efficiency of your filter. (A real water filtration plant would use the cleaner water.) Be careful as you pour your water. You do not want to disturb the gunk at the bottom of the beaker. You will want to catch the water coming from the bottom of your filter with another cup. To do this, obtain two or three wooden dowels, and place them inside the collecting cup as shown below. This arrangement will allow for enough space in the bottom cup for you to see how successful your filter has been. 1. Comment on how clean your filtered water looks now. Compare the water dripping from the bottom of the filter to the water you are pouring in at the top. UNIT 5 INTERACTIONS AND CHANGE V - 23 CALVIN COLLEGE
2. Do you think your water would become even cleaner if you passed it through the filter again? 3. What could you do to improve your filter? (Try it.) 4. Do you think filtration would remove heavy metals or dangerous chemicals in the water? Why or why not? 5. How well would filtration work if you did not have a settling process first? Filtration is done at water purification facilities before the final cleaning is performed. After filtration, chemicals (such as chlorine) may be added to kill small microbes living within the water. The water is also often exposed to ultraviolet light. The UV light is effective in killing many living organisms. Sometimes this is done by simply letting sunlight hit the water. Other times it is done by passing the water through a chamber containing ultraviolet lights. Filtration occurs naturally as water seeps downward through soil and rock in the earth. This process is known as percolation. Water retrieved from deep wells is often quite clean and drinkable because of percolation. UNIT 5 INTERACTIONS AND CHANGE V - 24 CALVIN COLLEGE
Thermal Pollution Not all pollution is related to harmful chemicals. Thermal pollution refers to the dumping of excess thermal energy into an environment. This often occurs near factories that utilize heat to run machinery. Some of the thermal energy is converted into the kinetic energy of the machinery, but there is always some excess thermal energy that must be passed out of the factory or plant. This thermal energy raises the temperature of the surrounding environment, and it can cause a variety of harmful effects. When the thermal energy is dumped into a water system, the aquatic system can be disturbed in a variety of ways, often resulting in the death of fish as plants grow out of control. The following activity demonstrates how the rates of chemical reactions can be affected by thermal energy increases. (Note: If effervescent tablets are not available, this same activity may be done by using vinegar and baking soda at different temperatures. In this case, do not cool of the vinegar by using ice, as this will dilute the vinegar. Instead, prepare the cold vinegar by placing it in a freezer ahead of time.) A) Fill one cup with ice water (without the ice), and fill another cup with hot water. B) Drop a single effervescent tablet in each cup, and note the rate at which the reactions occur. 1. What do you observe? 2. What do these results indicate about some naturally occurring chemical reactions that may be affected by thermal pollution? (Keep in mind that plants and animals depend on internal chemical reactions in order to survive.) UNIT 5 INTERACTIONS AND CHANGE V - 25 CALVIN COLLEGE
Noise and Light Pollution Two other types of non-chemical pollution that occur are light and noise pollution. Both of these occur near cities and factories that produce lots of light and noise. 1. How might noise pollution affect animals (such as whales and certain birds) that depend upon their sense of hearing to survive? 2. Light pollution affects people living near cities when they attempt to enjoy the beauty of the stars in the night sky. Explain how light pollution interferes with this endeavor. UNIT 5 INTERACTIONS AND CHANGE V - 26 CALVIN COLLEGE