<abstract> <p>Despite high medical and biological potential, the penetration of iron oxide nanoparticles (NPs) into a human body can cause their dissolution with subsequent accumulation of highly toxic iron compounds. The paper describes the agglomeration and dissolution behavior of differently sized α-Fe₂O₃ NPs in the simplest biological solutions. The average sizes of the initial NPs according to the BET analysis are 12, 32, and 115 nm. Within 30–60 min exposure, the particle size and concentration of iron released into the solutions increases in the suspensions, accompanied by an intensive change of NPs surface charge. After an hour of exposure, the colloidal properties do not change significantly, although the dissolution degree ambiguously fluctuates. It has been shown that the agglomeration of the particles in the simplest pulmonary fluid is lower than in the simplest sweat fluid, compared to the dissolution degree, which is much higher in the pulmonary fluid than in the sweat. The colloidal stability of suspensions reduces with a decrease of NPs' size, e.g., the average size of particles is 315,289, and 248 nm, while zeta potential is 2, 9, and 17 mV, respectively for 12, 32, and 115 nm NPs in 3-hour suspensions. It has been found that 24 h dissolution degree of α-Fe₂O₃ NPs reaches 2.3% and 0.4%, respectively, in the simplest pulmonary and sweat fluids. The mechanism of dissolution of hematite NPs in the slightly acidic and acidic mediums is proposed.</p> </abstract>

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