New research suggests that some 3-D printed materials are toxic.

Researchers at the University of California, Riverside have found parts produced by some commercial 3-D printers are toxic to certain fish embryos. The results raise questions about how to dispose of parts and waste materials from the printers.

The study comes as the popularity of 3-D printers is soaring. The value of the 3-D printing market grew from $288 million in 2012 to $2.5 billion in 2013 and is projected to grow to $16.2 billion by 2018, according to a report by Canalys.

"These 3-D printers are like tiny factories in a box," William Grover, an assistant professor of bioengineering in the Bourns College of Engineering, said in a statement. "We regulate factories. We would never bring one into our home. Yet, we are starting to bring these 3-D printers into our homes like they are toasters."

For the study, researchers examined two common types of 3-D printers: one that melts plastic to build a part, and another that uses light to turn a liquid into a solid part. They found that parts from both types of printers were measurably toxic to zebrafish embryos, and parts from the liquid-based printer were the most toxic. They also developed a simple post-printing treatment -- exposure to ultraviolet light -- that reduced the toxicity of parts from the liquid-based printer.

As the price of 3-D printers continue to drop, they are becoming widely available for consumers. Printers that use melted plastic are currently available for as little as $200, and the liquid-based printer used in this study can be bought for less than $3,000 -- they are moving beyond industry and research labs to homes and small businesses.

In the future, the researchers plan to further study the toxicity of the components of the 3-D printer material both individually and when mixed together in a completed part. They also want to find out at what level the material could be harmful to humans.

Other unanswered questions include how to dispose of the waste material - both solid and liquid - created by 3-D printers. At this point, the researchers think it is best to take it to a hazardous waste center.

"Many people, including myself, are excited about 3-D printing," Grover said. "But, we really need to take a step back and ask how safe are these materials?"

The findings are detailed in the journal Environmental Science & Technology Letters.