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During the twentieth century, scientific progress took precedence over quality of life. The impressive development of technology, its negative impact on the foodchain, and the ascendancy of productivity and profitability over quality reduced public confidence in thehealthiness of foods. In the present century, however, it is expected that goals connected with Food Safety, adiscipline concerned with the study of toxic substances present in foods, will be a priority in developedcountries. The metals and metalloids present in the earth's crust, soils, water, atmosphere, and biosphere, and consequently in foods, are stable compounds, persisting in the environment, having a slow rate of elimination, accumulating in tissues, and capable of undergoing transformations that increase their toxi-city. Among the metals and metalloids present in foods, lead, cadmium, arsenic, and mercury stand out because of their possible toxicological potential. These four elements can be considered the starelements, and systems of legislation in most countries have established limits that regulate their presence infoods. The criteria of toxicity for metals and metalloids have traditionally been established on the basis of totalcontent. During recent decades, however, it has been shown that their toxicity depends on their atomic ormolecular form. This has led to the need to carry out