Virus Passage through Track-Etch Membranes Modified by Salinity and a Nonionic Surfactant

Why do viruses sometimes not pass through larger pores in track-etch filters? Increasing the salinity (0.8 to 160 mM Na(+)) decreased φX174 and PRD1 passage through track-etch polycarbonate membranes (sodium dodecyl sulfate coated but not polyvinylpyrrolidone coated) and PRD1 passage through polyester membranes. Undiminished passage when 0.1% Tween 80 was added implied that nonionic virus adsorption occurred and indicated that high levels of salinity decreased virus passage by decreasing electrostatic repulsion that prevented adsorption.