Exam practice

DDT is a persistent poison: it doesn’t break down and builds up in the fat of animals. It kills useful insects along with pests, and it becomes more and more concentrated up the food chain (biomagnification), so fish-eating birds and other top predators are poisoned, lay thin-shelled eggs and fail to breed. When some living things in a food chain die out, the others that depend on them are affected too, so the balance of the ecosystem is upset.

Chemical pesticides are poisons: they harm the people who spray them and those who eat the residues on food (skin diseases, breathing problems, cancers); they kill useful insects such as bees and the pests’ natural enemies; they pollute soil, rivers and groundwater; and pests become resistant to them, so more and more must be used. Integrated pest management and biological methods protect crops with less harm.

Soap dissolves less in salty water. Adding common salt makes the soap separate from the mixture of soap, glycerol and water, and come up as a solid that can be filtered off (salting out), leaving the glycerol in the liquid.

Pickles contain preservatives such as salt, oil, vinegar or lemon and spices. Salt draws water out of the food and out of microbes (osmosis), so they can’t grow; oil keeps out air; vinegar and lemon make the pickle too acidic for most microbes; and mustard oil and spices kill some microbes. So the pickle doesn’t rot.

DDT: dichlorodiphenyltrichloroethane. BHC: benzene hexachloride.

Food preservatives are substances added to food to stop it from spoiling, by stopping or slowing the growth of bacteria, yeasts and molds. They are used to keep food for a long time without it going bad, to keep its nutrients, taste and color, to let food be stored and carried to markets far away, and to have seasonal food all year round.

Salt, sugar, vinegar and oil (natural); and, in small permitted amounts, sodium benzoate, sorbates (potassium sorbate), sulphur dioxide and sodium metabisulphite, nitrates and nitrites, BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene) and calcium propionate.

Drying in the sun (gundruk, sukuti, dried vegetables); keeping food in a cool place, or over water; salting; using sugar and honey; pickling with oil, lemon, vinegar and spices; mixing with wood ash or turmeric and oil; using titepati, neem or chuk; smoking; fermentation (gundruk, curd). Modern methods include pasteurization, freezing and cold stores.

Natural food preservatives come from living things, plants, animals, fungi and algae, or from traditional methods: salt, sugar, honey, vinegar, oil, spices, turmeric, lemon (chuk), neem, titepati.

Why they are better: they have been used safely for centuries and can be used in the needed amount; they don’t leave harmful residues, while some chemical preservatives (sulphites, nitrites, BHA) can cause allergies, asthma or long-term harm if overused; they are cheap and locally available; many (turmeric, garlic, spices) even add flavor and health benefits; and they don’t pollute.

But fairly: natural methods don’t suit every food (packaged juices or bread would spoil quickly without a chemical preservative), and too much salt or sugar is itself unhealthy. Chemical preservatives within legal limits are tested and considered safe. The best choice is fresh food, natural methods where possible, and checking labels.

Chemical methods:

• Ethylene gas: the fruit is kept in a closed ripening room with a small amount of ethylene, the natural ripening hormone, at a controlled temperature, for a day or two. This is the safe, modern method.
• Ethephon: a liquid that releases ethylene gas; it is put in a dish in the closed ripening room, not on the fruit. (Dipping or spraying fruit in it leaves a residue; India’s food rules forbid that.)
• Calcium carbide: packets are put among the fruit; with moisture it releases acetylene, which imitates ethylene. It is harmful (arsenic and phosphorus impurities), and Nepal’s food rules forbid selling fruit ripened with it.

Traditional methods (trap the fruit’s own ethylene and warmth): wrapping in a jute sack; packing with asuro leaves; putting the sack of fruit in a pit covered with soil; wrapping in a thick layer of husk or hay; keeping unripe fruit with ripe fruit.

1. Use only pesticides allowed by the Pesticide Management Act, 2076, bought on an agricultural technician’s advice; the most hazardous (Group IB) only on a crop protection officer’s direction.
2. Read and follow the label; use the least harmful pesticide that works, in the right amount.
3. Wear protective clothing, a mask, goggles and gloves while spraying; don’t spray against the wind.
4. Wash hands and bathe right after spraying; clean the equipment, but not near water sources.
5. Store pesticides in airtight, labeled containers, out of children’s reach and away from food.
6. Don’t harvest, eat or sell produce until the waiting period on the label has passed.
7. Use integrated pest management, and remember: all pesticides are poisons, not medicines.

A typical list: bathing soap, washing soap, detergent powder and liquid, shampoo, toothpaste, dishwashing bar or liquid, bleaching powder, phenyl and toilet cleaner (acid), glass cleaner (ammonia), hand sanitizer; and natural ones: reetha, wood ash, lemon.
Effects: soap is biodegradable and does little lasting harm. Detergents can foam and pollute rivers, and their phosphates feed algae that choke lakes and kill fish. Bleach and strong acid or alkali cleaners can harm water life and, mixed together, give off poisonous gases (never mix bleach with acid or ammonia cleaners). Plastic packets and bottles add to plastic waste. Natural cleaners do almost no harm.

Soap is made by saponification. Vegetable oil or animal fat is heated with sodium hydroxide solution, stirring, until it forms a thick paste; the fat breaks down into soap (the sodium salt of its fatty acids) and glycerol:
fat + sodium hydroxide → soap + glycerol, e.g.
$$(\text{C}_{17}\text{H}_{35}\text{COO})_3\text{C}_3\text{H}_5 + 3\text{NaOH} \rightarrow 3\text{C}_{17}\text{H}_{35}\text{COONa} + \text{C}_3\text{H}_5(\text{OH})_3$$
Common salt is added, which makes the soap separate as a solid (salting out). The mixture is filtered: the soap stays on the filter paper, and the filtrate contains glycerol. The soap is pressed into molds, left to set, and can have perfume and color added.

A detergent is a synthetic cleaning substance made from petroleum hydrocarbons; it cleans like soap and also works in hard water (a soapless soap). Examples: sodium lauryl sulphate, sodium alkylbenzene sulphonate.

Health: it can dry and irritate the skin, cause rashes and burns with long contact, irritate the eyes, and it is harmful if swallowed (keep washing powder away from small children).

Environment: older detergents didn’t break down and made rivers foam; modern ones mostly biodegrade, but the phosphates in washing powder fertilize algae, which cover lakes and use up the oxygen fish need; detergent foam also harms the gills of fish and the soil’s microbes. It fades clothes.

My argument: detergents are useful, especially in hard water, so we needn’t stop using them; but we should use the amount on the packet (more doesn’t clean better), choose phosphate-free products, and let the wastewater go to a soak pit or treatment plant, not straight into a river or field.

1. Train the farmers in integrated pest management: use chemicals only when really needed, the right one, in the right amount.
2. Use bio-pesticides and plant sprays: neem, jholmal, garlic and chilli; Bt and Trichoderma.
3. Use traps: yellow sticky cards, pheromone and light traps.
4. Protect natural enemies: ladybirds, spiders, frogs and birds.
5. Use good farming habits: crop rotation, mixed cropping, resistant varieties, removing diseased plants, clean seed.
6. Move towards organic farming with compost and farmyard manure; organic vegetables also sell for more.
7. Where pesticides must be used: protective clothing, safe storage, and keeping to the waiting period before harvest.
8. Ask the local government to arrange pesticide-residue testing and health checks, and awareness programs.

Chemical pollution is the spoiling of air, water and soil by harmful chemicals: pesticides, fertilizers, detergents, industrial wastes, plastics, fumes and smoke.

Effects: diseases in people (poisoning, skin and breathing problems, cancers, waterborne diseases); death of fish, bees, birds and useful soil life; biomagnification of persistent chemicals in food chains; loss of soil fertility; algae choking lakes; acid rain and global warming from gases; upset ecosystems.

Practical ways to reduce it: use fewer pesticides (IPM, bio-pesticides); use compost and manure with fertilizers only as advised; use the right amount of detergent and choose phosphate-free; send wastewater to soak pits or treatment plants; sort, reduce, reuse and recycle waste; never burn plastic; treat factory waste before releasing it; and raise awareness.

(A model answer; write about what you see in your own area.)

What is seen: cement dust from construction sites and open sacks blowing into the air; broken glass and ceramics thrown on roadsides and in rivers, cutting people and animals; plastic bags and bottles blocking drains and floating in rivers, and burnt in heaps, giving off toxic smoke; fertilizer washing into ponds, making them green with algae; soapy water from homes and washing places flowing into streams, with foam.

Causes: careless dumping, no separate collection of waste, burning of rubbish, overuse of fertilizer, drains that go straight to the river, and lack of awareness.

Management: sort waste at home (organic, recyclable, other); compost organic waste; sell plastics, glass and metal to the kabadi for recycling; keep cement covered and sprinkle water on construction sites; use fertilizers on expert advice and add compost; build soak pits for wastewater; never burn plastic; and ask the municipality for regular collection and proper landfill sites.