DDT is a pesticide that was once widely used to control insects. Both DDD and DDE are breakdown products of DDT. This profile includes: (1) The examination, summary, and interpretation of available toxicologic info. and epidemiologic evaluations on DDT/DDD/DDE to ascertain the levels of significant human exposure for the substance and the associated chronic health effects; (2) A determination of whether adequate info. on the health effects of DDT/DDD/DDE is available to determine levels of exposure that present a significant risk to human health of chronic health effects; and (3) Identification of toxicologic testing needed to identify the types or levels of exposure that may present significant risk of adverse health effects in humans. Illus.

This report considers the biological and behavioral mechanisms that may underlie the pathogenicity of tobacco smoke. Many Surgeon General's reports have considered research findings on mechanisms in assessing the biological plausibility of associations observed in epidemiologic studies. Mechanisms of disease are important because they may provide plausibility, which is one of the guideline criteria for assessing evidence on causation. This report specifically reviews the evidence on the potential mechanisms by which smoking causes diseases and considers whether a mechanism is likely to be operative in the production of human disease by tobacco smoke. This evidence is relevant to understanding how smoking causes disease, to identifying those who may be particularly susceptible, and to assessing the potential risks of tobacco products.