I don't think it would, especially in the small quantities used to ctb. Since SN isn't my method of choosing I don't exactly know how it works. I read that it works as a catalyst for the oxidation from iron II to iron III in your hemoglobin, preventing oxygen delivery. Being a catalyst would imply that SN itself wouldn't react/undergo significant changes (if I remember correctly), but even then it would have to somehow leave your body to cause harm. And, I'm guessing here, but I think it would react with something after a (short) while anyway. And maybe it already does initially, I never thoroughly researched the method.
But all in all, in the small quantities we're talking here, you really can't do much harm. The farmer using pesticides and fungicides on the field nearby does much more.
