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Chapter 7

WATER POLLUTION

Environmental Chemistry, 9th Edition

Stanley E. Manahan

Taylor and Francis/CRC Press

2010

For questions, contact: Stanley E. Manahan

manahans@missouri.edu

7.1 Nature and Types of Water Pollutants

• See list in Table 7.1

Markers of water pollution that show presence of pollution

sources

• Herbicides indicate agricultural runoff

• Fecal coliform bacteria indicate sewage sources

• Pharmaceutical metabolites in domestic wastewater

Biomarkers of water pollution are organisms that indicate

pollution

• May accumulate pollutants that appear in analysis

• May show effects from pollutant exposure

• Fish lipid tissue accumulates persistent organic pollutants

• Osprey at top of aquatic food web is a good biomarker

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7.2 Elemental Pollutants

Trace elements (harmful at a few parts per million or less)

• See list in Table 7.2

Heavy metals are among most harmful

• Cadmium • Mercury • Lead

• Most are sulfur seekers

Metalloids may be significant water pollutants

• Most important is arsenic

• Selenium and antimony can also be harmful

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7.3 Heavy Metals

Cadmium

• Highly toxic

• Chemically very similar to zinc

• From mining and industrial wastes (especially metal

plating

Lead

• Widely used and distributed in the past

• Plumbing (lead pipe, solder) used to be a major source

• Uses (such as in gasoline) have been greatly curtailed

Mercury

• Highly toxic

• Minimata Bay incident

• Mobilized by bacterial methylation—HgCH3+, Hg(CH3) 2

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7.4 Metalloids

Arsenic is the most significant

• From coal combustion

• Occurs with phosphate minerals

• Byproduct of copper, gold, lead refining

• Natural occurrence in some groundwaters

• Formerly in pesticides: Pb3(AsO4)2, Na3AsO3, Cu3(AsO3)2

• Bangladesh tube well poisonings may have affected

millions

7.5 Organically Bound Metals and Metalloids

Have metal (metalloid) bonded to carbon

• Alkyl groups such as ethyl in Pb(C2H5)4

• p (pi) electron donors such as ethylene, C2H4

• Carbonyls with bound CO

Tetraethyllead, C2H4, in gasoline introduced large quantities

of lead into the environment until it was banned

Methylation of mercury by anoxic bacteria mobilized

otherwise insoluble inorganic mercury

Organotin compounds were widely used as marine biocides

in ship and boat paints

• Tributyltin chloride commonly used industrial biocide

• Endocrine disruption in shellfish and oysters

• Uses now being phased out

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7.6 Inorganic Species

Cyanide (HCN, CN-)

• Extremely toxic

• Industrial uses including metal cleaning, electroplating

• Produced by coke ovens

• Water pollution and fish kills from mineral processing

• Concern for terrorist attacks on water supplies

Ammonia

• Generally as NH4+, NH3 at high pH

• Added to drinking water for residual disinfection from

chlorination

Free carbon dioxide, CO2

• In water from decay of organic matter, geochemical

sources

• Makes water corrosive, harmful to aquatic life

8 Hydrogen sulfide, H2S

• From industrial sources, decay of organosulfur

compounds, geochemical sources

• Foul odor, very detrimental to water quality, very toxic

• Precipitates heavy metals

Nitrite ion, NO2-, intermediate in reduction of NO3

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• Very toxic, but rare water pollutant

Sulfite ion, SO32-

• Added to water as O2 scavenger

Perchlorate ion, ClO4-

• Industrial pollutant in some cases

• Recognized as a pollutant fairly recently

Asbestos

• Causes cancer when inhaled, but unknown effects in water

• Asbestos-like fibers in Lake Superior, Reserve Mining

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7.7 Algal Nutrients and Eutrophication

Eutrophication means “well nourished”

Eutrophication in excess is detrimental causing heavy

growth of biomass followed by decay

• Consumes O2

• Fills shallow water bodies

Of numerous algal nutrients (Table 7.3) phosphorus is

generally limiting and is controlled to control eutrophication

7.8 Acidity, Alkalinity, and Salinity

Acid

• Pollutant acids generally strong acids

• One of the most common is acid mine water (H2SO4)

• Potential industrial sources of pollution

Alkalinity

• Generally due to NaHCO3

• From natural geological sources

• Can be worsened by irrigation practices

Salinity

• Salts such as NaCl and Na2SO4

• Increased in municipal water systems

• Increased by irrigation

• Major problem, especially in heavily irrigated areas

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7.9 Oxygen, Oxidants, and Reductants

Dissolved oxygen, DO, is important in water

• Depleted by oxidation of NH4+, Fe2+, SO3

2-, and especially

biodegradation of biomass, {CH2O}

{CH2O} + O2 CO2 + H2O

• Biochemical oxygen demand, BOD, refers to amount of

oxygen consumed in a volume of water by the

biodegradable organic matter in it

• Total organic carbon, TOC, is often substituted for BOD

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Figure 7.3 Oxygen sag curve resulting from the

addition of oxidizable pollutant to a stream

13 7.10 Organic Pollutants

Bioaccumulation of Organic Pollutants

Bioconcentration factor (BCF):

Substance concentration in organism

Substance concentration in water

Bioaccumulation factor, BAF, considers pollutant

concentration in food as well as water

Sewage

• Contains many pollutants including pathogenic

microorganisms, detergents, salts, solids (Table 7.4)

• Most significant pollutant in sewage is biodegradable

organic material ({CH2O}) manifested as biochemical

oxygen demand (BOD)

• Main objective of wastewater treatment is elimination of

BOD (Chapter 8)

Figure 7.4 Settling of solids from an ocean-floor

sewage discharge

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Soaps, Detergents, and Detergent Builders

Soaps are salts of long-chain fatty acids

• Sodium stearate: C17H35CO2-Na+

• Soaps produce insoluble salts with divalent metal ions,

predominantly calcium, which removes them from water,

but reduces their effectiveness as cleaning agents in hard

water

Calcium stearate: Ca2+(C17H35CO2-)2(s)

• Soaps form spherical micelles which

may entrain water-insoluble grease and

oil particles (right)

• Soap lowers water surface tension

which aids its cleaning action

• Soaps are biodegradable

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Detergents

Synthetic detergents lower water surface tension and

enable its cleaning action

• Do not form precipitates with hardness ions

• Amphiphilic structure with ionic “head” and hydrocarbon

“tail”

• Detergent surfactants concentrate at interfaces of water

with air, solids (dirt), and immiscible greases and oils

Poorly biodegradable ABS surfactants formerly used

Biodegradable LAS

surfactants now used

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Alkyl polyethoxylate surfactants (structural formula below)

• Used as detergents, dispersing agents, emulsifiers,

solubilizers, wetting agents

• Resist biodegradation

• Xenoestrogens of health concern

Detergent formulations have numerous components

• Examples: Alkalies, anticorrosive silicates

Builders added to improve performance have caused

problems

• Polyphosphates used in builders hydrolyze to phosphates

that cause eutrophication

Naturally Occurring Chlorinated and Brominated

Compounds

Produced mostly by marine organisms

• Chemical defense agents

Detected in arctic samples

• Air • Fish • Seabird eggs • Marine mammals • Human milk

Example below

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19 Microbial Toxins in Water

Toxins from aquatic bacteria and protozoa

Protozoal dinoflagellata toxins cause many maladies

• Gastrointestinal, respiratory, skin disorders in humans

• Mass kills of marine mammals

• Sometimes fatal paralytic conditions from eating infested

shellfish

Red tides from explosive growth of dinoflagellates

• Turn water red, yellow, olive-green

• Kill marine organisms

• Make sea spray very irritating to humans

Many, such as

Cylindrospermopsin from

cyanobacteria

20 7.11 Pesticides in Water

Numerous kinds of compounds added to soil and plants

• Insecticides • Herbicides • Molluscicides

• Fungicides • Bactericides • Slimicides • Avicides (birds)

• Piscicides (fish) • Plant growth regulators

• Plant defoliants • Plant desiccants

Insecticides and fungicides most important for human

exposure because of application near harvest time

Herbicides most important water pollutants because of

widespread application directly onto soil

Table 7.4 lists numerous pesticides that may be

encountered as water pollutants

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Pesticides and Other Chemicals of Concern for

Water Pollution

1. Highly biodegradation resistant compounds

2. Known or probable carcinogens

3. Substances with adverse reproductive or developmental

effects

4. Neurotoxins including cholinesterase inhibitors

5. Acutely toxic substances

6. Known groundwater contaminants

Natural Product Insecticides

• Nicotine from tobacco

• Rotenone from some legume roots

Pyrethrins

• Products such as pyrethrum I from chrysanthum varieties

grown in Kenya

• Used in China 2000 years ago

Pyrethroids are synthetic analogs of pyrethrins

• Allethrin • Fenvalerate • Cypermethrin

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23 Figure 7.6. Common botanical insecticides and synthetic

analogs of the pyrethrins.

24 DDT and Organochlorine Insecticides (Figure 7.7)

Organochlorine insecticides have been mostly phased out

of use because of persistence, harm to birds

• Endosulfan one of the last to be eliminated

25 Organophosphate insecticides (Figure 7.8)

• Though biodegradable and not generally

environmentally harmful, some very toxic effects

(acetycholinesterase inhibitors)

Malathion is a commonly used organophosphate because

mammals can hydrolyze it to non-toxic products

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27 Carbamates: Esters of Carbamic Acid (Figure 7.9)

• Biodegradable

• Acetylcholinesterase inhibitors but not unduly toxic

28 Fungicides

Figure 7.10 Examples of widely used fungicides that can be

water pollutants

29 Herbicides

Herbicides applied to millions of acres of cropland

worldwide to control weeds

Herbicides commonly occur in surface water and

groundwater, especially in intensely cropped areas

• Especially common are atrazine, simazine, and

cyanazine used for weed control on corn and soybeans

• Although widely used to control weeds on crops

genetically engineered to resist it, glyphosate has a very

strong affinity for soil and rarely gets into water

Figure 7.11 The two major bipyridilium herbicides

• Paraquat, used since 1965, has caused many deaths

because of its high toxicity

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31 Figure 7.12 Triazine herbicides of which atrazine is

especially common in water in corn-growing areas

32 Figure 7.13 Chlorophenoxy herbicides

• 2,4,5-T (“Agent Orange”) no longer used

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Figure 7.14 Miscellaneous herbicides (others shown in text)

Pollutants from Pesticide Manufacture

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or “dioxin”)

• Badly contaminated some areas in 1970s

• Highly toxic to some animals

Figure 7.15 Structural formula of TCDD

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Kepone, manufacture of which badly

contaminated the James River of

Virginia in the 1970s

35 7.12 Polychlorinated Biphenyls (PCBs)

Figure 7.16 Structural formula of PCBs (209 congeners)

Very high chemical, thermal, and biological stability

Had many uses, especially in electrical equipment

Highly persistent and found in water, sediments, bird and

fish tissues

Contamination of Hudson River sediments from electrical

equipment manufacture

Now banned

36 7.13 Emerging Water Pollutants, Pharmaceuticals,

Household Wastes

Emerging water pollutants are relatively new substance

coming into use that may get into water and that may have

undiscovered pollution effects

• Nanomaterials composed of very small particles with

many developing uses including pharmaceuticals

• Siloxanes (silicones) used in cosmetic products, water-

repellant windshield coatings, detergents

• Disinfection byproducts (trihalomethanes)

• Household wastes including surfactants, flame

retardants, and plasticizers (bisphenol-A)

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Pharmaceuticals and Partial Degradation Products

Figure 7.17 Some pharmaceuticals and pharmaceutical

metabolites found in water

Feminization of male fish exposed to sewage

Bactericides in water

Used in soaps, shampoo, deoderants, lotions, other

• Triclosan and its methyl derivative found in Swiss waters

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Estrogenic Substances in Wastewater

Disrupt endocrine gland activities regulating metabolism

and reproductive functions of organisms

Aquatic organisms (fish, frogs, alligators) exhibit

• Reproductive dysfunction • Altered sex characteristic

• Abnormal serum steroid levels

Substances include

• Oral contraceptives • Hormonal treatments

• Cancer treatments

Nonionic surfactant polyethoxylates are estrogenic

substances

• Much less potent than hormonal substances

• But released in enormous quantities

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Biorefractory Organic Pollutants

• Poorly biodegradable organics

• Also called persistent organic pollutants, POP

• Include prominently chlorinated hydrocarbons

• Examples are benzene, chloroform, tetrachloroethylene

Biorefractory compounds are not well removed by

biological treatment and may require physical means such

as carbon adsorption

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Perfluorinated Compounds as POPs

Brominated Compounds as POPs

Benzotriazole, tolyltriazoles and naphthenic acids are POPs

7.14 Radionuclides in the Aquatic Environment

Figure 7.18 Production of fission products from uranium

fission

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Radionuclides produce ionizing radiation as alpha particles,

beta particles, gamma rays

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See Table 7.5, Radionuclides that may be in water

Carbon-14 from cosmic processes

Radium-226 from uranium

• Especially significant water pollutant in some areas

Fission products important in health

• Strontium-90 that substitutes for calcium in bone

• Iodine-131 that affects thyroid

• Cesium-137 that substitutes for sodium

Radionuclides are characterized by half-lives in which half

of the radioisotopes decay

Radiation from radionuclides damages living organisms by

breaking bonds in biological macromolecules

• Bone marrow may be damaged in acute cases

• Genetic effects (damage to DNA) is of particular concern

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