Acids, Bases and the Environment

Acids Bases

Normal rain is slightly acidic, with a pH of about 5.6, because carbon dioxide in the air dissolves in water droplets to form weak carbonic acid. Acid rain is rain with a pH below 5.0, caused by additional acidic gases in the atmosphere.

Causes of acid rain

The main causes of acid rain are gases released by burning fossil fuels:

• Sulfur dioxide (SO2): Released when coal and oil containing sulfur are burned in power stations and factories.
• Nitrogen oxides (NOx): Released by car engines, power stations and industrial processes.

These gases dissolve in water vapour in the atmosphere to form sulfuric acid and nitric acid. The acidic droplets fall as rain, snow or fog.

Effects of acid rain

• Lakes and rivers: Acid rain lowers the pH of freshwater, making it toxic to fish and other aquatic life. In Sweden and Canada, thousands of lakes have become too acidic to support fish populations.
• Forests: Acid rain damages tree leaves, leaches nutrients from soil, and releases toxic aluminium ions that damage roots. Forests in Europe and North America have suffered significant damage.
• Buildings and statues: Acid rain reacts with limestone and marble (both forms of calcium carbonate), causing statues and buildings to erode and crumble. Famous monuments including the Parthenon in Athens have been damaged.

Solutions

• Scrubbers in power stations: Devices that remove sulfur dioxide from exhaust gases before they are released.
• Catalytic converters in cars: Reduce nitrogen oxide emissions from vehicle exhausts.
• Alternative energy: Using solar, wind and hydroelectric power instead of burning fossil fuels.
• International agreements: Treaties such as the Gothenburg Protocol have reduced sulfur dioxide emissions in many countries.

The world's oceans absorb about 30% of the carbon dioxide released by human activities. When CO2 dissolves in seawater, it forms carbonic acid, lowering the pH of the ocean. This process is called ocean acidification.

Since the Industrial Revolution, the pH of the surface ocean has dropped from about 8.2 to about 8.1. This might seem like a small change, but the pH scale is logarithmic, meaning this represents about a 30% increase in acidity.

Impact on marine life

Many marine organisms, including corals, shellfish and some plankton, build their shells and skeletons from calcium carbonate. In more acidic water, it becomes harder for these organisms to form and maintain their calcium carbonate structures. Existing shells can even begin to dissolve.

For Australia's Great Barrier Reef, ocean acidification is one of several threats (along with warming water and pollution). As the ocean becomes more acidic, coral growth slows and existing reef structures weaken. This affects not just the corals but the thousands of species that depend on reef habitats - fish, turtles, sharks and more.

What can be done?

• Reduce CO2 emissions: The most effective solution is to reduce the amount of carbon dioxide released into the atmosphere by transitioning to renewable energy and improving energy efficiency.
• Protect coastal ecosystems: Mangroves, seagrass beds and salt marshes absorb CO2 and can help buffer local acidity.
• Marine protected areas: Reducing other stressors (pollution, overfishing) helps marine ecosystems cope better with acidification.

Aboriginal and Torres Strait Islander Peoples have lived on this continent for over 65,000 years, developing deep knowledge of the land, water, plants and animals. This knowledge includes sophisticated understanding of chemistry that Western science is still learning from.

Natural indicators

Many Aboriginal communities have traditionally used plants as indicators of water quality and soil conditions. Certain plants only grow where water is fresh and clean; others indicate the presence of minerals or the pH of soil. This is practical chemistry applied through observation and accumulated knowledge over generations.

For example, some Aboriginal groups have used crushed leaves that change colour when placed in water of different qualities. While not identical to universal indicator paper, this represents the same chemical principle: substances that respond predictably to changes in their environment.

Soil chemistry and land management

Aboriginal fire management practices (cultural burning) demonstrate understanding of combustion chemistry and how it affects soil. Cool burns consume fuel without reaching temperatures that kill mature trees or alter soil chemistry dramatically. This preserves soil nutrients and structure.

Some Indigenous practices also involve adding specific plant materials to soils to change their properties - a form of soil amendment similar to how farmers today add lime to acidic soils. These practices show that Indigenous knowledge systems included practical applications of chemistry long before formal Western chemistry existed.

Treating knowledge with respect

Indigenous knowledge is protected under Indigenous Cultural and Intellectual Property (ICIP) protocols. This means that traditional knowledge should not be used without permission, and should always be attributed to the communities that hold it. When scientists study Indigenous practices, they should work in partnership with Indigenous communities rather than simply extracting information.