In trying to answer that question, a quick Goggle search of King Neptune Lead came up with an article about the guy who ran it being shut down by the government in 1992 for polluting his shop and neighborhood with not only toxic lead byproducts, but RADIOACTIVITY from using scrap lead from the nuclear energy industry.
So if you know anyone who has some Geiger-counters, you may want to test if yours is "hot".
Also, back when King Neptune was smelting, independent operators like him often used scrap car batteries. The problem with that is that due to the acid mixes those lead plates are soaked in, smelting them releases toxic gasses you don't want any part of. If these weights were made from that, and depending on the temp they were last melted, there could still be some of that toxicity in there waiting to be let loose once smelted again if you do it at too hot a temperature. This is one of the reasons why car batteries are no longer recycled here in the U.S. and they're all sent to Mexico, China or India, smelted down, then the raw lead sent back. (Which is why so much bullet production is now based in Lewiston, Idaho, the nation's farthest inland port, where a lot of the lead gets offloaded.)
