The term bioindicator defines organisms that respond to a pollutant load with changes in vital functions or accumulate pollutants (Arndt et al. 1987). The use of bioindicator organisms may allow researchers to evaluate the effects of mixtures of pollutants on ecosystems in time and space, depending on the selected species and approach (Hellawell 1986). In contrast, simple instrumental analyses of pollutants can provide extremely precise data about their accumulation in organisms, but they do not clearly reveal how different chemicals interact when they cooccur in complex mixtures (Maynard 2004). Bioindicator organisms are often used in environmental monitoring programs “to assess the condition of the environment, to provide an early warning signal of changes in the environment, or to diagnose the cause of an environmental problem” (Dale and Beyeler 2001). Such studies are designed to mirror the quality of natural environments and can either be passive, when bioindicator organisms are native inhabitants of the ecosystem, or active, when organisms of a known biological past are inserted into the site to be monitored (Markert 2007).