The overall average diffusion constant for the micelle-templated gold nanoparticles in this soil system is determined to be 1.1 ± 0.3 × 10 -10 m 2 s -1 . We note that this is a relatively slow diffusion, in comparison with ionic species in soil such as K + (10 -7 -10 -8 m 2 s -1 ) and NO3 -(10 - 6 -10 -7 m 2 s -1 ). This is in line with what one would expect from a much larger nanoparticle reagent, and indicates that these nanoparticles can be effective tracers for flow experiments