Bernt Damm correctly assumes that the white powder produced by
decomposition of lead tubing is white lead carbonate.  This mostly
forms on the inside of the pipework, usually in damp conditions.
The pipe normally used is not pure lead but an alloy of lead
containing antimony for increased strength.

If sensible precautions are used in disposing of old decomposing
lead tubing, such as not inhaling or ingesting any of it, there is
negligible health risk.  Fitting new lead alloy tubing is not risky
if normal hand hygiene is performed to avoid ingesting any lead.

Keith Reedman
England