Leaded Brass
November 29, 2010 Brass is an alloy of copper and zinc, so you wouldn't think it would be a health problem. After all, most residential water runs through copper pipes; and zinc compounds, typically zinc oxide, are taken orally, in moderation, as a mineral supplement. The details, however, can be surprising, as when you actually read the nutrition label and learn the real content of those health food bars you've been eating. If brass were only copper and zinc, that would be fine, but there are other metals in brass, some intentionally added, that complicate the issue. One of these added metals is lead, which is added to enhance machinability. Those of you who may have handled ammunition shell casings will understand that some brass alloys can be very hard, and therefore difficult to machine. Since the atomic size of lead (atomic radius, 175 pm) is much larger than that of either copper (atomic radius, 128 pm) or zinc (atomic radius, 134 pm), lead doesn't fit well in place of copper or zinc in an alloy phase, so it will segregate to grain boundaries. It's the lead at these boundaries between alloy crystals that allow the grains to slip against each other, so cutting and other machining processes are easier. I wrote about the environmental problems with lead and current mitigation tactics in an article in a general interest publication.[1] It's no surprise that the Journal of the American Water Works Association is not one of the journals on my watch list, but the November, 2010, issue has an interesting article about lead in brass fixtures used in potable water systems. Solders for potable water piping have been lead-free for quite some time. Lead was originally dismissed as a problem, since the natural formation of lead carbonate would shield the lead from contact with water. This is not the case when the pH is too low; that is, when the water is too acid. As a consequence, the Safe Drinking Water Act of 1974 was amended in 1986 to require the lead content of solder to be less than 0.2%. Potable water solders now contain a mixture of tin, copper, bismuth and silver. The international standard for brass pipe fittings allows 8% lead. Since January 1, 2010, California has a stricter standard of 0.25%, which nearly matches the standard for solder.[2] As often happens in science, the research leading up to the paper in the Journal of the American Water Works Association wasn't planned. It was the result of an accidental discovery. Large quantities of lead were found in a survey of potable water in a new laboratory building at the University of North Carolina at Chapel Hill in 2008. The water from two drinking fountains was found to have lead in excess of 300 parts per billion, well above the 15 micrograms per liter, or 15 parts per billion, action limit of the US Environmental Protection Agency.[3] As a first mitigation attempt, the university changed drinking fountains to those that meet the stricter California specification. When that didn't solve the problem, they were forced to dig more deeply. The culprit was a brass ball valve upstream from the fountains. These valves had 18% by weight lead on the surfaces in contact with water. Surprisingly, the valves met the established criterion of less than 8% lead overall, and the type of valve was listed as having passed the lead leaching standards of the National Sanitation Foundation International. Marc Edwards, the Charles Lunsford Professor of Civil Engineering at the University of North Carolina at Chapel Hill, an author of the paper and a 2007 MacArthur Fellow, is quoted as saying,[3]"Thankfully, UNC's procedures caught the problem before anyone could be exposed to the high lead in water, but in most other cases the issue would go undetected. The fact that some defective products, listed as safe, could be installed in schools and day care centers and harm children is very troubling"This is one area on which our government leaders are taking action. Senator Barbara Boxer of California, who's chairwoman of the Senate Committee on Environment and Public Works, has introduced a bill to lower the allowable amount of lead in brass plumbing fixtures from the current 8% to a weighted average of 0.25%. Says Boxer, "The bottom line is that there is no safe level of lead, a toxic heavy metal, in our drinking water."[3] Edward's research has been supported by the NSF, which in this case means the National Science Foundation, and not the National Sanitation Foundation.[4] Lead may have been a contributing factor to the decline and fall of the Roman Empire. The Roman elite drank their wine from lead goblets, and wine has a pH between 2.9 and 3.9
 | Romulus Augustus, the last Emperor of Rome |
References:
- D.M. Gualtieri, "Get the Lead Out," Phi Kappa Phi Forum, vol. 85, no. 2. pp. 6-7 (Summer 2005). Local PDF copy
- Brass page on Wikipedia
- Carolyn Elfland, Paolo Scardina, and Marc Edwards, "Lead-contaminated water from brass plumbing devices in new buildings," Journal of the American Water Works Association, vol. 102, no. 11 (November 2010).
- Patric Lane, "Study shows brass devices in plumbing systems can create serious lead-in-water problems," University of North Carolina at Chapel Hill News, November 11, 2010.
- National Science Foundation Press Release 05-131, "Your Tap Water: Will That Be Leaded or Unleaded? August 4, 2005.
- Brass page on Wikipedia