The bioaccumulation of metals in an animal depends on a multitude of factors: biotic ones, like its body dimensions and mass, age, sex, diet, metabolism, and position in the trophic web; and abiotic ones, such as thedistribution of metals in its environment, salinity, temperature, and pH of the water, habitat type, and interactions with other metals. But it is diet that has the greatest influence on the accumulation of metals in animal tissues. Bioaccumulation is a complex process, requiring the simultaneous examination of metal levels in the tissues of animals from at least two adjacent trophic levels. To illustrate the differences in metal concentrations in animals, data are presented on heavy metal levels in the tissues of different groups of animals (marine molluscs, crustaceans, echinoderms, fish, sea turtles, birds, and mammals) from various levels of the trophic pyramid. Most commonly, metal concentrations are higher in larger animals that are end members of a trophic chain than in the smaller organisms they feed on. Since to a large extent an animal’s habitat determines the level of metals in its body, these data are generally indicators of the extent of pollution of the water body in which it lives. It has been found that carnivorous species bioaccumulate far greater quantities of metals than herbivores or omnivores, and that metal levels are lower in organisms capable of detoxifying or excreting metals.