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Humic Acids


  1. Humus, humic acid and natural chelating agents
    by Craig Bingman <> (Sat, 1 Jun 1996)
  2. Humic Acid
    by Elizabeth Worobel <eworobe-at-cc.UManitoba.CA> (Sat, 1 Jun 1996)
  3. Humic Acids in Nature vs the Aquarium (Long)
    by "James Purchase" <jpp/> (Fri, 14 Feb 1997)

Humus, humic acid and natural chelating agents

by Craig Bingman <>
Date: Sat, 1 Jun 1996

> From: Stephen.Pushak-at-saudan.HAC.COM
> Date: Fri, 31 May 1996 15:03:07 PDT
> Subject: humus, humic acid and natural organic chelation agents
> What's in humic acid? Is it actually a mixture of several organic
> acids? Does it contain EDTA or other chelation agents? Are there
> other organic chelation agents in humus?

Humic acids are a complex mixture of partially "decomposed" and 
otherwise transformed organic materials.  The chemistry of their 
formation is quite complex, and freshwater humic acids can come from a 
variety of cources, most of which are on land (decomposing terrestrial 
vegetation.)  These substances wash into lakes and rivers, undergoing 
further transofrmations along the way, and ultimately into the ocean.  
Most but certainly not all of the marine humic acids also ultimately 
have their origin on land.  Almost all of the lignins found in marine 
environments originate on land.

There are several subclasses of humic acids, (tannins, lignins, 
fulvic acids) which are partially "resolvable" based on some fairly 
simple physicochemical criteria, but the criteria for these separations 
is primarily the convenience of the methods used, and to some degree 
elucidating their origins, as opposed to their functional impact on 
aquatic ecosystems, so I won't go into the different classes or how they 
are distinguished.  They all tint the water yellow and they all bind cations.

All share these characteristics:

A substantial fraction of the mass of the humic acids is in carboxylic 
acid functional groups, which endow these molecules with the ability to 
chelate positively charged multivalent ions (Mg++, Ca++, Fe++, most other
"trace elements" of value to plants, as well as other ions that have no 
positive biological role, such as Cd++ and Pb++.) This chelation of ions 
is probably the most important role of huic acids with respect to living 
systems.  By chelating the ions, they faciliate the uptake of these ions
by several mechanisms, one of which is prevneting their precipitation, 
another seems to be a direct and positive influence on their 
bioavailablity.  Many organisms can expliot dissolved organics to some 
degree if they are present, and humic acids may be taken up by this 
mechanism.  Another paradoxical effect of humic acids is the 
detoxification of heavy metals.  One might expect them to be made More, 
not less toxic by humic acids, but the studies that I've seen seem to 
indicate a detoxifying effect.

Humic acids also have a smaller fraction of phenolic functional groups, 
which can be detected various chemical methods.

They are derived from peptide, lipid and carbohydrate precursors.  Their 
formation and diagensis is partially mediated by aquatic bacteria and 

They are all complex chemically, polydisperse (having different 
composition and molecular weights) and eventually hit a diagenic state 
where it is difficult to change them further.

Terrestrial humic acids tend to be more "aromatic" in nature (having more 
benzene- and phenol-like components) while marine humic acids tend to be 
more aliphatic in nature.  The distributions seem to be overlapping, so 
this is a difference in degree.  There are certainly aliphatic (grease, 
oil, fat) like components in terrestrial humic acids, as there are 
aromatic components in marine humic acids (since I've measured phenolic 
compounds in marine aquaria in the past.)

I wrote an article for Aquarium Frontiers some time ago rgarding the 
effect of humic acids (and their clearance from the system) on visible 
and ultravioloet light penetration into aquaria.  HUmic acids are 
expected to have a similar role on light transmission in freshwater 
planted tanks.   It is not clear to me how sensitive your plants are to 
UV radiation, or how much UV output typefies the light sources you use.  
Dana Riddle will have an article in the coming issue of AF which 
describes the amount of UV emission from some (not all) light sources 
used in marine aquaria, which some of you may be using as well.  We have 
a freshwater planted tank in lab, I ought to do an activated carbon 
treatment on it at some point.  We are using incandescent light on it 
(wasn't my decision, I would have put metal halide pendants on it had it 
been my call) so I'm not likely to see any rapid and profound biological 
effects, because the UV emission in this case is virtually nonexistant.

You asked about EDTA.  EDTA is a synthetic compound,  
ethylenediaminetetraacetic acid.  It has four COO- groups on a very short 
aliphatic backbone.  It is a potent chelating agent, and can mimic to 
some degree the chelation of metal ions by aquatic humic acids.  While I 
don't know that EDTA has ever been isolated from natural humic acids, it 
might be present in vanishingly low concentrations.  The important part 
is that it is to some degree a "look-alike" and "function-alike" of humic 

Humic acids or molecules with similar properties have probably always 
been around, so life has been "safe" in being somewhat dependent on 
them.   Functionally similar molecules may well have been produced 
abiotically before life existed, and the "goop" that is found when you 
zap energy through a reducing mixture of gases like that found in the 
early earth's atmosphere has characteristics reminiscent of humic acids.  

Most trace element suppliments contain some sort of chelating agent (EDTA 
or functional equivalent) to help stabilize the transition metal ions in 
solution.  Peat is a rich source of humic acids, as are decaying 
driftwood, and the diagenisis of fish poo in the substrate of your 
aquaria.  ;)  "Blackwater extract" seems to be mainly humic acids.

Humic acids are removed by activated carbon.  There are clear 
implications for fate of trace elements in aquaria, perhaps Especially 
freshwater aquaria, in that statement.
Craig Bingman
Science Editor, AFQ

Humic Acid

by Elizabeth Worobel <eworobe-at-cc.UManitoba.CA>
Date: Sat, 1 Jun 1996

Humic acid is a condensed, refractive mixture of aromatic organic acids. 
It is complex and variable and has not been characterized (as far as I 
know) to any degree (except perhaps for some of the many functional 
groups). Humic acid contains Sulfur, Nitrogen and Phosphorus in varying 
amounts. It also contains metals such as Ca, Mg, Cu, Zn etc. which can be 
'chelated' in some undefined way. Humic acid can be broken down into two 
groups based on the polarity and size of the individual 'compounds'. The 
smaller, more polar fraction is generally termed fulvic acid and the 
larger, more nonpolar fraction is generally termed humic acid.
Humic acids are the endproduct of microbial degradation of plant and animal 
debris and are one of the most important constituents of fertile soils.

dave huebert

Humic Acids in Nature vs the Aquarium (Long)

by "James Purchase" <jpp/>
Date: Fri, 14 Feb 1997

Hi Everyone,

As some of you may recall, last month I was on a tear to find out what
level of Tannins and Humic Acids existed in tropical blackwater biotopes.
Some companies (and authors) seem to think that a certain level of these
substances are beneficial (why else would so many companies be peddling
"Blackwater Extracts"?) while others caution that these substances can be
harmful if present in excess.

My query was an attempt to determine what the natural levels of these types
of substances were. The fish have evolved over thousands of years in these
types of waters and I felt that if we had an idea of the concentrations in
Nature we would be in a better position to deal with them in an aquarium.

Several people on the list came forward with information, my thanks to
those who did. I also contacted several companies which produce "Blackwater
Extracts". Unfortunately, none of them bothered to even acknowledge my
query (Shame on you, Tetra/Second Nature!!!)  

I finally went to Dupla. Kaspar Horst of Dupla was kind enough to forward
my query to Prof Dr Rolf Geisler, who provided me with a detailed answer.
What follows is the translated text of that response, as prepared for me by
Dupla. Mr. Horst has givn his premission for this material to be placed on
this list.


A special answer for Mr. James Purchase, Toronto:
- - ------------------------------------------------------------
Concentration of humic acids and tanning agents in tropical black waters
- - ------------------------------------------------------------

Humates in their full sense - and not just humic acids - are an important
buffer systems for typical black waters with extremely low lime contents. A
precise analytical registration of the chemical complexe humates, dark
organic colloids, is very complicated and requires considerable technical
equipment that is only available in a few special laboratories. 

It is much easier to measure the content of "organic substances" and thus
also the humates contained in the water. All organic substances are carbon
linkages. In this way it is possible to determine the DOC (Dissolved
Carbon) or the TOC (Total Organic Carbon). This however requires the use of
gas chromatograph - a very expensive device - and a lot of technical

Since the beginning of tropic limnologic research a relatively simple
measurement method has been used: the determination of the co-called
potassium permanganate consumption (KMNO4-consumption in mg/l). In this
measurement the organic substances are destroyed by means of the oxydizing
agent potassium permanganat, thus becoming measurable. The determination is
carried out by cooking a given quantity of water with a permanganate
of exactly known content for about 10 minutes. For this method one needs a
certain laboratory equipment with chemicals, glass devices and cooking
facility - short: it is quite expensive !

Despite the well-known objections to this not really optimum determination
humates with the permanganate method, also recent tests of tropical fish
waters have been carried out in this way, so to allow comparison with
of former examinations. Unfortunately, there are no conversion factors for
permangante consumption to DOC or vice versa. 

Back to the initial question: Information about the permangante consumption
(sometimes indicated as "oxydisability") in biotops of tropical aquarium
and typical black waters is available. Here some figures: 

KMnO4-consumption in mg/l

up to 12                        low, gun-laying data for dringking-water
20 to 56                        biotope of Red Neon
26 to 59                        biotope of Discus Heckel
13 to 27                        biotope of "Brown Discus"
> 100, up to 250 max.   biotope of labyrinth fish is eas- and west (asia)

Now to the most important question: How is it possible to reach a certain
level of humates in the aquarium? 
There are various methods of supplying humates to an aquarium. Known is the
filtering over unfertilized peat, peat extracts, peat pallets, leaves,
oak-tree bark extracts and other preparations containing tanning agents.
These are many possibilities - but one important questions is still
unanswered. How much of the above mentioned substances is needed to reach
values as found in nature. It would be nice to have indications like,
so-and-so much peat granules or so-and-so many ml peat extract on a certain
quantity of water of clearly defined composition produce organic substances
corresponding to so-and-so many mg/l permanganate consumption. Why doesn't
this sort of information exist ?

First, the available sources of humates are not standardized, e.g. peat as
substance differs considerably depending on it's origin and storage place.
Indications such as " ... contains so-and-so many g peat extract" do not
really say anything about the quantity, since the concentration of the
extract is unknown or not indicated - admittedly also difficult to say!
important to know: The harder the water the more ineffective the humic
- - - more exactly: the dissolved lime in the water produces undissolvable
calcium humates. So, the higher the water hardness, the higher must be the
supply of humates in order to achieve an acidifying effect. The softer the
water, the less humates are needed and the better the effect. 

Conclusion: As the values of water hardness are worldwide different and the
concentration of humates are not standardized, to make a simple calculation
and state"In order to achieve a Neon water with 25 mg/l permanganate
consumption or a black water for chocolate-guramis with 80 mg/l, procede as
follows ..." Therefore the only things that will help an aquarist are his
experience and a water that is not too hard.

Further literature may be asked for at our editorial department.
> END 

James Purchase
Toronto, Ontario

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