DEAR DR. BLONZ: Besides fresh and frozen vegetables, I often use canned, especially tomatoes. I buy organic when available, and periodically they are imported. I recall lead solder used to be used in many brands of canned foods, mainly the imported ones. This type of solder seemed especially dangerous for acidic foods like tomatoes. Does the fact that the can is airtight make it safer, or are protective substances added to make it so the food won't react with the metal? -- F.S., San Jose, California
DEAR F.S.: Cans used to be made in three pieces: top, bottom and the cylindrical body, all soldered together into the familiar shape. Lead is an ideal soldering material, but its use where there would be contact with foods turned out to be risky business when we learned of its toxic effects in the human body. Lead is hazardous during pregnancy, infancy and childhood. (Read more about lead poisoning from the National Library of Medicine at b.link/c5yt9r.)
Domestically produced cans were the first to stop using lead solder; canned food manufacturers in the U.S. reported having stopped using it by 1991. Cans are now welded together or extruded into a two-piece shape that eliminates the need for the side seam. In all cases, the can materials are formulated to inhibit the leaching of metal ions into the food -- even when the goods inside are acidic. This sometimes involves using an enamel or vinyl liner substance designed to not react with the contents.
Food companies in developing countries have moved toward lead-free cans, but it is difficult to say that all are there yet. For those cans, the Food and Drug Administration has an action level of 250 parts per billion of lead in the food, a level considered to be safe. If a can exceeds that level, it can be seized by the FDA.
Although this may provide some comfort, it's not a safety guarantee. It is prudent to check the labels on any imported canned food, especially if it is one you would be purchasing on a regular basis. If there is no information on the label or product website, check with the supplier. Another option is to use test kits with swabs that turn a particular color when exposed to lead. These inexpensive kits, good to have around the house, can be used on cans, pottery, crystal, pitchers or any food-contact surface you want to examine.
While not raised in your question, another substance raising concern in food containers is bisphenol A, known as BPA, which is often used in can-lining materials. (Learn more about BPA at b.link/dzukfd.) The FDA regulates how much BPA can be present, and no longer permits its use in packaging and containers that will hold materials for infants. Manufacturers continue to phase out the use of BPA in cans; for more, see an article from the Environmental Working Group at b.link/48wu35.
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