Bài giảng slide water pollution

Pollution & Residence Time We can also apply the concept of residence times to toxic chemicals that are introduced into nature as human-created pollution Unfortunately, there is very li

Chapter 15

Water Pollution

Mean while, the quality of most of the

accessible water has been degraded

Residence Time

How much time each element spends in a

liquid reservoir, such as a river stream, lake or ocean, is called the residence time

Residence Time

The capacity, for a naturally occurring,

dissolved substance, is the concentration that can be reached before the reservoir becomes saturated and the substance precipitates

Residence Time

Residence times will differ for any given element

in different reservoirs with different capacities

The rate of influx of additional material is also important

Residence time is an average

For example, if a specific chemical has a

residence time of 20 years, then after 20 years about half of the chemical should be gone from the reservoir

Residence Time

Note that the residence time for sodium and chlorine

in the oceans is a very long time

In contrast, iron can precipitate out of

seawater very easily and the residence time is only 200 years

Pollution & Residence Time

We can also apply the concept of residence times

to toxic chemicals that are introduced into nature as human-created pollution

Unfortunately, there is very little scientific information about the behavior of many toxic chemicals and

pollutants in the environment

Pollution & Residence Time

Also, it makes a tremendous difference whether the pollution is

a one-time event or continues over time

In the worst case scenario, pollution can overwhelm a reservoir

Pollution Sources

Pollution sources may be divided into Point sources

Nonpoint sources

Pollution Sources

Point sources are sources from which pollutants are released from one readily identifiable spot

Examples include a sewer outlet, steel mill

or septic tank

Pollution Sources

Nonpoint sources are more diffuse

Examples include fertilizer runoff from a farm

or acid drain from a strip mine

The organic load in a body of water is described

by a parameter known as biochemical oxygen demand (BOD)

The BOD of a system is the amount of oxygen needed to break down the organic matter

aerobically

Specifically, BOD measures

the rate of uptake of oxygen

by microorganisms in the

sample of water at a fixed

temperature (20°C) and over

5 days in the dark

Most pristine rivers will have a 5 day BOD of less than 1 ppm

Heavily polluted rivers will have a

5 day BOD greater than 10 ppm

Oxygen Sag Curve

When organic waste is

dumped into a flowing

stream it can cause

partial oxygen depletion

An oxygen sag curve is a

graph of dissolved

oxygen content as a

function of distance from

the waste source

Organic Matter

In terms of sheer volume, organic matter from human and animal wastes are a major source of pollution in water

Almost all treated and untreated human sewage

is dumped into bodies of water

The Psyttalia Wastewater Treatment Plant in Greece is Europe’s largest sewage

treatment facility

Organic Matter

Feedlots and other animal-husbandry activities create large concentrations of animal wastes

Food-processing plants are another major

source of organic matter discharged into water

Typical uncontrolled waste runoff in a

feedlot will add organic wastes to local groundwater and streams

Further breakdown continues with anaerobic (without oxygen) decomposition

This releases nontoxic gases like methane and hydrogen sulfide

The breakdown of excess organic matter not only consumes oxygen, but it also releases a variety of compounds into the water, such as nitrates, phosphates and sulfates

The nitrates and phosphates are plant

nutrients that encourages the rapid and

excessive growth of aquatic plants,

especially algae

When this occurs, it is described as the

eutrophication of the water (or the body of water is described as eutrophic)

Sources of Eutrophication

Algal Bloom

The exuberant algal growth is called algal

bloom and appears as slimy green scum

floating on the water

Once this condition starts, it acts to

rapidly worsen the water quality

The scum blocks out the sunlight and the aquatic plants begin

to die

Algal Bloom

The dead plants sink to the bottom where they decay and increase the organic load by re-releasing nutrients into the water

Oxygen Concentrations

Dissolved oxygen concentration in the U.S.

Oxygen dissolves more readily in cold water than in warm, accounting for some regional differences

Phosphates in sewage and waste water behave

as plant nutrients and are harmful to the

environment

Phosphates were added to laundry detergents

to enhance their cleaning ability by softening the water, but their use in now restricted

Industrial Pollution

The National Research Council compiled a list of 66,000 drugs, pesticides and chemical used in industry

No toxicity data at all were available for 70% of them

Only 2% had complete health hazard evaluations

harmless to toxic levels

Mercury is classified as a heavy metal, a

group that includes lead, cadmium,

plutonium and others

Heavy metals tend to accumulate in the

bodies of living organisms, with no simple way of removing the accumulation

Therefore, their concentrations increase up

a food chain

It causes loss of sight, feeling and hearing, as well as nervousness, shakiness and death

Unborn babies and young infants are very

sensitive to mercury's effects

The symptoms are irreversible

However, they do not usually worsen unless there is additional exposure

Mercury is a neurotoxin that acts on the central nervous system of the human body

Back in the early 1800s, mercury vapors were used to make felt hats and most hat makers suffered terrible, permanent medical problems The “Mad Hatter” in Alice in Wonderland is based upon London’s felt hat makers

The severe toxic form of mercury occurs as the methylmercury (CH 3 Hg) cation which bonds

with organic compounds produced by

microorganisms in both fresh and salt water

These methylmercury compounds are taken up

by aquatic plants and small organisms at the bottom of the food chain

Eventually, the methymercury accumulates in fish, which are at the top of the food chain in aquatic environments

The problem is that people eat fish

Testing of mercury level in fresh and salt water fish in the 1960s and 1970s produced alarming results

People were advised to limit their intake of fish, especially tuna

The occurrence of methylmercury in ppb

Minamata, Japan

“Minamata is a small Japanese

fishing town living in the shadow

of the chemical factory of the

Chisso Corporation When the

factory began dumping large

amounts of mercury in the bay in

1956 thousands of people began to

develop symptoms of mercury

poisoning Almost all the towns

cats went insane Birds fell out of

the sky Panic gripped the city In

time, thousands of people would

die from the poisoning.”

Minamata, Japan

W Eugene Smith’s photographs

of the victims stunned the world

Minamata Disease

Adverse effects to nervous system caused

by methylmercury (Minamata Disease):

1 Gait disturbance, loss of balance & speech disturbance

2 Disturbance of peripheral areas in the visual fields

3 Stereo anesthesia

4 Muscle weakness, muscle cramp

5 Hardness of hearing

Arsenic is the 33 rd element in the period chart and is widely distributed in the Earth’s crust

It is classified as a metaloid

Arsenic and many of its compounds are

especially potent poisons

In large doses it is lethal and exposure to low and moderate doses can cause skin and

bladder cancer

It is accumulative in the human body, so

repeated exposure to low doses can add up

Arsenic naturally occurs in nature both as pure “native” arsenic (below) and in a variety

of minerals

In the U.S., prior to 2004, 40 million pounds of arsenic per year (in “chromated copper

arsenate”) was used to make “pressure

treated” lumber for outdoor decks and patios

Now they use

“alkaline copper quat” and “copper azole”, which are considered much safer

Arsenic is dissolved out of soils and rocks

where it naturally occurs and can enter the

groundwater, streams and lakes

The occurrence of arsenic in groundwater and hence in drinking water is a health concern

For many years, the drinking water standard for arsenic has been set at 50 ppb

The average natural concentration of arsenic

A point-map that shows locations and arsenic concentrations for 31,000 wells and springs sampled between 1973 and 2000

In the 1970s, international agencies headed

by the United Nations Children’s Fund (UNICEF) began pumping millions of dollars

of aid money into Bangladesh for wells to provide “clean” drinking water

Unfortunately, nobody bothered to test for arsenic

A very large percentage of the 900,000 wells had very high arsenic levels

Levels over 1000 times safe concentrations

So far, 8,500 people have died from the effects of accumulation of arsenic from drinking “clean” water

And the villagers continue to use the wells since they are the only source of water

Other Inorganic Pollutants

There are many nonmetallic elements commonly used in industry that are potentially toxic to aquatic life

Chlorine is commonly used to kill bacteria

in municipal water and sewage treatment plants and to destroy microorganisms that might foul the plumbing in power stations

Unfortunately, when released with waste water, the chlorine kills algae and harms fish populations

Other Inorganic Pollutants

Acid mine drainage remains

a double edged sword

On one hand the acids

seriously pollutes

groundwater, streams and

lakes

On the other hand, the acid

can leach additional toxins

from rocks, mine tailings and

soil, increasing the amount

of pollution released into the

environment

Asbestos is a family of

minerals that are valued

for their fire resistance

They were used as

insulation for decades,

especially around piping

carrying hot fluids

Unfortunately, asbestos

can cause cancer when

the fibers are breathed in

Asbestos litigation is the

longest, most expensive

mass tort in U.S history,

involving more than 6,000

defendants and 600,000

claimants

Analysts have estimated

that the total costs of

asbestos litigation in the

USA alone is over $250

billion

Unfortunately, wastes from asbestos mining and manufacturing were routinely dumped

into the Great Lakes and other bodies of water

By the time the full carcinogenic effects of

asbestos were realized, the public had been drinking asbestos-bearing water for 20 years

No one understands the potential long- term impact of

drinking asbestos

Organic Compounds

The majority of new chemical compounds created each year are organic (carbon-

containing) compounds

They are used in herbicides,

pesticides and a variety of

industrial processes such

as making plastics

Some are carcinogenic,

some are very toxic and

others accumulate in living

organisms as the heavy

metals do

Organic Compounds

Pesticides and herbicides are commonly spread over wide areas, where it is virtually impossible to confine them

Once released and dispersed, it may be

Dichlorodiphenyl trichloroethane (DDT) was the first modern pesticide and is arguably the best known organic pesticide

It was developed early in World War II, and

initially used with great effect to combat

mosquitoes spreading malaria, typhus, and other insect-borne human diseases and as an agricultural insecticide

Then the complications arose

Whole insect populations developed immunity

to DDT

Individual insects with a greater resistance

would survive and pass the resistance to their off spring

In 1962, American biologist Rachel Carson published

the book Silent Spring,

which charged that DDT caused cancer and harmed bird reproduction by

thinning egg shells

DDT is accumulative in living organisms

It was quickly passed up the food chain from

insects to fish to birds

It impaired calcium metabolism in birds and their eggs became too thin and fragile to survive

Whole colonies of aquatic birds were decimated

The book resulted in a large public outcry which eventually led to the

insecticide being banned for agricultural use in the U.S in 1972

This was one of the signature events in the birth of the environmental movement

It had been assumed that DDT quickly broke down out in the environment

Then came the stunning discovery that DDT was very resistant to

decomposing and could persist for decades

Over time, many wildlife populations recovered

Dioxin is the name given to a class of chemicals formed as a by-product of the manufacture, molding, or burning

of organic chemicals and plastics that contain chlorine

They are the most toxic organic chemicals known to science (only certain radioactive elements are worse)

Dioxin can cause serious health effects when it reaches as little as a

few parts per trillion in your body fat

Dioxins are present in minuscule amounts in a wide range of materials, including practically all substances manufactured using plastics, resins or bleaches

Dioxins build up primarily in fatty tissues over time, so even small exposures may eventually reach dangerous levels

Even small concentrations in contaminated

water can be concentrated up a food chain to dangerous levels

Dioxin levels in ppt Dioxin enters the human population almost exclusively from the ingestion of food

The most toxic dioxin, TCDD, became well known as a contaminant of Agent Orange herbicide used in the Vietnam War

Vinyl Chloride

Nearly 7 billion pounds of the toxic gas vinyl chloride are used each year by the plastics industry to manufacture polyvinyl chloride

Vinyl chloride can enter the air, soil and

groundwater following improper disposal of chemical wastes (as below in Ohio)

Vinyl Chloride

It is known that breathing very high levels of vinyl chloride over several years may cause liver damage, kidney damage, nerve damage and immune disorders

The problem is that it is not known if drinking water containing low levels of vinyl chloride over several years will cause these same

effects

The EPA has set a maximum contaminant

level of 2 micrograms of vinyl chloride per liter

of water for public drinking water supplies

Polychlorinated biphemyls (PCB) were used for nearly 20 years as insulating fluids in high voltage electrical equipment

Tests revealed that PCBs caused impaired

reproduction, stomach and liver problems

PCBs were banned in the U.S in 1977

Unfortunately, 900 million pounds of PCBs were produced and a significant

portion remains in the environment

where it imparts a bad odor

and foul taste

Estimates of removing

MTBE from groundwater

and soil contamination

range from $1 to $30 billion

California and New York, which together

accounted for 40% of U.S MTBE consumption, banned the chemical starting January 1, 2004

As of September, 2005, twenty-five states had signed legislation banning MTBE

Water Pollution

The number of river miles (left) and the lake

acres (right) under fish consumption advisories

in the U.S between 1993 and 2002

An advisory is a polite way of saying the fish are too polluted to eat