Superparamagnetic nanoparticles in tap water

Magnetization measurements are a useful tool in the characterization of corrosion products formed in municipal water pipes made of iron or steel. Fine particles formed in corrosion processes exhibit superparamagnetic behavior. The size of such particles, which determines their capacity to adsorb hazardous species, can therefore be found from magnetic measurements. Application of this methodology to samples extracted from flowing and stagnant tap water, respectively, has shown that the flowing water samples contained multidomain (>100 nm) ferromagnetic particles as well as aggregates of very fine superparamagnetic subdomain particles. The sizes of the fine particles are of the order of 3.2-5.6 nm. In addition to small subdomain superparamagnetic particles stagnant water samples also contained larger subdomain particles with average dimensions of 59-67 nm. Both large and small subdomain particles were trapped by the fine charcoal in household filters.