Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
Lead is superior in both weight and flexibility. So in the US, unless it specifically says lead-free, it's probably lead.
Some other countries have banned lead weights, more for disposal concerns that for the health of fish; and use zinc exclusively.
I wouldn't worry about the effects of lead in the aquarium. But with a little practice, you'll generally find weights unnecessary to successfully anchor plants.