A Bayesian approach for determining the no effect concentration and hazardous concentration in ecotoxicology.

This paper describes a Bayesian modeling approach to the estimation of the no effect concentration (NEC) and the hazardous concentration (HC(x)) as an alternative to conventional methods based on NOECs - the no observed effect concentration. The advantage of the proposed method is that it combines a plausible model for dose-response data with prior information or belief about the model's parameters to generate posterior distributions for the parameters - one of those being the NEC. The posterior distribution can be used to derive point and interval estimates for the NEC as well as providing uncertainty bounds when used in the development of a species sensitivity distribution (SSD). This latter feature is particularly attractive and overcomes a recognized deficiency of the NOEC-based approach. Examples using previously published data sets are provided which illustrate how the NEC/HC(x) estimation problem is re-cast and solved in this Bayesian framework.