Pollution and Human Health
Environmental Effects
∆ Pollution causes illnesses in two main ways. First,
pollution may cause illnesses directly by poisoning.
Second, pollution may cause illnesses indirectly by
infectious disease that are spread in polluted
environments.
∆ The World Health Organization (WHO) has begun to
collect data on how the environment affects human
health. They found that people in developed countries
suffer less from environmental causes of poor health. In
developing countries, environmental causes of poor
health are largely due to parasites and bacteria in
polluted water and insect-borne diseases.
Toxicology
∆ Almost any chemical can be harmful if large enough
amounts are taken in.
∆ To determine the effect of a pollutant on health, we to
know how much of the pollutant is in the environment
and how much gets into the body. We also need to
determine what concentration of the toxin damages the
body.
∆ The damage to health that results from exposure to a
given dose is called the response. This also depends on
the number of times a person is exposed, the person’s
size, and how well the person’s body breaks down the
chemical.
∆ Persistant chemicals are dangerous because more people
are likely to come in contact with them and they are
more likely to remain in the body.
∆ Exposure to any amount of the chemical less than the
threshold dose has no adverse effect on health.
Exposure to levels above the threshold dose usually
leads to more or increased adverse effects.
Epidemiology
∆ Epidemiologists collect data from health workers on
when and where cases of a disease have occurred.
Scientists then trace the disease to try to find its origin
and how to prevent it from spreading.
∆ In order to safeguard the public, health officials
determine the risk posed by particular pollutants. The
risk is the probability of a negative outcome.
∆ In the case of human health, risk is the probability of
suffering a disease, injury or death.
∆ During the process of risk assessment, scientists first
compile and evaluate existing information on the
substance. Then they determine how people might be
exposed to it. The third step is determining the toxicity
of the substance. Lastly, scientists characterize the risk
that the substances pose to the public.
∆ The Environmental Protection Agency (EPA)
formulates the regulations that are sometimes handed
down by the government of how and where substances
can be used.
Pollution from Natural Sources
∆ Naturally occurring pollutants usually become
hazardous to health when they are concentrated above
their normal levels in the environment.
∆ The most common pollutants from natural sources are
dust, soot and other particulates.
∆ Dangerous heavy metals include the elements arsenic,
cadmium, lead, and mercury. These metals occur
naturally in rocks and soil. Most of them cause nerve
damage when they are ingested beyond their threshold
dose.
Pollution from Human Activities
∆ Only about 10% of commercial chemicals have been
tested for their toxicity and about 1,000 new chemicals
are introduced every year.
∆ Things have improved, people living in the U.S. contain
lower levels of some toxic chemicals in their bodies, on
average, than they did in the recent past.
∆ In 2001, 2003, 2005 the Center for Disease Control and
Prevention (CDC) released studies on chemical residues
in the U.S. population. The levels of nicotine, mercury,
and other toxic chemicals were lower than what they
had been in 1991.
∆ Despite advances in public health resulting from
pollution control, air pollution is still a major health
problem. Major pollutants found in the air include
gases, carbon monoxide and particulates.
∆ Pesticides are beneficial in that they allow us to grow
more food by reducing pest damage. A downside is that
because they are designed to kill organisms, they are
often dangerous to humans in large doses.
∆ Most modern pesticides break down quickly in the
environment into harmless substances.
∆ We are exposed to low levels of industrial chemicals
every day, particularly inside new buildings that have
new furnishings.
∆ Often industrial chemicals are not known to be toxic
until they have been used for many years.
∆ Much of the pollution in our environment is a byproduct
of inadequate waste disposal. Examples of this include:
1. wastewater from cities
2. old landfills
3. sewage treatment plants
4. radioactive waste
Biological Hazards
∆ One of the reasons these diseases are now widespread is
that we have altered our environment in ways that
encourage them to spread.
The Environment’s Role in Disease
∆ Infectious diseases are caused by pathogens. Some
diseases are spread from person to person through air.
Other diseases are spread by drinking water that
contains the pathogen. Still other diseases are
transmitted by a secondary host.
Waterborne Disease
∆ Nearly three-fourths of infectious diseases are
transmitted through water. In developing countries,
where there is not enough water for basic needs, the
local water supply is often used for drinking, washing
and sewage disposal.
∆ The deadliest waterborne diseases come from drinking
water polluted by human feces. These pathogens cause
diseases such as cholera and dysentery.
∆ Malaria, another waterborne disease, was once the
world’s leading cause of death. No effective vaccine for
malaria exists, but preventative measures are used to
control mosquitoes.
Environmental Change and Disease
∆ Many ways in which we alter the environment make the
environment more suitable for pathogens to live and
reproduce.
∆ Our actions cause pathogens to evolve resistance to
antibiotics that are used to kill them.
∆ We also use enormous amounts of antibiotics to treat
human illnesses.
∆ The mosquitoes that transmit malaria are found in the
warmer parts of the world. Epidemiologists believe that
global warming may increase the areas that malaria
occurs
∆ Mosquitoes have evolved resistance to most of the
pesticides. Newer methods for controlling mosquitoes
involve spreading growth regulators that prevent
mosquito larvae from maturing into adults or that
sterilize the female mosquitoes.
∆ Most viral diseases spread directly from one person to
another. The virus invades the body through a cut or
through mucus membranes.
∆ We don’t have many effective drugs to treat viral
diseases, and the drugs we have are effect against
specific viruses. Our main defense against viral disease
is vaccination.
∆ The problem with vaccines is that they are very specific
and viruses evolve rapidly. When a new strain of viral
pathogen evolves, a new vaccine must be developed.
∆ In recent years, scientists have discovered an increasing
number of pathogens that have moved from one species
to another.
∆ The pathogens that cause these diseases have lived for
centuries in some species of wild animals and done little
damage. When the pathogens invade humans, the
pathogens cause serious diseases.
∆ Some ecologists think that the ways in which we are
altering the environment and destroying habitats ensure
that diseases like these will become more common in the
future.
∆ Because flu is so easily spread from one person to
another, epidemiologists predict that the greatest threat
to human health may be the outbreak of a new, very
virulent strain of influenza virus, which would spread
rapidly through crowded urban populations.