Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 1 Chapter 3 Water and Soil.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 2 The Earth’s Water  80 percent of Earth’s surface is covered with water  97% of the earth’s water is salt water (oceans)  3% of the earth’s water is fresh water (rivers, lakes, streams)  Only 1% of the fresh water is available for our use  The available fresh water amounts to a generous supply that is continuously collected, purified, recycled, and distributed in the solar-powered hydrologic cycle

Distribution of Water Reservoirs Oceans 97% Atmosphere 0.01% Rivers, Lakes, and Inland Seas 0.141% Soil Moisture 0.0012% Ground Water 0.4 – 1.7% Ice Caps and Glaciers 1.725%

6 The Water Cycle

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 7  Groundwater Available at point of need at little cost  Surface water Usually requires extensive purification  Ocean and brackish waters Costly to desalinate Sources of Freshwater

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 8  Body composition Body, 65% water; blood, 83%; bones, 25% Water loss: 1% thirst; 5% hallucinations; 15% death  Basic requirements for safe water Drinking: 2–3 liters/day Minimum acceptable standard for living (WHO) --20–50 liters/day for cooking and basic hygiene Freshwater Facts

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 9  Vulnerability of surface water to: Drought (not replenished); i.e., lakes, reservoirs Diversion of rivers for agricultural and urban use  Declining groundwater levels Failure to replenish Compaction of aquifers Saltwater intrusion  Surface water pollution from nonpoint sources  Groundwater pollution  Increasing competition for water supplies World’s available freshwater is not distributed evenly Current Water Issues

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 11  Water is essential to life  Our health depends on the quality and safety of water  Every 8 seconds a child dies of water-related disease  5 million per year die of illnesses linked to Unsafe drinking water Unclean domestic environments, and Improper excreta disposal  Nearly ¼ of humanity remains without proper access to water and sanitation  Water pollution and poor water resources are the big problem in China. There are 700 million people in China, whose drinking water is not safe. Water/Health Facts

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 12 Effects of Water Shortages 40% of the world’s population are now facing the experience of water shortages By 2025 at least 3 billion people in 90 countries are expected to face severe water stress Threaten their agriculture and industry and the health of their people

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 15 What is Water Pollution Definition: Any chemical, biological, or physical change in water quality that has a harmful effect on living organisms or makes water unsuitable for desired uses. A natural indicator of water pollution is the presence of coliform bacteria. 0 colonies is recommended, and 200 colonies per 100 milliliters is the maximum recommended level Most water pollutants are sediment and suspended matter. These consist of soil and solids eroded from land

Today’s Dying Water Child and Dying Fish Dying Duck by Oil Spill Dying Ocean because of dumping and floating waste

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 18 For Water Make a choice, where do you want to live? Unfortunately, today’s water looks more like in the right picture. Also, water condition is becoming even worse than ever. What are causes of water pollution? What do we have to do for saving our water?

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 20 Point Sources  Pollution is discharged from a single point  These sources discharge pollutants at specific locations through pipes, ditches, or sewers into bodies of water.  Point Pollution is relatively easy to regulate, although not as easy to enforce.  Ex. Factories, sewage treatment plants, active and abandoned mines, off-shore oil wells, and oil tankers

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 22 Nonpoint Sources  They are diffused across a broad area and their contamination cannot be traced to a single discharge point. usually large land areas that pollute water by runoff, subsurface flow, or depletion from the atmosphere  These pollutants including: –Excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas; –Oil, grease, and toxic chemicals from urban runoff and energy production; –Sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks; –Salt from irrigation practices and acid drainage from abandoned mines; –Bacteria and nutrients from livestock, pet wastes, and faulty septic systems

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 24 Nonpoint-source pollution Runoff!! Nonpoint source pollution can enter the water system from many different ways and is more difficult to control. 96% of water pollution is nonpoint source.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 31 Types of Water Pollution  Inorganic chemicals and minerals  Synthetic organic compounds  Oxygen-demanding wastes  Diseases-causing agents  Thermal pollution  Sediments  Oil

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 32  Heavy metal (cadmium, chromium, lead, mercury, copper, etc.), Cyanide, ammonia, hydrogen sulfide, etc.  Toxic substances (arsenic, fluoride, etc)  Sources: Industrial discharges, like bleaching and dyeing, gold milling Marine sediments  Toxic effects (direct or long term) Cancer Nervous system damage Harms aquatic life Lowers crop yields Corrosion of metals Odour Inorganic chemicals and minerals

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 33  Pesticides, gasoline, oil, plastics, solvents, detergents, PCBs, paints, DDT, etc.  Sources: Domestic sewage, agricultural, industrial and commercial operations, etc.  Certain chemicals, including PCBs, dioxin, and DDT, are very poisonous and non-biodegradable. They are resistant to biological breakdown and persist and accumulate in the environment  Toxic effects (threaten human and aquatic life) Cancer Nervous system damage Directly toxic to aquatic life Causing odours Synthetic Organic Compounds

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 34 PesticidesPesticides  During raining, flow into river or lake, cause immediate toxic effects on aquatic life or may accumulate along the food chain until a toxic level is reached  Toxic non-biodegradable  Soluble in fat  DDT was previously used and banned in many parts of the world

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 35 The detergents forms a foamy layer on the surface that reduces the penetration of light and the dissolution of oxygen. They also contain high phosphate content. It will causes algae bloom. Detergents Detergents

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 36  Water-soluble phosphates, nitrates, potassium, etc.  Sources: Fertilizers application in farming Sewage treatment plant effluents  Cause overgrowth of algae which leads to the depletion of dissolved oxygen and the death of fish ( eutrophication and algal blooming) Plant nutrients

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 38  All organic materials and wastes that can be decomposed by aerobic bacteria  It degrade water quality by depleting water of dissolved oxygen  Sources Sewage from domestic and animals sources Industrial wastes from food processing, papermills, tanning operations, meatpacking plants, etc Decay of dead plant and animals  Broken down or decomposed by bacterial and other biological activity (biodegradation) It consumes oxygen (oxygen demanding) It causes oxygen depletion in water Oxygen-Demanding Wastes

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 39 Oxygen in Water  Importance of oxygen in water –Basic requirement of almost all plant and animal life-forms in water body except for some anaerobic organisms –Insufficient amount of oxygen Bacteria will use up oxygen in the water. damaging the ecosystem by killing other aerobic organisms  What else can affect the amount of O 2 in the water –Temperature –Speed of water flow –Roughness of surface over which water flows

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 40  Pathogenic microorganisms Bacteria (E. coli with diarrhea, fecal coliform and pathogens) Viruses (hepatitis outbreaks, meningitis) Protozoa (Giardia and cryptosporidium causing diarrhea, cramps and fatigue) Parasitic worms (Tapeworms and roundworms – children)  Sources: sewage and untreated waste from human and other animals (hosts)  Spread diseases through drinking water consumption or through other water contact activities Disease-Causing Agents

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 41  Caused by the heat absorbed by the water used to cool industrial and power plants  Sources: Industrial and commercial operations Power plants  Heating up the aquatic environment Aquatic organisms may become physiologically stressed or even be killed Interference of the natural life processes, e.g. reproduction, growth rates, distribution of species Decreasing dissolved oxygen (DO) in water Thermal Pollution

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 42  Release of weathered sediments through runoff to water bodies; Ex. Insoluble particles of soil and other solids  Sources: Clearing and developments adjacent to water bodies Natural weathering of soils Sewage discharge Littering in water bodies  Effects Directly smother and kill aquatic life Directly destroy habitats and spawning areas Reduce the sunlight penetrating into water, reduce photosynthesis. Sediments

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 43  Caused by accidental spillage or illegal washings from oil tankers or seeping from ships (crude oil, petroleum, gasoline, etc)  Sources: Wastewater discharges, leaching, Recreational boating, Underground tank leakage Oil Pollution

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 44 Oil covering the water surface prevent oxygen from dissolving in water Oil soaked on the feathers of the sea birds prevents them from flying. It also reduce their insulating property to cause them die of clod.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 45  The crude oil kills marine living things like fish-eating birds by suffocation.  Destroys food chain  The shading may restrict light penetration and reduce photosynthesis of marine plant.  Destroys scenery The effects caused by oil pollution

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 46 Ocean Pollution Pollution of the ocean is a major concern. All water flows into the ocean, so runoff is a major problem. Each year about 37 million gallons of oil are spilled into the ocean by tanker accidents. Runoff is responsible for 200-300 million gallons a year.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 47 A special case: Groundwater What forms of pollution can affect groundwater All of them except thermal pollution! Renewal time of groundwater is important –Rivers: 12-20 days –Soil Moisture: 280 days –Groundwater: 300 years

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 48 Ground Water Pollution Pollutants are filtered as they travel through the permeable soil BUT: not all pollutants are removed. The rest find their way into the aquifers. A threat is now posed by an ever-increasing number of soluble chemicals from urban and industrial activities and from modern agricultural practices.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 51 Pollution in Lakes They receive inputs of nutrients and silt from the surrounding land as a result of natural erosion and runoff. Human activities accelerate the input of nutrients- a process called cultural eutrophication Increase in nitrate- and phosphate-containing effluents from sewage treatment plants, fertilizer and waste runoff, and erosion.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 52 What is Eutrophication It means “well fed”:  Nutrients such as nitrates and phosphates (from organic matter such as fertilizers, manure) enter the water body  algae growth is stimulated  some algae release toxins and result in fish deaths.  Also, algae start dying and settle at the bottom.  Decomposing bacteria decompose the algae.  As bacterial population explodes (especially in warmer temperatures), oxygen supply in the water decreases.  Eventually decomposing becomes anaerobic and foul smell results.  Fish and plants are deprived of oxygen (hypoxia) and die off.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 53 Cultural Eutrophication Discharge of untreated municipal sewage (nitrates and phosphates) Nitrogen compounds produced by cars and factories Discharge of treated municipal sewage (primary and secondary treatment: nitrates and phosphates) Discharge of detergents ( phosphates) Natural runoff (nitrates and phosphates Manure runoff From feedlots (nitrates and Phosphates,ammonia) Dissolving of nitrogen oxides (from internal combustion engines and furnaces) Runoff and erosion (from cultivation, mining, construction, and poor land use) Runoff from streets, lawns, and construction lots (nitrates and phosphates) Lake ecosystem nutrient overload and breakdown of and breakdown of chemical cycling chemical cycling

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 55 Preventing Lake Pollution Advanced waste treatment Bans or limits on phosphates in household detergents Soil conservation Land –use control to reduce nutrient runoff Bans on certain pesticides

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 56 Lake Cleanup Methods Dredging bottom sediments Removing excess weed Controlling undesirable plant growth with herbicides and algicides Pumping air through lakes and reservoirs to avoid oxygen depletion Remove excess nutrient buildup

Industry Nitrogen oxides from autos and smokestacks; toxic chemicals, and heavy metals in effluents flow into bays and estuaries. Cities Toxic metals and oil from streets and parking lots pollute waters; sewage adds nitrogen and phosphorus. Urban sprawl Bacteria and viruses from sewers and septic tanks contaminate shellfish beds and close beaches; runoff of fertilization from lawns adds nitrogen and phosphorus. Construction sites Sediments are washed into waterways, choking fish and plants, clouding waters, and blocking sunlight. Farms Run off of pesticides, manure, and fertilizers adds toxins and excess nitrogen and phosphorus. Red tides Excess nitrogen causes explosive growth of toxic microscopic algae, poisoning fish and marine mammals. Healthy zone Clear, oxygen-rich waters promote growth of plankton and sea grasses, and support fish. Oxygen-depleted zone Sedimentation and algae overgrowth reduce sunlight, kill beneficial sea grasses, use up oxygen, and degrade habitat. Toxic sediments Chemicals and toxic metals contaminate shellfish beds, kill spawning fish, and accumulate in the tissues of bottom feeders. Closed shellfish beds Closed beach Oxygen-depleted zone

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 59 Human and animal fecal wastes Domestic waste water Waste water of agriculture and industry Waterborne Diseases  Sources of waterborne pathogens  Pathogenic Microorganisms Bacteria –Typhoid fever, Cholera, Shigella (dysentery), Salmonella Viruses –Hepatitis A, poliomyelitis and Rotavirus –Are resistant to disinfection by chlorination Protozoans –Giardia Lambia, Cryptosporidium, amoebic dysentery. –Are resistant to desinfection by chlorination.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 61 Epidemic Characteristics of Waterborne Diseases  Outbreak prevalence when water contaminated by a lot of pathogenic bacteria at one time  Cases happened continuously all the year round when water is contaminated frequently  Incidence is in accord with water supply and distribution  Epidemic can be controlled after water treatment

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 62 Chemical Contaminants in Drinking Water Nitrates –Sources: from fertilizers or septic tanks –Example: “blue babies” methhemoglobinemia Mercury –Sources: Natural occurrence; Man-made sources –Example: Minamata-disease Arsenic –Sources: Natural occurrence –Example: Endemic arsenicosis Fluoride –Sources: air; water; soil; living organisms –Example: Endemic fluorosis

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 63 NitrateNitrate Sources  industrial and domestic wastewater  Runoff from fertilizer use  natural environment

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 64 nitrite nitrate nitrite nitrosamine nitrite nitrosamine amine Nitrate in natural environment or in vivo in GI tract

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 65 Potential Health Effects  Nitrate concentrations ( > 10 mg/L NO 3 - ) may cause Methemoglobinemia (Blue Baby Syndrome) in infants nitrite  The toxicity of nitrate in humans is a result of the reduction of nitrate (NO 3 - ) to nitrite (NO 2 - ) methemoglobin  By reacting with hemoglobin, nitrite forms methemoglobin (MHb), a substance that does not bind and transport oxygen to tissues. Thus, methemoglobin formation may lead to asphyxia

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 66 MercuryMercury  Minamata Disease In the 1950s, industries around Minamata Bay in Japan discharged so much mercury into the bay that people were poisoned by mercury that had found its way into the local seafood.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 68 Physical and chemical properties of mercury  A heavy, silver white liquid at ambient temperature (density 13.5g/ml)  A long liquid range of 396 ℃ (Melting point 38.89 ℃ ; Boiling point 357.25 ℃ )  Low electrical resistivity--- one of the best metallic electrical conductors  Highest volatility of any metal  Formation of amalgams (alloys) with silver and tin for dental fillings

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 69 Natural occurrence  Degassing of the earth’s crust  Emission from volcanoes  Evaporation from natural bodies of water

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 70 The uses of mercury by man  Chlor-alkali industry  Electric industry  Dental amalgam fillings  Gold extraction  Paint  Agriculture  Pharmaceuticals

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 71 The biological impacts  Mercury amplification in Food-Chain Methylmercury compounds are amplified by common food-chain, including man’s  Biologically methylated mercury can be converted non-enzymically or through microbial action into highly toxic methymercury

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 72 Rainbow smelt 1.04 ppm Zooplankton 0.123 ppm Phytoplankton 0.0025 ppm Water 0.000002 ppm Herring gull 124 ppm Lake trout 4.83 ppm Herring gull eggs 124 ppm

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 74 Main Symptoms of Methymercury Poisoning Methylmercury is neurotoxic to man. Clinically, diverse nervous signs and symptoms are manifest with high frequency.  Sensory disorders  Ataxia  Impairment of hearing  Constriction of the visual field  Central disequilibrium

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 75  Fetal type of methylmercury poisoning is said to be far more serious than adult type.  In the fetal type of this disease, cerebral infantile paralysis like symptoms are observed, such as mental retardation, retardation in development of speech, mastication, salivation and swallowing, and disturbances body morbidity Congenital Methylmercury Poisoning Congenital methymercury poisoning

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 76 Fluoride  Fluorides are organic and inorganic compounds containing the fluorine element. Only inorganic fluorides are the focus  Fluoride in water is dependent on source of water type of geological formation amount of rainfall  Surface waters generally have low fluoride while ground waters may have high concentrations of fluoride as has been found in many parts of the world.  It occurs in humans as dental and skeletal fluorosis

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 77 chalkiness of teethbrown stain on teeth brown wavy striations on teethsevere mottling Symptoms of Dental fluorosis

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 78 Symptoms of Skeletal Fluorosis A 30-year old adult affected by skeletal fluorosis with stiff neck and vertebral column. He has to turn his whole body sideways to see someone there; and has to lie on bed to see an airplane

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 79  Arsenic is a semi-metal element in the periodic table. It is odorless and tasteless  Arsenicosis is an endemic disorder caused mainly by drinking water having an arsenic content ranging from 10-50  g/l  The symptoms of arsenicosis are seen more commonly in hands, feet and chest and include spotted melanosis, lesions and keratosis, and skin cancer (Bowens carcinoma) Arsenic

Pigmentation and depigmentation Melanosis on handKeratosis on feet Skin cancer (Bowens carcinoma) Symptoms of Arsenicosis

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 81  Blackfoot disease (BFD) is a severe form of peripheral vascular disease (PVD), in which the blood vessels in the lower limbs are severely damaged, resulting eventually in progressive gangrene. It has been observed in Taiwan.  It is caused by arsenic poisoning Blackfoot Disease

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 82 Health Effects of Other Chemicals in Drinking Water  Asbestos lung disease; cancer  Cadmium kidney, liver, bone and blood damage  Chromium damage to liver, kidney circulatory and nerve tissues; skin irritation  Lead stroke and kidney disease; cancer  Copper gastrointestinal disturbance ; liver or kidney damage

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 83  Cyanide weight loss, thyroid effects, nerve damage  Thallium changes in blood chemistry; damage to liver, kidney, intestinal and testicular tissues; hair loss  Selenium hair and fingernail loss; damage to kidney and liver tissue, and the nervous and circulatory systems  Volatile Organic Chemicals (VOCs) cancer; liver and kidney damage  Dioxin a variety of reproductive effects, from reduced fertility to birth defects; cancer Health Effects of Other Chemicals in Drinking Water

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 86  Must destroy bacteria, viruses in water within a reasonable time despite all variations in water temperature, composition, and concentration of contaminants  Must not be toxic for humans and domestic animals, unpalatable, or otherwise objectionable Water Disinfection Requirements

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 87  Must be reasonable in cost and safe and easy to store, transport, handle, and apply  Residual concentration in the treated water must be easily and, preferably, automatically determinable  Must be sufficiently persistent so that the disappearance of the residual would be a warning of contamination Water Disinfection Requirements

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 90  Chlorination has the potential of reacting with some organic compounds present in the water supply to create trihalomethanes (THM; chloroform)  Surface water supplies, high in dissolved natural organic material (humics), are especially vulnerable to THM formation Chlorine Reaction Products  When free chlorine is the disinfectant, THM levels are generally higher in communities using rivers and treams as their source of drinking water than in communities using wells  THMs are potentially carcinogenic

Conclusion

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 93 Soil Pollution The introduction of substances, biological organisms, or energy into the soil, resulting in a change of the soil quality, which is likely to affect the normal use of the soil or endangering public health and the living environment.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 94 Soil contaminants are spilled onto the surface through many different activities. Most of these are the result of accidents involving the vehicles that are transporting waste material from the site at which it originated to the site at which it is to be disposed.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 95 Others involve accidents involving vehicles (automobiles, trucks and airplanes) not transporting wastes, but carrying materials, including fuel, that when spilled contaminate the soil.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 96 Still other spills are the direct action of humans pouring potentially toxic materials (solvents, paints, household cleaning agents, etc.) onto the ground surface rather than disposing these materials by more appropriate means.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 97 Pollutant on surface of soil When any liquid pollutant is on or just below the ground surface for any period of time, one of three things could happen to it, if it is not cleaned up first.

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 98  pollutant might be washed away by precipitation, causing little or no harm to the ground on which it was found ( however, pollutants will simply accumulate somewhere else)  the pollutant, if volatile, could evaporate, again causing little harm to the soil ( however, not a solution to the bigger pollution problem, as it might become a source of air pollution).  pollutant could infiltrate through the unsaturated soil, in much the same way as ground water. Pollutant on surface of soil

Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 1 Chapter 3 Water and Soil.

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Hygiene Department, College of Basic Medical Sciences, Dalian Medical University © 2006 1 Chapter 3 Water and Soil.

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