Heavy metal exposure risks from filaments used in 3D printing
Citation:
Wade, A., T. Luxton, L. Rand, D. Peloquin, M. Noerpel, G. Millard, A. Betts, J. Goetz, AND M. Arambewela. Heavy metal exposure risks from filaments used in 3D printing. ORISE Meets the World, Cincinnati, OH, November 03 - 11, 2022.
Impact/Purpose:
Heavy metal exposure risks from filaments used in 3D printing presentation. Preliminary conclusions: Metal filaments release microparticles pre and post-printing. Particles within size range capable of dermal adherence (< 150 µm). Raw filaments release more particles than printed, and synthetic solutions such as sweat have greater impact on certain elements. Fraction of the metal particles appear to be oxidized. Change in oxidation state may impact solubility and subsequent bioavailability. Next steps: Incorporate toxicology data and exposure limits and guidelines. Apply findings to realistic exposure scenarios.
Description:
Manufacturing advancements in three-dimensional (3D) printing of plastic polymers have outpaced our understanding of exposure risks for domestic use. One understudied aspect is the release of metal additives incorporated into plastic polymers before and after printing. Metal additives are not chemically bound to the plastic polymer and given that 3D printed objects have longer lifespans than single-use plastics, the potential for human exposure to these additives needs study. Here, we analyzed pre-ingestion human exposure risks from PLA and PLA/PHA thermoplastic filaments infused with copper, bronze, and stainless-steel fine metal powders. Raw and printed filaments were subjected to 2-hour release scenarios that simulated contact with water, synthetic sweat and synthetic saliva. Concentration, particle size and speciation of metal additives in the thermoplastics and leachates was determined using total metals analysis, sequential filtration, electron microscopy, and X-Ray Absorption Fine Structure Spectroscopy. Estimates on the impact of plastic degradation on metal additive release, for raw and extruded filaments, were accomplished by exposing thermoplastics to UV exposure equivalent to yearly-average insolation in Cincinnati, OH. The quantity of copper (Cu), tin (Sn), and chromium (Cr) released during 2-hour leaching periods were highest in synthetic sweat. Additionally, migratable concentrations of Cu, Sn, and Cr were higher in raw filament than printed filament, and higher in PLA/PHA plastic than PLA plastic. The quantity of Cu and Cr leached from the thermoplastics were higher than USEPA permissible limits of 1.3 mg/L for Cu and 0.1 mg/L for Cr in drinking water, with maximum concentrations topping 327 ppm and 7.0 ppm for Cu and Cr respectively. Photo degradation by UV weathering increased migratable concentrations of Cu, Sn, and Cr by one to two orders of magnitude. The majority of leached metals were in the particulate phase with size fractions below 150 um, indicating high potential for dermal adherence and subsequent ingestion. Our findings suggest dermal contact and subsequent ingestion with raw filament is a possible exposure pathway when working with metal additive 3D printing filaments. Appropriate filament storage should be used to minimize photo degradation of filament over time and proper filament handling to reduce incidental exposure during the printing process.