Lead, Mexico export

The importance of U.S. tolerances stems from both the stringency of the scientific evaluation process upon which they are based and the important role of the U.S. in international food trade. Some countries actually defer to U.S. tolerances in lieu of their own legislation for export purposes (e.g., Costa Rica, Mexico). It is expected that U.S. tolerances will be highly influential in future development of MRL policy within the NAFTA countries, particularly as regional harmonization efforts may some day lead to a system of NAFTA MRLs. The FQPA-mandated tolerance reassessment process has resulted in many changes in U.S. tolerances, particularly the loss or reduction of tolerances for some older products, and these changes have the potential to impact use and food export practices in U.S. trading partners. 

Recovered lead has a major role in the Mexican market of lead for example, in 1986 it constituted 26%, considering both primary and secondary lead. In spite of the important production of lead, with the exception of 1985, its reported uses decreased in Mexico from 1982 to 1987 also, most of the sales of lead registered for the internal market were exported after the industrialization process. Exports of lead have increased continuously in recent years (Table 4) (IMZPC 1986, 1987). In 1986, Mexico was the third world exporter of lead after Australia and Canada (IMZPC 1987). 

As an exception in the trends observed in the national market, the lead used to obtain tetraethyl lead has not only kept its level, but increased continuously (see Table 5) this is generally explained as due to the fact that this product is being exported to those countries that are still using it as a fuel additive (IMZPC 1987). However, it must not be forgotten that Mexico is also using large quantities of this substance. 

The USA was an exporter of refined lead until the 1920s, and remained largely self-sufficient until about 1950. Until very recently it remained (in most years) the largest individual importer of metal, but now appears to have lost this position to (the newly unified) Germany. The vast majority of US imports come from Canada and Mexico. The USA has also emerged, simultaneously, as an important exporter of refined lead, and its net import requirement has almost been eliminated. 

Australia, Canada and Mexico have been major suppliers of refined lead since early in the century, based on the processing of local ores. Mexican exports have been rather erratic in recent years, and production problems and strikes in Canada have reinforced Australia s position as largest exporter. 

The world production of arsenic trioxide was about 50,000 tons in 1977. The US comsumes about half the total world production, and produces about 50% of what it consumes [11]. According to the National Academy of Sciences, exporters of arsenic include Mexico, Sweden, France, the Republic of South Africa, Peru, and the Phillipines [10]. The amounts of arsenic in the various copper, lead, and zinc concentrates range from parts per million (ppm) up to 15.5%. 

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