Depends upon what you're curing and how.
Traditionally, meat, fish, cheese etc be cured with salt, smoke, drying, salt-petre and no doubt many other things. Wood ash too I think.
Non-edible things (such as skins and furs) can use more toxic stuff, such as alum, chrome compounds, tannin, as well as fat, smoke etc.
Factory-cured methods use all sorts of other chemicals.
Soaking in brine works fine for making your own preserved meats, perhaps with some vinegar and spices. Don't leave it in too long though or the salt'll need soaking out again before use.
Then there's pickling. Brine, vinegar, lactic-acid fermentation, alcohol ...