Andreas post form 3/2004 about mercury levels and toxic risk form specific areas.

Date:   3/21/2005 6:54:56 AM ( 19 y ago)

A great mercury understanding that Andreas
posted on his forum in 2004

I so appreciated the knowledge, kept it in my toxin group.


From: andmor | All andmor's Messages |
Date: 3/20/2004 2:10:00 PM


There are several forms of mercury,
of which Methylmercury is the most toxic form.
It affects the immune system,
alters genetic and enzyme systems,
and damages the nervous system,
including coordination and the senses of touch,
taste, and sight.


Methylmercury is particularly damaging
to developing embryos,
which are five to ten times more sensitive than adults.

Exposure to methylmercury is usually by ingestion,
and it is absorbed more readily
and excreted more slowly than other forms of mercury.


Elemental mercury on the other hand,
is absorbed relatively slowly
and may pass through the digestive system
without causing damage.


Ingestion of other common forms of mercury,
such as the salt HgCl2,
which damages the gastrointestinal tract
and causes kidney failure,
is unlikely from environmental sources.
Naturally grown plant foods don't contain methymercury.



People are exposed to methylmercury
almost entirely by eating contaminated fish
and wildlife
that are at the top of aquatic foodchains.


The National Research Council,
in its 2000 report on the toxicological effects
of methylmercury,
pointed out that the population at highest risk
is the offspring of women who consume large amounts of fish
and seafood.

The report went on to estimate
that more than 60,000 children
are born each year at risk
for adverse neurodevelopmental effects
due to in utero exposure to methylmercury.


In its 1997 Mercury Study Report to Congress,
the U.S. Environmental Protection Agency
concluded that mercury also may pose a risk to some adults
and wildlife populations
that consume large amounts of fish
that is contaminated by mercury.


Fish-eating birds in certain parts of the United States
may also ingest large amounts of methylmercury
in their diet.

_____________________________________________________


Sources of Mercury


Alkali and metal processing,
incineration of coal,
and medical and other waste,
and mining of gold and mercury
contribute greatly to mercury concentrations
in some areas,
but atmospheric deposition
is the dominant source of mercury
over most of the landscape.
Once in the atmosphere,
mercury is widely disseminated
and can circulate for years,
accounting for its wide-spread distribution.



Natural sources of atmospheric mercury include volcanoes,
geologic deposits of mercury,
and volatilization from the ocean.

Although all rocks, sediments, water,
and soils naturally contain small but varying amounts
of mercury,
scientists have found some local mineral occurrences
and thermal springs that are naturally high in mercury.



Methylation is a product of complex processes
that move and transform mercury.
Atmospheric deposition contains the three principal forms
of mercury,

although inorganic divalent mercury (HgII)
is the dominant form.
Once in surface water,
mercury enters a complex cycle
in which one form can be converted to another.


Mercury attached to particles
can settle onto the sediments
where it can diffuse into the water column,
be resuspended,
be buried by other sediments,
or be methylated.


Methylmercury can enter the food chain,
or it can be released back to the atmosphere
by volatilization.


The concentration of dissolved organic carbon (DOC)
and pH have a strong effect
on the ultimate fate of mercury in an ecosystem.
Studies have shown that for the same species of fish
taken from the same region,
increasing the acidity of the water
(decreasing pH) and/or the DOC content
generally results in higher mercury levels in fish,
an indicator of greater net methylation.


Higher acidity and DOC levels enhance the mobility
of mercury in the environment,
thus making it more likely to enter the food chain.


Mercury and methylmercury exposure to sunlight
(specifically ultra-violet light)
has an overall detoxifying effect.

Sunlight can break down methylmercury to Hg(II) or Hg(0),
which can leave the aquatic environment
and reenter the atmosphere as a gas.


Sampling mercury in water requires extra care
to avoid cross contamination
because concentrations in water are so low.



Although mercury is a globally dispersed contaminant,
it is not a problem everywhere.
Aside from grossly polluted environments,
mercury is normally a problem
only where the rate of natural formation of methylmercury
from inorganic mercury
is greater than the reverse reaction.


Methylmercury is the only form of mercury
that accumulates appreciably in fish.


Plants exposed to natural UV-light
during the growth process release any methylmercury.
Birds and fish are unable to do that.


Thank you for your vigilent comments
and helping to bring more clarity into this subject.


Andreas

Reference: http://www.usgs.gov/themes/factsheet/146-00/


Andreas can be contacted at his ASk Andreas forum
here on curezone.
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