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Special issue: SBiRM: Focus on impact of environmental toxicants on reproductive function. Preface.

There is ever increasing recognition of the potential for a detrimental impact of man-made compounds on reproductive efficiency, as well as the health of the resultant offspring. Actual determination of the frequency and magnitude of such effects, however, are complicated by many factors. These include the complexity of normal gametogenesis, fertilization, and embryonic development, genetic variation between ethnic groups as well as each individual, variations due to the maternal ‘‘host’’ environment, and critical windows of vulnerability during embryogenesis for development of abnormalities. This variation in biology is superimposed upon variations in exposure, including the uncertainty of the impact of dose-response versus threshold level relationships, the long (years, decades, or even trans-generational) length of time required to manifest effects, potential for low dose cumulative effects over prolonged periods of exposure, and the potential additive effects of exposure to multiple compounds, either concurrently or consecutively. This has begun to be highlighted in a series of papers recently published in Systems Biology in Reproductive Medicine [Wirth et al. 2008; Goetz et al. 2009; Penna et al. 2009]. In this special issue of System Biology in Reproductive Medicine, six noted authorities have authored manuscripts on select topics of particular interest. These contributions span a variety of compounds from industrial agents such as polychlorinated biphenols and toluene, to heavy metals, to agents whose exposure results from ‘‘recreational’’ events such as smoking. The papers have additionally been chosen to highlight the seemingly ubiquitious consequences of these compounds. Specific foci include phylogenetically different animals such as mice and alligators, as well as humans. It is hoped that the contributions included in this issue from Hamlin and Guillette [2010], Meeker and Hauser [2010], Bruner-Tran and Osteen [2010], Wirth and Mijal [2010], Rappolee et. al. [2010], and Hannigan and Bowen [2010] will be of interest and lead to the initiation of further investigations which will contribute to the elucidation of the impact, and the mechanisms there of, of environmental contaminants on reproduction.