Use of SSD to derive no-effect thresholds for water quality guidelines and ecological risk assessments in Canada
Environment Canada, Canada
Authors: A. Gosselin1, D.J. Spry1, S. Dixit1, S. Teed2 and M. Bonnell1
Affiliations: 1Environment Canada, Gatineau, Canada; 2Intrinsik Environmental Sciences Inc., Ottawa, Canada
In Canada, species sensitivity distributions are used to derive ‘no effect’ thresholds that serve to determine water quality guidelines for aquatic life as well as PNECs in ecological risk assessments of chemicals. The Federal Water Quality Guidelines (FWQGs) are developed to meet the needs of risk assessment and risk management of chemicals under the Canadian Environmental Protection Act, 1999 (CEPA, 1999). In addition, Canadian WQGs are developed under the auspices of the Canadian Council of Ministers of the Environment (CCME) based on priorities identified by federal, provincial and territorial jurisdictions. Moreover, under CEPA 1999, regulatory ecological and human health risk assessments are conducted for substances identified as priorities on Canada’s Domestic Substances List.
The FWQGs, CCME guidelines and PNECs used in ecological risk assessments all identify thresholds for aquatic ecosystems that are intended to protect all forms of aquatic life and all life stages for indefinite exposure periods. The methodology used to derive these thresholds is the “Protocol for the Derivation of Water Quality Guidelines for the Protection of Aquatic Life” (CCME, 2007). SSD is the preferred approach for FWQGs, CCME guidelines and PNECs. It follows these steps: toxicity data collection, evaluation and selection, SSD plotting, verification of statistical assumptions including determination of the goodness-of-fit (i.e. selection of the model), and determination of the FWQG, CCME guideline and/or PNEC. They are set at the 5th percentile of the SSD, which may, in the case of the PNEC used for risk assessment, be divided by an assessment factor if deemed necessary.
Examples of the use of SSDs in Canada were presented, including the Federal Water Quality Guidelines and risk assessment for metals (vanadium and uranium) and the antimicrobial triclosan.