How would lead molecules work their way through the solid solution that is brass to come from the middle of the piece up to the surface? There is no source for this because there is none.
CORROSION / Volume 48 / Issue 12 / CORROSION ENGINEERING
Leachability of Lead from Selected Copper-Base Alloys
Corrosion 48, 1040 (1992); doi:10.5006/1.3315907 (7 pages)
J. I. Paige and B. S. Covino, Jr.
Abstract
The Bureau of Mines has conducted research on the selective leaching of lead from copper-base alloys in high-purity water. The alloys in this study were selected as representatives of those used in various plumbing system fixtures such as faucets and valves. Leaching tests were conducted for a total period of 14 days and at temperatures of 25, 50, and 75°C. An acetic acid pretreatment was used in an effort to reduce the amount of lead that was leached from the alloys. The results show that, with the exception of the more complex yellow brasses, more lead is leached into water from alloys containing greater concentrations of lead and that the rate of lead leaching decreases with exposure time. Higher temperatures had relatively little effect on the leaching of lead. Lead was preferentially dissolved from all of the alloy groups. Of the small total amount of alloy dissolved, more Pb, 10 to 59 times, was dissolved than would be predicted from the proportional quantity of Pb present in the alloy (0.1 to 7.0 wt% Pb). Typically, the amount of Pb dissolved in any given test period exceeded the Environmental Protection Agency proposed action limit of 0.015 mg∕L.
...
Effect of Pretreatment
A preliminary study was conducted on alloy C83600 to determine if the smeared Pb film could be successfully removed by a pretreatment procedure. Samples of alloy C83600 were leached in 1.2 N acetic acid for 4 h-, 8 h-, and 24-h periods. Then, the sample surfaces were examined using EDS on the SEM. The examination revealed that approximately 50% of the Pb was removed after 4 h, approximately 75% was removed after 8 h, and it was difficult to find any traces of Pb remaining after 24 h of treatment.
Based on these findings, the second series of tests was conducted in a manner identical to the first series with the exception that all alloys were preleached in 1.2 N acetic acid for 4 h and the only temperature tested was 25C. A comparison of the results for series no. 1 and no. 2 can be seen in Figure 3 and Table 3. This shows that the total amount of lead leached from most of the alloys did not decrease.
In fact, the treated model alloys actually showed a substantial increase in the amount of Pb leached from the samples. However, an analysis of the percentage of lead leached during the first 24-h period shows that the pretreatment does have a positive effect. On average, one fourth of the total lead leached in 2 weeks, a reduction over non-pretreated samples, was leached out during the initial 24 h of the exposure period.