Downloaded By: [Canadian Research Knowledge Network] At: 13:44 23 July 2007 Human and Ecological Risk Assessment, 11: 1177–1191, 2005 Copyright C  Taylor & Francis Inc. ISSN: 1080-7039 print / 1549-7680 online DOI: 10.1080/10807030500346664 Simulation of Spatial and Temporal Variability of Chronic Copper Toxicity to Daphnia magna and Pseudokirchneriella subcapitata in Swedish and British Surface Waters F. De Laender, 1,2 K. A. C. De Schamphelaere, 1 F. A. M. Verdonck, 2,3 D. G. Heijerick, 3 P. A. Van Sprang, 3 P. A. Vanrolleghem, 2 and C. R. Janssen 1 1 Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, Ghent, Belgium; 2 BIOMATH, Department of Applied Mathematics, Biometrics and Process Control, Ghent University, Ghent, Belgium; 3 EURAS bvba, Zwijnaarde, Belgium ABSTRACT Water Quality Criteria (WQC) for metals are usually based on single species lab- oratory toxicity data. The influence of water characteristics of the surface waters on bioavailability to freshwater organisms is hence neglected, along with regional and temporal variability of these water characteristics. A methodology is presented to account for regional and temporal variability in the WQC setting for copper in the United Kingdom and Sweden. Bioavailability models were applied in a Monte-Carlo approach to account for temporal variability and a Geographic Information Sys- tem was used to account for geographical variability on the chronic copper toxicity to Daphnia magna and Pseudokirchneriella subcapitata. Fifth percentiles of distribu- tions of the No Observed Effect Concentration (NOEC) for both model species were derived in both study regions. For P. subcapitata, it was demonstrated that this fifth percentile can vary by a factor 10 in the UK study region. The ratio of these NOEC fifth percentiles (D. magna percentile divided by P. subcapitata percentile) was used to compare the ecotoxicity of copper to two model species. This ratio showed the highest variability (a factor 5) within the Swedish study region. The findings of this research stress the need for the use of region-specific WQC for copper. Key Words: bioavailability models, temporal and geographical variability, NOEC 5 , inter-regional and intra-regional variability, Monte-Carlo simulation. Received 19 November 2004; revised manuscript accepted 5 February 2005. Address correspondence to F. De Laender, Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, B-9000 Ghent, Belgium. E-mail: frederik.delaender@UGent.be 1177