Using Chemistry to Solve Environmental Challenges

Chemistry to the rescue

In the last lesson you saw how chemical reactions can create safety and environmental problems. But understanding the properties of substances and their reactions is also how we solve environmental problems. Expectation C1.2 gives three examples: renewing the Great Lakes, neutralizing acid spills and scrubbing smokestack emissions. In this lesson you will look at the chemistry of each, the Canadians who helped, and the careers that do this work today (A2.1, A2.2).

Neutralizing acid spills

When a truck or a factory spills an acid, it must be cleaned up quickly before it burns people, damages property or flows into a river. Responders use neutralization: they add a base to turn the acid into a salt and water.

They usually choose a weak, mild base, such as sodium hydrogen carbonate (baking soda), sodium carbonate (soda ash) or lime (calcium hydroxide or calcium carbonate), rather than a strong base like sodium hydroxide. A mild base is safer to handle, and adding too much of it does not create a new dangerous spill. The fizzing of carbon dioxide also shows workers when the acid has been used up.

H₂SO₄(aq) + 2NaHCO₃(s) → Na₂SO₄(aq) + 2H₂O(l) + 2CO₂(g)

Hazardous materials (hazmat) teams, firefighters and environmental emergency responders carry spill kits for exactly this job, and they follow the Safety Data Sheet for each chemical.

Scrubbing smokestack emissions and fighting acid rain

When coal is burned or when sulfide ores are processed (for example, the nickel and copper ores of the Sudbury area), sulfur is released as sulfur dioxide gas, SO₂. In the air, SO₂ reacts with oxygen and water to form sulfuric acid, which falls as acid rain. Around Sudbury, decades of emissions killed vegetation over large areas and acidified many lakes.

Scrubbers remove SO₂ from smokestack gases. In a common type, the gas passes through a spray of limestone (calcium carbonate) mixed with water:

CaCO₃(s) + SO₂(g) → CaSO₃(s) + CO₂(g)

The calcium sulfite is then reacted with oxygen to make calcium sulfate (gypsum), which can be used to make drywall:

2CaSO₃(s) + O₂(g) → 2CaSO₄(s)

Smelters can also capture SO₂ and turn it into sulfuric acid to sell, instead of releasing it. Since the 1970s, SO₂ emissions from Sudbury's smelters have been cut dramatically, and a community regreening program has spread crushed limestone on acidic soils (a neutralization) and planted millions of trees. Many lakes in the area have partly recovered.

Renewing the Great Lakes

In the 1960s, Lake Erie was covered by thick algal blooms. When the algae died and decayed, the decay used up dissolved oxygen, and fish died. Scientists argued about the cause: was it carbon, nitrogen or phosphorus?

Canadian scientist David Schindler and his team answered the question at the Experimental Lakes Area in northwestern Ontario. In 1973 they divided a whole lake (Lake 226) in two with a plastic curtain. They added carbon and nitrogen to both halves, but phosphorus to only one half. Only the half with phosphorus grew a huge algal bloom. Phosphorus was the key nutrient.

This evidence helped Canada and the United States limit phosphates in laundry detergents in the 1970s and reduce phosphorus from sewage under the Great Lakes Water Quality Agreement (first signed in 1972). Today, many wastewater treatment plants remove phosphate with a precipitation reaction: they add iron or aluminium compounds, which form insoluble phosphates that settle out:

Fe³⁺(aq) + PO₄³⁻(aq) → FePO₄(s)

Algal blooms have returned to parts of Lake Erie since the 2000s, largely because of phosphorus washing off farmland, so this work continues.

Water protectors

For many First Nations, protecting water is a responsibility. In Anishinaabe teachings, women have a special responsibility to care for water. Anishinaabe Grandmother Josephine Mandamin (1942 to 2019), from Wiikwemkoong Unceded Territory on Manitoulin Island, co-founded the Mother Earth Water Walk. Beginning with a walk around Lake Superior in 2003, she walked the shorelines of all five Great Lakes over the following years, carrying a copper pail of water, to call attention to protecting water. Others carry on Water Walks today. Indigenous knowledge of local waters, built over many generations, and Western science are increasingly used together in monitoring and protecting the Great Lakes.

Canadian scientists in chemistry

• David Schindler (1940 to 2021): showed that phosphorus causes algal blooms, which changed laws on detergents and sewage.
• John Polanyi (born 1929): University of Toronto chemist who shared the 1986 Nobel Prize in Chemistry for research on the dynamics of chemical reactions, studying the faint infrared light given off by molecules as they react.
• Gerhard Herzberg (1904 to 1999): worked at the National Research Council of Canada and won the 1971 Nobel Prize in Chemistry for his studies of the structure of molecules using light (spectroscopy).