In the field of bioassessment, tolerance has traditionally referred to the degree to which organisms can withstand environmental degradation. This concept has been around for many years and its use is widespread. In numerous cases, tolerance values (TVs) have been assigned to individual taxa or groups of taxa to represent their tolerance to pollution. The TVs are then often combined into metrics which describe characteristics of aquatic communities. Perhaps the most familiar example is the Hilsenhoff Biotic Index (HBI) (Hilsenhoff, 1977), an index that has been incorporated into many bioassessment programs. The HBI is typically very useful in distinguishing among sites of higher and lower water quality. To calculate the HBI, each environmental agency or organization typically uses its own set of tolerance values. However, the origins of these values, and rationales for their selection, are often obscure and unverifiable. Available methods for deriving TVs more objectively vary substantially in approach and complexity. Therefore, this study conducted systematic comparisons of existing lists of macroinvertebrate TVs and their resulting HBI scores. It also compared several objective TV derivation approaches, as well as bioassessment metrics derived from each, to determine their repeatability and sensitivity to disturbance. All analyses were run at the family and genus levels.

Title from title screen (viewed Sept. 19, 2007). "May 2006." "EPA 600/R-06/045."