The significance of a developmental stage approach

Adverse effects in children may result from exposure prior to conception (paternal and/or maternal), during prenatal development, or postnatally to the time of full maturity. Even within a given developmental stage, shorter intervals of exposure may determine susceptibility for particular outcomes. Different organ systems develop at different rates, but it has been shown that for each developmental stage, there are both broad windows of susceptibility and more specific periods of susceptibility (Faustman et al., 2000  

Selevan et al., 2000). This has been worked out in some detail for certain systems and agents (e.g. central nervous system development and radiation exposure) in most cases, however, the exact time when organ systems are susceptible to the actions of toxic chemicals is unknown. Limited data are available on susceptibility during the adolescent period, but with the current greater interest in the effects of hormonally active agents, more information is becoming available. 

As indicated previously, adverse health outcomes from early exposures may become apparent at any point in the lifespan. In some instances, they may be apparent only after long latency periods. Chapter 6 addresses the various methodologies that can be used to assess health outcomes. Studies have shown that the effects of toxic exposures on developmental processes may result from different mechanisms of action, and the toxic exposures may produce different health outcomes compared with the same exposures in adults. Some examples of health effects resulting from developmental exposures include those observed prenatally and at birth (e.g. miscarriage, stillbirth, low birth weight, birth defects), in young children (e.g. asthma, neurobehavioural and immune impairment), in adolescents (e.g. precocious or delayed puberty), and in adults (e.g. diabetes and heart disease). 

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