Exposure assessment of carbon nanotubes at pilot factory focusing on quantitative determination of catalytic metals

Abstract

Objectives: The application of multiwall carbon nanotubes (MWCNTs) currently extends to various fields. However, it has been reported that exposure to CNT causes hazardous effects on animals and cells. The purpose of this study was to quantify the exposure to MWCNT in MWCNT/polymer composites for exposure assessment. We focused on catalytic metals included in the MWCNT and the diameter of dust released during the working processes. Although the Co in MWCNTs is not a common catalyst, it was used as a tracer in this study. Methods: A field survey was conducted in a MWCNT/polymer composite pilot factory. Airborne MWCNTs were monitored using black carbon monitors (BCMs) and optical particle sizers (OPSs) and collected on a filter. The MWCNT powder, all polymer resins used during the working processes, and the filter were analyzed in our lab using inductively coupled plasma mass spectrometry (ICP-MS) and electron microscopic observation. Results: The mean concentration of airborne MWCNT contained in the collected dust was 0.92 μg/m3 a few meters away from the extruder during the working processes (using elemental analysis). The maximum concentration measured using BCMs was shown to be seven times higher than the base concentration during the pelletizing process of polycarbonate (PC) and MWCNT composites. However, free, isolated, and unbound agglomerated MWCNTs were not detected using scanning electron microscopic (SEM) observation. Conclusions: The result obtained by elemental analysis indicated it was possible to quantify MWCNT in composites. The mean concentration at this factory was lower than the recommended exposure limit. However, additional studies during the pelletizing process are required in the future.

Real-Time Emission and Exposure Measurements of Multi-walled Carbon Nanotubes during Production, Power Sawing, and Testing of Epoxy-Based Nanocomposites

“…An alternative monitoring method of airborne CNTs could have been elemental analysis of catalytic metals in the CNTs collected during filter sampling ( Maynard et al , 2004 ; Kato et al , 2017) . Analysis in the previously mentioned studies showed that the CNTs contained traces of different metal, such as Fe, Mo, Al, and Co.…”

“…The existing literature includes a few earlier studies of emission and exposure in connection to CNT composite production ( Cena and Peters, 2011 ; Fleury et al , 2013 ; Thompson et al , 2015 ; Kato et al , 2017) , as well as studies of machining processes such as sanding and sawing of CNT composites ( Bello et al, 2009 , 2010 ; Cena and Peters, 2011 ; Wohlleben et al , 2013 ; Ding et al , 2017 ; Kuijpers et al , 2019 ; Ogura et al , 2019 ). There is high-quality evidence that workers are occupationally exposed to CNTs during production of CNTs, mainly in handling tasks such as pouring, weighing, mixing, harvesting, extruding, sonication, and packaging of CNT powder or liquid suspensions ( Debia et al , 2016 ).…”

Yttrium Residues in MWCNT Enable Assessment of MWCNT Removal during Wastewater Treatment

“…While Y was chosen as the surrogate trace residual metal in this study, each MWCNT will have distinctive synthesis methods [26,38,39] and thus will likely have unique trace residual metal compositions. Consequently, other researchers used Y or different trace elements to track CNTs (e.g., Co, Ni, Mo) [15,16,17,18,19,20,21,22]. It will be important to understand these differences between MWCNTs and whether a unified method can be developed to quantify MWCNTs through spICP-MS or ICP-MS using trace residual metals or whether trace residual metals like Y can be useful as a marker in standardized testing of MWCNTs moving forward.…”

“…Current analytical techniques to detect and quantify carbon nanoparticles include programmed thermal analysis (PTA), Raman spectroscopy, UV-visible spectrophotometry, and microwave treatment with thermal analysis, but most available techniques have detection limits in solid matrices and water on the order of 10–100 mg kg −1 or 0.1–10 mg L −1 , respectively [14]. Recent studies evaluated the ability of single particle inductively coupled plasma-mass spectrometry (spICP-MS) to detect residual trace catalytic metals (e.g., Fe, Y, Ni, Co, Mo) that persisted in single- or multi-walled carbon nanotubes (SWCNTs) at ng L −1 levels in an aqueous matrix [15,16,17,18,19,20,21,22,23,24]. Therefore, we explored spICP-MS and ICP-MS directly for the detection of known specific commercial MWCNTs in complex wastewater matrices.…”