Current and Future Challenges in Sediment Toxicity Testing for Environmental Risk Assessment
Henry Krueger, Paul Sibley, Teresa Norberg-King, Matt McCoole
Sediment toxicity testing in support of sediment risk assessment has recently gained an increasing awareness within the scientific community. For example, in 2015, a scientific opinion on environmental risk assessment for sediment organisms was published by the European Food Safety Authority (EFSA). Also, the European CHemicals Agency (ECHA) updated the sediment section of the "Guidance on Information Requirements & Chemical Safety Assessment" in February 2016. Sediment toxicity risk assessments are guided by the methods outlined in ASTM and by the USEPA sediment testing guidance documents (e.g., OCSPP 850.1735 ). In the US, standardized acute (10-d) and chronic (e.g., 28-d) sediment (including spiked sediment) methods are available with several invertebrate freshwater and marine species (e.g., freshwater species, Hyalellaazteca, Chironomusdilutus; marine species, Leptocheirusplumulosus) while the available standardized and validated OECD spiked-water and spiked-sediment guidelines are available for two invertebrate species (e.g. Chironomusriparius, Lumbriculusvariegatus), and one adopted guideline with the macrophyte, Myriophyllum. There are a number of differences between the OECD and USEPA guidelines for performing spiked sediment tests, including the introduction of the compound into the test system, the use of natural or artificial sediment, equilibration time, and flow-through or static test design. These test method differences lead to changes in the physicochemical properties of the sediment, bioavailability of the test compound, and the concentrations of the test substance in the overlying water, pore water, and bulk sediment. Due to these differences, the results of studies performed according to OECD and USEPA test methods are difficult to compare. In recent years, the environmental matrix (pore water, overlying water, sediment, bulk sediment, total loading) most strongly associated with effects has been widely debated. For example, most test organisms are epibenthic and live on the sediment surface and not within the sediment. Therefore, being aware of differences between OECD and USEPA test methods and between EFSA and ECHA guidances, lead to uncertainty in comparing studies, including the relevant route of exposure and how to express test results to be used in the sediment risk assessment. In this session, presentations that compare the differences between the guidelines and compare and contrast the different approaches for an environmental risk assessment using data from both sources and guidance are planned. As the bioavailability in the different test systems is not always directly comparable, and different uptake pathways exist for the different taxonomic groups and species, discussions of how the approaches as outlined in the EFSA scientific opinion can be accomplished are encouraged. Further, the goal of this session is to highlight applied and theoretical innovations associated with sediment toxicity testing, including but not limited to the topics above, to improve test performance, interpretation of study results, and reduce uncertainty in the application of sediment toxicity data for ecological risk assessment.