Lead Release to Drinking Water from Galvanized Steel Pipe Coatings
Problems identified with elevated lead in drinking water associated with galvanized steel pipes were recently hypothesized to result from lead accumulation on galvanized steel pipe surfaces from upstream lead service pipes. However, historical research documents that the grade of zinc typically used for galvanizing contains a minimum of 0.5% lead and can itself be a significant long-term source of lead, which may explain some recent lead contamination problems associated with galvanized steel. Surface analysis of various galvanized steel pipes and fittings installed from 1950 to 2008 demonstrated that the concentration of lead in the original zinc coating can range from nondetect to nearly 2%, dependent on the manufacturer and fitting type. Since cadmium is also present in many zinc coatings, but not in lead pipe, leaded solder, or brass, correlation of zinc concentration to both lead and cadmium concentrations in water was considered as a possible fingerprint implicating the coating on galvanized steel as a lead source; bench-scale tests of metal leaching from harvested galvanized steel pipes were used to validate this approach. Using profile sampling, individual homes with galvanized steel pipes as a primary lead source were identified in Washington, DC, Providence, RI, Chicago, IL, and a city in Florida. In some cases, the levels of lead from this source were very significant (>100 μg/L) and can be exacerbated by installation of a copper pipe upstream during partial service line replacements.