LC50
Lethal
Concentration 50. An LC50 value
is the concentration of a material in air that will kill 50% of
the test subjects (animals, typically mice or rats) when
administered as a single exposure (typically 1 or 4 hours). This
value gives you an idea of the relative toxicity of the material.
This
value applies to vapors,dusts, mists and gases. Solids and
liquids use the closely related LD50 value
(50% lethal dose).
LD50
Lethal
Dose 50. It’s the amount of a solid or liquid material that it
takes to kill 50% of test animals (for example, mice or rats) in
one dose.
Toxic
Toxic
is defined by OSHA (Ocupational Safety and Health Administration)
29 CFR 1910.1200 App A as a chemical which falls in any of these
three categories:
A
chemical that has a median lethal dose (LD50)
of more than 50 milligrams per kilogram but not more than 500
milligrams per kilogram of body weight when administered orally
to albino rats weighing between 200 and 300 grams each.
A
chemical that has a median lethal dose (LD50)
of more than 200 milligrams per kilogram but not more than 1,000
milligrams per kilogram of body weight when administered by
continuous contact for 24 hours (or less if death occurs within
24 hours) with the bare skin of albino rabbits weighing between
two and three kilograms each.
A
chemical that has a median lethal concentration (LC50)
in air of more than 200 parts per million but not more than
2,000 parts per million by volume of gas or vapor, or more than
two milligrams per liter but not more than 20 milligrams per
liter of mist, fume, or dust, when administered by continuous
inhalation for one hour (or less if death occurs within one
hour) to albino rats weighing between 200 and 300 grams each.
Highly
toxic
Highly
toxic is defined by OSHA (Ocupational Safety and Health
Administration) as:
A
chemical that has a median lethal dose (LD50)
of 50 milligrams or less per kilogram of body weight when
administered orally to albino rats weighing between 200 and 300
grams each.
A
chemical that has a median lethal dose (LD50)
of 200 milligrams or less per kilogram of body weight when
administered by continuous contact for 24 hours (or less if
death occurs within 24 hours) with the bare skin of albino
rabbits weighing between two and three kilograms each.
A
chemical that has a median lethal concentration (LC50)
in air of 200 parts per million by volume or less of gas or
vapor, or 2 milligrams per liter or less of mist, fume, or dust,
when administered by continuous inhalation for one hour (or less
if death occurs within one hour) to albino rats weighing between
200 and 300 grams each.
Toxicology
Toxicology
is the study of the nature, effects, detection, and mitigation of
poisons and the treatment or prevention of poisoning.
Toxin
A
toxin is a toxic substance.
Toxins
that affect only specific types of cells or organs are called
cytotoxins.
What
is water pollution?
Water
pollution is any chemical, physical or biological change in
the quality of water that has a harmful effect on any living
thing that drinks or uses or lives (in) it. When humans drink
polluted water it often has serious effects on their health.
Water pollution can also make water unsuited for the desired
use.
|
What
are the major water pollutants?
There
are several classes of water pollutants. The first are
disease-causing agents. These are bacteria, viruses, protozoa
and parasitic worms that enter sewage systems and untreated
waste.
A
second category of water pollutants is oxygen-demanding
wastes; wastes that can be decomposed by oxygen-requiring
bacteria. When large populations of decomposing bacteria are
converting these wastes it can deplete oxygen levels in the
water. This causes other organisms in the water, such as fish,
to die.
A third class of water pollutants is
water-soluble inorganic pollutants, such as acids, salts and
toxic metals. Large quantities of these compounds will make
water unfit to drink and will cause the death of aquatic
life.
Another class of water pollutants are nutrients;
they are water-soluble nitrates and phosphates that cause
excessive growth of algae and other water plants, which
deplete the water's oxygen supply. This kills fish and, when
found in drinking water, can kill young children.
Water
can also be polluted by a number of organic compounds such as
oil, plastics and pesticides, which are harmful to humans and
all plants and animals in the water.
A very dangerous
category is suspended sediment, because it causes depletion in
the water's light absorption and the particles spread
dangerous compounds such as pesticides through the
water.
Finally, water-soluble radioactive compounds can
cause cancer, birth defects and genetic damage and are thus
very dangerous water
pollutants.
In
conclusion we must protect our environment!
|
|
|
|
