Additive Manufacturing for Occupational Hygiene: A Comprehensive Review of Processes, Emissions, & Exposures

Styrene lung cancer risk assessment: an alternative evaluation of human lung cancer risk assuming mouse lung tumors are potentially human relevant and operating by a threshold-based non-genotoxic mode of action

Rodent inhalation studies indicate styrene is a mouse lung-specific carcinogen. Mode-of-action (MOA) analyses indicate that the lung tumors cannot be excluded as weakly quantitatively relevant to humans due to shared oxidative metabolites detected in rodents and humans. However, styrene also is not genotoxic following in vivo dosing. The objective of this review was to characterize occupational and general population cancer risks by conservatively assuming mouse lung tumors were relevant to humans but operating by a non-genotoxic MOA. Inhalation cancer values reference concentrations for respective occupational and general population exposures (RfCcar-occup and RfCcar-genpop) were derived from initial benchmark dose (BMD) modeling of mouse inhalation tumor dose-response data. An overall lowest BMDL10 of 4.7 ppm was modeled for lung tumors, which was further duration- and dose-adjusted by physiologically based pharmacokinetic (PBPK) modeling to derive RfCcar-occup/genpop values of 6.2 ppm and 0.8 ppm, respectively. With the exception of open-mold fiber reinforced composite workers not using personal protective equipment (PPE), the RfCcar-occup/genpop values are greater than typical occupational and general population human exposures, thus indicating styrene exposures represent a low potential for human lung cancer risk. Consistent with this conclusion, a review of styrene occupational epidemiology did not support a conclusion of an association between styrene exposure and lung cancer occurrence, and further supports a conclusion that the conservatively derived RfCcar-occup is lung cancer protective.

Exposure to emissions generated by 3-dimensional printing with polycarbonate: effects on peripheral vascular function, cardiac vascular morphology and expression of markers of oxidative stress in male rat cardiac tissue

Three-dimensional (3D) printing with polycarbonate (PC) plastic occurs in manufacturing settings, homes, and schools. Emissions generated during printing with PC stock and bisphenol-A (BPA), an endocrine disrupter in PC, may induce adverse health effects. Inhalation of 3D printer emissions, and changes in endocrine function may lead to cardiovascular dysfunction. The goal of this study was to determine whether there were any changes in markers of peripheral or cardiovascular dysfunction in animals exposed to PC-emissions. Male Sprague Dawley rats were exposed to PC-emissions generated by 3D printing for 1, 4, 8, 15 or 30 d. Exposure induced a reduction in the expression of the antioxidant catalase (Cat) and endothelial nitric oxide synthase (eNos). Endothelin and hypoxia-induced factor 1α transcripts increased after 30 d. Alterations in transcription were associated with elevations in immunostaining for estrogen and androgen receptors, nitrotyrosine, and vascular endothelial growth factor in cardiac arteries of PC-emission exposed animals. There was also a reduction eNOS immunostaining in cardiac arteries from rats exposed to PC-emissions. Histological analyses of heart sections revealed that exposure to PC-emissions resulted in vasoconstriction of cardiac arteries and thickening of the vascular smooth muscle wall, suggesting there was a prolonged vasoconstriction. These findings are consistent with studies showing that inhalation 3D-printer emissions affect cardiovascular function. Although BPA levels in animals were relatively low, exposure-induced changes in immunostaining for estrogen and androgen receptors in cardiac arteries suggest that changes in the action of steroid hormones may have contributed to the alterations in morphology and markers of cardiac function.

Pulmonary evaluation of whole-body inhalation exposure of polycarbonate (PC) filament 3D printer emissions in rats

During fused filament fabrication (FFF) 3D printing with polycarbonate (PC) filament, a release of ultrafine particles (UFPs) and volatile organic compounds (VOCs) occurs. This study aimed to determine PC filament printing emission-induced toxicity in rats via whole-body inhalation exposure. Male Sprague Dawley rats were exposed to a single concentration (0.529 mg/m3, 40 nm mean diameter) of the 3D PC filament emissions in a time-course via whole body inhalation for 1, 4, 8, 15, and 30 days (4 hr/day, 4 days/week), and sacrificed 24 hr after the last exposure. Following exposures, rats were assessed for pulmonary and systemic responses. To determine pulmonary injury, total protein and lactate dehydrogenase (LDH) activity, surfactant proteins A and D, total as well as lavage fluid differential cells in bronchoalveolar lavage fluid (BALF) were examined, as well as histopathological analysis of lung and nasal passages was performed. To determine systemic injury, hematological differentials, and blood biomarkers of muscle, metabolic, renal, and hepatic functions were also measured. Results showed that inhalation exposure induced no marked pulmonary or systemic toxicity in rats. In conclusion, inhalation exposure of rats to a low concentration of PC filament emissions produced no significant pulmonary or systemic toxicity.

Everything falls apart: How solids degrade and release nanomaterials, composite fragments, and microplastics

To ensure the safe use of materials, one must assess the identity and quantity of exposure. Solid materials, such as plastics, metals, coatings and cements, degrade to some extent during their life cycle, and releases can occur during manufacturing, use and end-of-life. Releases (e.g., what is released, how does release happen, and how much material is released) depend on the composition and internal (nano)structures of the material as well as the applied stresses during the lifecycle. We consider, in some depth, releases from mechanical, weathering and thermal stresses and specifically address the use cases of fused-filament 3D printing, dermal contact, food contact and textile washing. Solid materials can release embedded nanomaterials, composite fragments, or micro- and nanoplastics, as well as volatile organics, ions and dissolved organics. The identity of the release is often a heterogenous mixture and requires adapted strategies for sampling and analysis, with suitable quality control measures. Control materials enhance robustness by enabling comparative testing, but reference materials are not always available as yet. The quantity of releases is typically described by time-dependent rates that are modulated by the nature and intensity of the applied stress, the chemical identity of the polymer or other solid matrix, and the chemical identity and compatibility of embedded engineered nanomaterials (ENMs) or other additives. Standardization of methods and the documentation of metadata, including all the above descriptors of the tested material, applied stresses, sampling and analytics, are identified as important needs to advance the field and to generate robust, comparable assessments. In this regard, there are strong methodological synergies between the study of all solid materials, including the study of micro- and nanoplastics. From an outlook perspective, we review the hazard of the released entities, and show how this informs risk assessment. We also address the transfer of methods to related issues such as tyre wear, advanced materials and advanced manufacturing, biodegradable polymers, and non-solid matrices. As the consideration of released entities will become more routine in industry via lifecycle assessment in Safe-and-Sustainable-by-Design practices, release assessments will require careful design of the study with quality controls, the use of agreed-on test materials and standardized methods where these exist and the adoption of clearly defined data reporting practices that enable data reuse, meta-analyses, and comparative studies.

Assessment of emissions and exposure in 3D printing workplaces in Taiwan

Three-dimensional (3D) printing is an emerging and booming industry in Taiwan. Compared to traditional manufacturing, 3D printing has various advantages, such as advanced customization, additive manufacturing, reduced mold opening time, and reduced consumption of precursors. In this study, the real-time monitoring of particulate matter (PM) and total volatile organic compound (TVOC) emissions from various filaments is investigated using fused deposition modeling with material extrusion technology, a liquid-crystal display, a stereolithography apparatus based on vat photopolymerization technology, and binder jetting for occupational settings. An exposure assessment for nearby workers using the 3D printing process was performed, and improvement measures were recommended. Nine 3D printing fields were measured. The generation rate of ultrafine particles ranged from 1.19 × 1010 to 4.90 × 1012 #/min, and the geometric mean particle size ranged from 30.91 to 55.50 nm. The average concentration of ultrafine particles ranged from 2.31 × 103 to 7.36 × 104 #/cm3, and the PM2.5 and PM10 concentrations in each field ranged from 0.74 ± 0.27 to 12.46 ± 5.61 μg/m3 and from 2.39 ± 0.60 to 30.65 ± 21.26 μg/m3, respectively. The TVOC concentration ranged from 0.127 ± 0.012 to 1.567 ± 0.172 ppm. The respiratory deposition (RDUFPs) dose ranged from 2.02 × 1013 to 5.54 × 1014 nm2/day. Depending on the operating conditions, appropriate control and protective measures should be employed to protect workers' health.

Exposure hazards of particles and volatile organic compounds emitted from material extrusion 3D printing: Consolidation of chamber study data

Ultrafine particles and volatile organic compounds (VOCs) have been detected from material extrusion 3D printing, which is widely used in non-industrial environments. This study consolidates data of 447 particle emission and 58 VOC emission evaluations from a chamber study using a standardized testing method with various 3D printing scenarios. The interquartile ranges of the observed emission rates were 109-1011 #/h for particles and 0.2-1.0 mg/h for total VOC. Print material contributed largely to the variations of particle and total VOC emissions and determined the most abundantly emitted VOCs. Printing conditions and filament specifications, included printer brand, print temperature and speed, build plate heating setup, filament brand, color and composite, also affected emissions and resulted in large variations observed in emission profiles. Multiple regression showed that particle emissions were more impacted by various print conditions than VOC emissions. According to indoor exposure modeling, personal and residential exposure scenarios were more likely to result in high exposure levels, often exceeding recommended exposure limits. Hazardous VOCs commonly emitted from 3D printing included aromatics, aldehydes, alcohols, ketones, esters and siloxanes, among which were various carcinogens, irritants and developmental and reproductive toxins. Therefore, 3D printing emits a complex mixture of ultrafine particles and various hazardous chemicals, exposure to which may exceed recommended exposure limits and potentially induce acute, chronic, or developmental health effects for users depending on exposure scenarios.

Health hazards of particles in additive manufacturing: a cross-disciplinary study on reactivity, toxicity and occupational exposure to two nickel-based alloys

The increasing use of additive manufacturing (AM) techniques (e.g., 3D-printing) offers many advantages but at the same time presents some challenges. One concern is the possible exposure and health risk related to metal containing particles of different sizes. Using the nickel-based alloys Hastelloy X (HX) and Inconel 939 (IN939) as a case, the aim of this cross-disciplinary study was to increase the understanding on possible health hazards and exposure. This was done by performing in-depth characterization of virgin, reused and condensate powders, testing in vitro toxicity (cytotoxicity, genotoxicity, oxidative stress), and measuring occupational airborne exposure. The results showed limited metal release from both HX and IN939, and slightly different surface composition of reused compared to virgin powders. No or small effects on the cultured lung cells were observed when tested up to 100 µg/mL. Particle background levels in the printing facilities were generally low, but high transient peaks were observed in relation to sieving. Furthermore, during post processing with grinding, high levels of nanoparticles (> 100,000 particles/cm3) were noted. Urine metal levels in AM operators did not exceed biomonitoring action limits. Future studies should focus on understanding the toxicity of the nanoparticles formed during printing and post-processing.

Occupational exposure and health surveys at metal additive manufacturing facilities

Introduction

Additive manufacturing is a novel state-of-the art technology with significant economic and practical advantages, including the ability to produce complex structures on demand while reducing the need of stocking materials and products. Additive manufacturing is a technology that is here to stay; however, new technologies bring new challenges, not only technical but also from an occupational health and safety perspective. Herein, leading Swedish companies using metal additive manufacturing were studied with the aim of investigating occupational exposure and the utility of chosen exposure- and clinical markers as predictors of potential exposure-related health risks.

Methods

Exposure levels were investigated by analysis of airborne dust and metals, alongside particle counting instruments measuring airborne particles in the range of 10 nm-10 μm to identify dusty work tasks. Health examinations were performed on a total of 48 additive manufacturing workers and 39 controls. All participants completed a questionnaire, underwent spirometry, and blood and urine sampling. A subset underwent further lung function tests.

Results

Exposure to inhalable dust and metals were low, but particle counting instruments identified specific work tasks with high particle emissions. Examined health parameters were well within reference values on a group level. However, statistical analysis implied an impact on workers kidney function and possible airway inflammation.

Conclusion

The methodology was successful for investigating exposure-related health risks in additive manufacturing. However, most participants have been working <5 years. Therefore, long-term studies are needed before we can conclusively accept or reject the observed effects on health.

Emissions and Exposures Associated with the Use of an Inconel Powder during Directed Energy Deposition Additive Manufacturing

Additive manufacturing (AM) has been linked to potential exposure-related health risks, however, there is a paucity of sufficient research. This study aimed to supply information regarding emissions and exposure during directed energy deposition (DED) AM using inconel 718, with the main constituents being nickel, chromium, and cobalt. By using standardized occupational hygiene methods, the measurement strategy consisted of a combined approach, including powder characterization, particle emission monitoring, and personal exposure monitoring of AM operators. Powder characterization of virgin and used powder indicated no significant difference in particle size, shape, or elemental composition. Particle number emissions ranged between 102 and 105 p/cm3 for submicron particles (<1 µm in size). There was no significant difference in the particle emission rate between the three phases of AM or the two types of DED machines (p > 0.05). The particle emission rate for submicron particles peaked at 2.8 × 109 p/min. Metals of concern to human health were detected during the AM process but were considerably lower than the relevant exposure limits. This study confirms particle emissions, predominantly in the submicron range, above the background concentration during DED AM and, although insignificant in terms of potential health effects, AM operators are exposed to detectable concentrations of the metal constituents of inconel.

Volatile Compound Emissions from Stereolithography Three-Dimensional Printed Cured Resin Models for Biomedical Applications

Stereolithography three-dimensional printing is used increasingly in biomedical applications to create components for use in healthcare and therapy. The exposure of patients to volatile organic compounds (VOCs) emitted from cured resins represents an element of concern in such applications. Here, we investigate the biocompatibility in relation to inhalation exposure of volatile emissions of three different cured commercial resins for use in printing a mouthpiece adapter for sampling exhaled breath. VOC emission rates were estimated based on direct analysis using a microchamber/thermal extractor coupled to a proton transfer reaction-mass spectrometer. Complementary analyses using comprehensive gas chromatography-mass spectrometry aided compound identification. Major VOCs emitted from the cured resins were associated with polymerization agents, additives, and postprocessing procedures and included alcohols, aldehydes, ketones, hydrocarbons, esters, and terpenes. Total VOC emissions from cubes printed using the general-purpose resin were approximately an order of magnitude higher than those of the cubes printed using resins dedicated to biomedical applications at the respective test temperatures (40 and 25 °C). Daily inhalation exposures were estimated and compared with daily tolerable intake levels or standard thresholds of toxicological concerns. The two resins intended for biomedical applications were deemed suitable for fabricating an adapter mouthpiece for use in breath research. The general-purpose resin was unsuitable, with daily inhalation exposures for breath sampling applications at 40 °C estimated at 310 μg day^-1 for propylene glycol (tolerable intake (TI) limit of 190 μg day^-1) and 1254 μg day^-1 for methyl acrylate (TI of 43 μg day^-1).

An explorative study on respiratory health among operators working in polymer additive manufacturing

Additive manufacturing (AM), or 3D printing, is a growing industry involving a wide range of different techniques and materials. The potential toxicological effects of emissions produced in the process, involving both ultrafine particles and volatile organic compounds (VOCs), are unclear, and there are concerns regarding possible health implications among AM operators. The objective of this study was to screen the presence of respiratory health effects among people working with liquid, powdered, or filament plastic materials in AM.

Methods

In total, 18 subjects working with different additive manufacturing techniques and production of filament with polymer feedstock and 20 controls participated in the study. Study subjects filled out a questionnaire and underwent blood and urine sampling, spirometry, impulse oscillometry (IOS), exhaled NO test (FeNO), and collection of particles in exhaled air (PEx), and the exposure was assessed. Analysis of exhaled particles included lung surfactant components such as surfactant protein A (SP-A) and phosphatidylcholines. SP-A and albumin were determined using ELISA. Using reversed-phase liquid chromatography and targeted mass spectrometry, the relative abundance of 15 species of phosphatidylcholine (PC) was determined in exhaled particles. The results were evaluated by univariate and multivariate statistical analyses (principal component analysis).

Results

Exposure and emission measurements in AM settings revealed a large variation in particle and VOC concentrations as well as the composition of VOCs, depending on the AM technique and feedstock. Levels of FeNO, IOS, and spirometry parameters were within clinical reference values for all AM operators. There was a difference in the relative abundance of saturated, notably dipalmitoylphosphatidylcholine (PC16:0_16:0), and unsaturated lung surfactant lipids in exhaled particles between controls and AM operators.

Conclusion

There were no statistically significant differences between AM operators and controls for the different health examinations, which may be due to the low number of participants. However, the observed difference in the PC lipid profile in exhaled particles indicates a possible impact of the exposure and could be used as possible early biomarkers of adverse effects in the airways.

Comprehensive Analysis of Two H13-Type Starting Materials Used for Laser Cladding and Aerosol Particles Formed in This Process

Laser cladding with H13 steel powders was performed and the related material transformations were studied for the particles emitted during this process. Fractions of various sizes of the aerosol particles formed during the laser cladding were collected on a cascade impactor, while the electromobility and the aerodynamic size of the particles were measured using a scanning mobility particle spectrometer and an aerodynamic particle sizer, respectively. The aerosol particles deposited onto the impactor plates were analyzed using scanning electron microscopy−energy-dispersive X-ray spectroscopy, as well as total-reflection X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Both the concentration and mean oxidation state of the major components were correlated with the aerosol particle size. The ultrafine aerosol particles (with a diameter less than about 100 nm) were predominantly oxidized and formed as the result of an evaporation−oxidation−condensation process sequence. The larger particles (>200 nm in geometric diameter) were primarily the residues of the original metal powder and exhibited a composition change as compared to the as-received metal powder. Correlations between the changes in the concentration ratio of the components were detected and explained.

Potential for Exposure to Particles and Gases throughout Vat Photopolymerization Additive Manufacturing Processes

Vat photopolymerization (VP), a type of additive manufacturing process that cures resin to build objects, can emit potentially hazardous particles and gases. We evaluated two VP technologies, stereolithography (SLA) and digital light processing (DLP), in three separate environmental chambers to understand task-based impacts on indoor air quality. Airborne particles, total volatile organic compounds (TVOCs), and/or specific volatile organic compounds (VOCs) were monitored during each task to evaluate their exposure potential. Regardless of duration, all tasks released particles and organic gases, though concentrations varied between SLA and DLP processes and among tasks. Maximum particle concentrations reached 1200 #/cm3 and some aerosols contained potentially hazardous elements such as barium, chromium, and manganese. TVOC concentrations were highest for the isopropyl alcohol (IPA) rinsing, soaking, and drying post-processing tasks (up to 36.8 mg/m3), lowest for the resin pouring pre-printing, printing, and resin recovery post-printing tasks (up to 0.1 mg/m3), and intermediate for the curing post-processing task (up to 3 mg/m3). Individual VOCs included, among others, the potential occupational carcinogen acetaldehyde and the immune sensitizer 2-hydroxypropyl methacrylate (pouring, printing, recovery, and curing tasks). Careful consideration of all tasks is important for the development of strategies to minimize indoor air pollution and exposure potential from VP processes.

Identification of effective control technologies for additive manufacturing

Additive manufacturing (AM) refers to several types of processes that join materials to build objects, often layer-by-layer, from a computer-aided design file. Many AM processes release potentially hazardous particles and gases during printing and associated tasks. There is limited understanding of the efficacy of controls including elimination, substitution, administrative, and personal protective technologies to reduce or remove emissions, which is an impediment to implementation of risk mitigation strategies. The Medline, Embase, Environmental Science Collection, CINAHL, Scopus, and Web of Science databases and other resources were used to identify 42 articles that met the inclusion criteria for this review. Key findings were as follows: 1) engineering controls for material extrusion-type fused filament fabrication (FFF) 3-D printers and material jetting printers that included local exhaust ventilation generally exhibited higher efficacy to decrease particle and gas levels compared with isolation alone, and 2) engineering controls for particle emissions from FFF 3-D printers displayed higher efficacy for ultrafine particles compared with fine particles and in test chambers compared with real-world settings. Critical knowledge gaps identified included a need for data: 1) on efficacy of controls for all AM process types, 2) better understanding approaches to control particles over a range of sizes and gas-phase emissions, 3) obtained using a standardized collection approach to facilitate inter-comparison of study results, 4) approaches that go beyond the inhalation exposure pathway to include controls to minimize dermal exposures, and 5) to evaluate not just the engineering tier, but also the prevention-through-design and other tiers of the hierarchy of controls.

Volatile organic compound and particulate emissions from the production and use of thermoplastic biocomposite 3D printing filaments

Biocomposites (BCs) can be used as substitutes for unsustainable polymers in 3D printing, but their safety demands additional investigation as biological fillers may produce altered emissions during thermal processing. Commercial filament extruders can be used to produce custom feedstocks, but they are another source of airborne contaminants and demand further research. These knowledge gaps are targeted in this study. Volatile organic compound (VOC), carbonyl compound, ultrafine particle (UFP), and fine (PM_2.5) and coarse (PM₁₀) particle air concentrations were measured in this study as a filament extruder and a 3D printer were operated under an office environment using one PLA and four PLA-based BC feedstocks. Estimates of emission rates (ERs) for total VOCs (TVOC) and UFPs were also calculated. VOCs were analyzed with a GC-MS system, carbonyls were analyzed with an LC-MS/MS system, whereas real-time particle concentrations were monitored with continuously operating instruments. VOC concentrations were low throughout the experiment; TVOC ranged between 34-63 µg/m³ during filament extrusion and 41-56 µg/m³ during 3D printing, which represent calculated TVOC ERs of 2.6‒3.6 × 10² and 2.9‒3.6 × 10² µg/min. Corresponding cumulative carbonyls ranged between 60-91 and 190-253 µg/m³. Lactide and miscellaneous acids and alcohols were the dominant VOCs, while acetone, 2-butanone, and formaldehyde were the dominant carbonyls. Terpenes contributed for ca. 20-40% of TVOC during BC processing. The average UFP levels produced by the filament extruder were 0.85 × 10²-1.05 × 10³ #/cm³, while the 3D printer generated 6.05 × 10²-2.09 × 10³ #/cm³ particle levels. Corresponding particle ERs were 5.3 × 10⁸-6.6 × 10⁹ and 3.8 × 10⁹-1.3 × 10¹⁰ #/min. PM_2.5 and PM₁₀ particles were produced in the following average quantities; PM_2.5 levels ranged between 0.2-2.2 µg/m³, while PM₁₀ levels were between 5-20 µg/m³ for all materials. The main difference between the pure PLA and BC feedstock emissions was terpenes, present during all BC extrusion processes. BCs are similar emission sources as pure plastics based on our findings, and a filament extruder produces contaminants at comparable or slightly lower levels in comparison to 3D printers.

Exposure to chemical substances and particles emitted during additive manufacturing

Additive manufacturing is an innovative technology that allows the production of three-dimensional objects replicating digital models. The aim of this study was to identify whether the use of this technology in a room without mechanical ventilation system may pose a health risk to its users due to the emission of chemical compounds and fine particles. Measurements were conducted in a furnished space with natural ventilation only, during additive manufacturing on a fused deposition modeling printer with 9 different filaments. Both chemicals and particles were sampled. Volatile organic compounds and phthalic acid esters were determined by gas chromatography-mass spectrometry detection. Carbonyl compounds were determined using the high-performance liquid chromatography with diode-array detection method. Fine particle emission studies were carried out using a DiSCmini particle counter (Testo). In the air samples, numerous chemical substances were identified including both the monomers of the individual materials used for printing such as styrene and other degradation products (formaldehyde, toluene, xylenes). Moreover, 3D printing process released particles with modal diameters ranging from 22.1 to 106.7 nm and increased the number concentration of particles in the workplace air. The results of analyses, depending on the type of material applied, showed the presence of particles and chemical substances in the working environment that may pose a risk to human health. Most of the identified substances can be harmful when inhaled and irritating to eyes and skin.

Organic compound and particle emissions of additive manufacturing with photopolymer resins and chemical outgassing of manufactured resin products

Photopolymer resins are applied at an increasing rate in additive manufacturing (AM) industry as vat photopolymerization (VP) and material jetting (MJ) methods gain more popularity. The aim of this study was to measure volatile organic compound (VOC), carbonyl compound, ultrafine particle (UFP), and particulate matter (PM₁₀) air concentrations emitted in 3D printer operations. Individual chemicals were identified when multiple photopolymer resin feedstocks were used in various VP and MJ printers. The size distributions of UFPs, and indoor air parameters were also monitored. Finally, the VOC outgassing of the cured resin materials was determined over 84 days. The data demonstrated that 3D printer operators were exposed to low concentrations of airborne exposure agents as follows: average concentrations of VOCs were between 41 and 87 µg/m³, UFP number levels ranged between 0.19 and 3.62 × 10³ number/cm³; however, no impact was detected on air parameters or PM₁₀ concentrations. A majority of the UFPs existed in the 10-45 nm size range. The identified compounds included hazardous species included sensitizing acrylates and carcinogenic formaldehyde. The outgassed products included similar compounds that were encountered during the AM processes, and post-processing solvents. Products heated to 37°C emitted 1.4‒2.9-fold more VOCs than at room temperature. Total emissions were reduced by 84‒96% after 28 days roughly from 3000-14000 to 100-1000 µg/m²/hr. In conclusion, resin printer operators are exposed to low concentrations of hazardous emissions, which might result in adverse health outcomes during prolonged exposure. Manufactured resin products are suggested to be stored for 4 weeks after their production to reduce potential consumer VOC hazards.

Towards sustainable additive manufacturing: The need for awareness of particle and vapor releases during polymer recycling, making filament, and fused filament fabrication 3-D printing

Fused filament fabrication three-dimensional (FFF 3-D) printing is thought to be environmentally sustainable; however, significant amounts of waste can be generated from this technology. One way to improve its sustainability is via distributed recycling of plastics in homes, schools, and libraries to create feedstock filament for printing. Risks from exposures incurred during recycling and reuse of plastics has not been incorporated into life cycle assessments. This study characterized contaminant releases from virgin (unextruded) and recycled plastics from filament production through FFF 3-D printing. Waste polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) plastics were recycled to create filament; virgin PLA, ABS, high and low density polyethylenes, high impact polystyrene, and polypropylene pellets were also extruded into filament. The release of particles and chemicals into school classrooms was evaluated using standard industrial hygiene methodologies. All tasks released particles that contained hazardous metals (e.g., manganese) and with size capable of depositing in the gas exchange region of the lung, i.e., granulation of waste PLA and ABS (667 to 714 nm) and filament making (608 to 711 nm) and FFF 3-D printing (616 to 731 nm) with waste and virgin plastics. All tasks released vapors, including respiratory irritants and potential carcinogens (benzene and formaldehyde), mucus membrane irritants (acetone, xylenes, ethylbenzene, and methyl methacrylate), and asthmagens (styrene, multiple carbonyl compounds). These data are useful for incorporating risks of exposure to hazardous contaminants in future life cycle evaluations to demonstrate the sustainability and circular economy potential of FFF 3-D printing in distributed spaces.