In this report, mercury, nickel and tin are considered. Representative background levels of these pollutants in air, soil, water and diet due to natural and man-made sources are indicated. The intake rates by man are estimated and distribution and retention in the body are discussed. For each pollutant, a pathway analysis is conducted in which quantitative transfer relationships are developed. The contributions of inhalation and ingestion pathways to the current concentrations of the pollutants in man are evaluated.