About the PLA fumes - this has actually been extensively studied and there's no notable amounts of decomposition at normal PLA melt temperatures - that is, if there's no visible charring on your part, there's no measurable decomposition fumes. ABS fumes are much more significant, but they appear to be at about the same level as searing meat in a frying pan. I'm sure if you put a zebrafish embryo near frying pan fumes it would be harmed, but that isn't saying much.