The nature of the surface activity in the soft anions remains a matter of debate. Whereas continuum electrostatics predicts that all ions are repelled from the air/water interface , early MD simulations using polarizable force fields suggested that soft anions are not only present at the interface but in fact partition preferentially there . More recent work, however, has suggested that these concentration enhancements were exaggerated by the force fields in use at the time , which aligns with the interpretation of some of the early experiments . According to this point of view, surface activity may simply reflect the absence of depletion of soft anions at the interface , rather than a concentration enhancement.