Are there “safe” resins?

TL;DR:
AFAIK there are NO current UV cured 3d printer resins which are safe in liquid form for skin contact or disposal by pouring down the drain - specifically including water used for cleaning “water washable” resins. ALWAYS wear gloves, and never pour resin or any liquid used to clean your prints down the drain.

Some newer resins are marketed as safer, easier to use, and environmentally friendly. There seems to be a common and VERY dangerous misconception that these are much safer to handle in their liquid form, before they’re cured. The issue is that some people will see “bio degradable” and all the “safety” claims and think it means the liquid is safe to handle. Most resin is non-toxic when cured, but that doesn’t keep plastics from causing issues, so it’s reasonable to market CURED bio-resin as more environmentally friendly. But of course, while never directly stating that the liquid resin is safe, I’ve yet to see marketing which makes that distinction obvious (i.e. anywhere near where they have all the pretty bits about how safe it is). Nor have I seen vendors making efforts to correct this common misunderstanding in social media, which IMHO is extremely irresponsible on their part.

AFAIK the main benefit with BIO resins is that you end up with a CURED print which is bio-degradable, and water washable doesn’t require harsher (also potentially toxic) stuff like IPA for cleaning before curing. By far the most useful source if you want a quick check yourself on how toxic they are, read the SDS (Safety Data Sheet) for the resin. I haven’t seen ANY (including bio and water washable) SDS that suggest a UV resin is anywhere near as safe in liquid form as some seem to think. Some resins may be “less bad” than others, but you could similarly state that tripping into a campfire is usually “less bad” than being hosed down by a flame thrower. Neither are particularly “good”.

I’m not a chemist or a medical professional, so I might not have this all 100% correct - BUT I’ve researched this a bit and I’ve drawn this from some credible sources. Here’s my current understanding :

ANY liquid UV cured resin which gets in you skin is bad news, because eventually it will get enough UV to cure IN YOUR SKIN, which your body doesn’t like and reacts to - and the more it reacts, the more sensitive your system gets. You can eventually develop a severe allergic reaction to very minor exposure. Part of the risk of cleaning with IPA/methanol is that it makes it even easier for your skin to absorb the nasty bits from liquid resin, so you could consider water washable resins to be indirectly safer than using a resin with IPA as your cleaner, but that’s still far from safe.

Some of serious environmental risk (if liquid resin is not disposed of properly) comes from the photo initiator, not the monomers and cross linkers which are the “bio” derived bits in “eco friendly” resins. Doesn’t matter whether it’s regular, “eco friendly”, water washable, … that part of the liquid resin is VERY nasty for the environment if it gets into the water system.

An example?

AnyCubic specifically is a bit misleading with their “Plant-based UV resin” . They have all kinds of pretty charts and impressive safety standard claims which could very plausibly lead one to think that the liquid form is safe. BUT the EN 71-3  test they mention might actually be for the cured form “Category III: Scrapped-off toy material” ??? ) and is missing most of what is in a typical resin MSDS report. And if you read to the very end of their product page, in a “Precautions” section without any fancy pictures, they say “wear a mask and gloves”, “do not drink it”, etc. But they do NOT state that it’s hazardous to dispose of uncured resin, nor do they have the MSDS anywhere easy to find online (and they’ve ignored requests to provide it . Interestingly, there is an SDS available  which unlike the EN71-3 report (which describes the sample as “Plant-based resin” and includes a picture of a bottle of “Eco Resin”) only describes the product as “UV RESIN” and has no pictures. However, it also says “soya … is not classified in this SDS”, and lists “Fatty acids, soya, epoxidized, Bu esters” as 45% of the composition of the resin. Soybean (also known as soya bean) oil is “plant” part of their “Eco” resin. And the date on the report is three days after the date on the EN 71-3 report. And THIS report is for a resin which is clearly hazardous if handled improperly, especially for aquatic life. If this is the SDS for their Eco/plant-based resin, it kinds seems like they’re intentionally trying to obscure that fact.OTOH, AnyCubic has stated  that they will NOT be releasing (and so far they have not) a water washable resin, basically (if you read between the lines) to avoid the “resin’s effect on water and water creatures” from people inevitably disposing of the water improperly. . So they’re not totally irresponsible.