ENVIRONMENTAL QUALITY BENCHMARKS FOR PROTECTING AQUATIC ECOSYSTEMS Site-specific water quality guidelines: 1. Derivation approaches based on physicochemical, ecotoxicological and ecological data R. A. van Dam & C. L. Humphrey & A. J. Harford & A. Sinclair & D. R. Jones & S. Davies & A. W. Storey Received: 31 January 2013 / Accepted: 26 April 2013 / Published online: 12 July 2013 # Crown Copyright as represented by: Australian Government Department of Sustainability, Environment, Water, Population and Communities 2013 Abstract Generic water quality guidelines (WQGs) are developed by countries/regions as broad scale tools to assist with the protection of aquatic ecosystems from the impacts of toxicants. However, since generic WQGs cannot adequate- ly account for the many environmental factors that may affect toxicity at a particular site, site-specific WQGs are often needed, especially for high environmental value ecosystems. The Australian and New Zealand Guidelines for Fresh and Marine Water Quality provide comprehensive guidance on methods for refining or deriving WQGs for site-specific pur- poses. This paper describes three such methods for deriving site-specific WQGs, namely: (1) using local reference water quality data, (2) using biological effects data from laboratory- based toxicity testing, and (3) using biological effects data from field surveys. Two case studies related to the assessment of impacts arising from mining operations in northern Australia are used to illustrate the application of these methods. Finally, the potential of several emerging methods designed to assess thresholds of ecological change from field data for deriving site-specific WQGs is discussed. Ideally, multiple lines of evidence ap- proaches, integrating both laboratory and field data, are recommended for deriving site-specific WQGs. Keywords Water quality guidelines . Site specific . Reference data . Toxicity . Field studies Introduction The contamination of aquatic ecosystems with natural and anthropogenic chemical substances (referred to herein as tox- icants) has been identified as a key global threat to water security and biodiversity (Vorosmarty et al. 2010). As such, it is essential that we understand, as best as possible, the amounts (i.e. concentrations and/or loads) of toxicants that can exist in aquatic ecosystems without causing unacceptable environmen- tal harm. Internationally, the key means for assessing the protection of aquatic ecosystems from toxicant impacts is through the derivation and application of water (and/or sedi- ment) quality guidelines (WQGs; also variously termed bench- marks, triggers, limits, thresholds, standards and criteria; although important differences in terminology definitions do exist between jurisdictions). Water quality guidelines are science-based numerical concentrations that represent the level of risk that the community is willing to take based on what it believes the environment can withstand and the ecosystem condition it is prepared to accept (ANZECC/ARMCANZ 2000; Leung et al. 2013). Water quality guidelines are typically derived at the national level (e.g. Australia and New Zealand–ANZECC/ARMCANZ Responsible editor: Philippe Garrigues R. A. van Dam (*) : C. L. Humphrey : A. J. Harford : D. R. Jones Environmental Research Institute of the Supervising Scientist, Supervising Scientist Division, Department of Sustainability, Environment, Water, Population and Communities, GPO Box 461, Darwin, Australia 0801 e-mail: rick.vandam@environment.gov.au A. Sinclair Office of the Supervising Scientist, Supervising Scientist Division, Department of Sustainability, Environment, Water, Population and Communities, GPO Box 461, Darwin, Australia 0801 S. Davies : A. W. Storey School of Animal Biology, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia D. R. Jones DR Jones Environmental Excellence, 7 Edith St, Atherton, QLD 4883, Australia Environ Sci Pollut Res (2014) 21:118–130 DOI 10.1007/s11356-013-1780-0