Toxicity Identification Evaluation

Identification of what is “toxic” in aquatic toxicity tests is most often determined quantitatively through the regulatory process as permit limits or objectives and no definitive standards have been defined or are universally used. Although no universal definitions exist, several measures of toxicity are more commonly employed and seem to have achieved greater acceptance. These include the use of the “no observed effect concentration” (NOEC) or “no observed effect level” (NOEL). The NOEC and NOEL use hypothesis testing to identify statistically significant differences relative to a nontoxic control. The NOEC or NOEL is defined as the highest concentration not significantly different from the control. Another commonly used analysis involves various point estimation techniques. These quantitative analyses use dose–response data to estimate “safe” or “nontoxic” concentrations or effects using metrics such as the LC50 (lethal concentration causing a 50% effect) or EC/IC25 (effective or inhibition concentration causing a 25% effect). Due to the large amount of toxicity testing required in the TIE process, reductions in testing replication and exposure volume and duration are often made to save on sample and staffing resources. Keywords: toxicity; toxicity identification evaluation TIE; toxicity reduction evaluation TRE