On the Role of Atmospheric Weathering on Paint Dust Aerosol Generated by Mechanical Abrasion of TiO2 Containing Paints

1. Introduction

Engineered nanomaterials (ENMs) have been integrated into construction materials including paints [1]. These nano-enabled products (NEPs) are commercially desirable due to their improved structural integrity, thermal conductivity, fire prevention, and self-cleaning features as compared to conventional products, and, as such, they are extensively used in commercially available consumer products [2,3,4,5]. Despite these advantages, most commercially available NEPs are not properly identified as containing nanomaterials. Moreover, knowledge about their health and environmental effects is scarce, particularly throughout the lifecycle of the product. For paint, it includes preparation and application on indoor and outdoor surfaces, environmental weathering and aging, and final removal, typically by mechanical abrasion. Many ENMs, such as carbon nanotubes, silicon dioxide (SiO₂), titanium dioxide (TiO₂), and copper oxide (CuO) have been shown to be harmful to humans, with pristine nanoparticles translocating from the lungs into the circulatory, lymphatic, and nervous systems [6,7,8,9,10].

Exposures of painters and other construction workers are most likely to occur at the early and last stages of the paint lifecycle. The sanding dust of walls and wood coated with nano-containing products was dominated by particles in the 100–300 nm size range [11]. TiO₂ and Ag nanoparticles were found in 80% of the collected paint dust particles [12]. The size of TiO₂-containing paint dust and the abundance of nano-sized TiO₂ agglomerates was related to the sandpaper grit size [13]. As a result, there is potential for occupational exposures to nanoparticles in paints. This may increase the probability of various diseases that involve the lungs, as painters already have consistently higher lung cancer mortality than other construction workers [14]. Additionally, the probability of a painter developing chronic obstructive pulmonary disease (COPD) is the second highest among all construction workers, following roofers [15].

Exposure to environmental conditions including weather and chemicals affects the integrity and stability of paint over time, leading to deterioration, breaks, and the release of chemical species. Kaegi et al. [16] determined that leachate from a two-year-old weather-exposed façade had significantly less ENMs than a freshly coated façade. Silver ENMs leaching showed that the first two months of exposure resulted in 30% of total ENM loss [17]. Atmospheric pollution can also be detrimental to coatings over time. Acid deposition is...