Derivation of Predicted No Effect Concentrations (PNECs) for Heavy Metals in Freshwater Organisms in Korea Using Species Sensitivity Distributions (SSDs)

Abstract

Natural and artificial heavy metal exposure to the environment requires finding thresholds to protect aquatic ecosystems from the toxicity of heavy metals. The threshold is commonly called a predicted no effect concentration (PNEC) and is thought to protect most organisms in an ecosystem from a chemical. PNEC is derived by applying a large assessment factor (AF) to the toxicity value of the most sensitive organism to a chemical or by developing a species sensitivity distribution (SSD), which is a cumulative distribution function with many toxicity data for a chemical of diverse organisms. This study developed SSDs and derived PNECs using toxicity data of organisms living in Korea for four heavy metals: copper (Cd), cadmium (Cu), lead (Pb), and zinc (Zn). Five distribution models were considered with log-transformed toxicity data, and their fitness and uncertainty were investigated. As a result, the normal distribution and Gumbel distribution fit the data well. In contrast, the Weibull distribution poorly accounted for the data at the lower tails for all of the heavy metals. The hazardous concentration for 5% of species (HC5) derived from the most suitable model for each heavy metal was calculated to be the preferred PNEC by AF 2 or AF 3. PNECs, obtained through a suitable SSD model with resident species and reasonable AF, will help protect freshwater organisms in Korea from heavy metals.