Behavior of TiO₂ Released from Nano-TiO₂-Containing Paint and Comparison to Pristine Nano-TiO₂

Abstract

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

Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland

“…Even if ENMs are released in an untransformed state, they may not be nano-relevant because the ENMs are often embedded in matrix fragments (Froggett et al, 2014). These fragments face different fates and have different effects compared to pristine nanomaterials (Al-Kattan et al, 2014;Kaiser et al, 2013a). This shows that simply knowing the overall flows of ENMs in the construction sector is insufficient; there must be detailed information on the fate and behavior of particles in the environment.…”

Review of nanomaterial aging and transformations through the life cycle of nano-enhanced products

“…However, it has to be noted that in this study a conventional paint containing only pigment TiO 2 was investigated and not a nano-paint. However, Al-Kattan et al found similar matrix-bound particles in leaching studies with paints containing nano-TiO 2 and nano-SiO 2 (Al- Kattan et al, 2013Kattan et al, , 2014Kattan et al, , 2015. Kaegi et al found a similar result when investigating Ag ENPs in aged paint, with some evidence from EDX analysis to suggest the formation/release of Ag 2 S. Depending on the nature of the TiO 2 ENPs (synthesis process, annealing), the "TiO 2 ENP film" can show super hydrophilic properties (Thongsuwan et al, 2011) that are susceptible to increase the surface degradation rate.…”

Agglomeration of Ag and TiO2 nanoparticles in surface and wastewater: Role of calcium ions and of organic carbon fractions

“…Silver and TiO 2 are among the most commonly encountered nanoparticles applied in consumer products in recent years (www.nanotechproject.org). However, their prevalent usage is of concern because of their possible release to the environment (Al-Kattan et al, 2014;Gondikas et al, 2014;Gottschalk and Nowack, 2011;Hedberg et al, 2014;Kaegi et al, 2013;Lombi et al, 2014), which may result in exposure of the ecosystem components and lead to adverse effects (Ali et al, 2014). Agglomeration and dissolution studies are providing valuable contributions for the speciation of the nanoparticles in the environment which are essential to develop an understanding of the mobility and transformation of ENPs.…”