I was at a talk a few years ago given by a manufacturer of propolis products for humans. Their testing (in the UK) showed all propolis samples to contain lead. The govt demanded either they remove the lead before selling, or the govt would mandate it be done. As far as I know, the name brand stuff is all dissolved in alcohol and filtered many, many times before being sold for human use.
Ok. So it was a manufacturer of propolis products that told everyone else (in a round about way) that ALL propolis (that THEY had tested....probably one sample....their own) contained lead. I bet a few beekeepers decided based on those tidbits to forget about propolis. Makes you wonder about why they would mention lead.
They probably scraped the edges of painted boxes. Other than that, how could a pure product produced by bees contain lead. This is not the way to collect propolis. And I highly doubt the bees had lead in the propolis as they brought it into the hive.
Of course, they are not the only producer doing this. Anybody asking how to, or suggesting using water to clean the propolis of wood and wax, probably should not be producing it. If you need to freeze, crush, and use water to separate the junk, are they really producing propolis in a proper way? I would so no.
I sell propolis to two main buyers. They buy most of my propolis and I call when I have a few pounds. If I have some extra, I sell it by the quarter pound, for 48 dollars per pound. I sell all I can produce.
From the comments sent to me from buyers, they must buy some real crap from others. Because they say it is some of the best they have bought. And I don't do much to clean it beyond some bee legs and such. But I do not scrape the box edges to produce it.