3D printing could be bad for fish
Researchers in the University of California have been doing testing using two common types of 3D printers - ones that use melted plastic and others that use light to solidify liquid resin. And it turns out these materials, used in this way, can cause problems when they interact with certain breeds of fish, for example the embryos of the zebrafish. In some cases the effects were extreme, with the fish all dying after exposure to the liquid-resin material in particular.
The short version is that 3D printed items can certainly be toxic and it's reasonable to assume that they could have some kind of negative effect on human users in significant amounts. Another issue is how these materials should be disposed of, with the researchers recommending that 3D printing waste be treated as a hazardous material in the future.
More study is needed to determine the long term effects of these materials, especially if we're going realise the full potential of 3D printing.