Hi jeremy,
All the latex you are likely to encounter (whether it’s Dunlop or Talalay or synthetic, natural, or a blend of the two) are non toxic and safe. They are all tested by either OekoTex or EcoInstitut for harmful substances and VOC’s so there would be no safety or toxicity issues with any of them.
Of course there are many people who prefer 100% natural latex (either Talalay or Dunlop) for reasons other than safety (or in some cases they may believe that they are a “safer” choice) and these are also good choices even if they aren’t any less toxic than other types or blends of latex.
There is more about the different types and blends of latex in post #6 here and some of the better sources for toppers (that includes all types of latex) are listed in post #4 here.
You won’t generally find fire retardants added to latex mattresses (which generally use either wool or an inherent fire barrier rather than chemicals) but toppers aren’t required to pass the fire regulations that apply to mattresses so fire retardants are not an issue with latex toppers.
Phoenix