ALFONSO DE LEÓN*
In 1992, the metallic containers industry in Mexico stopped producing tin cans with lead soldering as food containers, substituting instead a process that closes tin cans with electrical solder. Mexican public health authorities are now interested in determining whether a quantifiable reduction in population blood lead levels, especially in children, has occurred as a result of this voluntary industry change.
The National Chamber for Metallic Containers of Mexico represents more than 85 percent of steel tin can and 100 percent of aluminum tin can production, making it the leading manufacturer of metallic containers in Mexico. The process leading to the total elimination of lead soldering in food cans was begun as a voluntary initiative by industry, although the increased pace of change in the latter phases of conversion was dictated by external events. This process is described briefly below.
Metallic containers have been used to hold and conserve food for more than 180 years. In the beginning, tin was used in soldering, but it resulted in little flexibility and a fragile seam. Lead rapidly replaced tin in solder because it is a ductile material that easily adheres to the tin plate and can be mixed with the tin to produce a more flexible and less fragile soldering. At one point the solder commonly used contained 90 percent lead and 10 percent tin. Such soldering was universally adopted and, with it, many billions of cans were produced globally, without an understanding that lead in external soldering posed a public health hazard.
When medical and public health authorities began to acknowledge concerns about the effects of lead exposure on human health, attempts were made to identify the different sources of the metal. Leaded gasoline, paints, and ceramicware glazes and food cans containing leaded solder were rapidly identified as important sources.
National Chamber for Metallic Containers, Mexico City, Mexico.