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Aflatoxins are highly toxic and carcinogenic naturally occurring products of spoilage molds that are widely encountered as contaminants of commonly consumed food staples, including cereal grains and nuts. This human exposure scenario is especially prominent in hot, humid environments found in low-income countries. Aflatoxin B 1 , the most abundant and potent member of a group of related compounds, has been designated as a major risk factor for human liver cancer and an important contributor to nearly 700 000 cancer deaths per year. Importantly, in experimental systems, it also induces pleiotropic toxic effects such as growth retardation and immune suppression, but the potential for aflatoxins to induce maternal and early-life toxicities in children has received only limited study. However, this possibility is gaining attention since nutritional interventions alone have had only modest effects in reducing the prevalence of health problems such as stunting and wasting. Thus, mitigation of aflatoxin exposures through primary and secondary prevention strategies holds promise for broadly improving health status in developing countries.

Mycotoxins are a diverse array of toxins produced by fungi that contaminate foods that induce a spectrum of biological effects in humans and animals. Initial recognition of the adverse effects of mycotoxins was determined from associations of acute toxicities to exposure. With the advent of biomarker strategies, chronic effects in humans and animals are now being elucidated. Regulatory concerns about mycotoxins have focused on these toxic effects. As we continue to study this class of contaminants, and explore the consequences of multiple mycotoxin interactions, we will refine our understanding of the toxicological effects of this vast number of chemicals.

Epidemiological research fundamentally involves the identification of relationships between previous exposures to putative causative agents and subsequent adverse biological effects in study populations. Molecular epidemiology encompasses the use of biomarkers in epidemiological research through the incorporation of molecular, cellular, organ system, and other biochemical and physiological measurements into studies of association, etiology, prevention, and control of health risks encountered by human populations. Application of validated biomarkers to traditional epidemiological studies helps to delineate the continuum of events between an exposure and resulting disease, to identify smaller exposures to specific xenobiotics, to indicate earlier events in the natural history of diseases and reduce misclassification of dependent and independent variables, to enhance individual and group risk monitoring and assessments, and to reveal toxicological mechanisms by which an exposure and a disease are related. This field of research has been most extensively explored in cancer, but in recent years, the use of molecular biomarkers reflecting the progression pathways in cardiovascular disease and neurological disorders has been rapidly increasing. Thus, methods to more accurately and sensitively characterize exposure, effects, and susceptibility are needed in research involving environmental agents. Collectively, these data also help to inform the risk assessment process, where regulations can be tested against biological measurements of exposure to determine the efficacy of the regulations, and most recently, these tools have been applied to the problems of assessing cumulative risk.