Passivation of New Materials That Contain Lead
The Safe Drinking Water Act (SDWA) of 1986 defines "lead free" as no greater than 8% lead content in a metal alloy. The amount of lead leached can vary considerably depending on how the materials of a given fixture or component part were processed (e.g., molded, machined, fabricated, etc.). Therefore, EPA expanded the ‘lead free' definition to include leaching standards that are now contained in American National Standards Institute/ NSF International (ANSI/NSF) Standard 61.
EPA has noted that some new fixtures, valves, and fittings can leach lead for a "considerable" amount of time after installation, even though they meet the "lead free" requirements of the SDWA. They leach lead for a variety of reasons; one is that the water has not yet built up a protective scale on the inside of the fixture. Passivation is the process of leaching of surface lead residual and deposition of a solid that contains the corroding metal.
Lead levels in tap water immediately after installation of the fixture can vary, spiking higher than the 20 ppb action level before passivating to a point where very little, or no, lead is leached. There is no easy way to predict exactly when after installation a fixture will reach a ‘steady state' (ceases to leach lead at levels near or above 20 ppb).
Factors influencing passivation:
- Materials: This includes the manufacturing process and amount of lead in the materials of the fixture. Metal alloys can vary in the amount of lead they contain. Further, the manufacturing process influences the availability of the lead for leaching. ANSI/NSF Standard 61 and California Proposition 65, discussed below, address leaching from specific components.
- Water Chemistry: The specific characteristics of the water in contact with the materials influences the length of time it takes for the components to passivate.
- Corrosiveness of water, including pH, velocity of flow, chlorine level, temperature, and dissolved oxygen.
- Presence of corrosion inhibitors such as orthophosphate-based chemicals.
- Faucet Usage Rate: The time to ‘steady state' will be related to the usage rate of the fixture, which is further influenced by the presence or absence of a corrosion inhibitor, and any residual lead in the plumbing materials.
ANSI/NSF Standard 61
ANSI/NSF Standard 61 specifies tests methods to be used for measuring chemical contaminants in drinking water, including lead (Pb). Standard 61 sets a maximum limit of 11 ppb for lead leached from the material into drinking water.
The NSF test protocol is a static test (in contrast to running water). Faucets are filled with water, and flushed every 2 hours for over an 8-hour period to simulate use of the faucet, followed by a 16-hour "overnight" period with no flushing. Following the 16-hour period, a sample is collected daily for 19 days and tested for lead. Because of variability among the 19 data points, NSF applies a statistical analysis to the lead leaching data collected over 19 days to reach an estimated overall leaching number. The unit must have a leaching number below 11 ppb in order to be ANSI/NSF certified.
More information about Standard 61 can be found on the NSF web site.
California Proposition 65
California Proposition 65 (a.k.a. The Safe Drinking Water and Toxic Enforcement Act of 1986) requires the Governor to publish a list of chemicals that are known to the State of California to cause cancer, birth defects or other reproductive harm. Lead appears on the list because it is a reproductive toxin. Proposition 65 established "safe harbor levels" -- no significant risk levels (NSRLs) for carcinogens and maximum allowable daily levels (MADLs) for chemicals that cause reproductive toxicity. The NSRL is the daily intake level calculated to result in one excess case of cancer in an exposed population of 100,000, assuming lifetime (70- year) exposure at the level in question. The MADL is the level at which the chemical would have no observable adverse reproductive effect assuming exposure at 1,000 x that level. The MADL for Lead is 0.5 micrograms/day. This level represents the no observable effect level (NOEL) for the chemical, divided by 1,000. The NOEL is based on a 70 kg person who consumes 2 L water/day. Materials leaching less than 0.5 micrograms/day meet the California Proposition 65 standard.
More information can be found the on web site for California's Office of Environmental Health Hazard Assessment.
Chemical Corrosion Inhibitors - a study
A study was performed of a building which had considerable lead levels in water from brass fittings and fixtures (Lytle, D. et al. "Investigation in Techniques and Control of Building Lead and Copper Corrosion by Orthophosphate and Silicate" Paper No. 69, the NACE International Annual Conference and Corrosion Show, 1995). Three chemical corrosion inhibitors – zinc orthophosphate, alkali metal orthophosphate, and sodium silicate were tested in different areas of the building's plumbing to determine their effectiveness in reducing the lead levels. All of the inhibitors effectively reduced lead and copper levels.
The study concluded that general water usage did not appear to reduce lead levels in the drinking water during the duration of the study. Results indicated that lead reductions may take more than 8 months, with continuous water usage. The addition of a chemical corrosion inhibitor, however, reduced lead and copper levels and nearly eliminated random spikes in daily monitoring. Tables accompanying the studies showed significantly decreased lead levels and few, if any spikes, after 80 days.
A related study is Lytle, D.A., Schock, M.R., and T.J. Sorg. "Controlling Lead Corrosion in the Drinking Water of a Building by Orthophosphate and Silicate Treatment". Jour. NEWWA, 110:3:202 (Sept. 1996).
Conclusions / Recommendations
It is not possible to definitively determine passivation time for a newly installed fixture. However, the following parameters can be used to gain confidence in remediation actions.
- Any new fixture or fitting installed as a remedy for reducing lead levels to below 20 ppb must meet ANSI/NSF Standard 61. Using the NSF test protocol as an indicator, NSF personnel estimated that a faucet that meets the standard would exhibit reduced variability for lead leaching after 19 days.
- Consider the materials and manufacturing process used. Some new brass alloys contain less than 1% lead and would, therefore, potentially mitigate the need for passivation.
- Fixtures and fittings that also meet California Proposition 65 provide additional confidence that the materials will reach an acceptable steady state in a reasonable time.
- Since corrosive water inhibits the passivation process, corrosion inhibitors are preferred means of passivation. Adjusting the pH, if practical, can also contribute to passivation.
- Any newly installed outlets should be tested after installation before being returned to normal use. Interim measures such as daily flushing of the outlet before use should be implemented until the outlet reaches a steady state below 20 ppb.