Lack of knowledge of the normal physiological ranges of biomarkers has impeded their applied use,and, in many cases, this gap in understanding reflects a lack of understanding of the fundamental biochemistry of many aquatic organisms. In a medical context, the normal ranges of values quoted are ranges from a skewed distribution
calculated to include 95% of the values obtained from a healthy population (Depledge 1994). Schlenk (1999) recommends the use of a ‘‘safety factor’’ that takes into account
variability in the susceptibility of individuals, whereas Depledge (1994)