B. Matter, Chemical Trends, and Chemical Bonding · Matter, Chemical Trends, and Chemical BondingCommonly Used Chemicals and the Environment
B1.1 A1.1 A1.3 A1.5 A1.9 A2.1About 75 minutes
Learning goals- I can analyse a commonly used substance's properties, benefits and environmental effects.
- I can explain eutrophication, persistence and biomagnification.
- I can propose realistic ways to lessen a substance's impact or identify safer alternatives.
- I can evaluate the reliability of sources about chemical issues.
Words to know
persistent
Breaking down very slowly, so it remains in the environment for a long time.
bioaccumulation
The build-up of a substance in an organism's tissues over time.
biomagnification
The increase in concentration of a persistent substance at each higher level of a food chain.
eutrophication
Over-enrichment of water with nutrients, causing algal blooms and loss of dissolved oxygen.
leaching
The movement of dissolved substances down through soil, for example into groundwater.
green chemistry
Designing chemical products and processes to reduce or eliminate harm.
household hazardous waste
Leftover household products that are toxic, corrosive, flammable or reactive and need special disposal.
Useful chemicals, unintended effects
Every winter, Canadian road crews spread millions of tonnes of road salt (mostly sodium chloride) to keep highways and sidewalks safe. It works: salt lowers the freezing point of water so ice melts. But in spring, the meltwater carries the dissolved salt into streams, wetlands and groundwater. In 2001 an Environment Canada assessment concluded that road salts harm plants, animals and aquatic life when they build up in the environment, and a national code of practice now guides how they are used.
Road salt is a good example of what expectation B1.1 is about: a commonly used chemical that is beneficial but potentially harmful. In this lesson you will learn a method for analysing such substances, look at several case studies, and practise proposing ways to lessen their impact or replace them.
How to analyse a potentially harmful substance
For any substance, ask five questions:
- What is it used for? What are the benefits? (Safety, food production, cleaning, energy storage...)
- What are its chemical and physical properties? Is it soluble in water (so it travels with runoff and groundwater)? Is it persistent (slow to break down)? Is it toxic, and to which organisms? Does it bioaccumulate (build up in living tissue)?
- How does it get into the environment? Runoff, leaching from landfills, air emissions, wastewater.
- What effects does it have on ecosystems and human health?
- How can its impact be lessened? The main strategies are: reduce the amount used; use it more precisely (right amount, right time, right place); modify the substance or product so it is less harmful; substitute a safer alternative; and recover or recycle it so it does not reach the environment.
The idea of designing chemicals and processes to reduce harm from the start is called green chemistry.
Worked exampleExample 1: Analysing road salt
Use the five questions to analyse sodium chloride used as road salt, and propose two ways to lessen its impact.
- Use and benefit: melts ice on roads and sidewalks, reducing collisions and falls.
- Properties: NaCl is very soluble and does not break down; the Na⁺ and Cl⁻ ions stay in solution. Chloride in particular is not removed by soil.
- Route: dissolved in meltwater, it runs into storm drains, streams and wetlands, and soaks into groundwater, including wells.
- Effects: high chloride levels harm freshwater organisms; salt spray and salty soil damage roadside trees and plants; salt also speeds up corrosion of cars and bridges.
- Lessen the impact: (1) reduce the amount: pre-wet salt with brine so it sticks to the road instead of bouncing off, calibrate spreaders, and shovel before salting; (2) substitute in sensitive areas: sand for traction, or alternatives such as calcium magnesium acetate (less harmful to plants, but more expensive).
Road salt has real safety benefits, but its solubility and persistence let it build up in water. Using less, more precisely and alternatives in sensitive areas lessens its impact.
Case study: fertilizers and phosphates
Fertilizers supply plants with nitrogen (as nitrate NO₃⁻ or ammonium NH₄⁺), phosphorus (as phosphate PO₄³⁻) and potassium (K⁺). They are a major reason modern farms can feed so many people.
The problem: all nitrates are soluble, so excess nitrate can leach into groundwater, and nitrate in drinking water is a health concern for babies. Phosphate and nitrate washed into lakes cause eutrophication: too many nutrients trigger huge algal blooms. When the algae die, bacteria decompose them and use up the water's dissolved oxygen, which can kill fish. Some blooms (of cyanobacteria) also produce toxins that make water unsafe to drink.
Lessening the impact: soil testing and the "4R" approach promoted to Canadian farmers (right source, right rate, right time, right place); slow-release fertilizers; planting buffer strips of vegetation along streams; and limiting phosphates in detergents, which Canada did for household laundry and dishwasher detergents.
Case study: household cleaners
Cleaning products work because they are reactive, and that is also why they can be dangerous.
- Never mix bleach with ammonia (found in some glass cleaners): the reaction produces toxic chloramine gases.
- Never mix bleach with acids (vinegar, some toilet-bowl cleaners): the reaction releases toxic chlorine gas.
- Many cleaners are corrosive (strong bases such as sodium hydroxide in oven and drain cleaners) and must be stored safely, in their original containers, away from children.
Lessening the impact: use the mildest product that does the job (baking soda, vinegar and soap handle many tasks); use the amount on the label; never mix products; and take leftover hazardous products to a municipal household hazardous waste drop-off instead of pouring them down the drain.
Just for funVinegar is about 5% acetic acid. It is one of the few cleaning chemicals you can also pour on your fries, a very Canadian piece of green chemistry. (Just never mix it with bleach.)
Case study: batteries and electronics
Batteries store energy in chemicals, and several of those chemicals are hazardous: lead and sulfuric acid (car batteries), cadmium and nickel (rechargeable Ni-Cd batteries), and lithium compounds with flammable electrolytes (lithium-ion batteries in phones, laptops and e-bikes). Heavy metals such as lead and cadmium are toxic and persistent: they do not break down. Damaged lithium-ion batteries in garbage or recycling trucks have started fires.
Lessening the impact: take batteries and old electronics to a collection drop-off (many stores and municipal depots accept them; Ontario requires battery producers to fund collection and recycling); recycle to recover metals; choose rechargeable batteries to reduce the number used; and design products so batteries can be removed and replaced.
Case study: mercury and the English–Wabigoon River
Mercury is a liquid metal that was once widely used in industry. From 1962 to 1970, a chemical plant connected to a pulp-and-paper mill in Dryden, Ontario released about 9 tonnes of mercury into the English–Wabigoon River system. Bacteria in the water convert mercury into methylmercury, a form that bioaccumulates in fish and becomes more concentrated at each step up the food chain (biomagnification).
The Anishinaabe communities of Grassy Narrows First Nation (Asubpeeschoseewagong Netum Anishinabek) and Wabaseemoong Independent Nations, whose ways of life, food and economies are closely connected to the river and its fish, continue to live with serious, long-lasting health effects. Community members have led a decades-long campaign for cleanup, health care, compensation and recognition. Ontario has committed funding to clean up the river system, and the federal government has committed funding for a Mercury Care Home in Grassy Narrows to provide specialized care.
This case shows why chemists study persistence and bioaccumulation before a substance is released, and why the people most affected must be part of decisions about cleanup.
Evaluating sources (A1.9)
When you research a chemical issue, check each source: Who wrote it, and what is their purpose? (A company selling a product, an advocacy group and a government agency may present the same data differently.) Is it based on evidence, with data and references? Is it current? Peer-reviewed studies and government science agencies (Health Canada, Environment and Climate Change Canada) are usually reliable starting points, but still compare several sources.
Careers in this field (A2.1)
People who work on these problems include environmental chemists (who measure pollutants in water, soil and air), water quality technicians at municipal treatment plants, agronomists and crop advisers (who help farmers use fertilizer efficiently), chemical engineers (who redesign processes to make less waste), and environmental health officers. Most of these careers start with a college diploma or university degree that includes Grade 12 Chemistry.
Hands-on activityInvestigate: does road salt affect plant growth?
You need: 3 small pots or clean yogurt cups with drainage holes poked by a grown-up, potting soil, fast-growing seeds (cress, radish or bean), table salt, measuring spoons, 3 labelled jars of water, a ruler and a notebook.
- Question and hypothesis: How does the concentration of salt in water affect seedling growth? Write a hypothesis.
- Prepare solutions: jar A, plain tap water (control); jar B, ¼ teaspoon of salt in 500 mL water (low); jar C, 1 teaspoon of salt in 500 mL water (high).
- Plant the same number of seeds (for example 10) at the same depth in each pot. Keep all pots in the same place with the same light and temperature.
- Water each pot with the same volume of its own solution every day or two (for example 30 mL).
- Record for 7 to 10 days: number of seeds sprouted, and average height of seedlings. Make a data table and a bar graph.
- Conclude: Did the data support your hypothesis? Identify one source of error, and suggest how cities could use your results.
What to look for: fewer seeds sprouting and shorter seedlings in the salty pots, especially the high-salt pot. Wash hands after handling soil, and do not use the salty soil for houseplants afterwards.
Your turn
1List the five questions used to analyse a potentially harmful substance.
- Uses/benefits; 2. properties (solubility, persistence, toxicity, bioaccumulation); 3. route into the environment; 4. effects; 5. ways to lessen the impact.
2Why does road salt build up in streams and groundwater instead of disappearing?
NaCl is very soluble and does not break down; the dissolved ions travel with meltwater and stay in the water.
3Explain how phosphate runoff can kill fish in a lake.
Phosphate causes an algal bloom; when the algae die, decomposing bacteria use up dissolved oxygen, so fish suffocate.
4Why must bleach never be mixed with vinegar?
The acid reacts with bleach to release toxic chlorine gas.
5Give two ways to lessen the environmental impact of household batteries.
Any two: recycle at a drop-off, use rechargeable batteries, tape lithium battery ends before drop-off, choose products with replaceable batteries.
6What is biomagnification? Give an example.
The increase in concentration of a persistent substance at each level of a food chain, e.g. methylmercury in fish and the people or animals that eat them.
More practice: warm-up
1What does "persistent" mean for a chemical in the environment?
It breaks down very slowly and stays in the environment for a long time.
2Name the three main nutrients in fertilizers.
Nitrogen, phosphorus, potassium (N, P, K).
Designing chemical products and processes to reduce or eliminate harm to people and the environment.
4Name a household product that contains ammonia.
Some glass cleaners (check the label).
5Where should leftover hazardous household chemicals go?
To a municipal household hazardous waste drop-off.
More practice: on your own
1Why are nitrate fertilizers more likely than phosphate fertilizers to reach groundwater?
All nitrates are soluble, so they move down with water through soil. Many phosphates bind to soil particles and move mostly with eroded soil and surface runoff.
2Explain the "4R" approach and how it reduces harm.
Right source, right rate, right time, right place: applying only the fertilizer plants need, when and where they can use it, leaves less excess to run off or leach.
3Calcium magnesium acetate is less harmful to plants than sodium chloride but is not used on every road. Suggest a reason, and where it would be most worth using.
It is much more expensive. It is most worth using in sensitive areas, such as near drinking-water sources, wetlands or bridges where corrosion is a concern.
4A website selling a "natural" cleaner claims all other cleaners are toxic. Evaluate this source.
The source has a commercial bias (it sells a competing product) and makes a sweeping claim. Look for evidence, references and independent sources (e.g. Health Canada) before accepting it.
5Why is mercury more dangerous to people who eat a lot of fish from a contaminated river than to people who only drink the water?
Methylmercury bioaccumulates and biomagnifies: concentrations in fish can be many times higher than in the water, so eating fish delivers a much larger dose.
Challenge
1Choose a commonly used substance not analysed in this lesson (for example, a lawn pesticide, antifreeze or a lead-acid car battery). Write a brief analysis using the five questions and propose one realistic way to lessen its impact.
Model answer (antifreeze, ethylene glycol): Use: prevents engine coolant freezing. Properties: soluble in water, toxic if swallowed, sweet taste attracts pets and children. Route: leaks and improper disposal down drains or onto ground. Effects: poisoning of animals and people; contamination of water. Lessen: store sealed and labelled, fix leaks, take used coolant to a hazardous waste depot or recycler, or choose a less toxic propylene glycol formula.
2Ontario banned the use of pesticides for cosmetic purposes (for example, on lawns) in 2009 but still allows many pesticides on farms. Give one argument for this difference and one stakeholder who might disagree.
Argument: lawn use is mainly for appearance, so the benefit is small compared with the risk, while farm use protects food production, a large benefit. A stakeholder who might disagree: lawn-care companies (lost business), or environmental groups who want stricter farm rules.
3Explain why reducing phosphate in detergents alone did not end algal blooms in Lake Erie.
Detergents were only one source of phosphorus. Agricultural runoff (fertilizer and manure), sewage overflows and other sources continue, and warmer water also favours blooms. Lasting solutions must address all major sources.
Quiz
1. Which property makes road salt likely to build up in streams and groundwater?
2. Eutrophication is caused mainly by
3. Mixing bleach with ammonia-based cleaners is dangerous because it
4. Which strategy is an example of substitution?
5. Biomagnification means that a substance
6. Which source is most likely to be biased about the safety of a pesticide?
Big idea: Expectation B1.1 asks students to analyse the properties of commonly used but potentially harmful chemical substances and how they affect the environment, and to propose ways to lessen their harm or find alternatives. The five-question method in this lesson is a framework students can reuse for research assignments.
Safety: please handle cleaning products yourself and remind your teen never to mix them. The plant-growth experiment uses only table salt and seeds.
A sensitive topic: the mercury case study involves First Nations communities that continue to live with its effects. Talk about it respectfully, focusing on the science of persistence and bioaccumulation and on the communities' leadership in seeking cleanup and care.
How to help: Look for real examples nearby: salt stains on boots and roadsides, the battery drop-off box at a store, the hazardous waste depot schedule in your municipality.
Common difficulties:
- Listing only harms. A good analysis weighs benefits too.
- Vague solutions ("use less chemicals"). Encourage specific, realistic proposals with a reason.
- Accepting any website as a source. Practise asking who wrote it and why.