Sources of Lead Exposure
Lead exists in the earth’s crust, and occurs naturally in the environment through a variety of mechanisms including volcanic emissions and geochemical weathering. The majority of lead pollution, however, derives from human activity to extract and exploit the metal. Lead has been put to many uses and is important in plumbing materials, gasoline additives, batteries, pigments and ammunition. Potential sources of lead exposure may vary, both within and between countries. In the United States of America (USA), for example, lead in paint is an important source of exposure, while for Mexico this source is largely irrelevant and lead-glazed ceramics are more important (Hernandez-Avila et al., 1999). Identifying lead-containing materials in individual cases is not necessarily straightforward and van Alphen (1999) lists, alphabetically, some of the possible idiosyncratic sources and consumer goods containing lead(Table #). A framework for a number of lead exposure pathways is given in Figure 1. In the decision-making process for a national study, this framework can form a starting point, by acting as a checklist for likely local exposure pathways. It should be remembered that some exposure pathways can be quite obscure, as highlighted in the preceding list. Another illustration of an unexpected source is provided by the outbreak of lead poisoning in Egypt that was caused by lead solder used in flour mill grinding stones (Falk, 2002).
Lead is found in mineral deposits in nature and accounts for only 0.002% of the earth’s crust. It has been used for hundreds of products because of its malleability, low melting point, and ability to form compounds. Industries as disparate as plumbing, electrical, plastics, and nuclear have found lead to be efficacious. Products that may contain lead include pipes, solder, brass fixtures, ceramics, crystal, electric cable, paint, radiation shielding, gasoline, batteries, nonWestern (eg, Ayurvedic) medications, and cosmetics. Lead may be found in unexpected household items, such as window blinds, zippers, painted furniture, and mineral supplements. Other significant exposures result from poorly controlled industrial emissions at metal refineries and battery recycling plants, maintenance work on bridges and boats, and demolition of old housing. If target shooting is conducted in poorly ventilated spaces and lead-containing bullets are used, frequent visitors or employees at the range are at risk of increased lead absorption{{424 Markowitz,M. 2000; }}.
Worldwide, six categories of products account for most cases of lead exposure: gasoline additives, food can soldering, lead-based paints, ceramic glazes, drinking water systems, and folk remedies. Mexican pottery has been implicated most often as a source of food contamination, especially if acidic fluids are stored in it. Topical agents applied around the eyes such as surma or kohl, which are used in Asian and Arabic countries, may be ingested, and traditional or “folk” remedies for gastrointestinal or urologic disorders may consist largely of lead. Toys or crayons of Chinese manufacture have been found to contain lead. Even imported spices and dried fish may be contaminated{{424 Markowitz,M. 2000; }}.
