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Water Pollution

Chapter 17

Phytoplankton andsediments in Gulf of

MexicoPhoto from NASA

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General Principles The fresh groundwater and surface water

on the continents constitutes less than 1%of the water in the hydrosphere Any natural water contains dissolved

chemicals some are unhealthy and

some are produced by a variety of humanactivity (agriculture, industry, and aspeople live)

General Principles : Geochemical Cycles Residence Time Residence Time and Pollution

Point and Non-point Pollution Sources

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Geochemical Cycles All of the chemicals in the environment

participate in geochemical cycles of some kind,similar to the rock cycle

Simplified cycle Precipitation Weathering Ions transported as dissolved load in stream or

ground water Minerals precipitate out and cycle continues Many systems become more complex because of

subcycles

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Simplified calcium cycle

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Residence Time Residence Time = Capacity/Rate of Influx

Residence Time how quickly a substancecycles through each of reservoirs

Capacity maximum concentration of asubstance a reservoir can reach beforesaturation occurs

Rate of Influx how much of a substance astream or ground water system brings into thereservoir

Oceanic residence times for differentelements vary widely

Humans can alter the rate of influx or otherparts of this equation by our activity

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Residence Time and Pollution

Residence times for many naturalcompounds are known and understood

Residence times for more complex

chemicals and compounds, includingsynthetic ones, are not well known Chemical behavior of complex and

synthetic compounds often need time tobe studied and understood that time isntalways available before these compoundsare introduced into the market place

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Point and Nonpoint Pollution Sources

Sources of pollution may besubdivided into two categories

Point source pollution enters a systemfrom one, identifiable spot. The pointsources are often easier to identify aspotential pollution problems

Nonpoint source pollution enters asystem from multiple and more diffusesources. We can still identify them by using

natural geochemical tracers

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Organic Matter Nature and Impacts

In general organic matter is the substances ofliving or dead organisms and their by products

Algae in a pond Human or animal waste

Run off from an animal feedlot Discharge from food processing plants Run off from municipal streets or highways

In time organic matter is broken down bymicroscopic organisms (bacteria)

If ample oxygen is available then aerobic decomposition occurs

If oxygen is depleted then anaerobic decomposition

occurs

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Uncontrolled runoff from a livestock yard

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Organic Matter Biochemical Oxygen Demand (BOD)

Measure of organic-matter load in a body ofwater

BOD of a system is the measure of the amount

of oxygen required to breakdown the organicmatter aerobically

The more the organic matter, the higher the BOD BOD may exceed the amount of dissolved oxygen

in the system An oxygen sag curve is a graph of dissolved

oxygen content as a function of distance from awaste source

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Effects of wastewater and organic matter on dissolved-oxygen content

Oxygen shows sharp depletion near the source andrecovering downstream

Persistent oxygen depletion occur in a body of standingwater, such as lakes or reservoirs

Flowing water is better mixed and circulated

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Dissolved-oxygen concentrations in U.S. surface

waters in the 1980s, a climate factor

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Organic Matter Eutrophication complex breakdown of excess

organic matter that enriches water with plantnutrients (nitrates, phosphates, and sulfates)plants such as algae thrive on these nutrientsand can produce algal blooms

Algal growth proceeds in the photic zone and chokesout other plants These dead plants drop to the bottom of the pond

where they become part of the organic-matter load andincrease the BOD

This process consumes oxygen and re-releasesabundant nutrients into the water and the cycle isrepeated

Layers of water become depleted in oxygen and will

kill oxygen dependent animals

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Algal Bloom

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Industrial Pollution

Hundreds of new chemicals are created byindustrial scientists each year

Out of 66000 drugs, pesticides, and otherindustrial chemicals, no toxicity data at all wereavailable for 70% of them; a complete healthhazard evaluation was possible for only 2%

In 1990, ten millions of new chemicals have been

created or identified since 1957It is not possible to have a complete toxicityassessment for many substances

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Industrial Pollution Inorganic Pollutants Metals

Manufacturing, mining, and mineral processingactivities can increase the influx of metals to a system

These increases can range from natural levels to toxiclevels

Some metals, such as heavy metals which includecadmium, lead, mercury , plutonium, and others, willaccumulate in the bodies of simple organisms

These simple organisms are food for more complexorganisms and concentrations of heavy metalsincrease up the food chain

In humans, heavy metals can cause central nervoussystem problems and brain damage; usually these areirreversible

Heavy metal poisoning can cause death or cancer

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Arsenic in ground water

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Industrial Pollution Other Inorganic Pollutants

Nonmetallic elements can reach toxic levelsin aquatic systems

Chlorine, used to kill bacteria in municipalwaste water systems, can kill algae and harmfish populations

Acids, from industrial plants or mine drainage,may act to leach out toxic metals from rocksor mine tailings

The toxic effects of certain asbestos mineralswere not manifested or well defined until longafter initial release into the environment byhuman activities

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Industrial Pollution Organic Compounds (carbon containing

compounds) New herbicides, pesticides, and insecticides are createdeach year

Some are toxic or carcinogenic to humans Examples include DDT and dioxin

Oil spills occur each year from intentional dumping andaccidental spillage Other compounds such as PCBs and MTBE are found in

natural systems Problems of Control

As efficiency of removal of pollution substances increase,the costs tend to sky rocket

Few systems to treat this waste are 100 % clean The benefits of these compounds sometimes out way the

risk or the cost

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Use of DDT

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Pesticides in sediments

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Industrial Pollution Thermal Pollution release of excess or

waste heat into the environment Excess heat is given off as a by product of

generating power

Waste heat is given off from automobiles orheating systems Impact may not be apparent to humans but to

fish and migratory animals it can be devastating

Streams kept unseasonably warm may trap warm-water dependent animals near power plants Local food supply may be stripped of the food these

animals need

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Agricultural Pollution Pollution associated with agricultural activity

Fertilizers and Organic Waste Nitrates, phosphates, and potash are common

constituents of fertilizer Fertilizers, when not applied to the land correctly,

buildup toxic levels in run off water These fertilizers contribute to eutrophication problems Proper application of fertilizers, plus crop rotation

strategies, may help reduce these problems Animal feedlots create problems because of the

concentration of many animals in a small area Rain runoff will dissolve nutrients and carries them

into the environment

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Potential nonpoint-source pollution from nitrogen

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Agricultural Pollution

Sediment Pollution Farmland is exposed to wind and rain that cancarry away soil into local waterways

This loss is typically fine-grained sedimentsthat choke waterways and reduce sun lightpenetration

Fish, animal, and plant success is reduce bymurky water

Solutions require planning such as contourplowing, terracing, and installing wind breaksand settling ponds

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Sediment pollution in stream

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Surface runoff and settling pond

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Agricultural Pollution

Herbicides and Pesticides Farmers are using these chemical additives at

all time high rates

Inappropriate use can expose animals andhumans to toxic levels of pollution Often application of more chemical than is

needed occurs and too much is wasted andruns off into streams (for example: DDT)

New technology and education may helpreduce this hazard in the future

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Reversing the Damage Surface Water

Dredging: of a pond, or lake, may permanently remove

the fine sediments that are laden with toxic

compounds that are attached to thesediments

We must be sure these dredged sedimentsare removed from the environment also

An expensive but often necessary operationin many places in the future

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Reversing the Damage Surface Water

Physical Isolation or Chemical Treatmentof Sediments Barriers can be constructed to isolate polluted

sediments in a pod or portion of a stream Plastic (impermeable) liners can also isolated

toxic water in a system

Careful addition of salts of aluminum, calcium,or iron to phosphorous laden sediments mayreduce the risk of eutrophication

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Surface water pollution

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Reversing the Damage Surface Water

Decontamination Toxic spills often require treatment to

decontaminate water, animals, and sediments Aeration

Oxygen levels in a lake that is oxygen-depleted can be restored by aeration

A simple fountain may be required to keep adecorative pond from eutrophication in anarea where fertilizers are used

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Groundwater Pollution Pollution is difficult to detect and remediate since

groundwater is not visible Requires testing and monitoring A matter of routine for municipalities, but a

burden for a single private well homeowner A significant time lapse between the introduction

of a pollutant into the system in one spot and itsappearance in ground or surface waterelsewhere

But, groundwater pollution in karst areas mayspread unexpectedly swiftly

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Nitrate pollution susceptibility of groundwater

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Groundwater Pollution Recharge zones must be protected from improper use of

herbicides, pesticides, and insecticides Polluted recharge water will pass into the subsurface

where they may remain dissolved and can result inpollution of ground water

Residence times are important because recharge water

may be discharged from a well before the residence timehas elapsed Migration of polluted ground water by a pollution plume

can result from a point source Monitoring wells and knowledge of ground water flow

direction and flow rates are required to remediate apollution plume

Often they are found near landfills, waste sites, orabandoned tanks

h

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Reversing the Damage Ground Water

Often the most effective and economical way totreat polluted ground water is allow naturalprocesses to remove or destroy pollutants

Commonly, polluted groundwater is only treatedafter it is extracted for use

Deco ntam inat ion afte r ex t rac t ion , also calledpump-and-treat , is useful if ground water isneeded before residence times elapse

Air s t r ipp ing , where air is pumped into theextracted water laden with volatile organicpollution, transfers the pollution into air ratherthan leaving it in the water

Ac t iva ted charco al filters and absorbs many