The No-Significant-Effect Concentration

Updated: 2026-01-12

An alternative toxicity estimate to the no-effect concentration (NEC) has been developed - the no-significant-effect concentration (NSEC). The no-effect concentration (NEC) is the preferred threshold metric for single-species toxicity tests applied to derive safe concentration thresholds for contaminants in the environment for use in species sensitivity distributions, but is only suitable when concentration–response (C-R) data exhibit a threshold response. The no-significant-effect concentration (NSEC) is better suited to C-R data for which the response is a monotonically decreasing function of concentration and no threshold effects are evident. A flexible, three-parameter sigmoidal function is used to describe the C-R relationship and detail both Bayesian and frequentist approaches to estimation and inference for the NSEC.