Straining is the physical filtration of particles in wedges formed by narrow pores of porous media such as soils. It is a likely process for large particles, as the chance is of course higher that during their transport these get stuck in narrow pores. Straining has been postulated to occur also for engineered nanoparticles, but it has been suggested that the nanoparticles tend to undergo homoaggregation or heteroaggregation first, thus forming aggregates that in turn get stuck in narrow pores. 

There is no need to determine experimentally a separate fate descriptor for straining, since straining is a process embedded in the attachment process and therefore accounted for in the attachment efficiency obtained from saturated column tests. Straining is dependent on the pore geometry of the soil. The smaller the pores, the higher the chance of straining, yielding a higher attachment rate

Occurs in


Fate descriptors



\(\Psi =(\frac{d_{50}+z}{d_{50}})^{-\beta }\)

Attachment efficiency Straining Calculation

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Visit the NanoFASE Library:

NanoFASE Report D7.2 Soil property - NM fate relationships and geographical distribution of possible NM transport distances in Europe 

Bradford, S.A., et al. (2003) Modeling Colloid Attachment, Straining, and Exclusion in Saturated Porous Media. Environmental Science & Technology, 37(10): p. 2242-2250 

Bradford S A, et al. (2006) Significance of straining in colloid deposition: Evidence and implications. Water Resources Research. 42: W12S15.

Shangping X, et al. (2006) Straining of colloidal particles in saturated porous media. Water Resources Research. 42:W12S16. 




Karin Norrfors

Swedish University of Agricultural Sciences (SLU)





Geert Cornelis

Swedish University of Agricultural Sciences (SLU)