Chapter 10 — Soil Pollution

Soil is the loose upper layer of the Earth's crust in which plants grow. It is not merely crushed rock; it is a mixture of four things. Mineral particles, about 45 per cent by volume, are sand (coarse, 0.05 to 2 mm), silt (fine) and clay (finest, below 0.002 mm), derived from the weathering of rock; their proportions give the soil its texture, sandy, loamy or clayey. Organic matter, 1 to 5 per cent, is the remains of plants and animals in every stage of decay, ending as the dark, sticky humus that gives topsoil its colour and fertility. Water, about 25 per cent, fills the smaller pores and carries dissolved minerals to roots. Air, about 25 per cent, fills the larger pores and supplies oxygen to roots and soil animals. To these must be added the living organisms: bacteria, fungi, actinomycetes, algae, protozoa, nematodes, mites, springtails, ants, termites, earthworms, and the roots of plants. A gram of fertile soil holds several thousand million bacteria.

Soil forms by weathering: rock is broken by heat and cold, by water and ice, by wind and by the roots and acids of lichens and plants, into smaller and smaller particles, and these are mixed with organic matter by plants, animals and microbes. The process is slow. Under Indian conditions it takes roughly 200 to 1,000 years to form 2.5 centimetres of topsoil. Soil is thus a resource that is renewable only over centuries, in effect non-renewable within a human lifetime.

A vertical cut through soil shows its profile of layers or horizons. The O horizon is the surface litter of leaves and dead matter. The A horizon or topsoil, dark with humus and full of roots and organisms, is the fertile layer, usually 10 to 30 cm deep. The B horizon or subsoil is lighter in colour, with less organic matter and more clay and minerals washed down from above. The C horizon is weathered parent rock, and below it is the bedrock. Nearly all the life and fertility is in the topsoil, so it is the loss or poisoning of the topsoil that matters.

The soils of Andhra Pradesh are of several kinds: the fertile alluvial soils of the Krishna and Godavari deltas; the black cotton soils of Guntur, Prakasam and Kurnool, rich in clay, that swell when wet and crack when dry; the red soils of Rayalaseema and the uplands, formed from granite, low in humus and nitrogen; the laterite soils of the Eastern Ghats; and the coastal sandy and saline soils. Each responds differently to pollution: clay soils hold pollutants tightly, sandy soils let them leach down to groundwater.

Soil performs services on which we depend: it grows almost all our food, fibre and timber; it filters and stores rainwater and feeds springs and wells; it decomposes wastes and recycles nutrients; it stores more carbon than all the world's forests; it is the home of a quarter of all known species; and it is the foundation on which we build. Pollution damages every one of these services.

Soil pollution (soil contamination) is the presence in soil of substances, or of natural substances in abnormal amounts, that reduce its fertility, harm the organisms living in it, endanger the plants, animals and people that depend on it, or pass into water and air. More broadly, soil degradation includes any decline in the quality of soil: pollution by chemicals, but also erosion, salinisation, water-logging, compaction and loss of organic matter. This chapter uses soil pollution in the broad sense that the Andhra Pradesh syllabus gives it, covering both chemical contamination and physical degradation.

The pollutants of soil fall into a few groups. Agricultural chemicals: the excess of chemical fertilisers, pesticides (insecticides, fungicides, herbicides), and the salts they leave. Industrial wastes: heavy metals (lead, mercury, cadmium, chromium, arsenic, nickel), acids and alkalis, cyanides, phenols, dyes, solvents, fly ash from thermal power stations, slag and tailings from mines and smelters. Urban wastes: household garbage, plastics, paper, glass, construction rubble, electronic waste, sewage and sewage sludge, and hospital (biomedical) waste. Petroleum products: leaking oil, grease, petrol and diesel from garages, pipelines and tankers. Radioactive substances: from nuclear tests, accidents, uranium mining and improperly disposed medical and industrial sources. Biological agents: pathogenic bacteria, viruses, protozoa and worm eggs from open defecation, untreated sewage, animal carcasses and slaughterhouse waste. And atmospheric deposition: acid rain, dust from cement plants, and lead from old petrol that settled along roads.

Soil pollutants also differ in how they behave. Biodegradable pollutants such as sewage, food waste, paper and plant residues are broken down by soil organisms and, in moderate amounts, even enrich the soil; they become pollutants only when they arrive faster than decomposers can handle them. Non-biodegradable pollutants such as plastics, glass, heavy metals and many synthetic pesticides are not broken down, or only over decades or centuries; they accumulate, and this is the more serious class. A related distinction is between point sources, a factory outfall, a dump, a leaking tank, which can be traced and controlled, and non-point (diffuse) sources such as fertiliser and pesticide use spread over thousands of fields, which are much harder to control.

Why does soil pollution matter so much? First, unlike air and water, soil does not flow away or disperse; a pollutant deposited in soil stays there and accumulates. Second, soil is the base of the land food chain, so what enters the soil enters the crop and then the animal and the person who eats it. Third, polluted soil pollutes water, as rain leaches pollutants into wells and rivers, and air, as dust and volatile chemicals rise from it. Fourth, cleaning polluted soil is far more difficult and costly than cleaning water. Prevention is therefore the only sensible policy.

The following topics take the sources one by one, beginning with agriculture, the largest diffuse source in a state where most land is farmed.

Chemical fertilisers, urea, diammonium phosphate, muriate of potash and the NPK complexes, were the second pillar of the Green Revolution and remain essential for high yields. They become pollutants when they are used in excess, in the wrong balance, or without organic matter, and all three are common in Andhra Pradesh, where cheap subsidised urea is applied far above the recommended dose and the N:P:K ratio in many districts is 8:3:1 instead of the recommended 4:2:1.

The effects on the soil are several. Loss of organic matter and structure. A field fed only with chemicals receives no humus; the existing humus is burnt up by the microbial activity that nitrogen stimulates; the soil loses its crumb structure, becomes hard, compact and poorly aerated, holds less water and erodes more easily. Continuous fertiliser-only rice-wheat cropping in Punjab has reduced soil organic carbon by a third. Acidification. Ammonium fertilisers such as ammonium sulphate and urea release hydrogen ions as the ammonium is converted to nitrate; the soil becomes acidic, aluminium and manganese become soluble and toxic to roots, and calcium and magnesium are leached away. Salt accumulation. Every fertiliser is a salt, and in dry areas with little leaching the salts build up in the topsoil, raising its osmotic pressure so that roots cannot take up water; muriate of potash also adds chloride, which harms tobacco, grapes and citrus. Micronutrient imbalance. Heavy doses of NPK raise yields and remove zinc, iron, boron and sulphur faster than they are replaced, so that deficiencies of zinc in rice and of sulphur in oilseeds are now widespread; phosphate fertiliser also locks up zinc. Damage to soil life. High salt and acidity kill earthworms, reduce nitrogen-fixing bacteria and mycorrhizal fungi (which the plant no longer needs when phosphorus is abundant), and shift the microbial community. Toxic impurities. Rock phosphate, from which phosphatic fertilisers are made, contains cadmium, fluoride and traces of uranium, which accumulate in soil after decades of application; cadmium enters rice and wheat grain.

The effects reach beyond the field. Nitrate not taken up by the crop, often half of what is applied, leaches into groundwater; nitrate in well water above 45 mg per litre causes methaemoglobinaemia ('blue baby syndrome') in infants and is linked to stomach cancer, and wells in the intensively farmed areas of Guntur and Krishna districts exceed this limit. Nitrogen and phosphorus run off into tanks, lakes and rivers and cause eutrophication: dense growth of algae and water hyacinth, followed by decay that exhausts the oxygen and kills fish; Kolleru lake receives such runoff from thousands of hectares of rice and fish ponds. Fertilised soil releases nitrous oxide, a greenhouse gas about 300 times as powerful as carbon dioxide, and ammonia that adds to air pollution and acid rain. Excess nitrogen also makes plants soft and sappy and more attractive to sucking pests and fungal diseases, which then need pesticides.

The remedy is not to abandon fertilisers but to use them correctly: soil testing and the Soil Health Card, balanced NPK with micronutrients, split doses of nitrogen timed to the crop's demand, placement near the root rather than broadcasting, neem-coated or slow-release urea, combination with manures and green manures, legumes in the rotation, and biofertilisers, the whole approach called integrated nutrient management. Andhra Pradesh's natural farming programme goes further, replacing purchased fertiliser with farm-made inputs on several lakh hectares.

Pesticides are chemicals used to kill organisms that damage crops or carry disease: insecticides against insects, fungicides against fungi, herbicides (weedicides) against weeds, rodenticides against rats, and nematicides, acaricides and molluscicides. They protect crops and have saved millions from malaria, but most are poisons that do not distinguish the pest from other living things, and a large fraction of every spray, often more than 90 per cent, misses the target and ends in the soil, where it persists.

The chief chemical groups are these. Organochlorines such as DDT, BHC (lindane), aldrin, dieldrin, endosulfan and heptachlor are the most persistent, lasting years to decades in soil, dissolving in fat and accumulating in living bodies; most are now banned or restricted in India, but DDT is still used against malaria mosquitoes and its residues are found in Indian soils, milk and human fat. Organophosphates such as malathion, parathion, monocrotophos, chlorpyrifos and dimethoate break down within weeks but are acutely poisonous to people and animals, acting on the nervous system; monocrotophos, banned in most countries, is still widely sprayed in Andhra Pradesh and is the commonest agent in farmers' poisoning. Carbamates such as carbaryl and carbofuran act similarly. Synthetic pyrethroids such as cypermethrin are less toxic to mammals but deadly to fish and bees. Neonicotinoids such as imidacloprid are absorbed into the plant and harm bees. Herbicides such as 2,4-D, atrazine, paraquat (banned in many countries, still used here) and glyphosate; and fungicides containing copper, mercury (now banned) and various organic compounds.

In soil a pesticide may be degraded by microbes, sunlight and chemical reaction, adsorbed on clay and humus, leached to groundwater, volatilised to air, taken up by plants, or washed off to water bodies. The time taken for half of it to disappear is its half-life: days for some organophosphates, months for atrazine, years for DDT and dieldrin. Persistent pesticides accumulate with repeated spraying, so that soils of cotton and chilli fields in Guntur carry residues of a dozen compounds.

The effects on soil are serious. Pesticides kill non-target soil organisms: earthworms, springtails, predatory mites and beetles, nitrogen-fixing bacteria (Rhizobium, Azotobacter, blue-green algae), nitrifying bacteria and mycorrhizal fungi; a fumigated soil is almost sterile and its fertility collapses. They kill the natural enemies of pests, ladybirds, spiders, parasitic wasps, so that after spraying the pest returns faster than its enemies, a resurgence, and formerly harmless insects become pests. Pests exposed to sub-lethal doses evolve resistance, so that the cotton bollworm that one spray once controlled needed a dozen sprays by the 1990s, driving farmers into debt. Residues taken up by crops enter food; vegetables in Indian markets regularly carry residues above permitted limits. Leached pesticides reach groundwater, and runoff kills fish, frogs and the birds that eat them; the decline of vultures, sparrows and frogs in farm areas is partly due to pesticides. And pesticides poison the people who handle them: sprayers without masks or gloves, farm workers re-entering sprayed fields, and children who play in them; about 200 people die of pesticide poisoning in India every week, by accident or by suicide with the poison that lies in every farmhouse.

The remedy is to spray less and more wisely: integrated pest management, resistant varieties, crop rotation, biological control, pheromone and light traps, neem and other botanical pesticides, spraying only when the pest crosses the economic threshold, choosing the least persistent chemical, correct dose and timing, protective clothing, and safe disposal of containers. Andhra Pradesh's natural farming and the non-pesticidal management movement that began in Punukula village of Khammam district, where the whole village gave up chemical pesticides in 2000 and found its cotton healthier and its debts gone, show that it can be done.

Some pollutants do not stay where they fall. Persistent, fat-soluble chemicals that organisms cannot break down or excrete are taken up from soil and water, stored in body fat, and passed on to whatever eats the organism. Because each animal eats many organisms below it in the food chain over its lifetime, the concentration of the pollutant increases at each step, so that the top predator carries a dose thousands or millions of times higher than the soil or water it came from. This is biomagnification (biological magnification), and the build-up within one organism over its life is bioaccumulation.

The classic case is DDT. In a lake studied in the United States, water contained 0.000003 parts per million (ppm) of DDT; plankton contained 0.04 ppm; small fish 0.5 ppm; large fish 2 ppm; and fish-eating birds such as the grebe and the osprey 25 ppm, an increase of nearly ten million times. The birds did not die outright, but DDT interfered with the calcium in their eggshells, which became so thin that they broke under the incubating parent; the bald eagle, the peregrine falcon and the brown pelican nearly vanished from North America before DDT was banned there in 1972, and their recovery since is the proof. Rachel Carson's book Silent Spring (1962) brought this to the world's notice and started the modern environmental movement. In India, DDT residues in human breast milk in farm districts have been among the highest recorded anywhere, and the Indian vulture population crashed by more than 95 per cent in the 1990s, though in that case the poison was diclofenac, a veterinary drug in the carcasses the vultures ate, another route by which a chemical put into one animal reaches another.

Heavy metals biomagnify too. The most famous case is mercury at Minamata, Japan, where a chemical factory discharged mercury into the bay from the 1930s to the 1960s; bacteria in the sediment converted it to methyl mercury, which passed from plankton to shellfish to fish to the fishing families, who suffered numbness, loss of vision and speech, paralysis, madness and death, and whose children were born deformed. Cadmium from mine wastes in the Jinzu river basin of Japan entered rice and caused itai-itai ('ouch-ouch') disease, in which the bones became so brittle that they broke on coughing. In India, mercury from the thermometer factory at Kodaikanal contaminated soil and the food chain of a hill lake, and chromium from tanneries has entered vegetables around Kanpur and Ranipet.

Biomagnification depends on three properties of the pollutant: it must be persistent, not broken down by organisms; fat-soluble, so that it is stored in tissue rather than excreted in urine; and biologically active, so that it does harm at high concentration. Organochlorine pesticides, polychlorinated biphenyls (PCBs) from old transformers, dioxins from burning plastics, mercury, cadmium and lead have all three. Water-soluble or quickly degraded chemicals, such as most organophosphates, do not biomagnify though they may be acutely poisonous.

The lesson for soil pollution is that a concentration that looks harmless in a soil test may be dangerous by the time it reaches the eagle, the fish-eater, the cow's milk, or the human being at the top of the chain. Human beings, who eat grain, vegetables, milk, eggs, meat and fish, sit at the top of several food chains at once, and it is in our bodies that persistent soil pollutants finally collect. This is why the control of persistent pesticides and heavy metals in soil is a matter of public health and not only of agriculture.

Industry pollutes soil in three ways: by dumping solid wastes on land, by discharging liquid effluents that soak into it, and by releasing gases and dust that settle on it. Andhra Pradesh has heavy industry at Visakhapatnam (steel, petroleum refining, fertiliser, shipbuilding), at the Kakinada and Krishnapatnam ports, in the pharmaceutical belt of Visakhapatnam and the old Hyderabad region, in the paper mills of Rajahmundry, the cement plants of Nalgonda and Kurnool, the thermal power stations at Vijayawada and Nellore, and thousands of small units, and each has its characteristic wastes.

Heavy metals are the most dangerous industrial soil pollutants because they never degrade. Lead comes from battery manufacture and recycling, paints, old petrol and smelters; it damages the nervous system, lowers children's intelligence and causes anaemia. Mercury comes from chlor-alkali plants, thermometers, fluorescent lamps and coal burning; it attacks the brain and kidneys. Cadmium comes from zinc smelting, electroplating, nickel-cadmium batteries and phosphate fertiliser; it damages the kidneys and bones. Chromium, especially the hexavalent form, comes from tanneries, electroplating and dye works; it causes ulcers and cancer; the tanneries of Ranipet in Tamil Nadu have left a hill of chromium sludge that has poisoned wells for kilometres. Arsenic comes from mining, smelting, wood preservatives and some pesticides, and occurs naturally in the groundwater of the Ganga basin; it causes skin lesions and cancers. Nickel, copper and zinc from smelting and plating are toxic to plants at high levels. Heavy metals in soil are taken up by crops, especially leafy vegetables and rice, and reach us directly or through milk and meat; they also poison soil microbes and earthworms, so that contaminated land becomes barren.

Acidic and alkaline effluents from chemical plants, textile mills and pickling of steel change the soil pH so severely that nothing grows. Organic chemicals, phenols, solvents, dyes, pharmaceutical intermediates and residues of the drugs themselves, contaminate soil and groundwater around the pharmaceutical units of Visakhapatnam and the Patancheru area; antibiotics in such wastes breed resistant bacteria in the soil. Cyanides from electroplating and gold extraction are acute poisons.

Fly ash from coal-fired thermal power stations is generated in enormous amounts, a 1,000 megawatt station producing about a million tonnes a year; dumped in ash ponds it blows onto surrounding fields, coats leaves, raises the soil pH and adds arsenic, boron, selenium and heavy metals. Fly ash can instead be used in bricks, cement and road building, and a large share of India's fly ash now is. Mining strips the topsoil, piles up overburden and tailings (the crushed rock left after ore extraction, often laden with sulphides that turn to sulphuric acid and heavy metals in rain), and leaves land that cannot be farmed for decades; the iron and manganese mines of the Eastern Ghats, the bauxite proposals in the Visakhapatnam agency, the limestone quarries of Kurnool and the uranium mine at Tummalapalle in Kadapa district, whose tailings pond has been accused of contaminating nearby groundwater with uranium, are examples. Sand mining in river beds of the Krishna and Godavari removes the filter that recharges groundwater and lowers the water table.

Industrial soil pollution is controlled by treatment of effluents before discharge, by secure landfills lined with clay and plastic for hazardous wastes, by recovery and recycling of metals from wastes, by reuse of fly ash and slag, by restoration of mined land through refilling, spreading stored topsoil and planting, and by the enforcement of the Hazardous Waste Rules and the Environment Protection Act by the State Pollution Control Board. In practice enforcement is weak and many units, especially small ones, dump untreated waste on open land, in drains or in abandoned quarries at night.

Every town and city produces a mountain of municipal solid waste: kitchen and food waste, paper and cardboard, plastics, glass, metals, cloth, rubber, leather, garden waste, construction rubble, ash, electronic goods, batteries and much else. An Indian city dweller produces about 0.3 to 0.6 kg a day, and India as a whole about 62 million tonnes a year, of which barely a fifth is treated. Visakhapatnam and Vijayawada each generate around a thousand tonnes a day. Most of it goes to open dumps on the edge of the city, where it is neither covered nor contained.

An open dump pollutes soil in several ways. Leachate, the dark, foul liquid that forms as rain percolates through rotting waste, carries dissolved organic matter, ammonia, salts, heavy metals from batteries and electronics, and pathogens down into the soil and the groundwater; wells near dumps in many Indian cities are unfit to drink. The organic fraction decays without oxygen, producing methane, a greenhouse gas that also causes dump fires, and the smouldering of plastics releases dioxins and furans, among the most toxic and persistent chemicals known, which settle on the soil around. Dumps breed flies, rats, stray dogs and cattle that scavenge and spread disease, and the soil beneath and around them becomes unusable for generations. Construction rubble, though inert, buries fertile land and blocks drainage. Electronic waste, discarded phones, computers and televisions, contains lead, mercury, cadmium, beryllium and brominated flame retardants; when dismantled and burnt by informal recyclers to recover copper and gold, as at Seelampur in Delhi, these poisons enter the soil, the workers and the neighbourhood.

Plastics deserve special attention. Polythene bags, bottles, wrappers, sachets, disposable cups and plates, and the thin film of multi-layer packaging are non-biodegradable: a polythene bag may last 500 years in soil. India generates about 3.5 million tonnes of plastic waste a year, much of it single-use. In soil, plastic blocks the movement of water and air, prevents seeds from germinating and roots from growing, and is eaten by cattle, whose stomachs fill with bags until they starve; hundreds of cows die this way every year in Indian cities. Plastic waste clogs drains and causes floods, chokes rivers and reaches the sea, where turtles, fish and sea birds die of it. Under sunlight and abrasion plastics break into microplastics, particles below 5 mm, which are now found in farm soils (partly through the sewage sludge and compost applied to them), in earthworms, in vegetables, in drinking water, in salt and in human blood. Burning plastic in the open, the commonest disposal in villages, releases dioxins, furans and heavy metals into air and soil.

The management of solid waste rests on segregation at source, separating wet (biodegradable) waste, dry (recyclable) waste and hazardous waste in the home, which the Solid Waste Management Rules of 2016 make compulsory. Wet waste is composted or converted to biogas; dry waste is recycled; the remainder goes to a sanitary landfill with a lined base, leachate collection and daily soil cover, not an open dump. The principle is reduce, reuse, recycle: refuse single-use plastic, carry a cloth bag and a steel bottle, repair rather than replace, and buy less. India banned certain single-use plastic items in 2022 and Andhra Pradesh has phased out plastic carry bags below a set thickness in several cities. Extended producer responsibility makes manufacturers responsible for collecting their packaging. Cities such as Indore and, in Andhra Pradesh, Visakhapatnam and Tirupati have shown that door-to-door collection of segregated waste, decentralised composting and recycling can keep almost everything out of the dump.

Not all soil pollution is chemical. Soil can be polluted by living organisms, the bacteria, viruses, protozoa and parasitic worms that cause disease, and their chief sources are human and animal excreta, untreated sewage and the wastes of hospitals and slaughterhouses.

Open defecation was practised by more than half the rural population of India until recently, and though the Swachh Bharat programme has built tens of millions of toilets since 2014, it has not ended everywhere. Human faeces deposited in fields and along paths carry the eggs of roundworm (Ascaris), hookworm, whipworm and tapeworm, the cysts of Entamoeba and Giardia, and the bacteria and viruses of cholera, typhoid, dysentery, hepatitis A and polio. Roundworm eggs survive in soil for years; hookworm larvae hatch in warm moist soil and enter the body through the bare feet of the people who walk on it, causing anaemia that stunts children's growth. Flies carry the germs from the soil to food; rain washes them into wells and tanks; vegetables grown in such soil and eaten raw carry them to the table. Hookworm and roundworm infections remain among the commonest diseases of Indian children, and they are diseases of polluted soil.

Sewage, the waste water of houses, is often discharged untreated into drains that end in fields, low ground or rivers, and sewage sludge, the solid residue of treatment plants, is spread on land. Both contain pathogens, and both contain heavy metals, detergents, pharmaceutical residues and, increasingly, microplastics, because industrial and domestic wastes enter the same drains. Sewage farming, the irrigation of vegetables with raw sewage, is practised around most Indian cities; the vegetables grow lushly on its nitrogen and phosphorus but carry worm eggs, bacteria and heavy metals. Properly treated sewage and composted sludge, by contrast, are a valuable source of water and nutrients, and the answer is treatment, not prohibition.

Biomedical waste from hospitals, clinics, laboratories and veterinary centres includes used syringes and needles, dressings soaked in blood, body parts, cultures of pathogens, expired drugs, and radioactive and chemical wastes. About 15 per cent of hospital waste is infectious or hazardous. When it is dumped with ordinary garbage, as it often is, it exposes waste pickers, children and animals to hepatitis B, hepatitis C, HIV and tetanus, and it pollutes soil with drugs and disinfectants. The Biomedical Waste Management Rules require segregation into colour-coded bags, disinfection by autoclaving or chemicals, incineration of infectious waste at high temperature, shredding of plastics and needles, and deep burial of anatomical waste in secure pits, all done through licensed common treatment facilities.

Animal wastes add to the load. Slaughterhouse waste, carcasses of dead animals left in the open, poultry litter and the dung of large dairies carry Salmonella, E. coli, anthrax spores (which survive in soil for decades) and worm eggs, and overwhelm the soil's capacity to decompose them. Antibiotics fed to poultry and cattle pass out in their dung and breed antibiotic-resistant bacteria in the soil, which then reach people; this is one of the most serious emerging health threats.

Biological soil pollution is controlled by sanitation: toilets and their proper use, sewage treatment, safe disposal of sludge, composting of animal wastes at high temperature that kills pathogens, rendering of carcasses, proper biomedical waste management, and the simple practices of washing hands, wearing footwear and washing raw vegetables. The Swachh Bharat campaign is, at bottom, a campaign against the biological pollution of soil.

Three further sources of soil pollution are less widespread than farm and city wastes but are among the most serious where they occur.

Petroleum products. Crude oil, petrol, diesel, kerosene, lubricating oil and grease enter soil from leaking storage tanks and pipelines, from spills at refineries, ports and railway sidings, from the washing of tankers and engines, from the used oil that garages pour on the ground, and from oil spills at sea that wash onto beaches, as happened on the Chennai coast in 2017. Oil coats soil particles, filling the pores and making the soil water-repellent, so that neither water nor air can enter and roots suffocate; a heavily oiled soil is black, sticky and dead. Its hydrocarbons are toxic to seeds, seedlings and soil animals; the lighter fractions evaporate but the heavy ones persist for years; and benzene, toluene and polycyclic aromatic hydrocarbons leach into groundwater, where a single litre of petrol can make a million litres of water undrinkable. Used engine oil also carries lead, cadmium and zinc. Oil pollution is prevented by double-walled tanks, leak detection, bunds around storage, collection and re-refining of used oil, and is treated by removing the soil, or by bioremediation, spreading nutrients and oil-degrading bacteria such as Pseudomonas (the 'oil-zapper' developed in India) that consume the hydrocarbons within months.

Radioactive substances. Radioactive isotopes emit radiation that damages living cells and causes cancer and genetic defects, and they remain dangerous for the time of their half-lives, from days to thousands of years. They enter soil from nuclear weapons tests (the strontium-90 and caesium-137 from the atmospheric tests of the 1950s and 1960s are still in soils worldwide), from accidents at nuclear power plants (Chernobyl in 1986 contaminated farmland across Europe; the Fukushima accident of 2011 made hundreds of square kilometres of Japanese farmland unusable), from the mining and milling of uranium (the tailings at Jaduguda in Jharkhand and Tummalapalle in Andhra Pradesh), from the disposal of radioactive wastes of power plants and reprocessing, and from carelessly discarded medical and industrial sources such as the cobalt-60 that killed a scrap dealer in Delhi in 2010. Strontium-90 behaves like calcium and enters bones through milk; caesium-137 behaves like potassium and enters all tissues; iodine-131 concentrates in the thyroid. Plants take them up from soil and pass them to grazing animals and to us. Radioactive contamination cannot be neutralised; it can only be contained and left to decay, so radioactive wastes must be sealed in glass or concrete and stored in deep, stable rock, and contaminated soil must be removed and stored. Natural radioactivity is also present in some soils: the monazite sands of the Kerala and Andhra coasts contain thorium, and granite areas release radon gas.

Acid rain. Sulphur dioxide from coal-burning power stations and smelters, and nitrogen oxides from vehicles and furnaces, dissolve in atmospheric moisture to form sulphuric and nitric acids that fall as acid rain, snow, fog or dry deposition, sometimes hundreds of kilometres from the source. Acid rain acidifies the soil, lowering its pH; it dissolves and leaches away the calcium, magnesium and potassium that plants need; it releases aluminium from clay minerals, which poisons roots and kills the fine root hairs and mycorrhizal fungi; it kills soil bacteria and earthworms and slows decomposition; and it mobilises heavy metals such as cadmium and mercury already in the soil, so that they enter crops and water. Forests in Europe and North America died over large areas in the 1970s and 1980s from acid rain, and lakes lost their fish. In India the soils around thermal power stations and the industrial belts of Singrauli, Korba and Angul show acidification, and the marble of the Taj Mahal is corroded by the same acids. The black cotton soils of Andhra Pradesh, being alkaline and rich in calcium carbonate, buffer acid rain well, but the red and laterite soils of the uplands, already acidic and poor in calcium, do not. Acid rain is controlled at its source by desulphurisation of flue gases, low-sulphur fuels, catalytic converters in vehicles and cleaner energy, and its effect on soil can be corrected by liming, the addition of calcium carbonate or dolomite.

Irrigation has doubled and trebled the yields of the Krishna and Godavari deltas and the Nagarjuna Sagar and Tungabhadra commands, but irrigation without drainage slowly destroys the very soil it waters, through two linked processes that together affect about seven million hectares in India.

Water-logging occurs when more water is applied to the land than drains away, or when seepage from unlined canals raises the water table until it reaches the root zone, within a metre or so of the surface. The pores of the soil fill with water and the air is driven out. Roots and soil organisms cannot get oxygen; roots rot, nitrogen is lost as gas by denitrification, toxic compounds of iron, manganese and sulphide form, and the soil becomes cold and sticky and impossible to plough. Rice tolerates it; almost every other crop fails. Water-logging is worst in flat, clayey command areas with heavy canal irrigation and no field drains, such as parts of the Nagarjuna Sagar left bank canal command in Guntur and Prakasam districts, the tail ends of the delta, and the Indira Gandhi canal areas of Rajasthan.

Salinisation follows. All irrigation water, even good river water, contains dissolved salts, typically 200 to 500 milligrams per litre, and groundwater far more. Plants take up the water and leave the salts behind. In a region with enough rain and good drainage the salts are washed down below the roots each monsoon; in dry regions with poor drainage they accumulate. Where the water table is high, capillary action draws salty water up to the surface, it evaporates in the sun, and the salts are left as a white crust, the reh or usar of north India, the chowdu soils of Andhra Pradesh. A saline soil has an excess of soluble salts, mostly chlorides and sulphates of sodium, calcium and magnesium; its high osmotic pressure prevents roots from absorbing water even when the soil is wet, so plants wilt, their leaf tips burn, and germination fails. A sodic (alkaline) soil has an excess of sodium on its clay particles; the clay disperses, the soil becomes structureless, sealing when wet and setting hard as brick when dry, with a pH above 8.5 that makes iron, zinc and phosphorus unavailable. Coastal soils suffer a third form, the intrusion of seawater into groundwater when wells are over-pumped, and the flooding of fields by cyclone surges, as after the 1977 Diviseema cyclone and the 2014 Hudhud cyclone, which left thousands of hectares saline.

The signs are unmistakable: white crusts on the surface in the dry season, patches where nothing grows, salt-tolerant weeds, stunted crops with scorched leaf margins, and yields falling year by year. Over 20 per cent of the world's irrigated land is affected, and ancient Mesopotamia, the first irrigated civilisation, was ruined by it.

The remedies are drainage and reclamation. Drainage comes first: open field drains, buried perforated pipes (subsurface drainage), and lined canals to stop seepage, so that the water table falls and salts can be leached downward. Leaching with good-quality water flushes the salts out of saline soils once drainage exists. Gypsum (calcium sulphate) is applied to sodic soils; its calcium replaces the sodium on the clay, which is then leached away, and the soil regains its structure; pyrite and sulphur work similarly by forming acid. Organic matter, green manuring with dhaincha, and growing salt-tolerant crops and varieties (barley, rice varieties bred for salinity, date palm, casuarina, prosopis) help reclamation. Above all, prevention: irrigating only as much as the crop needs, by drip or sprinkler rather than flooding, using the conjunctive use of canal and well water so that the water table is kept down, and not extending canal irrigation without providing drainage at the same time.

The most widespread damage to soil is not chemical at all: it is the physical loss of the topsoil itself. Soil erosion is the removal of soil by water, wind, ice or gravity faster than it forms. India loses about 5,300 million tonnes of soil a year, roughly 16 tonnes from every hectare, and with it the nutrients of billions of rupees of fertiliser; about a third of the country's land is affected. A soil that took a thousand years to form can be washed away in one monsoon.

Water erosion begins with raindrop splash, which detaches particles from bare soil; then sheet erosion removes a thin, almost invisible layer from the whole surface, taking the finest, richest particles first; then runoff concentrates into rills, small channels a few centimetres deep, and finally into gullies, ravines metres deep that cut fields to pieces, as in the Chambal badlands and the ravines along many Deccan streams. Stream-bank erosion eats away river banks and floods carry the soil to the sea; the Krishna and Godavari run brown with the Deccan's topsoil every monsoon and silt up the reservoirs, reducing their storage year by year. Landslides on deforested slopes in the Eastern Ghats and the Himalaya carry away entire hillsides. Wind erosion strips dry, bare, sandy soils in the Thar and in the drought years of Rayalaseema, raising dust storms and burying fields in sand dunes; in the American Dust Bowl of the 1930s, ploughed prairie blew away in clouds that darkened cities a thousand kilometres away.

Erosion is a natural process, but human action multiplies it many times. Deforestation removes the canopy that breaks the rain's force and the roots and litter that hold and absorb it. Overgrazing by too many cattle, sheep and goats strips the grass cover and compacts the soil so that water runs off instead of soaking in. Faulty farming, ploughing up and down the slope, leaving the land bare between crops, burning crop residues, monoculture, and cultivating steep slopes without terraces, invites erosion; the podu shifting cultivation of the Eastern Ghats, once sustainable with long fallows, now erodes the hills because fallows have shortened. Mining, quarrying, road building and construction strip vegetation and leave loose spoil. Over-irrigation and urban sprawl add to it.

Desertification is the end point: the degradation of land in dry and semi-arid regions until it can no longer support crops, grass or trees, and becomes desert. It is caused by the same factors, deforestation, overgrazing, over-cultivation, over-pumping of groundwater, salinisation, and by drought and climate change. About a quarter of India's land shows some degree of desertification, and the Thar advances into the neighbouring districts of Haryana and Rajasthan. In Andhra Pradesh, Anantapur district, with the second-lowest rainfall in the country after Jaisalmer, is the most vulnerable: its red soils have lost their trees and grass cover to grazing and groundnut monoculture, its tanks are silted, its water table has fallen below 200 metres in places, and dust and sand now blow across fields that once bore millets.

The remedies are the practices of soil conservation. Vegetative cover: afforestation and social forestry on hill slopes and wastelands, shelter belts and windbreaks of trees across the wind, grass cover on bunds, and cover crops and mulches that keep the soil surface covered between crops. Contour farming: ploughing, sowing and bunding along the contour so that each furrow holds water, and strip cropping of alternating close-growing and row crops across the slope. Terracing of steep slopes into level steps, as the hill tribes of the Eastern Ghats and the Himalaya have done for centuries. Gully control with check dams, brushwood and planting. Controlled grazing and stall feeding of animals. Conservation tillage, leaving crop residues on the surface instead of burning them and ploughing as little as possible. Watershed management that treats the whole catchment. And the stabilisation of sand dunes with grasses and shrubs. These not only stop erosion but raise groundwater, restore pastures and bring back a second crop, as the watershed villages of Anantapur and the Ralegan Siddhi example of Maharashtra have shown.

Because soil is alive, the first victims of soil pollution are the organisms that live in it, and because those organisms make the soil fertile, their loss is felt by every plant and, through plants, by every animal.

Effects on soil organisms. A healthy gram of topsoil holds thousands of species of bacteria and fungi, and a square metre holds hundreds of earthworms and thousands of arthropods; together they decompose litter, release nutrients, fix nitrogen, build the crumb structure and control pests and diseases. Pesticides, heavy metals, acids, salts, oil and radiation kill or inhibit them. Fumigants and broad-spectrum insecticides kill earthworms outright; copper fungicides accumulate and sterilise vineyard soils; heavy metals at quite low concentrations stop nitrogen fixation by Rhizobium and Azotobacter and the nitrification that converts ammonium to nitrate; acidity and salinity kill earthworms and change the microbial community to acid- or salt-tolerant species that do less useful work. Antibiotics from animal manures and sewage select resistant bacteria. When the decomposers die, litter piles up undecomposed, nutrients are not recycled, the soil loses its structure and compacts, and the soil food web that keeps pests and pathogens in check collapses. A polluted soil is often a silent soil, without the earthworm casts, the ant hills and the termite mounds of a living one.

Effects on plants. Plants suffer both from the loss of soil life and directly from the pollutants. Reduced fertility and poor structure starve and suffocate roots. Salts prevent water uptake, causing wilting and leaf scorch; sodicity seals the soil and locks up nutrients. Acidity releases aluminium and manganese that stunt roots and cause yellowing. Heavy metals are taken up in place of nutrients: cadmium in place of zinc, lead and arsenic in place of phosphorus; they inhibit photosynthesis, enzymes and root growth, produce chlorosis and necrosis of leaves, and reduce yield, and they accumulate in leaves, roots and grain to levels dangerous to the eater. Herbicide residues and drift damage the following crop and neighbouring fields, as when 2,4-D from a rice field curls the leaves of cotton nearby. Oil kills seedlings and prevents germination. Excess nitrogen gives lush, weak growth prone to lodging, pests and disease. Fluoride from fertiliser and industry causes leaf tip burn, and boron from fly ash is toxic beyond a narrow range. Pollutants also reduce germination, seedling survival, nodulation in legumes and mycorrhizal colonisation, so that a polluted soil produces less and needs more inputs, a spiral that ends in abandonment.

The effects extend to natural vegetation: acid rain and heavy metals have killed forests around smelters; salinisation kills mangroves and orchards; erosion removes the seed bank and the soil in which regrowth could occur. And they extend in time, because most pollutants are persistent and their effects last for decades.

Pollution indicators. Some organisms show the state of the soil. Earthworms, sensitive to pesticides, metals, acidity and salt, are the best-known bioindicator: their number and diversity fall sharply in polluted soil. Lichens on trees and rocks record air-borne pollution. Salt-loving weeds such as Suaeda mark saline patches; parthenium and Cassia mark disturbed, degraded land; and the absence of nodules on legume roots reveals a soil whose Rhizobium has been killed. Soil enzyme activity, respiration (carbon dioxide release) and the rate at which a buried cotton strip decays are measured by scientists as indices of soil health. A farmer needs none of these instruments; the smell of a fresh-turned, earthy, crumbly soil full of worms tells the same story.

Everything that grows in polluted soil carries the pollution onward, and the animals and people at the end of the chain suffer the accumulated dose.

Effects on animals. Grazing animals eat the pollutants on and in the plants and the soil they swallow with them: cattle grazing near a smelter or on fly-ash-coated pasture take in lead, cadmium and fluoride, developing lameness, mottled teeth (fluorosis), poor growth and low milk yield, and passing the metals into their milk. Pesticide-treated fodder and sprayed fields poison cattle and goats; grazing in freshly sprayed cotton fields kills sheep every season. Plastic swallowed with garbage kills cows, and polythene fills the stomachs of the deer and monkeys around picnic sites. Earthworms, insects and the birds that eat them, frogs, lizards and snakes decline in sprayed fields, and the loss of insects removes the food of insectivorous birds; the sparrow, once everywhere, has almost vanished from farm areas. Pesticides and heavy metals washed from soil into ponds kill fish and frogs, and DDT and the veterinary drug diclofenac reduced eagles, falcons and vultures by biomagnification. Anthrax spores in soil kill cattle decades after an infected carcass was buried. Wild animals lose habitat as land is eroded, salinised and dumped upon.

Effects on human health. Human beings meet soil pollution by four routes: eating crops, milk, eggs, meat and fish grown on or fed from polluted soil; drinking groundwater into which pollutants have leached; breathing dust and vapours from polluted soil and burning waste; and direct contact, through bare feet, hands and children's play. The diseases that follow are these. Pesticides cause acute poisoning (vomiting, convulsions, respiratory failure) in sprayers and in accidental and deliberate ingestion, and chronic effects: cancers, particularly lymphoma and leukaemia, damage to the nervous system, infertility, birth defects and the endocrine disruption now linked to organochlorines; the cluster of deformed children among cashew-plantation families sprayed with endosulfan from the air in Kasaragod, Kerala, led to its ban. Nitrate in well water causes blue baby syndrome. Heavy metals: lead lowers children's intelligence and causes anaemia and kidney damage; mercury causes Minamata disease; cadmium causes kidney failure and itai-itai bone disease; arsenic causes skin lesions and cancers of skin, lung and bladder; chromium causes ulcers and lung cancer; and fluoride from fertiliser, fly ash and naturally fluoride-rich groundwater causes the dental and skeletal fluorosis that cripples people in Nalgonda, Prakasam and Anantapur districts. Biological pollutants cause worm infestations, anaemia, diarrhoea, cholera, typhoid, hepatitis and tetanus, the diseases that still kill Indian children in their thousands. Dioxins from burning plastic waste cause cancer and birth defects. Radioactive contamination causes leukaemia and thyroid cancer, as after Chernobyl. And beyond disease, polluted and eroded soil means less food and poorer food: crops low in zinc and iron from exhausted soils are one cause of the anaemia and stunting of Indian children, and the loss of farmland pushes families into poverty and migration.

Children are most at risk, because they eat, drink and breathe more for their size, play on the ground, put things in their mouths, and their brains and bodies are still developing; lead, mercury and pesticides do their worst damage before the age of five. Farm workers, waste pickers, tannery and battery workers and the poor who live beside dumps and factories carry the heaviest burden. Soil pollution is thus a question of justice as well as health.

The connection between soil and health was known to the ancients, who chose the sites of cities by the quality of their soil and water, and it is written into the modern idea of One Health: that the health of soil, plants, animals and people is a single system, and that we cannot poison one part and keep the rest healthy.

Soil pollution can be prevented far more easily than it can be cured, and most of the means are already known and in use somewhere in Andhra Pradesh. They fall under two heads: how we farm, and how we deal with waste.

Sustainable farming. The first step is integrated nutrient management: a soil test before fertilising, balanced NPK with micronutrients in the recommended dose and no more, nitrogen in split applications timed to the crop, farmyard manure, compost and vermicompost to restore organic matter, green manuring with dhaincha and sunn hemp, legumes in rotation, and biofertilisers such as Rhizobium, Azolla and phosphate-solubilising bacteria. The second is integrated pest management: resistant varieties, crop rotation and intercropping, trap crops and pheromone traps, biological control with Trichogramma and ladybirds, botanical pesticides from neem, and chemical sprays only when the pest crosses the economic threshold, choosing the least persistent chemical, applying it correctly and never near water. Persistent organochlorines are banned; the most toxic organophosphates such as monocrotophos should follow. The third is organic and natural farming, which the state promotes through its community-managed natural farming programme on several lakh hectares, replacing purchased chemicals with jeevamrutham, mulching and diversity; and the fourth is soil and water conservation: contour bunds, mulches, cover crops, conservation tillage, drip and sprinkler irrigation, drainage of irrigated land, and gypsum for sodic soils. Crop residues should be composted or incorporated, never burnt, and plastic mulch films and pesticide containers collected, not left in the field.

Waste management rests on the hierarchy reduce, reuse, recycle, recover, dispose. Reduce: buy less, refuse single-use plastic, use cloth bags and refillable bottles. Reuse: containers, clothes, repaired goods. Recycle: paper, glass, metal, and the plastics that can be, through segregation at source and the informal recyclers who handle most of India's recycling. Recover: composting and vermicomposting of wet waste in homes, apartments, markets and village compost yards, and biogas from food waste, dung and sewage, which turns a pollutant into fuel and manure. Dispose: only the residue, in a sanitary landfill with liner, leachate treatment, gas collection and cover, never an open dump. Sewage must be treated in sewage treatment plants, and treated water and composted sludge reused on land. Industrial wastes must be treated at source, hazardous wastes sent to secure landfills or incinerators, heavy metals recovered, fly ash and slag used in bricks and roads, and mined land restored. Biomedical waste goes to licensed treatment facilities. Electronic waste goes to authorised recyclers, not to backyard burners. And used oil, batteries and paint tins must be returned to collection points.

Cleaning up polluted soil is possible but expensive. Contaminated soil may be excavated and treated or landfilled; washed with water or solvents; heated to drive off organics; or stabilised with lime, cement or clay so that metals do not leach. The gentlest and cheapest methods are biological. Bioremediation uses microbes to break down pollutants: oil-degrading Pseudomonas and the Indian 'oil-zapper' consortium clean oil spills and refinery sludge; bacteria and fungi degrade many pesticides; composting destroys many organic pollutants. Phytoremediation uses plants: Indian mustard, sunflower and the fern Pteris vittata take up lead, cadmium and arsenic from soil into their shoots, which are then harvested and safely disposed of; vetiver grass stabilises polluted slopes and tailings; water hyacinth, for once useful, absorbs metals from polluted water; and trees planted on dumps and mine spoil rebuild the soil over decades. Mycoremediation uses fungi that digest oil and pesticides. These methods are slow, taking years, but they restore the soil's life rather than merely removing the pollutant.

None of this works without knowledge: farmers who understand what a soil test means, citizens who segregate their waste, and officials who enforce the rules. Education, of which this chapter is a part, is itself a means of control.

Soil belongs to no single generation, and its protection is written into law and into the duties of citizens.

Laws and rules. India has no single soil protection act, but soil is covered by several. The Environment (Protection) Act, 1986, passed after the Bhopal disaster, gives the central government power to set standards and control pollution of any kind, and under it are framed the Hazardous and Other Wastes Rules (2016), the Solid Waste Management Rules (2016), the Plastic Waste Management Rules (2016, amended 2022 to ban selected single-use items), the Bio-Medical Waste Management Rules (2016), the E-Waste Rules (2022), the Construction and Demolition Waste Rules and the Fly Ash Notification that requires its use. The Water (Prevention and Control of Pollution) Act, 1974 created the Central and State Pollution Control Boards, which license industries and monitor effluents that would otherwise reach soil; the Air Act, 1981 controls the emissions that fall as acid rain and dust. The Insecticides Act, 1968 registers and can ban pesticides; DDT (for agriculture), BHC, aldrin, endosulfan and others have been banned under it, and a list of hazardous pesticides is under review. The Fertiliser Control Order fixes quality and composition. The Forest (Conservation) Act, 1980 restricts the diversion of forest land that would expose soil to erosion. The Mines and Minerals Act requires mine closure plans and restoration. The Constitution itself, in Article 48A, directs the state to protect the environment, and in Article 51A(g) makes it the fundamental duty of every citizen to protect and improve the natural environment. The National Green Tribunal, set up in 2010, hears environmental cases, and the Supreme Court has applied the polluter pays principle, under which the polluter must bear the cost of cleaning up, in cases such as the tanneries of Tamil Nadu.

Institutions and programmes. The State Pollution Control Board inspects industries and dumps; the Department of Agriculture runs soil-testing laboratories and the Soil Health Card scheme that gives every farmer a nutrient report and recommendation; the Krishi Vigyan Kendras and Acharya N. G. Ranga Agricultural University train farmers; the state's community-managed natural farming programme reaches lakhs of farmers; the Swachh Bharat mission built toilets and set up waste collection; watershed and MGNREGA works build bunds, farm ponds and check dams; and the Forest Department runs afforestation. Internationally, the United Nations Convention to Combat Desertification, which India hosted in 2019, sets the goal of land degradation neutrality, restoring as much land as is degraded, and India has pledged to restore 26 million hectares by 2030. The World Soil Day on 5 December reminds everyone of the soil.

The citizen's role. Laws are only as good as the people who follow them, and much of soil pollution is the sum of small individual acts. Every student and family can: segregate waste into wet, dry and hazardous and hand it to the collection system; compost kitchen and garden waste at home; refuse single-use plastics and carry a cloth bag and a bottle; never burn waste, leaves or crop residues in the open; return batteries, electronic goods, medicines and used oil to collection points and never throw them on the ground; use pesticides in the garden sparingly or not at all; plant and protect trees; keep the neighbourhood, school and village clean; use toilets and see that everyone can; save water; and speak up, to the panchayat, the municipal ward, the pollution control board or the courts, when a factory, a dump or a spray is poisoning the soil. Farming families can adopt soil testing, organic manures, IPM and natural farming, and protect their own topsoil with bunds and trees.

The soil that a Class 9 student walks on today was made over thousands of years and will feed people a thousand years hence if it is not destroyed in the next fifty. The lesson of this chapter is that it is ours to keep or to lose, and that keeping it is a daily habit, not a single act.