Fate and transport of anthropogenic nanomaterials in water

Nanomaterials may carry adverse effects on the environment and pose a potential risk for human health. The objective of this research is to evaluate the fate and transport of anthropogenic nanomaterials in aquatic environments by addressing the following issues: (1) characterization and dispersion of nanomaterials; (2) the influence of pH, electrolytes and surface functional groups (capping ligands) on stability of nanomaterials; (3) the removal of nanomaterials by water treatment processes; and (4) the impact of natural organic matter (NOM) on stability and removal of nanomaterials.; Commercial metal oxide nanoparticles formed aggregates during synthesis procedure and storage period. Neither sonication nor dispersants could break them up to primary nanoparticles in water. Except for silica, other metal oxide nanoparticles were unstable in tap water. The stability of silica is related to its low Hamaker constant. The addition of potassium chloride destabilized all metal oxide nanoparticles by compressing their electrical double layers. During simulated water treatment processes, 40% to 80% of metal oxide nanoparticles were removed from the water.; In contrast, quantum dots (QDs) presented as primary nanoparticles and remained stable in potassium chloride solutions due to their capping ligands. The protonation of capping ligands and multi-valent cations complexation with capping ligands caused the CID aggregation. However, the complexation of hydrated aluminum ions with capping ligands prevented the formation of aluminum hydroxide flocs; so it required alum dosages higher than the solubility of aluminum ion to remove QDs from nanopure water by sedimentation. In tap water, because divalent cations induced the formation of OD flocs, 70% of QDs settled out even without alum.; NOM plays an important role on determining the behaviors of nanoparticles. NOM adsorption enhanced the stability of nanoparticles by imparting negative charge and increasing their absolute surface potentials. For NOM-coated nanoparticles, calcium ions caused their aggregation by reducing their negative surface charge and increasing the ionic strength. During water treatment processes, a high alum dosage (200 mg/L) was required to remove nanoparticles from the buffered NOM solution. The findings indicate that the co-existing NOM and sodium bicarbonate stabilized aluminum hydroxide precipitates to prevent the formation of settleable flocs.