Water pollutants
1. List and discuss 6 categories of water pollutants.
=Infectious
Agents,
Oxygen-Demanding
Wastes,
Inorganic
Pollutants,
Organic
Chemicals, Sediment (Particulates), Thermal Pollution
2.
Discuss how sewage is related to biological oxygen demand (BOD), dissolved
oxygen, and eutrophication.
= Eutrophication is a natural process in which water is generally over-enriched with
nutrients such as nitrogen and phosphorus. This concentrated nutrient causes an
explosive increase in the population of seaweeds and other aquatic plants. BOD is the
amount of dissolved oxygen that aquatic microbes consume. Thus, the biochemical
oxygen demand (BOD) required by the large number of populations increased by
Eutrophication will be significantly greater than if it did not occur and will also affect
the amount of dissolved oxygen. This can be solved through restrictions on the use
of fertilizers, run off and soil erosion control.
3.
Discuss the problems associated with pesticide use.
Use DDT as a specific
example.
=In general, a pesticide is a chemical or biological agent (such as a virus, bacterium,
or fungus) that deters, incapacitates, kills, or otherwise discourages pests. Along with
these benefits, pesticides also have drawbacks, such as potential toxicity to humans
and other species.
=Pesticide use raises a number of environmental concerns. Over 98% of sprayed
insecticides and 95% of herbicides reach a destination other than their target species,
including non-target species, air, water and soil.
=In addition, pesticide use reduces biodiversity, contributes to pollinator decline,
destroys habitat (especially for birds), and threatens endangered species.
Pests can develop a resistance to the pesticide (pesticide resistance), necessitating a
new pesticide. Alternatively a greater dose of the pesticide can be used to counteract
the resistance, although this will cause a worsening of the ambient pollution problem.
=In order to reduce negative impacts, it is desirable that pesticides be degradable or
at least quickly deactivated in the environment.
=4,4'-Dichlorodiphenyltrichloroethane,
commonly
known
as
DDT,
is
a
colorless,
tasteless, and almost odorless crystalline chemical compound, an organochlorine,
originally developed as an insecticide, and ultimately becoming infamous for its
environmental impacts. It was first synthesized in 1874 by the Austrian chemist
Othmar Zeidler. DDT's insecticidal action was discovered by the Swiss chemist Paul
Hermann Müller in 1939. DDT was used in the second half of World War II to
control malaria and typhus among civilians and troops.
DDT is a persistent organic pollutant that is readily adsorbed to soils and sediments,
which can act both as sinks and as long-term sources of exposure affecting
organisms. Depending on conditions, its soil half-life can range from 22 days to 30
years. Routes of loss and degradation include runoff, volatilization, photolysis and
aerobic and anaerobic biodegradation. Due to hydrophobic properties, in aquatic
ecosystems DDT and its metabolites are absorbed by aquatic organisms and adsorbed
on suspended particles, leaving little DDT dissolved in the water (however, its half-life
in aquatic environments is listed by the National Pesticide Information Center as 150
years). Its breakdown products and metabolites, DDE and DDD, are also persistent
and have similar chemical and physical properties. DDT and its breakdown products
are transported from warmer areas to the Arctic by the phenomenon of global
distillation, where they then accumulate in the region's food web.
Because of its lipophilic properties, DDT can bioaccumulate, especially in predatory
birds. DDT is toxic to a wide range of living organisms, including marine animals such
as crayfish, daphnids, sea shrimp and many species of fish. DDT, DDE and DDD
magnify
through
the
food
chain,
with
apex
predators
such
as
raptor
birds
concentrating more chemicals than other animals in the same environment. They are
stored mainly in body fat. DDT and DDE are resistant to metabolism; in humans, their
half-lives are 6 and up to 10 years, respectively. In the United States, these chemicals
were detected in almost all human blood samples tested by the Centers for Disease
Control in 2005, though their levels have sharply declined since most uses were
banned. Estimated dietary intake has declined, although FDA food tests commonly
detect it.
Despite being banned for many years, in 2018 research showed that DDT residues are
still present in European soils and Spanish rivers.
4. Why were PCBs thought to be a ‘miracle chemical’?
Why is this organic chemical
an ‘environmental curse’.
PCBs do not easily break down or degrade, which made them attractive for
industries. PCB mixtures are resistant to acids, bases, oxidation, hydrolysis, and
temperature
change.
They
can
generate
extremely
toxic
dibenzodioxins
and
dibenzofurans through partial oxidation. Intentional degradation as a treatment of
unwanted PCBs generally requires high heat or catalysis.
But PCB is an environmental curse because it is environmentally and biologically toxic.
PCBs
have
entered
the
environment
through
both
use
and
disposal.
The
environmental fate of PCBs is complex and global in scale.
Because of their low vapour pressure, PCBs accumulate primarily in the hydrosphere,
despite their hydrophobicity, in the organic fraction of soil, and in organisms. The
hydrosphere is the main reservoir. The immense volume of water in the oceans is still
capable of dissolving a significant quantity of PCBs.
<Humans>
The most commonly observed health effects in people exposed to extremely high
levels of PCBs are skin conditions, such as chloracne and rashes, but these were
known to be symptoms of acute systemic poisoning dating back to 1922. Studies in
workers exposed to PCBs have shown changes in blood and urine that may indicate
liver damage. In Japan in 1968, 280 kg of PCB-contaminated rice bran oil was used
as chicken feed, resulting in a mass poisoning, known as Yushō disease, in over 1800
people. Common symptoms included dermal and ocular lesions, irregular menstrual
cycles and lowered immune responses. Other symptoms included fatigue, headaches,
coughs, and unusual skin sores. Additionally, in children, there were reports of poor
cognitive development. Women exposed to PCBs before or during pregnancy can give
birth to children with lowered cognitive ability, immune compromise, and motor
control problems.
There is evidence that crash dieters that have been exposed to PCBs have an elevated
risk of health complications. Stored PCBs in the adipose tissue becomes mobilized into
the blood when individuals begin to crash diet. PCBs have shown toxic and
mutagenic effects by interfering with hormones in the body. PCBs, depending on the
specific congener, have been shown to both inhibit and imitate estradiol, the main
sex
hormone
in
females.
Imitation
of
the
estrogen
compound
can
feed
estrogen-dependent breast cancer cells, and possibly cause other cancers, such as
uterine or cervical. Inhibition of estradiol can lead to serious developmental problems
for both males and females, including sexual, skeletal, and mental development issues.
citation needed. In a cross-sectional study, PCBs were found to be negatively
associated with testosterone levels in adolescent boys.
High PCB levels in adults have been shown to result in reduced levels of the thyroid
hormone triiodothyronine, which affects almost every physiological process in the
body, including growth and development, metabolism, body temperature, and heart
rate. It also resulted in reduced immunity and increased thyroid disorders.
<Animals>
Animals that eat PCB-contaminated food even for short periods of time suffer liver
damage and may die. PCBs that have dioxin-like activity are known to cause a variety
of teratogenic effects in animals. Exposure to PCBs causes hearing loss and symptoms
similar to hypothyroidism in rats.
<Cancer>
In 2013, the International Agency for Research on Cancer (IARC) classified dioxin-like
PCBs as human carcinogens. According to the U.S. EPA, PCBs have been shown to
cause cancer in animals and evidence supports a cancer-causing effect in humans. Per
the EPA, studies have found increases in malignant melanoma and rare liver cancers
in PCB workers.