I checked it again and actually I think my KI is not USP but ACS (we have different labels for purity here - mine KI is 99.6% pure and I think that's the same as ACS?) I live in Russia (distant area in Siberia in the middle of nowhere) and I buy from local chemical supplier. They provide documents with each chemical you buy from them. Documents contain the list of all possible impurities - and there's nothing bad there. Just a tiny bit of calcium, magnesium, chlorides, etc.