From nano to micrometer size particles – A characterization of airborne cement particles during construction activities
Graphical abstract
Introduction
An increasing number of nanotechnology-based products are making its way into the construction sector (Zhu et al., 2004). One such product is photocatalytic cement made by adding nano-scaled (less than 100 nm in size) titanium dioxide (TiO2) particles. This gives the cement self-cleaning properties (Lan et al., 2013; Paz et al., 1995). The increasing use of nanomaterials have led to an increased need for hazard and exposure information on these materials in order to anticipate, recognize, evaluate, and control factors in the workplace, which otherwise may cause impaired health among workers.
TiO2 was classified as “possibly carcinogenic to humans” (class 2B) by the International Agency for Research on Cancer (IARC) (IARC, 2017; WHO, 2010). In the U.S., the National Institute for Occupational Safety and Health (NIOSH) provided a more nuanced assessment by classifying only ultrafine (nanoscale) TiO2 as a potential carcinogen, while considering the data to be insufficient for making such a statement for fine (larger) TiO2 (NIOSH, 2011). The hazard associated with exposures to nano-sized TiO2 particles (nano TiO2) has been reported by a series of studies (NIOSH, 2009). Nano TiO2 was found to increase reactive oxygen species (ROS) production (Arenberg and Arai, 2020; Ma et al., 2012; Sayes et al., 2006; Lee et al., 2010; Long et al., 2006), and induce DNA damage (Falck et al., 2009; Ghosh et al., 2010; WHO, 2010; Sha et al., 2015) and cell toxicity (Xue et al., 2015a; Sha et al., 2015; Lee et al., 2010; Sayes et al., 2006). Furthermore, nano TiO2 can be translocated to different organs and accumulate in the kidneys, lymph nodes, heart, liver, and brain (Wang et al., 2008; Kreyling et al., 2010; Geiser and Kreyling, 2010; Shi et al., 2013; Shinohara et al., 2015).
Nano TiO2 particles are highly photoreactive. They react with organic and inorganic gases (Chen and Poon, 2009; Lim et al., 2000; Dalton et al., 2002; Diesen and Jonsson, 2014; Fujishima and Zhang, 2006) and induce phototoxicity in microorganisms (Lan et al., 2013; Carp et al., 2004; Banerjee et al., 2015; Chen and Poon, 2009; Lee et al., 2010; Ge and Gao, 2008). This biocidal effect is one of the reasons why nano TiO2 is an interesting additive because it renders building surfaces “self-cleaning” because it kills any organic growth.
Photocatalytic cement is mainly regular cement with TiO2 nanoparticles and additives. Regular cement has been used since the Roman era to build strong structures by mixing cement with water, rock, and sand (Foulke, 2008). Only 2−3 wt% nano TiO2 were added to cement to produce photocatalytic cement (Ma et al., 2015; Jimenez-Relinque et al., 2015; Batsungnoen et al., 2019). The particle size distributions of aerosolized photocatalytic cement generated during work activities are not known. Given that nano TiO2 is not chemically bound to the cement particles, they might still behave like nanoparticles, and may easily be released (Aitken et al., 2004; Ostiguy et al., 2006; Friedlander and David, 2003; Ding et al., 2017).
The risk for work related diseases over a lifetime in a construction trade is 2–6 times greater compared to non-construction work. About 16 % of construction workers develop chronic obstructive pulmonary disease (COPD) (Ringen et al., 2014). Cement dust exposures are one of the health concerns. They are generated during many construction activities (van Deurssen et al., 2014) such as abrasive blasting, bag emptying, cement mixing, concrete drilling, concrete block cutting, sawing, and sweeping. Inhalation is the most common route of entry for airborne cement as well as for nanoparticles. Inhaled cement dust can lead to multiple lung diseases such as chronic respiratory symptoms, lung function impairment, bronchitis, COPD, pneumoconiosis, silicosis, and lung cancer (Eom et al., 2017; Maciejewska and Bielichowska-Cybula, 1991; Meo, 2004; Penrose, 2014; Nordby et al., 2011; Yang et al., 1996; Moghadam et al., 2017).
Cement also contains silicon dioxide (SiO2). Crystalline silica, as quartz and cristobalite, are carcinogenic to humans (IARC, 2012, 2017; IARC, 1997). Moreover, crystalline silica causes chronic bronchitis, COPD, and silicosis (Kaewamatawong et al., 2005; Napierska et al., 2010; Soutar et al., 2000).Higher concentrations of amorphous silica might cause pneumoconiosis, granuloma formation, reversible inflammation, and emphysema (McLaughlin et al., 1997; Merget et al., 2002; Kaewamatawong et al., 2005). For crystalline silica, NIOSH recommends an exposure limit of 0.05 mg/m3 (OSHA, 2018), and for amorphous silica 6 mg/m3 (NIOSH, 2018).
The construction industry employs millions of workers. Many die or suffer from occupational diseases arising from accumulated exposure to hazardous substances (ILO, 2014). Managing hazardous exposures properly can reduce the burden of disease, but can only be done effectively if exposures have been characterized. Currently, there are no studies characterizing airborne nano TiO2 in cement during work activities.
Our aim was to characterize airborne nano- and micrometer particle exposures during typical construction work activities for photocatalytic and regular cement. Our results can be directly used in developing risk management strategies among construction workers using photocatalytic cement. In addition, it will enhance our understanding of airborne nanoparticles and their size distributions, concentrations, and morphologies in mixtures with other particles.
Section snippets
Materials
Portland cement type I (cement-clinker; CE number 266-043-4) was obtained from Jura cement (Wildegg, Switzerland). Photocatalytic cement was acquired as a sample from the manufacturer (TX-Active®, Italcementi group, Nazareth, US). Fine sand used to make concrete was bought from a general home improvement store in Switzerland.
Characterization of the two cement types
Airborne particles were characterized by assessing their size distribution, number and mass concentration, morphology, phase analysis, and elemental composition. The
Cement bag emptying
Particle number concentrations during activity and post-activity were similar for the two cement types. For photocatalytic cement, bag emptying generated 3.7 × 103 particles per cubic centimeter (pt/cm3) giving a GMD of 322 nm and a GSD of 2.90; and 3.6 × 103 pt/cm3, GMD 227 nm and GSD 3.31 for regular cement. Fig. 4A shows nanoparticle number concentrations and size distributions for both photocatalytic and regular cement during bag emptying measured with the SMPS. Cement bag emptying
Discussion
In experiments with photocatalytic cement, we observed much larger mass-fractions of airborne particle-bound TiO2 during sweeping (9.7 wt%) and during bag emptying (16.5 wt%) than what we found in the bagged cement (2 wt%). This shows that nano TiO2 was easily airborne during activities with cement powder. It is in agreement with our previous dustiness study conducted with the same cement type where we observed nano TiO2 to become airborne far easier than the remainder of the cement powder (
Conclusion
The airborne nano TiO2 concentration was far greater than the labeled 2 wt% in the photocatalytic cement bag during simulation, increasing to 9.7 wt% during sweeping and 16.5 wt% during bag emptying. Work activities studied in the exposure chamber such as sweeping and bag emptying gave rise to nano TiO2 air concentrations while concrete cutting did not. Thai and Swiss construction workers using regular cement had different exposure profiles. Thai workers were mostly exposed during sweeping and
CRediT authorship contribution statement
Kiattisak Batsungnoen: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Writing - original draft, Writing - review & editing, Visualization. Michael Riediker: Conceptualization, Methodology, Writing - review & editing, Visualization, Supervision. Guillaume Suárez: Conceptualization, Methodology, Validation, Investigation, Resources, Writing - review & editing, Visualization, Supervision. Nancy B. Hopf: Conceptualization, Methodology, Validation,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Funding was received from Center for Primary Care and Public Health (Unisanté), Department of Occupational and Environmental Health (formerly known as Institute for Work and Health, IST), Switzerland, the Royal Thai Government, and the Ministry of Science and Technology, Thailand. We greatly appreciate help from Dr. Nicolas Concha Lozano for the morphology, crystalline silica analysis, and elemental composition analysis. We would like to thank Ms. Nicole Charriere, Mr. Benoit Allaz, Mr. Nicolas
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