Water Pollution

Chapter 16

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 human activity (agriculture, industry, and as people live)

General Principles:– Geochemical Cycles– Residence Time– Residence Time and Pollution– Point and Non-point Pollution Sources

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

Figure 16.1 Simplified calcium cycle

Residence Time• Residence Time = Capacity/Rate of Influx

– Residence Time – how quickly a substance cycles through each of reservoirs

– Capacity – maximum concentration of a substance a reservoir can reach before saturation occurs

– Rate of Influx – how much of a substance a stream or ground water system brings into the reservoir

• Oceanic residence times for different elements vary widely

• Humans can alter the rate of influx or other parts of this equation by our activity

Residence Time and Pollution

• Residence times for many natural compounds are known and understood

• Residence times for more complex chemicals and compounds, including synthetic ones, are not well known

• Chemical behavior of complex and synthetic compounds often need time to be studied and understood – that time isn’t always available before these compounds are introduced into the market place

Point and Nonpoint Pollution SourcesSources of pollution may be subdivided into two categories

• Point source – pollution enters a system from one, identifiable spot. The point sources are often easier to identify as potential pollution problems

• Nonpoint source – pollution enters a system from multiple and more diffuse sources. We can still identify them by using natural geochemical tracers

Figure 16.2 Point sources of water pollution

Figure 16.3 Acid mine drainage

Organic Matter• Nature and Impacts

– In general organic matter is the substances of living 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 by microscopic organisms (bacteria)

• If ample oxygen is available then aerobic decomposition occurs

• If oxygen is depleted then anaerobic decomposition occurs

Figure 16.4 Uncontrolled runoff from a livestock yard

Organic Matter

• Biochemical Oxygen Demand (BOD)– Measure of organic-matter load in a body of

water– BOD of a system is the measure of the amount

of oxygen required to breakdown the organic matter 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 a waste source

Figures 16.5 a and b Effects of wastewater and organic matter on dissolved-oxygen content

Oxygen shows sharp depletion near the source and recovering downstream

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

Flowing water is better mixed and circulated

Figure 16.6 Dissolved-oxygen concentrations in U.S. surface waters in the 1980s, a climate factor

Organic Matter• Eutrophication – complex breakdown of excess

organic matter that enriches water with plant nutrients (nitrates, phosphates, and sulfates) plants such as algae thrive on these nutrients and can produce algal blooms– Algal growth proceeds in the photic zone and chokes

out other plants– These dead plants drop to the bottom of the pond

where they become part of the organic-matter load and increase the BOD

– This process consumes oxygen and re-releases abundant nutrients into the water and the cycle is repeated

– Layers of water become depleted in oxygen and will kill oxygen dependent animals

Figure 16.7 Algal Bloom

Industrial Pollution

Hundreds of new chemicals are created by industrial scientists each year

Out of 66000 drugs, pesticides, and other industrial chemicals, no toxicity data at all were available for 70% of them; a complete health hazard evaluation was possible for only 2%

In 1990, ten millions of new chemicals have been created or identified since 1957

It is not possible to have a complete toxicity assessment for many substances

Industrial Pollution• Inorganic Pollutants – Metals

– Manufacturing, mining, and mineral processing activities can increase the influx of metals to a system

– These increases can range from natural levels to toxic levels

– Some metals, such as heavy metals which include cadmium, lead, mercury, plutonium, and others, will accumulate in the bodies of simple organisms

– These simple organisms are food for more complex organisms and concentrations of heavy metals increase up the food chain

– In humans, heavy metals can cause central nervous system problems and brain damage; usually these are irreversible

– Heavy metal poisoning can cause death or cancer

Figure 16.9 Arsenic in ground water

Industrial Pollution• Other Inorganic Pollutants

– Nonmetallic elements can reach toxic levels in aquatic systems• Chlorine, used to kill bacteria in municipal

waste water systems, can kill algae and harm fish populations

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

• The toxic effects of certain asbestos minerals were not manifested or well defined until long after initial release into the environment by human activities

Industrial Pollution• Organic Compounds (carbon containing

compounds)– New herbicides, pesticides, and insecticides are created

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

– Oil spills occur each year from intentional dumping and accidental 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

Figure 16.11 Use of DDT

Figure 16.11 Pesticides in sediments

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 or

heating 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

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

Fig. 16.12 Potential nonpoint-source pollution from nitrogen

Agricultural Pollution

• Sediment Pollution– Farmland is exposed to wind and rain that can

carry away soil into local waterways– This loss is typically fine-grained sediments

that choke waterways and reduce sun light penetration

– Fish, animal, and plant success is reduce by murky water

– Solutions require planning such as contour plowing, terracing, and installing wind breaks and settling ponds

Figure 16.14 Sediment pollution in stream

Figure 16.15 Surface runoff and settling pond

Agricultural Pollution

• Herbicides and Pesticides– Farmers are using these chemical additives at

all time high rates– Inappropriate use can expose animals and

humans to toxic levels of pollution– Often application of more chemical than is

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

– New technology and education may help reduce this hazard in the future

Fig. 16.16 herbicide and pesticide runoff

Reversing the DamageSurface Water

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

the fine sediments that are laden with toxic compounds that are attached to the sediments

– We must be sure these dredged sediments are removed from the environment also

– An expensive but often necessary operation in many places in the future

Reversing the DamageSurface Water

• Physical Isolation or Chemical Treatment of 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 may reduce the risk of eutrophication

Figure 16.17 Surface water pollution

Reversing the DamageSurface 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 a

decorative pond from eutrophication in an area where fertilizers are used

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 its appearance in ground or surface water elsewhere

• But, groundwater pollution in karst areas may spread unexpectedly swiftly

Figure 16.18 Nitrate pollution susceptibility of groundwater

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 in pollution of ground water

• Residence times are important because recharge water may be discharged from a well before the residence time has 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 a pollution plume

• Often they are found near landfills, waste sites, or abandoned tanks

Fig. 16.20 Groundwater pollution

Reversing the DamageGround Water

• Often the most effective and economical way to treat polluted ground water is allow natural processes to remove or destroy pollutants

• Commonly, polluted groundwater is only treated after it is extracted for use

• Decontamination after extraction, also called pump-and-treat, is useful if ground water is needed before residence times elapse

• Air stripping, where air is pumped into the extracted water laden with volatile organic pollution, transfers the pollution into air rather than leaving it in the water

• Activated charcoal filters and absorbs many organic compounds from water