This article was submitted to Nanotoxicology, a section of the journal Frontiers in Toxicology
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This study monitored particulates, and volatile organic compounds (VOCs) emitted from 3-D printers using acrylonitrile-butadiene-styrene copolymer (ABS) filaments at a workplace to assess exposure before and after introducing exposure mitigation measures. Air samples were collected in the printing room and adjacent corridor, and real-time measurements of ultrafine and fine particle were also conducted. Extensive physicochemical characterizations of 3-D printer emissions were performed, including real-time (size distribution, number concentration) nanoparticle characterization, size-fractionated mass distribution and concentration, as well as chemical composition for metals by ICP-MS and VOCs by GC-FID, real-time VOC monitors, and proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS). Air sampling showed low levels of total suspended particulates (TSP, 9–12.5/m3), minimal levels (1.93–4 ppm) of total volatile organic chemicals (TVOC), and formaldehyde (2.5–21.7 ppb). Various harmful gases, such as formaldehyde, acrolein, acetone, hexane, styrene, toluene, and trimethylamine, were detected at concentrations in the 1–100 ppb by PTR-TOF-MS when air sample was collected into the Tedlar bag from the front of the 3-D printer. Ultrafine particles having an average particle size (30 nm count median diameter and 71 nm mass median diameter) increased during the 3-D printing operation. They decreased to the background level after the 3-D printing operation, while fine particles continually increased after the termination of 3-D printing to the next day morning. The exposure to 3-D printer emissions was greatly reduced after isolating 3-D printers in the enclosed space. Particle number concentration measured by real-time particle counters (DMAS and OPC) were greatly reduced after isolating 3-D printers to the isolated place.
The newly developed technology of 3-D printing, a collective term for additive manufacturing or fused deposition modeling (FFD), is penetrating the marketplace fast and can be found in many teaching laboratories in universities and 1–12 grade schools, as well as in research laboratories and industrial settings. During 3-D printing, objects are manufactured from a computer-assisted design model by successively adding material layer by layer. The composition of the filament used in 3-D printing is modified to meet final product specifications, and increasingly, more filament options are available. Acrylonitrile-butadiene-styrene copolymer (ABS) or Polylactic acid (PLA) filaments are used for fused filament fabrication (FFF) or FFD printing machines. ABS filaments require a higher extruder nozzle to form thermoplastic resins in the solid-state than PLA which melts at a lower temperature (
The health effects caused by 3-D printing exposure drew attention in Korea recently, after two teachers who used 3-D printers frequently for teaching science courses in their high schools were diagnosed with sarcoma. Moreover, four more teachers in three different high schools were confirmed to have developed cancer, three with sarcomas and one with another type of cancer. 3-D printers were widely distributed and used in more than 50% of these elementary, middle, and high schools (
The current study measured the 3-D printer emission particles and VOC concentrations at a workplace equipped with two 3-D printers (Sindoh - 3-DWOX 7X and AFINIA 3-D - H800+) and Universal Robots (UR). In addition, VOC sampling was conducted outside the corridor of the workplace.
Two differential mobility analyzing systems (DMAS) combining differential mobility analyzer (DMA-20, 4220, range 6–225 nm, HCT Co., Ltd. Korea; TSI, United States) and condensation particle counters (CPC, 3775, size range 4 nm- 1, TSI INC., Shoreview, MN 0–108 particles/cm3 detection range) were used to monitor the particle size distribution with an electrical mobility diameter ranging from 15 to 710.5 nm. Meanwhile, three types of dust monitors (Model 1.109, range 0.25–32, Grimm, Douglasville, GA; Model PS-1601PM, range 0.25–10, HCTm, Co. Incheon, Korea; PS-1601PMe, range 0.25–10 μm, HCTm, Co. Incheon, Korea) were used to monitor the particle size distribution with a diameter ranging from 0.25 to 32 µm. The workplace air was sampled at a flow rate of 0.3 and 1.2 L/min for the DMAS and dust monitor, respectively. The DMAS scanned the particle sizes at a time resolution of 2.5 min (120 s for up-scan and 30 s for retrace), while the average time for the dust monitor was 1 min. The real-time aerosol monitoring lasted 3 days at the 3-D printing workplace. All the sequences of events that might affect particle monitoring were recorded (
Benzene, styrene, and formaldehyde were measured at six locations by area sampling using Coconut Charcoal sorbent tubes (SKC Cat. 226-01) (
Since most of the VOCs, evaluated by the NIOSH NMAM 1301 (GC FID) (
The MMAD of particles generated from the 3-D printer was measured using a foil filter for each stage (diameter, 47 mm; pore size, 5 mm; SKC, Inc., Eighty-Four, PA, United States) with a Nano MOUDI impactor (MOUDI 125 NR, MSP Co., MN, United States) composed of 13 stages (0.01, 0.018, 0.032, 0.056, 0.10, 0.18, 0.32, 0.56, 1.0, 1.8, 3.2, 5.6, and 10 mm). The geometric standard deviation (GSD) for the MMAD was derived from the cumulative mass distribution of the micro-orifice uniform deposition impactor (MOUDI).
An electrostatic precipitator ESPnano (Model 100; ESPnano, Spokane, WA, United States), operating at the standard sampling flow rate of 0.1 L/min, was used to collect aerosol particles on electron microscopy grids. The TEM nickel grid (Formvar/Carbon 200 mesh, TEDpella, CA, United States) or holey TEM grid (Quantifoil 656-200-Cu; Tedpella, Inc., Redding, CA, United States) were further examined under a transmission electron microscope (TEM, H - 7650; Hitachi, Tokyo, Japan) equipped with an EDX (energy dispersive X-ray analyzer, TM200; Oxford Instruments PLC, Oxfordshire, United Kingdom) at an acceleration voltage of 100 kV (
After noticing the 3-D printer emission exposure status, the company took an exposure mitigation measure, as shown in
The workplace average temperature was 26.9°C and ranged 22.7°C at 8:33 to 28.8°C at 16:47. Relative humidity ranged from 37.3% at 8:41 to 31.1% at 13:44. Carbon dioxide concentrations were 550 ppm at 8:44–9:08 and 1515 ppm at 16:52 (
TSP concentrations determined from gravimetric analysis during the 9-h of work shift at various locations ranged 0.008–0.011 mg/m3. Sampling inside of the housing of the printer resulted in a non-detectable mass change on the filter concentration (limit of detection µg/m3) (
Concentrations of total suspended particulate (TSP) at various sites and particle concentration measured by DMAS, PM sensor, and OPS.
TSP mass concentration (mg/m3) | ||||
---|---|---|---|---|
Time | Sampling time min | mg/m3 | 8 h TWA (mg/m3) | |
Area-1 | 544 | 0.011 | 0.0125 | |
Area-2 | 544 | 0.008 | 0.009 | |
Area-3 | 544 | 0.011 | 0.0125 | |
Area-4 | 544 | 0.009 | 0.0102 | |
Area-5 | - | - | - | |
Inside of printer enclosure | 86- | ND | ND | |
Particle number concentration before exposure mitigation | ||||
AM | Min | Max | ||
PM 2.5 (#cc) | 0.001 | 0.000 | 0.013 | |
DMAS (#/cc) | 16,290 ± 4,468 | 2,569 | 27,005 | |
OPS (#/L) | 37 ± 7 | 27 | 72 | |
Particle number concentration after exposure mitigation | ||||
DMAS (#/cc) | 4981 | 2698 | 7719 | |
OPS (#/L) | 71 | 36 | 185 |
ND, not detected; Area-1, behind of Worker 2; left side of 3-D printer-1; Area-3; top of 3-D printer A; Area-4 in front of 3-D printer-2; Area-5, Corridor; AM. Arithmetic mean; Min, minimum; Max, maximum.
Benzene and styrene measured at various time points were not detected. The TVOC concentrations ranged from 0.2 to 4 ppm with an average of 1.93 ppm. Formaldehyde at various locations was detected at 2.5–21.7 ppb, whereas the inside of the printer was 19.7 ppb, much less than ACGIH TLV-TWA (100 ppb) (2017). Total PAH levels from PAS 2000 were less than 1 ng/m3 throughout the measurement time (
Concentrations of formaldehyde before and after
Formaldehyde (ppb) | ||||||
---|---|---|---|---|---|---|
Before exposure mitigation | After exposure mitigation | |||||
Time | 8:30–11:50 | 13:30–16:00 | 16:20–17:40 | Time | 9:00–13:00 | 13:00–15:00 |
Area-1 | 10.2 | 16.0 | 9.2 | Area-6 | 23.1 | 9.2 |
Area-2 | 9.4 | 16.8 | 18.6 | Area-7 | 26.3 | 18.6 |
Area-3 | 7.9 | 13.7 | 21.7 | - | - | |
- | ||||||
Area-4 | 8.8 | 13.2 | 20.9 | - | - | - |
Area-5 | 4.6 | 2.5 | - | Area-9 | 42.6 | 11.2 |
Inside of printer enclosure | - | - | 19.7 | Inside of printer booth enclosure (Area-8) | 25.9 | 11.7 |
Outdoor formaldehyde concentration during 9:00–15:30 was 11.5 ppb.
A wide variety of harmful gases were detected at low concentrations down to the ppb level (
Concentrations of VOCs by PTR-TOF-MS.
VOCs | Mean | S.D. | Min | Max |
---|---|---|---|---|
Formaldehyde | 29.8 | 1.8 | 26.9 | 33.4 |
Acetaldehyde | 8.4 | 0.2 | 8.0 | 8.8 |
Acetone | 1493.6 | 18.5 | 1461.4 | 1540.8 |
Acrolein | 6.3 | 0.8 | 5.4 | 10.7 |
Benzene | 0.4 | 0.0 | 0.4 | 0.4 |
1,3-Butadiene | 0.2 | 0.0 | 0.1 | 0.2 |
Chloroethylene | 1.1 | 0.1 | 1.0 | 1.2 |
Chloroform | 3.3 | 0.1 | 3.0 | 3.5 |
Dimethyl disulfide | 2.4 | 0.1 | 2.1 | 2.7 |
Ethanol | 181.5 | 7.2 | 174.2 | 214.5 |
Ethylbenzene | 1.3 | 0.1 | 1.2 | 1.4 |
Hexane | 10.6 | 0.5 | 9.9 | 12.2 |
Isopropyl Alcohol | 66.3 | 5.3 | 58.4 | 78.2 |
Methylethylketone | 4.3 | 0.4 | 3.5 | 4.8 |
Methanol | 102.5 | 0.9 | 100.3 | 104.4 |
PGME |
9.4 | 0.6 | 8.0 | 11.0 |
Phenol | 8.2 | 0.6 | 6.7 | 9.6 |
Propene | 124.9 | 10.3 | 109.4 | 147.3 |
Styrene | 2.7 | 0.3 | 2.4 | 3.6 |
Toluene | 13.0 | 0.4 | 12.4 | 14.2 |
Trimethylamine | 13.1 | 0.8 | 11.8 | 15.3 |
Xylene | 1.3 | 0.1 | 1.2 | 1.4 |
Unit: ppb
Propylene glycol monomethyl ether.
UFPs measured by DMAS ranged between 2,569–27,005 particle/cm3 with an average of 16,290 ± 4,468 particle/cm3 during the operation of 3-D printers (
Real-time particle measurement in 3-D printing workplace.
After the initial exposure assessment, the management of the workplace noticed the status of exposure to the 3-D printer emission and initiated exposure mitigation. They isolated the two 3-D printers in the enclosed space, which has ventilation on the ceiling (
Count median diameter (CMD) measured by DMAS was 30 nm (
Size distribution of 3-D printer emissions measured by DMAS and Nano-MOUDI.
Well dispersed ABS particles were observed with TEM, where some particles were aggregated (
TEM micrograph of ABS particles and EDX-analysis.
This study has conducted a comprehensive characterization of exposures, including VOCs, particle number and mass concentration, size distribution, and elemental composition/morphology. Exposure assessment documented low levels of total suspended particulates (9–12.5 µg/m3), minimal levels (1.93–4 ppm) of TVOC as measured by real-time monitor, and formaldehyde (2.5–21.7 ppb), with no detectable levels of benzene and styrene by GC-FID. However, PTR-TOF-MS analysis of grab samples detected various chemicals at low concentrations, the majority of which were in the low ppb. The reason is that PTR-TOF-MS has much better analysis sensitivity than GC/FID. UFPs emitted from 3-D printers had an average particle size of 30 nm CMD and 71 nm MMAD, and their size continued to increase after the termination of 3-D printing through the night until the next day morning. The particle number concentration reduced greatly after installation of an ventilated enclosure for the 3-D printers.
Our particle size measurement of 3-D printing emission from the inside of the 3-D printer-1 enclosure indicated that 3-D printer-1 emissions generated as vapors of semi-volatile organics could not be measured with DMAS, and as they cooled off, the vapors condensed to form the nucleation stage, where their size is measurable by DMAS, to further coagulation stage where their size is measurable by OPC or dust monitor. In contrast, emissions taken from 3-D printer-2 showed 1.73-2.50 × 106 particle/cc depending on the 3-D printing process. Our UFP concentration of 16,000 particle/cc during printer operations was similar to the range reported by other studies (
Potential health effects of the particulates and VOC compounds emitted by 3D printers were studied by various authors using either acellular or
There are several exposure mitigation strategies in the workplace;
A comprehensive characterization of exposures to 3-D printer emission including VOCs, particle number concentration, mass concentration, size distribution, and elemental composition/morphology resulted in low levels of total suspended particulates (9–12.5 µg/m3), minimal levels (1.93–4 ppm) of TVOC, and formaldehyde (2.5–21.7 ppb), with no detectable levels of benzene and styrene by GC-FID. PTR-TOF-MS analysis of grab samples detected various chemicals at low concentrations, most of which were in the low ppb. UFPs emitted from 3-D printers had an average particle size of 30 nm CMD and 71 nm MMAD, and their size continued to increase after the termination of 3-D printing through the night until the next morning. After recognizing emissions from 3-D printers, the workplace initiated 3-D printer emission exposure mitigation by encapsulating the 3-D printers. After mitigation, the exposure assessment showed a reduction of 3-D printer emissions and some indication of VOC reduction, as indicated by VOC reduction indicated by formaldehyde concentration.
The original contributions presented in the study are included in the article/
BK experimental and manuscript preparation; JS, experimental preparation; HoK, experimental preparation, MJ, experimental preparation; HeK, aerosol measurement; JL, advice and manuscript review; HL, aerosol measurement; SH, advice and manuscript review; NK, advice and manuscript review; MG, advice and manuscript review; DB, advice and manuscript review; and IY, experimental planning, manuscript preparation and review. All authors read and approved the final manuscript.
Authors HoK, MJ, HeK, HL, and IY were employed by HCTm and IY is employed by HCT, Co.
The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
Authors are recognizing a service from APM Engineering Co, Ltd (Korea) for supporting PTR-TOF-MS analysis. Also, authors are appreciating Dasom Jung for helping with the analysis of GC and HPLC.
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