Editing Humic substance (section)

==Concepts of humic substances==
The formation of HS in nature is one of the least understood aspects of humus chemistry and one of the most intriguing. Historically, there have been three main theories to explain it: the lignin theory of [[Selman Waksman|Waksman]] (1932), the polyphenol theory, and the sugar-amine condensation theory of [[Louis Camille Maillard|Maillard]] (1911).<ref>Stevenson, F.J. (1994). ''Humus Chemistry: Genesis, Composition, Reactions'', Wiley & Sons, New York, 1994, pp. 188-210. {{ISBN|0471594741}}.</ref><ref>Tan, K. H. (2014). ''Humic matter in soil and the environment: principles and controversies''. 2nd ed. Boca Ranton: CRC Press. {{ISBN|1482234459}}.</ref>  Humic substances are formed by the microbial degradation of [[biotic material|dead biota matter]], such as [[lignin]], [[cellulose|cellulose. ligno-cellulose]] and [[charcoal]].<ref>{{citation |last1=Ponomarenko |first1=E.V. |last2=Anderson |first2=D.W. |title=Importance of charred organic matter in Black Chernozem soils of Saskatchewan |year=2001 |journal=Canadian Journal of Soil Science |volume=81 |issue=3 |pages=285–297 |quote= The present paradigm views humus as a system of heteropolycondensates, largely produced by the soil microflora, in varying associations with clay (Anderson 1979). Because this conceptual model and the simulation models rooted within the concept do not accommodate a large char component, a considerable change in conceptual understanding (a paradigm shift) appears imminent. |doi=10.4141/s00-075}}</ref><ref>{{cite journal|year=2012|title=Abundant and stable char residues in soils: implications for soil fertility and carbon sequestration|journal=Environmental Science and Technology|volume=46|issue=17|pages= 9571–9576 |doi=10.1021/es301107c|pmid=22834642|url=https://www.researchgate.net/publication/230571591
|last1=Mao|first1=J.-D.|last2=Johnson|first2=R. L.|last3=Lehmann|first3=J.|last4=Olk|first4=D. C.|last5=Neves|first5=E. G.|last6=Thompson|first6=M. L.|last7=Schmidt-Rohr|first7=K.|bibcode=2012EnST...46.9571M|citeseerx=10.1.1.698.270}}</ref>  Humic substances in the lab are resistant to further biodegradation. Their structure, elemental composition and content of functional groups of a given sample depend on the water or soil source and the specific procedures and conditions of extraction. Nevertheless, the average properties of lab extractes HS from different sources are remarkably similar.

=== Fractionation ===
<!-- The first paragraph of this section contains a repetition: two times the same extraction/purification procedure with slightly different wording. Need to be merged and simplified without losing information -->
Historically, scientists have used variations of similar methods for extracting HS from NOM and separating the extracts into HA and FA. The [[International Humic Substances Society]] advocates using standard laboratory methods to prepare humic and fulvic acids. Humic substances are extracted from soil and other solid sources using 0.1 M NaOH, under a nitrogen atmosphere, to prevent abiotic oxidation of some of the components of HS. The HA is then precipitated at pH 1. The soluble fraction is treated on a resin column to separate fulvic acid components from other acid soluble compounds.<ref>{{Cite web |title=Isolation of IHSS Soil Fulvic and Humic Acids {{!}} IHSS |url=https://humic-substances.org/isolation-of-ihss-soil-fulvic-and-humic-acids/ |access-date=2024-10-24 |language=en-US}}</ref> The fraction of NOM not extracted by 0.1 NaOH is humin. Humic and fulvic acid are extracted from natural waters using a resin column after microfiltration and acidification to pH 2. The humic materials are eluted from the column with NaOH, and humic acid is precipitated at pH 1. After adjusting the pH to 2, fulvic acid is separated from other acid soluble compounds, using a resin column as with solid phase sources.<ref>{{Cite web |title=Isolation of IHSS Aquatic Humic and Fulvic Acids {{!}} IHSS |url=https://humic-substances.org/isolation-of-ihss-aquatic-humic-and-fulvic-acids/ |access-date=2024-10-24 |language=en-US}}</ref> An analytical method for quantifying humic acid and fulvic acid in commercial ores and humic products, has been developed based on the IHSS humic acid and fulvic acid preparation methods.<ref>{{Cite journal |last1=Lamar |first1=Richard T |last2=Olk |first2=Daniel C |last3=Mayhew |first3=Lawrence |last4=Bloom |first4=Paul R |date=2014-05-01 |title=A New Standardized Method for Quantification of Humic and Fulvic Acids in Humic Ores and Commercial Products |url=https://academic.oup.com/jaoac/article/97/3/721-730/5654784 |journal=Journal of AOAC International |language=en |volume=97 |issue=3 |pages=721–730 |doi=10.5740/jaoacint.13-393 |pmid=25051616 |issn=1060-3271}}</ref>

Scientists associated with the IHSS have also isolated the entire NOM from [[blackwater river]]s using [[reverse osmosis]]. The retentate from this process contains both humic and fulvic acids, predominately humic acid. The NOM from hard water streams has been isolated using reverse osmosis and [[electrodialysis]] in tandem.<ref>{{Cite web |title=Isolation of NOM by Reverse Osmosis {{!}} IHSS |url=https://humic-substances.org/isolation-of-nom-by-reverse-osmosis/ |access-date=2024-10-24 |language=en-US}}</ref>

Extracted humic acid not a single [[acid]]; instead, it is a complex mixture of many different acids containing [[carboxyl]] and [[phenol]]ate groups so that the mixture behaves functionally as a [[dibasic acid]] or, occasionally, as a [[tribasic acid]]. Commercial humic acid used to amend soil is manufactured using these well-established procedures. Humic acids can form [[coordination complex|complex]]es with ions that are commonly found in the environment creating humic [[colloid]]s.<ref>{{cite web|url=http://www.vetservis.sk/media/object/433/effects_of_humic_acid_on_animals_and_humans.pdf|title=Effects of Humic Acid on Animals and Humans: An Overview of Literature and a Review of Current Research|website=vet servis}}</ref>

A sequential chemical fractionation can isolate more homogeneous humic fractions and determine their molecular structures by advanced spectroscopic and chromatographic methods.<ref>{{cite journal |author= Nebbioso A. and Piccolo A.|doi=10.1016/j.aca.2012.01.027|pmid=22365124|title=Advances in humeomics: Enhanced structural identification of humic molecules after size fractionation of a soil humic acid|journal=Analytica Chimica Acta|volume=720|pages=77–90|year=2012}}</ref> Substances identified in humic extracts and directly in soil include mono-, di-, and tri-[[hydroxycarboxylic acid]]s, [[fatty acid]]s, [[dicarboxylic acid]]s, linear alcohols, [[phenolic acid]]s, [[terpenoid]]s, carbohydrates, and amino acids.<ref>{{cite journal |author= Drosos M. and Piccolo A.|doi=10.1002/ldr.2989|title=The molecular dynamics of soil humus as a function of tillage|journal=Land Degradation & Development|volume=29|issue=6|pages=1792–1805|year=2018|s2cid=135445097 }}</ref> This suggests humic molecules may form a supramolecular structures held together by [[non-covalent]] forces, such as [[van der Waals force]], [[Stacking (chemistry)|π-π]], and CH-π bonds.<ref name="Piccolo, A. 2002 57–134">{{cite book |author=Piccolo, A. |title=The Supramolecular structure of humic substances. A novel understanding of humus chemistry and implications in soil science |year=2002 |isbn=978-0-12-000793-6 |series=Advances in Agronomy |volume=75 |pages=57–134 |doi=10.1016/S0065-2113(02)75003-7}}</ref>