Effects of Acidity on the Environment

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Acids are all around you, but have you ever though about how acids impact the environment? This lesson will focus on acid rain and ocean acidification, discussing the chemical reactions that take place and the organisms affected.

Acid In the Environment

Let's face it, you're surrounded by acid. Whether that is the lemonade and soda in your refrigerator or the digestive juices in your stomach, acids are an everyday occurrence in your life. But what is an acid, exactly? Acids share the following characteristics:

  • A pH less than 7 (pH is just a scale)
  • A substance that releases hydrogen ions when dissolved in water
  • Sour and bitter tasting
  • Sticky

So if acid is all around you, what's the big deal if it gets into the environment? Excellent question. Acid can be found in the environment naturally. For example, rain, some soils, and certain lakes are naturally slightly acidic. However, when acid gets into the environment through acid rain or ocean acidification, problems can arise.

What is Acid Rain?

Like its name implies, acid rain is rain that is acidic. Specifically, it has a pH between 4.2 and 4.4, but some acid rain can have a pH as low as 2. Keep in mind that normal rain has a pH around 5.6. So, what makes the rain acidic? While erupting volcanoes can cause acid rain, the main culprits are nitrogen oxides, sulfur dioxide, and carbon dioxide, which are released into the atmosphere from vehicles, power plants, and manufacturing plants.

Let's check out the reactions that create acid rain.

  • The first reaction is when carbon dioxide and water react to form carbonic acid. This is the reaction that makes rain naturally acidic, however, more carbon dioxide in the environment can make things worse.
    acid42
  • Let's check out the nitrogen oxide reactions. In the first reaction, nitrogen monoxide (from internal combustion engines) combines with oxygen in the atmosphere to make nitrogen dioxide. The nitrogen dioxide dissolves in water and this makes nitric acid and nitrous acid.
    acid
  • The last reaction we will highlight is sulfur dioxide. Sulfur dioxide is released from the burning of coal. The sulfur dioxide combines with water to make sulfurous acid. Further reactions produce sulfuric acid.
    acidt5

Effects of Acid Rain

You wouldn't think a decrease from 5.6 to 4.4 would cause that many problems, but it does. Take a look at the list of harmful effects from acid rain:

Acid rain has destroyed a forest in Europe
acidrain2

  • Acid rain increases acidity in bodies of water like streams and lakes. This alone damages aquatic organisms; however, an increase in acidity also causes aluminum that is found in soil to be leached into bodies of water. The combined impact of aluminum and acidity causes damage to aquatic ecosystems.
    • Example: many fish eggs cannot hatch at a pH of less than 5. Fish that are able to survive in acidic bodies of water often have no food because the aquatic plants die.
  • Acid rain impacts the soil in forests. The combination of acidity and increased aluminum makes it difficult for trees to uptake the nutrients they need.
  • Acid rain also impacts man-made structures.
    • Limestone is made up of calcium carbonate and when exposed to acid, calcium carbonate breaks down. This results in the dissolving of many statues and structures.
    • Acid rain can corrode, or breakdown, metals such as zinc, copper, bronze, nickel, and some types of steel. When these are used as building materials, acid rain can cause them to breakdown prematurely.

What is Ocean Acidification?

Another concern is ocean acidification, which is the lowering of the pH of the world's oceans. The bodies of water on earth absorb the carbon dioxide in the atmosphere and the carbon dioxide reacts with the water, creating an acid. Remember this reaction from before?

acid42

All of the bodies of water on earth absorb one-third of the man-made carbon dioxide each day. Carbon dioxide is the byproduct of burning fossil fuels and other industrial processes. So, how much carbon dioxide is absorbed by the world's bodies of water each day? About 22 million tons! In the last 200 years, the pH of the ocean has gone from 8.2 to 8.1. While that seems small, that is around a 25% increase in ocean acidity.

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