RV anti-freeze is generally used to keep the potable water lines in an RV from bursting in the winter... So I would suspect it doesn't have much of a toxicity to it. Everyone I have seen is used with GRAS ingredients.
Clear booze like gin or vodka make a fine RV antifreeze and will also work to clear ice without much soil effect and the alcohol will eventually evaporate. DO NOT use automotive antifreeze because it is poisonous and will kill animals. Dogs will dig and eat the contaminated soil.