A method for antimicrobial treatment comprising applying to microbes a composition containing a diluting solvent (e.g., water), an antimicrobially-active solvent having a density different from the density of the diluting solvent, and an optional cosolvent, surfactant, or additional antimicrobial agent, wherein the amount of antimicrobially-active solvent or additional antimicrobial agent is sufficiently high and the amount of cosolvent or surfactant is sufficiently low so that the composition will provide greater than a 1-log order reduction in the population of bacteria or spores of Bacillus cereus within 10 seconds at 60 C. Preferred methods of the invention employ compositions containing an additional antimicrobial agent such as peroxyacetic acid. Compositions for use in the method can be prepared as concentrates, and used full strength or in diluted form.