Soil humic acid aggregation by dynamic light scattering and laser Doppler electrophoresis

• Published in: Journal of plant nutrition and soil science Vol. 176; no. 5; pp. 674 - 679
• Main Authors: JOVANOVIC, Uroš D, MARKOVIC, Mirjana M, CUPAC, Svjetlana B, TOMIC, Zorica P
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.10.2013; WILEY‐VCH Verlag; Wiley-VCH; Wiley Subscription Services, Inc
• Subjects: Adsorption; Aggregates; Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Elliot soil; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Ions; Organic matter; particle size; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Rendzic Leptosol; Soil science; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; zeta potential; Organic matter; Particle size; Light scattering; Rendzic Leptosol; zeta potential; Optical equipment; Organic acids; Elliot soil; Aggregation; Soils; Humus; Laser; Electrophoresis; Electrokinetic potential; Humic substance; Soil science; Soil plant relation; Humic acid
• ISSN: 1436-8730; 1522-2624
• DOI: 10.1002/jpln.201200346

Humic acids (HAs), similar to other fractions of humic substances (HSs), have a large number of reactive functional groups enabling them to aggregate in solutions. Regardless of the origin of humic acid (aqueous or soil), this aggregation process is dependent on environmental conditions and strongly influences the mobility of soluble ionic and molecular pollutants. The aim of this work was to monitor the aggregation process of two humic acids isolated from different mineral soils (IHSS Elliot soil HA standard and Rendzic Leptosol HA) in the 2–11 pH range. Changes in aggregate size in HA sols were followed up using dynamic light scattering (DLS), while zeta potential (ZP) measurements in the same pH range were performed applying laser Doppler electrophoresis (LDE) technique. The effect of HA sol concentration and soil source on aggregation was examined as well. Besides, HA samples were characterized using Fourier transform infrared (FT‐IR) spectroscopy. By inspecting HA‐particle‐size dependence on pH, it can be concluded that both HAs in corresponding sols behave as molecular aggregates or supramolecular structures, formed from small individual moieties (sizes < 10 nm) at higher pH values. The ZP vs. pH curve for both HAs revealed the ZP minimum in the 5–7 pH range, caused most likely by dissociation of acidic functional groups prevailing at lower pH values and deaggregation predominating over dissociation at higher pH values.