3-D Printing Is Getting Huge Hype, But It Could Be One Massive Health Risk
For geeks who ardently wish those Star Trek replicators were for real, the dream is coming closer to reality in the form of three-dimensional printing. The technology is changing the way prototyping, testing, and even manufacturing parts is done for everything from knee joints to jet engine fuel injectors. It’s also sweeping the world of do-it-yourself garage tinkerers and home-based jewelry designers. The 3-D printing market totaled $3.07 billion last year and sales of desktop 3-D printers under $5,000 grew by 346 percent between 2008 and 2011, according to a May 2014 report from Wohlers Associates, a Fort Collins, Colorado consulting firm. Desktop models are about the size of a large PC tower and require only normal household power. The least expensive machines range from $100 to $500.
Descended from the inkjet printer, a 3-D printer is a machine can use a digital recipe to create a three-dimensional object from a raw material. 3-D printing is the next logical step beyond computer-assisted design and robotic manufacturing technologies. 3-D enthusiasts claim the technology will democratize formerly centralized industrial processes that required large, expensive and slow infrastructure.
3-D printers can use a variety of raw materials, ranging from thermoplastics to metal and ceramic powders. Design-obsessed chefs will love the countertop model that can print any desired shape in sugar or chocolate.
Like the personal computer and the cell phone, 3-D printing appears to be irresistible. But the temptation to exploit the technology may lead enthusiasts to disregard important information. For example, a recent study found that desktop machines can emit extremely high levels of ultrafine particles (UFPs), also called nanoparticles (less than 100 nanometers, in the size range of viruses). The specific biological behavior and health effects of these particles are largely unknown, but other research on UFPs suggests caution.
Evaluating the safety of UFPs “should be of highest priority given their expected worldwide distribution for industrial applications and the likelihood of human exposure, directly or through release into the environment,” wrote Gunter Oberdörster, a professor in the Department of Environmental Medicine at the University of Rochester Medical Center School, in a 2005 review of nanotoxicology and UFPs.
The most common feedstocks are plant-based polylactic acid (PLA) and petroleum-derived acrylonitrile-butadiene-styrene (ABS). These come in spools of filament that are threaded into the machine and then melted and extruded out a nozzle that moves back and forth across a base. The whole contraption looks like a more complicated version of the machines that will etch your dog’s name onto a bone-shaped piece of stainless steel at the pet supply store. Free software is available to create a digital file that tells the printer what to do.
The temperatures necessary to melt 3-D feedstocks vary. PLA filament must be heated to around 350 degrees Fahrenheit, whereas ABS has to reach about 500 degrees. Whatever gases and UFPs are released during printing will come out into the ambient air unless the machine is attached to a ventilating and/or filtration system. Most inexpensive printers do not even have enclosures around the print surface.
Users describe the smells of printer operation in different ways. Shashi Jain, who organized a 3-D printer group in Portland, Oregon, says the ABS filament smells like a hot burner on an electric stove. The makers of the 3Doodler, a hand-held pen, assure potential customers that the smell of ABS is “less noxious than a permanent marker” and that PLA smells like corn.
These statements imply that because the emissions from 3-D printers do not have overwhelming and repellent odors, they are safe.
“One needs to be aware of what might come out of [3-D printers],” says Oberdörster. “There [is] reason for concern.”
3-D printing offers designers and manufacturers enormous benefits. Prototypes can be printed, analyzed, tested and refined quickly at small scales, vastly speeding up the process. Some architects have abandoned the laborious process of building balsa wood models of their designs and now print out scale models in a fraction of the time. Biomedical engineering is adopting the technology in dramatic ways – for example, in 2011, an 83-year-old Belgian woman with oral cancer received a new jawbone created by a 3-D printer using titanium powder. Her new jaw was based on a CT scan of her original one.
UFPs are very common in the environment, from natural sources like forest fires and volcanoes and from human sources like engine exhaust. But regardless of their source, it is well established that UFPs can trigger inflammation and cause serious cardiovascular and respiratory problems when inhaled, particularly for people with pre-existing heart or lung disease. Since 3-D printers are a new source of unintentional UFP production and some of their feedstocks like ceramic and metal powders are very new engineered nanomaterials, their health effects have not been studied.
Thus the thousands of “makers,” as 3-D printing enthusiasts call themselves, who set up in small businesses or their homes, don’t know exactly what risks they face. And assumptions about the chemistry and typical exposure scenarios for the feedstock materials in their typical forms may be far off base for 3-D printing, for an important reason: size matters.
In 2013 Brent Stephens, assistant professor of architectural engineering at the Illinois Institute of Technology in Chicago, published a study of five typical 3-D printers in a retail store. The room was about the size of a “small bedroom,” Stephens says. He and his students measured the concentrations of particles in the room before the printers were operating, during operation, and during a post-printing resting phase. Peak particle concentrations when two PLA printers and three ABS printers were running simultaneously reached 150,000 UFPs per cubic centimeter – nearly fifteen times background levels. ABS printers emitted particles at ten times the rate of the PLA printers. None of the machines was enclosed.
It’s important to note, Stephens says, that in terms of UFP emission numbers, “3-D printers are right smack in the middle” of the pack of common devices, including toaster ovens, laser printers and air popcorn poppers. Popcorn seems benign, he says, so maybe 3D printers are harmless too – or, he adds, maybe it’s the other way around. “Could there be something we don’t know about popping corn?” he asks.
What materials do at “normal” scale doesn’t determine their nano-behavior. UFPs have much more surface area relative to their mass compared to their bulk forms. This not only changes their physical behavior, but it can affect their chemistry as well, says Oberdörster. For example, their extra surface area makes them more reactive than their bulk forms and more likely to catalyze chemical reactions.
This is worrisome, particularly regarding ABS. The U.S. Environmental Protection Agency has classified acrylonitrile as a probable human carcinogen and butadiene as a known human carcinogen. Styrene is deemed “reasonably anticipated to be a human carcinogen” by the National Toxicology Program. These ingredients are monomers that combine to form the polymer ABS.
Scott Lusk, director of plastics communications with the American Chemistry Council, says that makers are unlikely to be exposed to these carcinogens because “[W]hen monomers are reacted to form polymers the monomer is generally fully reacted into the polymer. So the potential for exposure to a monomer (even a hazardous monomer) from use of a polymer would ordinarily be expected to be quite low – if at all.”
But no one knows how ABS UFPs really behave in the body. They can move through the skin and lungs to reach the bloodstream. And there’s another disturbing property of ultrafine particles: when inhaled into the nose, they can travel through the olfactory nerve to the olfactory bulb in the brain. They can also move along neurons and spread into the cerebrospinal fluid, according to a 2009 review of research on UFPs and the brain by Oberdörster.
It’s the inhalation route that is the most concerning in the context of 3-D printing, because that’s a major route of exposure for makers, and because the olfactory route to the brain bypasses the blood-brain barrier, which protects that organ against most external bodily insults. Furthermore, as Oberdörster noted in his 2009 review, low-level but chronic inhalation of UFPs may lead to their “significant accumulation” in distant organs even if the transfer rate from the point of entry is low. So if a brain is exposed to a repeated parade of UFPs from a 3-D printer, what happens? Scientists do not know.
There is currently no governmental regulation specific to 3-D printing. The EPA does not regulate indoor air. The Consumer Products Safety Commission has not yet developed a policy regarding the equipment. The American Chemistry Council has not taken a position regarding the possible health risks of 3-D printing, says Lusk.
Nor are there occupational protections in place. The National Institute of Occupational Health and Safety “does not have any recommended limits for exposure of particulate matter,” says Celeste Monforton, an assistant professor in the department of environmental and occupational health at George Washington University in San Marcos, Texas “This is an example of technology moving ahead while our environmental and safety standards are back in the dark ages.”
That leaves the millions of excited and creative would-be users in a quandary.
Stephens would like to see further research on the actual composition of the emitted nanoparticles, including their toxicological profiles, as well as “more information on realistic exposures in real environments,” he says. If the results are problematic, he adds, “Let’s explore ways to build enclosures, add filtration systems, and [set] more stringent guidelines for use.”
In the meantime, there are some things 3-D printing practitioners can do at home or at work to mitigate the risks: buy an enclosed printer; ensure good ventilation in the room where the printer operates; and use a mechanical (non-electronic) air purifier with an ultra-low penetration air (ULPA) filter. These precautions must serve until regulations are in place or true replicators arrive, and either may be a long time coming.