Fulvic acid

Fulvic acids are a family of organic acids, natural compounds, and components of the humus (which is a fraction of soil organic matter).[1] They are similar to humic acids, with differences being the carbon and oxygen contents, acidity, degree of polymerization, molecular weight, and color.[2] Fulvic acid remain in solution after removal of humic acid from humin by acidification.[3][4][5]

  • Extraction stage

Fulvic acid, one of two classes of natural acidic organic polymers that can be extracted from humus found in soil, sediment, or aquatic environments. Its name derives from Latin fulvus, indicating its yellow colour. This organic matter is soluble in strong acid (pH = 1) and has the average chemical formula C135H182O95N5S2. A hydrogen-to-carbon ratio greater than 1:1 indicates less aromatic character (i.e., fewer benzene rings in the structure), while an oxygen-to-carbon ratio greater than 0.5:1 indicates more acidic character than in other organic fractions of humus (for example, humic acid, the other natural acidic organic polymer that can be extracted from humus). Its structure is best characterized as a loose assembly of aromatic organic polymers with many carboxyl groups (COOH) that release hydrogen ions, resulting in species that have electric charges at various sites on the ion. It is especially reactive with metals, forming strong complexes with Fe3+, Al3+, and Cu2+ in particular and leading to their increased solubility in natural waters. Fulvic acid is believed to originate as a product of microbial metabolism, although it is not synthesized as a life-sustaining carbon or energy.[6]

Fulvic acid is created in extremely small quantities under the influence of millions of useful microbes, working on the decay of plant matter in a soil environment with sufficient oxygen.[7]

Fulvic acids cannot be readily synthesized[8] because of their extremely complex nature, although lignosulfonates from the paper industry can appear similar to fulvic acids in certain tests as discussed below.[9]

At the same time, the main problem is not extraction, but subsequent purification, in particular, the breaking of the molecular bond with Cl, Fe, which together with FA form toxic dihaloacetonitriles[10] and have the property of accumulating in the body before reaching the critical point.

Methods of determination in extract

Until recently, there has been no standardized analytical method that the scientific community could rely on for consistent accuracy to determine the quantity of fulvic acid in an extract. Without an industry standard, manufacturers and sellers of fulvic products used methods that resulted in various claims being made on labels, marketing literature and websites of commercial fulvic acid products. These claims have caused many scientists and consumers to question the validity and accuracy of these claims about fulvic acid content, which made the evaluation of fulvic products very difficult.

Analytical quantification methods in the past measured both humic and fulvic acid as one substance. This created analytical challenges and mass confusion for those products that are fulvic isolates, having no measurable or very low humic acid in them. It is also the primary reason that fulvic acid content claims were usually inaccurate and much higher than is being brought to light with the new standardised method.

Lamar standardized method

The Lamar standardized method[11] involves combining the sample with one litre of a 0.1M sodium hydroxide solution, mixing for at least an hour, removing insoluble material with a centrifuge, precipitating humic acids by acidifying to pH 1 with hydrochloric acid, and absorbing the unprecipitated fulvic acids onto a macroporous absorbent resin. The isolated humic and fulvic acids are then separately dried, and weighed before and after ashing in a furnace.

The method was developed by a team of scientists and individuals from various organizations involved in soil science. The Lamar method was recently accepted as the standardized method for fulvic acid quantification by Association of American Plant Food Control Officials, the Humic Products Trade Association, and the International Humic Substances Society.

Butler method

Until the emergence of the standardized Lamar method in 2015, this has been the most accurate of all testing methods for fulvic acid and may still hold promise since the results produced, with regards to fulvic acid content, are somewhat similar to the Lamar method.

Fulvic acid is condensed tannin and can be absorbed by a resin whereby it can be quantified much more accurately by reading the vanillin conjugates of the sample. The one disadvantage to this method, as compared to the Lamar method, is that it does not purify or separate the lignin sulfates from the fulvic acid fraction leading to some inaccuracies in the final FA result.

Colorimetric

Humic acid is exposed to light; the amount of light absorbed is compared to the quantification value of a Sigma-Aldrich standardized sample taken from a mine in Germany. Although quick and easy, this method lumps the fulvic acid in with the humic acid producing poor quantification of fulvic isolates.

California method (CDFA)

This test was developed by the California State Department of Agriculture. This method does separate the humic and the fulvic but it then discards the fulvic solution and only measures the remaining liquid also including the organic ash content as part of the quantification result with no purification steps performed to remove the ash. This of course leads to various analytical inaccuracies. This is the only method that the California departments of agriculture will accept when registering a product. California does not recognize fulvic acid as separate substance from humic acid and requires that all label registrations list the content as humic acid only. Until 2017, Oregon also required using this method but has recently switched to the Lamar Method of fulvic acid quantification and now allows the label registration of fulvic acid as a substance apart from humic acid.

Verploegh and Brandvold method

The Verploegh and Brandvold method (V&B) quantifies both humic and fulvic acid and is a quick, cost effective, and easy test to perform. It does not go through purification of the chemical reagents used to separate the humic and fulvic acids. This results in various inaccuracies that can produce inflated fulvic acid content readings since amino acids, lipids, carbohydrates and lignin sulfates are all lumped in with the quantification.

References
  1. Bremner, J. M. (1951-01-01). "A Review of Recent Work on Soil Organic Matter Part I". Journal of Soil Science. 2 (1): 67–82. doi:10.1111/j.1365-2389.1951.tb00591.x. ISSN 1365-2389.
  2. "Properties of humic substances". karnet.up.wroc.pl. Retrieved 2016-11-17.
  3. Aiken, G. R.; McKnight, D. M.; Thorn, K. A.; Thurman, E. M. (1992-07-01). "Isolation of hydrophilic organic acids from water using nonionic macroporous resins". Organic Geochemistry. 18 (4): 567–573. doi:10.1016/0146-6380(92)90119-I.
  4. Chefetz, Benny; Chen, Yona; Hadar, Yitzhak; Hatcher, Patrick G. (1998-03-04). "Characterization of Dissolved Organic Matter Extracted from Composted Municipal Solid Waste". Soil Science Society of America Journal. 62 (2): 326. doi:10.2136/sssaj1998.03615995006200020005x. ISSN 0361-5995.
  5. Perdue, Dr. E. Michael. "IHSS - Welcome Page". www.humicsubstances.org. Retrieved 2016-11-17.
  6. "Fulvic acid | chemical compound".
  7. Environment with adeequate oxygen — Schnitzer, M. (1977). Recent findings of the characterization of humic substances extracted from soils from widely differing climatic zones. Proceedings of the Symposium on Soil Organic Matter Studies, Braunsweig (117—131)
  8. Murray, K., & Linder, P. W. (1983). Fulvic acids: Structure and metal binding. I. A random molecular model. Journal of Soil Science, 34, 511—523
  9. Senesi, N., Chen, Y., & Schnitzer, M. (1977b). the role of humic acids in extracellular electron transport and chemical determination of pH in natural waters. Soil Biology and Biochemistry, 9, 397—403
  10. Oliver, B. G (1983). "Dihaloacetonitriles in drinking water: Algae and fulvic acid as precursors". Environmental Science & Technology. 17 (2): 80–83. doi:10.1021/es00108a003. PMID 22295957.
  11. Richard T. Lamar, Daniel C. Olk, Lawrence Mayhew, and PauL R. Bloom (2014). "A New Standardized Method for Quantification of Humic and Fulvic Acids in Humic Ores and Commercial Products" (PDF). Journal of AOAC International. 97 (3): 721–730. doi:10.5740/jaoacint.13-393.CS1 maint: multiple names: authors list (link)
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