Exposure characterisation and sources of nanoparticles in workplace environments

Abstract

Exposure to micro- and nano-scaled particles has been widely linked to adverse health effects including pulmonary, cardiovascular and nervous system disease leading to increased mortality and morbidity rates. With regard to population exposure, indoor microenvironments constitute a particularly vulnerable source given that adults spend on average 60 - 80% of their time indoors, and approximately 50% of it in the workplace.

The fast development and spread of innovative technologies and processes used in many industrial sectors (with and without relation to nanotechnology) have benefited from advances but new risks and uncertainties related to possible exposure to unknown nanoparticle types and concentrations may arise. In the workplace, workers may be exposed to nanoscale particles while dealing with engineered nanoparticles (ENP) or process-generated nanoparticles (PGNP) during specific industrial processes involving unintentional nanoparticle release or the formation of nanoparticles from gaseous precursors. Due to the relative novelty of “nanosafety” as a field of research, relevant studies about ENP and PGNP release and exposure under real-world conditions are relatively scarce. Furthermore, adequate analytical techniques and monitoring instrumentation have only recently become available. To date, specific online instrumentation for the targeted detection of nanoparticles in real-time is lacking.

The goals of this PhD thesis were to (i) assess the performance of novel instrumentation for nanoscale aerosol measurements, and (ii) to carry out exposure assessments to nanoparticles emitted in workplaces under real-world operating conditions, focusing on ENP and PGNP. The scenarios selected for exposure characterisation were single- walled carbon nanotubes (SWCNT) manufacturing and application processes, and tile ablation and sintering with laser technologies used in the ceramic industry. In addition to emissions and potential particle transformations in workplace air, the potential for particle release to the outdoor environment, and the effectiveness of control measures were assessed in both types of exposure scenarios. The results obtained are presented in the form of five research articles.

Results regarding the assessment of monitoring instrumentation concluded that only through the combination of diverse monitoring techniques and parameters does it become possible to obtain a detailed characterisation of nanoparticle exposure routes and scenarios.

In the study where workers’ quantitative exposure to SWCNT while manufacturing conductive thin films was assessed, it was found that the conventional production and application of SWCNT showed only very limited nanoparticle emissions into the workplace air, with exposure concentrations below the occupational exposure limits available. However, a failure of the local exhaust ventilation in reactor process may give rise to high airborne nanoparticle concentrations near the worker breathing zone (exceeding the recommended exposure limits).

The measurements performed in ceramic industries showed that ENP are not the only source of workplace exposure to nanoparticles. Also important can be the exposure to PGNP. High-thermal processes applied frequently in ceramic industries such as tile sintering and ablation, may give rise to nanoparticle exposure concentrations which are significantly higher than those registered in industries which use ENP as input materials. Nanoparticle exposure concentrations in workplace air during these high-thermal processes were, in addition, statistically significant and considered above the exposure limit (4 x 104 cm-3). Thus, the contributions of PGNP to the total nanoparticle workers exposure should not be ignored in risk assessments. Industrial control measures should be proposed and tested specifically for this type environment, tailored to its needs. The effectiveness of the mitigation measures in place in the environments assessed during this PhD thesis were tested and results showed that the use of appropriate strategies may reduce worker exposure to nanoparticles (ENP and PGNP) by up to 98%.