Water-dispersible colloids extraction methods: combining methodological data analysis and batch experiments to explore trends, feasibility, and impact on colloidal characteristics

Abstract Background Water-dispersible soil colloids (WDC) play a significant role in various soil processes, such as in nutrient storage and release. Therefore, it is essential to investigate and characterize WDC to understand their behavior and characteristics. However, a diversity of methods used to extract WDC for characterization is found in literature, which consequently makes interstudy comparison of colloidal data challenging. In this study, we analyzed methodological data on WDC extraction obtained from literature through Principal Component Analysis (PCA) and K-means clustering to examine methodological trends and similarities. Selected extraction methods from the methodological clusters (and the type of dispersant used) were evaluated experimentally to assess how different extractions influence WDC characteristics, and in terms of their feasibility. Results PCA of methodological information showed that most methodological parameters were drivers of extraction method diversity. From the K-means clusters of the four Principal Components, three extraction methods were identified for comparison. The first method employed sedimentation and centrifugation to separate the WDC fraction, yielding 0.2–0.4% (w/w) of WDC relative to the fresh soil mass. The second method only used sedimentation and extracted the highest WDC quantity (0.6–2.0%), but with the highest proportion of particles with diameters > 1000 nm. The third method involved centrifugation and filtration, extracting 0.02–0.08% of WDC, with an average maximum colloidal particle diameter of 638 nm. While the use of different dispersants did not have an influence on WDC yield, it influenced the particle size distribution (PSD) of WDC extracted, specifically in organic soil. Furthermore, the individual influence of the extraction method and dispersant and their interaction effects on WDC elemental composition vary with soil and the element of concern. Conclusion Our findings demonstrate that extraction methods influence WDC characteristics in terms of yield, PSD, and elemental composition. The type of dispersant also affects the PSD of WDC in organic soil, and its influence on elemental composition varies depending on soil type and elemental component. Among the extraction methods compared, the first method emerged as the most balanced and reliable approach in extracting WDC in terms of yield and feasibility.