Lead-soldered containers

Lead based solders (tin/lead solders) contain up to 60 % of lead, which can be released into water through galvanic corrosion. The corrosion rate is increased by high concentrations of chloride and nitrate but is inhibited by sulfate, silicate and orthophosphate. Lead concentrations at the tap depend not only on the corrosion rate but also on the number of leaded joints in the plumbing, the area of solder exposed to water at each joint, and the water usage pattern (Gregory, 1990). 

Two areas of U.S. FDA activity related to food Pb levels spelled out in statute concern lead-releasing containers and tableware that come into contact with food. The first major action within this category was the effort to reduce the use of and ultimately ban lead-soldered containers for canned food in general and infant dietary components in particular. This activity was discussed in the earlier chapter on dietary Pb exposures. The agency in 1979 brokered a voluntary agreement by the food and beverage container industry to carry out a scheduled phase-out of production of lead-sealed containers (see NAS/NRC, 1993 U.S. ATSDR, 1988 U.S. EPA, 1986, Ch. 7). 

By the late 1980s to early 1990s, such lead-seamed containers had largely disappeared from the American food and beverage scene, and by 1991 the industry had completely converted to alternative containers. In 1996, the U.S. FDA took formal action [ 201, 402, 409, 701 of the FFDCA (21 U.S.C. 189.240)] to ban lead-seamed cans (60 FR 33106—33109 June 27, 1995). The formal ban served at that point to limit canned food imports in lead-soldered containers for domestic canned food inventories. 

Lead—silver alloys are used extensively as soft solders these contain 1—6 wt % silver. Lead—silver solders have a narrower free2ing range and higher melting point (304°C) than conventional solders. Solders containing 2.5 wt % silver or less are used either as binary alloys or combined with 0.5—2 wt % tin. Lead—silver solders have excellent corrosion resistance. The composition of lead—silver solders is Hsted in ASTM B32-93 (solder alloys) (7). 

The presence of the so-called heavy metals, eg, lead, cadmium, and antimony, iu traditional solders has become an important environmental issue owiag to concerns for health and safety. As a result, solders containing no lead and antimony such as tin—silver are finding a growing number of apphcations (Table 2). 

Soldered joints present their own characteristic corrosion problems usually in the form of dissimilar metal attack often aided by inadequate flux removal after soldering. Such joints have always been a source of concern to the electrical industry. Lead-containing solders must be used with caution for some types of electrical connection since PbfOHjj.PbCOj may be found as a corrosion product and can interrupt current flow. Indium has been found to be a useful addition to Sn-Pb solders to improve their corrosion resistanceHowever, in view of the toxicity of lead and its alloys, the use of lead solders, particularly in contact with potable waters and foodstuff s, is likely to decline. 

Cases of lead poisoning have been related to less common sources of exposure. Illicit "moonshine" whiskey made in stills composed of lead-soldered parts (e.g., truck radiators) may contain high levels of... 

Most solder contains elements such as lead, tin, antimony, etc. Current passage through such metals could readily lead to their oxidation, with subsequent contamination of the analyte solution. Furthermore, such redox processes greatly complicate - if not invalidate - any coulometric analyses. 

Tin-plated steel was long the mainstay of the U.S. aerosol industry and still represents a very large volume. The tin coating provides both protective internal and external surfaces and the means for soldering the flat body plate into a leakproof cylinder. Both tin and lead solders are used, and both frequently contain small (5%) amounts of other metals, such as antimony and silver, for additional strength. In some products, the tin coating is removed sacrificially by the product attack on steel is avoided only as long as some of the tin remains. 

In the past, lead solder was used to seal canned foods and lead pipes were used to carry drinking water. Tetraethyl lead was once routinely added to gasoline as an antiknock agent certain vehicles may still use leaded gasoline (e.g., agricultural vehicles). Lead was commonly used in paint, with certain formulations containing up to 50% lead. 

---