Sources of variation in sediment toxicity of hydrophobic organic chemicals: Meta-analysis of 10-14-day spiked-sediment tests with Hyalella azteca and Chironomus dilutus.

Spiked-sediment toxicity tests with benthic organisms are routinely used to assess the potential ecological impact of sediment-associated hydrophobic organic contaminants. Although several sediment tests have been standardized, experimental factors such as spiking methods still vary between laboratories. To identify the experimental factors that affect the bioavailability of contaminants and account for the highest percentage of the variability of toxicity values (i.e., 50% lethal concentration; LC50), we performed a meta-analysis of published 10-14-day spiked-sediment toxicity tests with the standard test species Hyalella azteca and Chironomus dilutus. Analysis of 172 test records revealed that the variability of sediment LC50s for a given combination of chemical and test species was large. The mean coefficient of variation (CV) was 65%, even after organic carbon normalization, and was slightly larger than the CV in water-only tests (49%). Regression analyses revealed that the most important factor contributing to the variability of the sediment LC50s was sediment type (i.e., environmental or formulated sediment) and that use of formulated sediment (i.e., composed of peat, cellulose, or leaves as organic carbon source) tended to cause higher toxicity than use of environmental sediment. This might be caused by the difference in partitioning the coefficient of organic contaminants and the resulting difference in the bioavailability between sediment types. The effects of other factors, including aging periods and spiking methods, were insignificant or specific to certain chemicals. These discoveries facilitate refinement of the methodologies used in sediment toxicity testing and the correct interpretation of test results. Integr Environ Assess Manag 2021;00:1-11.