Estimating population-level HC5 for copper using a species sensitivity distribution approach

yDepartment of Civil Engineering, Tokyo Institute of Technology, Tokyo, JapanzCenter for Environmental Risk Research, National Institute for Environmental Studies, Tsukuba, Ibaraki, JapanxResearch Institute of Science for Safety and Sustainability, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan(Submitted 2 October 2012; Returned for Revision 29 October 2012; Accepted 12 January 2013)Abstract: Estimation of population-level benchmark concentrations for protecting aquatic organisms from chemicals is important forvalue-relevant ecological risk assessments. By employing a species sensitivity distribution (SSD) approach, the authors aimed to derivethe population-level hazardous concentration for 5% of species (PHC5) for copper. Based on available information on copper toxicityand population models, the authors estimated population threshold concentrations at which the population size is stable (that is,0 net population growth) for 13 freshwater species (3 algal, 6 invertebrate, and 4 fish species). The PHC5 for copper was then estimated(6.8 mg/L; 95% confidence interval [CI], 1.8–13.6 mg/L), by fitting a log-normal distribution to the population threshold concentrationsobtained.Thecloseoverlapbetweenthepresentstudy’sestimateofthePHC5andafield-derivedthresholdconcentrationsuggeststhatthepopulation-levelSSDapproachprovidesareasonablelevelofprotectionforspeciesrichnessinthenaturalenvironment.Bycontrast,andcounterintuitively, the authors’ estimate was comparable with the individual-level HC5 reported in the European Union risk assessment.Althoughthepresentstudycannotdeterminetheunderlyingreasonsforthesimilarfigures,theresultprovidesanindicationthatthemarginbetweenindividual-levelandpopulation-levelbenchmarksderivedfromSSDapproachescanbeverysmall.Theresultsthereforesuggestthat attention is needed to achieve population-level protection using an individual-level SSD approach. Environ Toxicol Chem2013;32:1396–1402. © 2013 SETACKeywords: Hazardous concentration Population growth rate Ecological risk management Metals Population modelingINTRODUCTION