Colloid Release from Soil Aggregates: Application of Laser Diffraction

Abstract

The content of water‐dispersible colloids (WDC) has a major impact on soil functions and structural stability. In addition, the presence of mobile colloids may increase the risk of colloid‐facilitated transport of strongly sorbing environmental contaminants. The WDC content was measured in 39 soils, using laser diffraction, by agitating the samples using a wet‐dispersion unit. This approach eliminated the need for long sedimentation times required by the more classical end‐over‐end shaking approach and provided information about the time‐dependent release of WDC. The total clay content of the soils ranged from 0.1 to 0.44 kg kg−1. The WDC content was measured on air‐dry and moist 1‐ to 2‐mm aggregates. The WDC content at a reference time was highly correlated to the total clay content (r > 0.91, P < 0.001) for all soils. Only for two sites was the WDC content correlated to the content of clay not associated with organic C (r > 0.89, P < 0.001), calculated as a function of total organic C and total clay. The colloid release rates were highly correlated with the total clay content (r > 0.84, P < 0.001). The WDC content in moist aggregates measured using laser diffraction was correlated with the WDC content measured using a more classical end‐over‐end method (r > 0.89, P < 0.05) and in 100‐cm3 undisturbed soil cores (r > 0.89, P < 0.05). The universal correlation between the contents of WDC and total clay could be highly useful in risk assessments of colloids and colloid‐facilitated transport of environmental contaminants.