Transcript File - Environmental Science

Unit VI: Our Health and Our Future
Chapter 20: The Environment &
Human Health
20-1 Pollution and Human Health
Pollution causes illness in 2 main ways:
1. directly – poisoning us
2. indirectly – many infectious diseases spread in
polluted environments (ex. cholera, malaria)
•
WHO = World Health Organization
Toxicology: study of the harmful effects of
substances on organisms
• Toxic: poisonous
Know This Table
• Toxicity: How dangerous is it?
– Almost any chemical is harmful if ingested
(taken in) in large enough amounts
– Is the concentration of any particular
chemical in the environment high enough to
be harmful?
• Dose: amount of a harmful chemical to
which a person is exposed
– Response: damage to health that results
from exposure to a given dose
– Persistent Chemicals: break down slowly in
the environment (ex. DDT)
• More people likely to come into contact
• More likely to remain in the body
– Dose-Response Curve: the relative effect
of various doses of a drug or chemical on
an organism
– Threshold Dose: less than = no bad effect.
greater than = worse effects
Epidemiology: study of the spread of
diseases
• Epidemiologists – try to find the origins
and preventive measures of outbreaks
• Risk Assessment: estimate of the risk
posed by an action or substance
– Used to form government regulations on
substances (by the EPA – Environmental
Protection Agency)
Pollution from Natural Sources
• Usually become hazardous when concentrated above
normal levels
• Ex. Radon – gas seeps from granite bedrock into
buildings  people unknowingly breathe it in 
cause cancer
• Particulates: particles in the air small enough to
breathe into the lungs (ex. dust, soot)
– Can cause lung irritation – making conditions like bronchitis
and emphysema worse
– Some natural sources: dust storm, volcanic eruption,
wildfires
• Heavy Metals – occur naturally in rocks and soil (ex.
arsenic, cadmium, lead)
– Most cause nerve damage when ingested beyond threshold
dose
Most Pollutants come from Human
Activities
• Only about 10% of commercial chemicals have been
tested for their toxicity
– About 1,000 new chemicals are introduced every year
• Recent Improvements – U.S. regulations have
helped reduce our exposure
• Burning Fuels – in vehicles, home furnaces, power
plants, factories
– Creates an enormous amount of air pollutants (ex. carbon
monoxide, many particulates)
– Gasoline & Coal burning contribute to many premature
deaths each yr. from asthma, heart disease & lung disorders
– It may be possible to predict an area’s death rate based on
the amount of pollution
• Pesticides: chemicals designed to kill
unwanted organisms (insects, fungi, weeds)
–  Allow us to grow more food by reducing pest
damage
– :( Often dangerous to humans in large doses
– Most in the U.S. break down quickly in the
environment into harmless substances
– Organophosphates: pesticides that replaced
persistent pesticides like DDT
• BUT… are very toxic causing nerve damage and perhaps
cancer
– Persistent Chemicals – still used in many
developing countries
• Pose greatest risk to children – internal organs are still
developing, eat & drink more in relation to body weight
than adults
• Industrial Chemicals
– Exposed to low levels every day
– Especially in new buildings w/ new furnishings
– In building materials, carpets, cleaning fluids,
furniture, etc.
– Older buildings often have lead-based paint
(directly linked to brain damage & learning
disabilities)
– Often not known to be toxic until used for many
years
• Ex. PCBs (polychlorinated biphenyls) – oily fluids used as
insulation in electrical transformers – don’t break down in
the environment – children in the womb can develop
learning problems and IQ deficits – pregnant women
warned not to eat fish from the Great lakes – adults
develop memory loss
• Waste Disposal – much of our pollution is a
byproduct of inadequate waste disposal
– Methods have improved
– Many old landfills are leaking
– Many communities still release raw sewage into a
river or the ocean after heavy rains
– Laws are not always enforced
– Radioactive Waste - US government has not
decided how to dispose of waste from nuclear
power plants
• Most is stored in barrels at or near the plants
• Small quantities of radioactive elements leak into nearby
waterways
20-2 Biological Hazards
• Pathogens: organisms that cause disease
(cause most of the diseases that have an
environmental component)
• Host: an organism in which a pathogen
lives all or part of its life
The Most Deadly Infections
Diseases Worldwide
Waterborne Disease
• Almost 75% of infectious diseases are transmitted
through water
• Vectors: organisms that transmit diseases to people
(i.e. mosquitoes)
• Widespread construction of irrigation canals and dams
has increased the habitat for vectors
• Cholera & Dysentery – enter the water in human
feces, cause dehydration by diarrhea & vomiting
– Cause most of the infant mortality around the world
• Malaria: caused by parasitic protists, transmitted by
mosquitoes, no effective vaccine exists
Environmental Change & Disease
• Soil Erosion spreads pathogens, parasites, and
chemicals in polluted soil
• Antibiotic Resistance
– Large quantities fed to livestock
– Salmonella, E. coli and other bacteria live in livestock and
evolve resistance to antibiotics
– Misuse of antibiotics in humans has led to drug-resistant
strains of pneumonia and tuberculosis (TB)
• Malaria: mosquitoes that transmit it live in warm
places
– Global warming may increase the range of malaria
– Historically combated with pesticides – mosquitoes have
evolved resistance
– Newer methods involve spraying growth regulators
Environmental Change & Disease
• Emerging Viruses: previously unknown
viruses
– Ex. AIDS (acquired immune deficiency syndrome) –
caused by HIV (human immune deficiency virus),
hanta virus, Ebola virus, West Nile virus
– Not many effective drugs to fight viral diseases
– Main defense is vaccinations
• But… vaccines are very specific and viruses evolve
rapidly
Environmental Change & Disease
• Cross-Species Transfers: pathogens move from one
species to another (on the rise)
– HIV & West Nile have lived for centuries in some species w/
little damage
– Some ecologists think the way we are altering the
environment & destroying habitats ensure that diseases like
these will become more common in the future.
– Examples
• Hanta Virus – carried by rodents – cause internal bleeding
• Influenza (flu) – highly contagious
– The Greatest Threat to Human Health (as predicted by
epidemiologists):
• Outbreak of a new, very virulent strain of flu virus – spread rapidly
through crowded urban populations