humic acids anyone?

[Honorio Americo Campos]

Jean-Pierre Herveg,Louvain, <Herveg at bian.ucl.ac.be> says

%Humic acids! I learn the existence of these compounds from Hagelberg
E.:
%Humic acids contaminate some archaeological bones ... , they are
extracted
%together with the DNA! So when regions of mtDNA are submitted to PCR
%amplification for haplotype determination, they inhibit the DNA Pol!

%How can we purify this DNA to avoid this kind of contamination, easy
to
%recognize because the DNA solution is colored in brown!
%The purification technology requires some knowledge about those
compounds,
%What are they, what property can be used to separate them from DNA?

%Another question, What are the monomers of humic acids?
...........................................................
"Humic substances are probably the most widely distributed natural
products on 
the earths surface...". "Organic matter of soils and waters consists
of a 
mixture of plant and animal products in various stages of
decomposition. Organic
matter is usually divided in two groups 1) non humic substances 2)
humic 
substances. Non humic are compounds that exhibit still recognizable
chemical 
characteristics (carbohydrates, proteins, fats, waxes, etc, etc).  The
bulk of 
the organic matter consists on humic substances, they are amorphous,
brown or 
black, hydrophillic, acidic, polydisperse substances of molecular
weights 
ranking from several hundreds to tens of thousands". They are further 
classified, according to their solubility in acid and alkali, in a)
humic acids 
b)fulvic acids c)humin.
All humic fractions are resistant to microbial degradation and able to
form 
stable water-soluble and water-insoluble salts and complexes with
metal ions and
hydrous oxides and to interact with clay minerals and organic
chemicals.
My only reference about the topic (listed below) talks about 4
theories for 
their origin, nevertheless I believe it has been proved that they come
from the 
incomplete degradation of lignin and complex polyfenolic substances. I
would 
appreciate if somebody has more updated news on the subject (my
reference is 
from 72)

I am just geting into this, but there is a good basic book, rather old
(but 
basic, good chemistry does not change, just keeps geting  better !!!)
on humic 
acids...
HUMIC SUBSTANCES IN THE ENVIRONMENT
 by  M.SCHNITZER AND S.U. KHAN
MARCEL DEKKER, INC, NY 1972
 
lots of chemistry there, could probably give a key on how to sort DNA
from HA.(I
wonder why they mix, too... both are negatively charged, perhaps both
adsorb to 
positively charged clay particles in the soil and geting there
together you 
cannot isolate one from the other)(pure especulations, so please dont
be hard on
me...) 

Thanks a lot for the input received and for the references !!!

Miguel Villegas