Chemicals used in Daily Life

Here are some chemicals you can find at home and in a shop, sorted by what they are used for. Add more of your own and discuss them in class.

Used as food	Used to preserve food	Used for cleaning	Used as pesticides
salt, sugar	salt, sugar	soap	rat poison (a rodenticide)
vinegar, baking soda	vinegar, oil	detergent powder	mosquito coil and spray
turmeric, spices	turmeric, oil, lemon	bleach, phenyl (floor cleaner)	insecticide for vegetables
oil, ghee	spices	shampoo, toothpaste	weed killer

Food spoils because microbes, bacteria, yeasts and molds, grow in it and feed on it. They need four things: water, warmth, food and (most of them) air; many also can’t stand acid. Every way of keeping food takes at least one of these away.

Food preservatives are the substances used to keep food from spoiling for a long time. They are used to keep cereals, pulses, vegetables, fruits and animal products such as meat, milk, curd and fish. They stop or slow the growth of bacteria, yeasts and molds, and help keep the food’s nutrients.

First-class and second-class preservatives

Preservatives are also sorted into two classes:

• First-class preservatives come from natural sources and can be used in the amount needed: sugar, salt, vinegar, honey, spices, edible oils.
• Second-class preservatives are chemicals made in factories and may be used only in small, limited amounts, set by law: sodium or potassium nitrate, benzoic acid and its salts, sulphur dioxide. Not more than one kind of second-class preservative should be used in any one food.

Food is preserved in many ways, old and new: drying, cooling in a fridge, salting, soaking in sugar syrup, and adding chemicals. Some chemicals put into food, or used to ripen fruit quickly, harm health and the environment when used carelessly. Wear a mask and gloves while handling them, wash your hands with soap afterwards, never use more than allowed, and use natural preservatives as much as possible.

Food preservatives are of three kinds: chemical preservatives, natural preservatives, and the chemicals used to ripen fruit.

1. Chemical food preservatives

Salt and oil control the growth of microbes, and so do these factory-made chemicals, each used in small, permitted amounts:

Preservative	What it does	Found in
sodium benzoate	stops yeasts and molds in acidic foods	sauces, ketchup, juices, soft drinks
sorbates (potassium sorbate)	stop molds and yeasts	cheese, bread, jam
sulphur dioxide, sodium metabisulphite	stop microbes and keep color	dried fruit, squash, wine
nitrates and nitrites	stop the bacteria of botulism; keep meat pink	sausages, ham, salami
BHA and BHT (butylated hydroxyanisole and hydroxytoluene)	stop fats going rancid (antioxidants)	chips, instant noodles, biscuits, oils
calcium propionate	stops mold	bread, cakes

2. Natural food preservatives

Natural food preservatives come from living things: plants, animals, fungi and algae. In Nepal, people have long used titepati (mugwort) leaves among stored grain and clothes, neem oil and leaves, and chuk (a thick, sour concentrate of lemon or chuk amilo). Traditional ways of keeping food are natural too: drying in the sun, keeping it in a cool place or over water, mixing it with wood ash, coating it with turmeric and oil.

Newer methods, used in towns and villages alike, include pasteurization (heating milk to about 72 °C for 15 seconds and cooling it quickly, which kills the harmful bacteria without boiling the milk), freezing, and cold stores for potatoes and apples. All these methods control what microbes need to grow.

3. Chemicals that ripen fruit

Mangoes and bananas are picked hard and green, so that they survive the journey to market; then they take a long time to ripen. To speed this up, ripening agents are used: calcium carbide, ethylene gas (ethene) and ethephon.

The real ripening signal is ethylene, C₂H₄, the alkene you met in Unit 18. Ripening fruit makes it naturally, and it tells the fruit (and the fruit next to it) to soften, sweeten and change color. Ethylene gas in a closed ripening room, and ethephon (a liquid that releases ethylene, used to make the gas in a ripening room), work the way nature does.

Calcium carbide works differently. With moisture it gives off acetylene (ethyne), which acts a little like ethylene:

$$\text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_2 + \text{Ca(OH)}_2$$

Industrial calcium carbide carries traces of arsenic and phosphorus compounds, which are poisonous, and the fruit ripens on the outside while it stays raw and sour inside. It is cheap and easy, so it is still misused, but Nepal’s food rules forbid making, selling or keeping for sale fruit ripened with carbide (India’s rules forbid it too), and in the mango season the food department warns traders and checks fruit shops and stores for it. It can cause skin irritation and burns, blisters, eye irritation, and fluid in the lungs; workers who handle it are at the greatest risk.

Traditional ways to ripen fruit work by trapping the fruit’s own ethylene: wrapping it in a jute sack, packing it with leaves of asuro (Malabar nut), burying the sack of fruit in a pit and covering it with soil, or wrapping it in a thick layer of husk or hay.

Natural cleaning materials

Long before shops sold soap, people in Nepal cleaned with what grew around them: reetha (soapberry), peena (mustard seed cake), wood ash, lemon juice and sajiban.

Reetha (soapberry)

Reetha fruits contain saponins, natural chemicals that make a lather in water, so reetha works as a soft natural soap. It has been used for centuries to wash the body, hair, clothes and jewelry. The reetha tree (Sapindus mukorossi) grows in Nepal, India and China and is used in Ayurvedic medicine; powdered reetha is a foaming agent in herbal shampoos.

Peena (mustard seed cake)

Peena, the cake left after the oil is pressed out of mustard seeds, has long been used in Nepal to wash hair and make it soft and strong. It contains B vitamins such as folate, niacin, thiamine and vitamin B6, and it is said to reduce hair fall and keep the hair healthy.

Wood ash

Wood ash mixed with a little water makes a paste that scrubs (an abrasive cleaner): it brightens metal utensils, cleans dirty pots, and even removes sticky glue. It works partly because ash is alkaline: it contains potassium carbonate (potash), which turns grease into a kind of soap. Ash is also a good source of potassium, phosphorus and magnesium for plants, so it can be used as a fertilizer.

Sajiban (Jatropha curcas)

Sajiban grows wild in many parts of Nepal and has many uses:

• Animals don’t eat it, so it makes a good living fence around fields.
• Its leaves make compost; its juice is put on burns; its twigs are used to clean the teeth (datiwan).
• Its seeds are rich in oil, which is used to make soap, to light lamps, to produce glycerine, and on skin diseases and aching muscles and joints; its juice and oil are put on cattle to kill lice.
• It is a good source of nitrogen, phosphorus and potash, so the seed cake is an organic fertilizer.
• Its oil can be refined into biodiesel. A sajiban seed is about 30–48% oil, and about 3 kg of seeds give 1 liter of oil.

Lemon juice

Lemon juice contains a lot of citric acid. Its low pH and its germ-killing properties make it a good natural cleaner and a mild bleach. It smells pleasant and doesn’t harm wood or cloth. It cleans copper and brass well and makes them shine: the acid dissolves the dull green-black layer of copper compounds on the surface. (That is why tamarind and lemon are used to clean the copper and brass of temple vessels.) Lemon juice has also been used as a home remedy for a very long time.

Soap

Soaps are the sodium or potassium salts of long-chain fatty acids. They are made from animal fat or vegetable oil (coconut, olive, cottonseed, mustard), sodium hydroxide (caustic soda), and sodium chloride (common salt).

When oil or fat is heated with sodium hydroxide, it splits into soap and glycerol. This process, making soap by the hydrolysis of an oil or fat with an alkali, is called saponification:

fat or oil + sodium hydroxide → soap + glycerol

For example, with the fat tristearin:

$$\underset{\text{fat (tristearin)}}{(\text{C}_{17}\text{H}_{35}\text{COO})_3\text{C}_3\text{H}_5} + 3\text{NaOH} \rightarrow \underset{\text{soap (sodium stearate)}}{3\text{C}_{17}\text{H}_{35}\text{COONa}} + \underset{\text{glycerol}}{\text{C}_3\text{H}_5(\text{OH})_3}$$

Check the balance: C 57 = 54 + 3; H 110 + 3 = 105 + 8; O 6 + 3 = 6 + 3; Na 3 = 3. ✓

Then common salt is added. Soap dissolves less in salty water, so it separates and floats to the top as a solid crust, leaving the glycerol behind in the water (salting out).

How soap cleans

Water alone can’t wash away oil and grease, because oil and water don’t mix. A soap molecule solves this by having two different ends:

• a long hydrocarbon tail (like the alkanes of Unit 18), which hates water but dissolves in oil (hydrophobic, “water-fearing”);
• a small ionic head, –COO⁻ Na⁺, which loves water (hydrophilic).

In soapy water, the tails dig into the grease, and the heads stay in the water. The soap molecules surround tiny droplets of grease, forming balls called micelles, with the oil inside and the heads outside. Rubbing breaks the grease into many such droplets, and they are rinsed away with the water.

Soap and hard water

Hard water contains dissolved calcium and magnesium salts (from rocks like limestone). Many wells, deep tube wells and taps in Nepal give hard water. Soap reacts with the calcium and magnesium ions to make an insoluble scum, the gray curds on a bucket or the ring in a bathtub:

$$2\text{C}_{17}\text{H}_{35}\text{COONa} + \text{CaCl}_2 \rightarrow \underset{\text{scum}}{(\text{C}_{17}\text{H}_{35}\text{COO})_2\text{Ca}} + 2\text{NaCl}$$

The soap used up in scum can’t clean, so in hard water soap makes little lather and is wasted. But soap is biodegradable: microbes break it down, so it doesn’t pollute for long.

Detergent

A detergent is a cleaning substance made mostly from petroleum hydrocarbons, not from fats. It cleans in the same way as soap (it also has a water-loving head and an oil-loving tail), but its head is a sulphonate or sulphate group instead of a carboxylate. Its calcium and magnesium salts dissolve, so detergents work in hard water too, and they dissolve in water better than soap. Because it cleans like soap but isn’t a soap, a detergent is also called a soapless soap.

Examples: sodium lauryl sulphate (the foaming agent in most shampoos and toothpastes), alkylbenzene sulphonates (in washing powders); washing powders also contain helpers such as sodium pyrophosphate and other phosphates that soften the water. Detergents come as powders and liquids. Many “beauty bars” and perfumed bars sold as soap are in fact partly detergent.

Problems with detergents: they can irritate or burn the skin, fade the colors of clothes after long use, and pollute soil and water. The first detergents were non-biodegradable: in the 1950s and 60s, rivers in Europe and the USA were covered in mountains of foam, because microbes couldn’t break down their branched tails. Since then, most countries have switched to detergents with straight tails, which microbes do break down. Today’s bigger problem is the phosphates in washing powder: they are a fertilizer for water plants, and wastewater full of them makes lakes and slow rivers choke with algae, which use up the oxygen the fish need.

Soap	Detergent
Sodium or potassium salt of a long-chain fatty acid.	Sodium salt of a sulphonic acid or alkyl sulphate (made from petroleum).
Made from animal fat or vegetable oil.	Made from petroleum hydrocarbons.
Forms scum with hard water; little lather.	Works in hard water and soft water.
Biodegradable.	Older ones non-biodegradable; most modern ones biodegradable, but phosphates pollute water.
Mild; good for the skin.	Stronger; can irritate the skin and fade colors.

Pesticides are poisonous substances used to remove, destroy, kill or control harmful pests: insects, mites, worms, fungi, weeds, rats. They protect seeds, crops, trees, animals, human health and buildings.

Nepal’s Pesticide Management Act, 2076 BS (2019) defines a pesticide as any organic, plant-based, biological or chemical material used to protect plants, crops, forests and forest products, living beings, livestock, human health, stores, packaging and buildings from any harmful disease, insect, mite, nematode, weed or rodent.

DDT came to Nepal in the 1950s to control malaria mosquitoes: spraying began in the Chitwan valley in 1952. In 2015, Nepal’s Department of Agriculture put the country’s average use at about 396 grams of pesticide (active ingredient) per hectare of farmland, up from 142 grams two years before; vegetable farms used about four times the average, around 1.6 kg per hectare. Most of a spray never touches a pest: it lands on the soil and plants or drifts into the air and water, where some pesticides take a long time to break down, kill the useful living things in the soil, and seep into rivers and groundwater.

Types of pesticides

Pesticides are grouped in three ways: by their effect on the environment, by the pests they kill, and by how they act.

1. By their effect on the environment

a. Biodegradable (non-persistent) pesticides are broken down into harmless compounds by microbes and other living things in a fairly short time, helped by water, air, light and heat. Examples: dimethoate (sold as Nugor, Rugor, Dimet), malathion.

b. Non-biodegradable (persistent) pesticides don’t break down easily; they stay in the environment and in food chains for years. Most countries have banned them, and in Nepal their use, import and export are banned. Examples: DDT, aldrin.

2. By the pests they kill

Kind	Kills or controls	Examples
insecticides	harmful insects	malathion, cypermethrin, fenvalerate, nitenpyram
fungicides	fungi and the diseases they cause (blights, rusts, mildews)	dimethomorph, mancozeb, carbendazim, and mixtures sold under trade names such as Sectin
herbicides (weedicides)	unwanted plants (weeds) in crop fields	butachlor, isoproturon, atrazine
rodenticides	rats and other rodents: mice, squirrels, hamsters, porcupines	zinc phosphide, bromadiolone, coumatetralyl
miticides (acaricides)	mites	bifenazate, fenazaquin, propargite, fenpyroximate

3. By how they act

a. Contact pesticides kill pests such as aphids (lahi), caterpillars (larvae), thrips and whiteflies when the pest’s body touches the poison. Examples: malathion, chlorpyrifos.

b. Internal (stomach) pesticides kill pests that eat leaves, flowers or fruits carrying the poison. Examples: malathion, cypermethrin, fenvalerate.

c. Systemic pesticides are absorbed by the roots or leaves and carried through the whole plant in its sap, so the plant itself becomes poisonous to insects that suck its juice or eat it (aphids, larvae, thrips, whiteflies, leaf miners, stem borers). Examples: thiamethoxam, dinotefuran.

d. Fumigants give off poisonous gases in air, which kill pests. They are used mostly to protect grain and other farm produce in storage. Examples: aluminium phosphide, methyl bromide.

Safety in using and storing pesticides

Follow these rules strictly:

• a.Import, make, sell or use only the pesticides allowed by the Pesticide Management Act, 2076.
• b.Buy pesticides only on the advice of an agricultural technician, and store what is left over safely.
• c.Keep the labels clear and whole.
• d.Store pesticides out of children’s reach, and never near food.
• e.Keep them in airtight, leak-proof containers.
• f.Read and follow the instructions on the label: one careless mistake can cause an accident.
• g.Use only the least harmful pesticide that works. While spraying, wear protective clothing covering the whole body, a mask over nose and mouth, goggles and gloves.
• h.Clean the sprayer and other equipment right after use, and store them safely, but not near a river, well or pond.
• i.Wash your hands and bathe right after spraying.
• j.Follow integrated pest management as far as possible.
• k.Don’t eat or sell vegetables, fruits or crops soon after spraying: wait for the time on the label (the waiting period).
• l.The most dangerous pesticides, listed as Group IB (highly hazardous), may be bought only on the direction of a crop protection officer.
• m.Never forget the saying: “All pesticides are poisons; they are not medicines.”

Pollution makes life harder for people and all living things. It spoils the quality of air, water and soil and upsets the balance of ecosystems. Air pollution spreads airborne diseases; water pollution spreads waterborne diseases. Polluted air also adds carbon dioxide, which is warming the Earth (Unit 16), and that affects all living things.

Pollution by pesticides

Pesticides are poisons. They kill the harmful insects, but also useful ones: bees that pollinate crops, ladybirds that eat aphids, earthworms that make soil. This upsets the balance of the ecosystem.

DDT (dichlorodiphenyltrichloroethane) pollutes both the living and non-living environment. It washes into water and harms animals in water and on land, damages their reproductive systems, and causes breathing problems. Fish and birds grow and breed less. Birds lay fewer eggs, some of which are infertile; and the eggs that are fertile have such thin shells that they break under the parent bird before they hatch. Other persistent pesticides, such as BHC (benzene hexachloride), methoxychlor, aldrin and dieldrin, have similar effects.

Why do birds suffer most, when they were never sprayed? Because DDT doesn’t break down and isn’t passed out of the body; it builds up in fat. Each animal eats many of the animals below it in the food chain, and keeps all their DDT. So the poison becomes more concentrated at every step up the chain. This is called biomagnification.

Insecticides such as DDT, BHC, aldrin and dieldrin were used in the name of modern farming, along with too much chemical fertilizer. Washed by rain into rivers, ponds and lakes, they harm the life there and can kill fish. Crops do need protection from pests, so pesticides have a place; but they also pollute the soil. Insecticides, fungicides and weedicides are a major source of pollution, and chemicals like DDT, aldrin, dieldrin and parathion lower the quality of the soil.

Pollution by industrial chemicals

Cement, ceramics, glass, plastics, fibers, chemical fertilizers, soaps and detergents, used and thrown away carelessly, spoil the air, water and soil, and upset ecosystems. They must be used and disposed of properly, and never dumped into rivers, ponds or farmland.

Think of the Sisdole landfill site in Nuwakot, where Kathmandu’s rubbish was dumped for years, piled with ceramics, glass, plastic and fibers. Discuss:

• a.What happens to the environment when such waste is dumped carelessly?
• b.What can be done to control this pollution?

Proper management of industrial chemicals:

• a.Don’t throw glass, ceramics, plastics and fibers anywhere; collect them and take them to proper places (and recycle them where possible).
• b.Keep sacks of cement tied and covered, so the dust doesn’t blow.
• c.Use organic manure or compost instead of chemical fertilizers.
• d.Use chemical fertilizers and pesticides only as advised by an agricultural expert.
• e.Don’t let soapy and detergent water run straight into rivers, wells or fields; collect it separately (in a soak pit, or a drain to a treatment plant).

1. Choose the correct option

2. Write the differences between

3. Give reasons

4. Answer the following questions