ABSTRACT
The term biomarker has been gaining acceptance in recent years, albeit with some inconsistency in definition. Here we define biomarkers as any biological response to an environmental chemical at the individual level or below demonstrating a departure from the normal status. Thus biochemical, physiological, histological, morphological, and behavioral measurements are to be considered as biomarkers. Some examples of biomarkers at different organization levels are given in Table 10.1. Biological responses at higher organizational levels — population, community, and ecosystem — are considered as bioindicators. Notwithstanding the importance of any changes at these higher levels (considered in Chapters 12, 15, and 16 ), these changes are too general to be considered as specific biomarkers. The relationship between biomarkers and bioindicators regarding their specificity and ecological relevance is shown diagrammatically in Figure 10.1. In general, it can be said that it is difficult to relate biochemical changes to ecological changes (although eggshell thinning caused by
p,p
′
-DDE and imposex in dog whelks caused by TBT, discussed in Chapter 16, show that a physiological change can be related to a massive population change). It is also difficult to relate ecological changes to specific chemical causes.
