According to John Palmer in Appendix B - Brewing Metallurgy, surface lead can be removed from brass by the following technique:
Some brewers use brass fittings in conjunction with their wort chillers or other brewing equipment and are concerned about the lead that is present in brass alloys. A solution of two parts white vinegar to one part hydrogen peroxide (common 3% solution) will remove tarnish and surface lead from brass parts when they are soaked for 5-10 minutes at room temperature. The brass will turn a buttery yellow color as it is cleaned. If the solution starts to turn green and the brass darkens, then the parts have been soaking too long and the copper in the brass is beginning to dissolve, exposing more lead. The solution has become contaminated and the part should be re-cleaned in a fresh solution.
I tried this on a lot of brass parts, all new and unused, consisting of barb fittings, quick disconnects, garden hose fittings, and compression fittings. I followed the proportions and procedure that John gives above. After about 6 minutes of soaking, the solution started turning bluish green, an indication of the copper dissolving out of the part. I dumped it and rinsed all the parts well.
I sorted out the bright and shiny parts, but about 10% of them darkened slightly turning the color of lightly weathered brass. Those parts had some darker tarnished mottling here and there too. So I repeated the procedure, this time leaving the parts for no more than 3 minutes. Again, the solution starting turning a dirty-bluish green color. The only change in appearance is that now some of the parts show a greenish cast; otherwise they are still have the slightly weathered look.
What gives? Will another cleaning be worthwhile, or will it only continue to turn the parts weathered and green?
The insides of these parts will be transporting hot wort or water. Even considering the number of fittings, there will be relatively little of the weathered/darkened/tarnished brass in contact with wort. I'm inclined to just use them as is.