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Inhalation of polycarbonate emissions generated during 3D printing processes affects neuroendocrine function in male rats

Updated July 3, 2023

July 2023
NIOSH Dataset RD-1069-2023-0

Introduction

Three-dimensional printing (3DP) of manufactured goods has increased in the last 10 yrs.  The increased use of this technology has resulted in questions about the health effects of inhaling emissions generated during printing.  The goal of this study was to determine if inhalation of particulate and toxic chemicals generated during printing with polycarbonate (PC) plastic affected the neuroendocrine system.  Male rats were exposed to 3D-printer emissions (500 µg/cm3) or filtered air for 1, 4, 8, 15 or 30d for 4d/week (4h/day).  The effects of these exposures on hormone concentrations, and markers of function, injury and/or oxidative stress in the olfactory bulb, hypothalamus and testes were measured after 1, 8 and 30d of exposure.  Thirty days of exposure to 3D-emissions resulted in reductions in  thyroid stimulating hormone, follicle stimulating hormone and prolactin.  These changes were accompanied by increases in markers of cell injury and reductions in active mitochondria in the olfactory bulb, gonadotropin releasing hormone cells and fibers and tyrosine hydroxylase immunolabeled fibers in the arcuate nucleus, and reductions in spermatogonium.  PC plastics contain high concentrations bisphenol A and these results are consistent with the hypothesis that the health effects of inhaling 3D-printer emissions may be due to bisphenol A.

Data Collection Methods

Animals.  Male Sprague Dawley rats ([H1a: (SD) CVF, n = 6 rats/group (N=60); 6-7 weeks of age, 200 – 250 g) were obtained from Hilltop Lab Animals, Inc., Scottdale, PA.  All animals were free of viral pathogens, parasites, myoplasm’s, Heliobacter and cilia-associated respiratory (CAR) bacillus.

Exposure  After 1 week of acclimation to the facility, animals were exposed to filtered-air (controls) or emissions generated by 3D printing.  More specifically, 3 desktop 3D-printers (LuluBot Mini, Fargo Additive Manufacturing Equipment 3D LLC, Fargo, ND) were placed in an airtight stainless-steel chamber. Black polycarbonate filament was fed into each printer and the printers were operated continuously during the 4 h exposure period. The emissions were blown into an exposure chamber where animals were housed in individual chambers (12 animals/exposure). Analysis of volatile organic compounds by GC/MS. Emissions were collected using the canister method (NIOSH Manual of Analytic Methods (NMAM 3900))

and were analyzed by GC/MS over a 4-h collection period. Particulate was also collected onto glass fiber filters and bisphenols were measured by HPLC (BVNA labs; Novi, MI)

Tissue collection:  Animals were exposed for 4 h/day 4 days/week.  Groups of animals (6 air control and 6 treated) were euthanized by injection of pentobarbital (100 mg/kg i.p.) 24 h after 1, 4, 8, 15 or 30 days of exposure.  Brains were collected and half the brain along with the pituitaries were frozen on dry ice and stored at -80ºC until sectioned by histology and immunohistochemistry.  The other half was dissected and individual regions of interest were stored at  -80Cº until assayed. Plasma was separated from whole blood and stored at -80Cº until assayed.  Testes were fixed in 10% formalin, paraffin embedded and sectioned for histological and immunohistochemical analyses.

Tissue preparation: Histology.  The left hemisphere of the brain was sectioned (20 µm) for histological or immunohistochemical analyses, one slide from each animal and each region was processed. The right testis was also dissected from each animal and placed in 10% buffered formalin and sectioned (10µm) for immunohistochemistry and histology.

Microscopy.  Fluorescent-labeled slides were examined using an Olympus microscope (new microscope) photomicrographs were taken at a magnification of 20x using DP73 camera and CellSense version 510 (Fisher Scientific, Indianapolis IN).  Densitometry was performed on photomicrographs using ImageJ.  To perform densitometry, a threshold was set to identify regions that were immuno-stained.  The area to be quantified was outlined and the total area of the outlined structure was measured along with area of the immunolabeled cells that were at or above the set threshold.  Depending on the region, 3-5 sections were analyzed.  The average immune-stained area was calculated and used for analyses.

ELISAs.  ELISAs for estradiol, prolactin, thyroid stimulating hormone (TSH) and follicle stimulating hormone (FSH) were performed using plasma samples collected from animals after 1, 4, 8, 15 or 30 days of exposure.  ELISAs were performed using methods supplied by the manufacturers.

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR).  qRT-PCR was performed to determine if exposure to 3D printing fumes resulted in changes in transcript levels in the olfactory bulb and hypothalamus described in (Krajnak et al., 2006).

Citation

Krajnak K, Farcas M, McKinney W, Waugh S, Mandler K, Knepp A, Jackson M, Richardson D, Hammer M, Matheson J, Thomas T, Qian Y.  Inhalation of polycarbonate emissions generated during 3D printing processes affects neuroendocrine function in male rats. J Toxicol Environ Health A. 2023 Jun 23:1-22. doi: 10.1080/15287394.2023.2226198.

Acknowledgements

When a publication makes use of this data set, acknowledgement of the development of the data set should be attributed to National Institute for Occupational Safety and Health (NIOSH), Health Effects Laboratory Division (HELD).  This project was funded through an Interagency agreement with the United States Consumer Product Safety Commission (6132060618H0019) NIOSH CAN 893909NC.

Authors

Kristine Krajnak         ksk1@cdc.gov
Mariana Farcas            mfarcas@wvu.edu
Walter McKinney       wdm9@cdc.gov
Stacey Waugh             ztz6@cdc.gov
Kyle Mandler              oex1@cdc.gov
Alycia Knepp              ydt0@cdc.gov
Mark Jackson              moj8@cdc.gov
Diana Richardson       drw9@cdc.gov
MaryAnne Hammer    mcy2@cdc.gov
Joanna Matheson        jmatheson@cspc.gov
Treye Thomas             tthomas@cpsc.gov
Yong Qian                  yaq2@cdc.gov

Contact

Physical Effects Research Branch (PERB), Health Effects Laboratory Division (HELD)
National Institute for Occupational Safety and Health (NIOSH), Morgantown, WV
304-285-6265