Behavior\nof TiO₂ Released from Nano-TiO₂‑Containing\nPaint and Comparison to Pristine Nano-TiO₂

Abstract

In the assessment of the fate and\neffects of engineered nanomaterials\n(ENM), the current focus is on studying the pristine, unaltered materials.\nHowever, ENM are incorporated into products and are released over\nthe whole product life cycle, though mainly during the use and disposal\nphases. So far, released ENMs have only been characterized to a limited\nextent and almost nothing is known about the behavior of these materials\nunder natural conditions. In this work we obtained material that was\nreleased from aged paint containing nano-TiO₂, characterized\nthe particulate materials, and studied their colloidal stability in\nmedia with different pH and ionic composition. A stable suspension\nwas obtained from aged paint powder by gentle shaking in water, producing\na dilute suspension of 580 μg/L TiO₂ with an average\nparticle size of 200–300 nm. Most particles in this suspension\nwere small pieces of paint matrix that also contained nano-TiO₂. Some free nano-TiO₂ particles were observed by\nelectron microscopy, but the majority was enclosed by the organic\npaint binder. The pristine nano-TiO₂ showed the expected\ncolloidal behavior with increasing stability with increasing pH and\nstrong agglomeration above the isoelectric point and settling in the\npresence of Ca. The released TiO₂ showed very small variations\nin particle size, ζ potential, and colloidal stability, even\nin the presence of 3 mM Ca. The results show that the behavior of\nreleased ENM may not necessarily be predicted by studying the pristine\nmaterials. Additionally, effect studies need to focus more on the\nparticles that are actually released as we can expect that the toxic\neffect will also be markedly different between pristine and product\nreleased materials.