No single biomarker can unequivocally measure environmental degradation. The ability to differentiate between clean and polluted sites would be at best incomplete using a singlebiomarker approach (Galloway et al. 2004a). A suite of end points, at different levels of biological organization, allows for a better evaluation of the hazard
(Schlenk 1996). Sole´ (2000) found when determining the effects of environments chronicallyexposed by organic pollution that no single biomarker could be adopted as a surrogate indicator but that a battery of biomarkers coupled with chemical analysis provided the most comprehensive indicator of ecosystem health. Furthermore,
by using a suite of biomarkers, a weight-of-evidence approach can be adopted that will minimize the influence of natural variation and allow the discrimination of clean healthy and polluted/unhealthy sites. Indices of environmental quality are
often used by environmental managers as a practical approach to classifying sampled sites on a scale such as ‘‘clean to highly polluted’’ or ‘‘good to poor.’’ Usually, 4 or 5 levels of chemical or ecological classifications are used to minimize errors.
Various attempts have been made to try and develop a biomarker-based index for minimizing random errors and variations so that biomarkers can be used in ERA. Bodin et al.(2004)