Estimating toxic effect of copper on population of microalgae through a three-dimensional toxic effect growth model

A newly proposed three-dimensional model for the effects of heavy metals on the growth of batch cultures of algae that allows the estimation of the no detected toxic effect concentration (NDEC) is presented. Two batch assays with exposure to copper were investigated in situ (ship-based enclosure). As an endpoint in these studies, the carrying capacity B(f), a parameter of the logistic growth model, possesses higher sensitivity and reliability than routine ecotoxicological endpoints. Using B(f) as the endpoint, the NDEC from the proposed model is compared to the no observed effect concentration (NOEC), Lowest Observed Effect Concentration (LOEC), the 5% effect concentration (EC₀₅) and no effect concentration (NEC) also calculated from field-derived data. The results show the confidence interval for the NDEC was wholly contained within the corresponding interval between the NOEC and LOEC, as well as within the corresponding much wider confidence interval for EC₀₅. Though the width of the confidence interval for NEC was basically equivalent to the corresponding width for NDEC, the NEC was somewhat higher than the corresponding NDEC. The results indicate that the NDEC is a promising possible alternative parameter to the NOEC.