What level of effect is a no observed effect?

The no observed effect concentration (NOEC) is currently a major summary st atistic in ecotoxicity testing. Its use is heavily criticized, partly becau se it is a poor estimator of "safe" chemical concentrations. In this short communication, we review the limited information available on the percentag e effect that corresponds with the NOEC, a value designated the ECNOEC, and calculate ECNOEC values for fish growth data. The average ECNOEC for diffe rent test protocols was found to vary widely, with values for chronic studi es ranging from 10 to 34%. Individual results varied even more widely. This analysis suggests that the NOEC is neither a consistent summary statistic nor an indicator of safe concentrations of toxic chemicals.