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Today it is well accepted that chemical exposure
from ingestants, injectants, contactants and inhalants have devastating
effects on the human body. As simple as this concept is, few among
us take it seriously enough to put concentrated effort into avoiding
daily new chemical exposure, or detoxing from past exposures.
A few people suffer tremendous damage from even
a small amount of chemical exposure and it is these people who,
in spite of ridicule and grumbling by employers, co-workers, friends
and even family members who are at a loss to help, cry out against
the unbridled dumping of new chemicals into our water, our food
and our environment.
The Human Body - Tenacious
Survival
The human body is so adaptable, and so tenacious
in attempts to survive, that for most of us the daily onslaught
of chemical exposure doesn't appear to have damaging effects.
It is only when the bio-accumulation becomes a toxic overload
that we begin to experience fatigue, infertility, joint pain,
cancers - all with the word "unexplained" tacked on.
 Defining Bioaccumulation
Bioaccumulation
means an increase in the concentration of a chemical in a biological
organism over time, compared to the chemical's concentration in
the environment. Compounds accumulate in living things any time
they are taken up and stored faster than they are broken down
(metabolized) or excreted.
Understanding the on-going and ever-changing process
of bioaccumulation is very important in protecting human beings
and other organisms from the adverse effects of chemical exposure,
and it has become a critical consideration in the regulation of
chemicals.
Understanding Bioaccumulation
A number of terms are used in conjunction with bioaccumulation.
Uptake describes
the entrance of a chemical into an organism - such as by breathing,
swallowing, absorbing it through the skin, or injecting it into
the muscles or bloodstream--without regard to its subsequent storage,
metabolism, and excretion by that organism.
Storage, a
term sometimes confused with bioaccumulation, means the temporary
deposit of a chemical in body tissue or in an organ. Storage is
just one facet of chemical bioaccumulation. (The term also applies
to other natural processes, such as the storage of fat in hibernating
animals or the storage of starch in seeds.)
Bioconcentration
is the specific bioaccumulation process by which the concentration
of a chemical in an organism becomes higher than its concentration
in the air or water around the organism. Although the process
is the same for both natural and manmade chemicals, the term bio-concentration
usually refers to chemicals foreign to the organism. For fish
and other aquatic animals, bioconcentration after uptake through
the gills (or sometimes the skin) is usually the most important
bioaccumulation process.
Biomagnification describes a process that results
in the accumulation of a chemical in an organism at higher levels
than are found in its food. It occurs when a chemical becomes
more and more concentrated as it moves up through a food chain
- the dietary linkages between single-celled plants and increasingly
larger animal species.
A typical food chain includes algae eaten by the
water flea eaten by a minnow eaten by a trout and finally consumed
by an osprey (or human being). If each step results in increased
bioaccumulation, that is, biomagnification, then an animal at
the top of the food chain, through its regular diet, may accumulate
a much greater concentration of chemical than was present in organisms
lower in the food chain.
Biomagnification is illustrated by a study of DDT
which showed that where soil levels were 10 parts per million
(ppm), DDT reached a concentration of 141 ppm in earthworms and
444 ppm in robins. Through biomagnification, the concentration
of a chemical in the animal at the top of the food chain may be
high enough to cause death or adverse effects on behavior, reproduction,
or disease resistance and thus endanger that species, even when
levels in the water, air, or soil are low. Fortunately, bioaccumulation
does not always result in biomagnification.
The Bioaccumulation Process
Can be a Very Good Thing
Bioaccumulation is a normal and essential process
for the growth and nurturing of organisms. All animals, including
humans, daily bioaccumulate many vital nutrients, such as vitamins
A, D and K, trace minerals, and essential fats and amino acids.
What concerns toxicologists is the bioaccumulation of substances
to levels in the body that can cause harm. Because bioaccumulation
is the net result of the interaction of uptake, storage and elimination
of a chemical, these parts of the process will be examined further.
Uptake is Still Not Fully
Understood
Bioaccumulation begins when a chemical passes from
the environment into an organism's cells. Uptake is a complex
process that is still not fully understood. Scientists have learned
that chemicals tend to move, or diffuse, passively from a place
of high concentration to one of low concentration. The force or
pressure for diffusion is called the chemical potential, and it
works to move a chemical from outside to inside an organism.
A number of factors may increase the chemical potential
of certain substances. For example, some chemicals do not mix
well with water. They are called lipophilic, meaning "fat
loving," or hydrophobic, meaning "water hating."
In either case, they tend to move out of water and enter the cells
of an organism, where there are lipophilic microenvironments.
Why the Human Body Stores
Toxins
The same factors affecting the uptake of a chemical
continue to operate inside an organism, hindering a chemical's
return to the outer environment. Some chemicals are attracted
to certain sites, and by binding to proteins or dissolving in
fats, they are temporarily stored. If uptake slows or is not continued,
or if the chemical is not very tightly bound in the cell, the
body can eventually eliminate the chemical.
One factor important in uptake and storage is water solubility;
the ability of a chemical to dissolve in water. Usually, compounds
that are highly water soluble have a low potential to bioaccumulate
and do not leave water readily to enter the cells of an organism.
Once inside, they are easily removed unless the cells have a specific
mechanism for retaining them.
Why Heavy Metals are so
Dangerous
Heavy metals like mercury and certain other water-soluble
chemicals are such an exception, because they bind tightly to
specific sites within the body. When binding occurs, even highly
water-soluble chemicals can accumulate. This is illustrated by
cobalt, which binds very tightly and specifically to sites in
the liver and accumulate there despite its water solubility. Similar
accumulation processes occur for mercury, copper, cadmium, and
lead.
Many fat-loving (lipophilic) chemicals pass into
organism's cells through the fatty layer of cell membranes more
easily than water-soluble chemicals. Once inside the organism,
these chemicals may move through numerous membranes until they
are stored in fatty tissues and begin to accumulate.
The storage of toxic chemicals in fat reserves serves
to detoxify the chemical, or at least removes it from harms way.
However, when fat reserves are called upon to provide energy for
an organism the materials stored in the fat may be remobilized
within the organism and may again be potentially toxic. If appreciable
amounts of a toxin are stored in fat and fat reserves are quickly
used, significant toxic effects may be seen from the remobilization
of the chemical.
Can You Break Down These
Toxins and Eliminate Them?
Another factor affecting bioaccumulation is whether
an organism can break down and/or excrete a chemical. The biological
breakdown of chemicals is termed metabolism. This ability varies
among individual organisms and species and also depends on characteristics
of the chemical itself.
Chemicals that dissolve readily in fat but not in
water tend to be more slowly eliminated by the body and thus have
a greater potential to accumulate. Many metabolic reactions change
a chemical into more water soluble forms called metabolites, that
are readily excreted.
There are exceptions, however. Natural pyrethrins,
insecticides that are derived from the chrysanthemum plant, are
highly fat-soluble pesticides, but they are easily degraded and
do not accumulate. The insecticide chlorpyrifos, which is less
fat-soluble but more poorly degraded, tends to bioaccumulate.
Factors affecting metabolism often determine whether a chemical
achieves its bioaccumulation potential in a given organism.
What Happens When Chemical
Toxins Enter The Human Body?
When a chemical enters the cells of an organism,
it is distributed and then excreted, stored or metabolized. Excretion,
storage, and metabolism decrease the concentration of the chemical
inside the organism, increasing the potential of the chemical
in the outer environment to move into the organism. During constant
environmental exposure to a chemical, the amount of a chemical
accumulated inside the organism, and the amount leaving, reach
a state of dynamic equilibrium.
To understand this concept of dynamic equilibrium,
imagine a tub filling with water from a faucet at the top and
draining out through a pipe of smaller size at the bottom. When
the water level in the tub is low, little pressure is exerted
on the outflow at the bottom of the tub. As the water level rises,
the pressure on the outflow increases. Eventually, the amount
of the water flowing out will equal the amount flowing in, and
the level of the tub will not change. If the input or outflow
is changed, the water in the tub adjusts to a different level.
Constant Exposure to Millions
of Chemicals Results in An Overload of Toxins in the Human Body
It is the same concept with living organisms. An
environmental chemical will at first move into an organism more
rapidly than it is stored, degraded, and excreted. With constant
exposure, its concentration inside the organism gradually increases.
Eventually, the concentration of the chemical inside the organism
will reach an equilibrium with the concentration of the chemical
outside the organism, and the amount of chemical entering the
organism will be the same as the amount leaving. Although the
amount inside the organism remains constant, the chemical continues
to be taken up, stored, degraded, and excreted.
If the environmental concentration of the chemical
increases, the amount inside the organism will increase until
it reaches a new equilibrium. Exposure to large amounts of a chemical
for a long period of time, however, may overwhelm the equilibrium
(for example, overflowing the tub) potentially causing harmful
effects.
Likewise, if the concentration in the environment
decreases, the amount inside the organism will also decline. Should
the organism move to a clean environment, so that exposure ceases,
then the chemical eventually will be eliminated from the body.
Specific Disease Can Be
Traced to Specific Toxins
Some chemicals bind to specific sites in the body,
prolonging their stay, whereas others move freely in and out.
The time between uptake and eventual elimination of a chemical
directly affects bioaccumulation. Chemicals that are immediately
eliminated, for example, do not bioaccumulate.
Similarly, the duration of exposure is also a factor
in bioaccumulation. Most exposures to chemicals in the environment
vary continually in concentration and duration, sometimes including
periods of no exposure. In these cases, an equilibrium is never
achieved and the accumulation is less than expected.
Bioaccumulation varies between individual organisms
as well as between species. Large, fat, long-lived individuals
or species with low rates of metabolism or excretion of a chemical
will bioaccumulate more than small, thin, short-lived organisms.
Thus, an old lake trout may bioaccumulate much more than a young
bluegill in the same lake.
An Ever-Changing Equilibrium
Can end up in Disease
Bioaccumulation results from an ever-changing equilibrium
between exposure from the outside environment and uptake, excretion,
storage, and degradation within an organism.
The extent of bioaccumulation depends on: the concentration
of a chemical in the environment, the amount of chemical coming
into an organism from the diet, or environment, and the time it
takes for the organism to acquire the chemical and then excrete,
store, and/or degrade it.
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Heavenly Bodies Clinic Bio Detoxification Center