Understanding chemical exposure in sediment contact tests for improved effect extrapolation from laboratory to field

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The goal of this research project was to bridge the gap between the laboratory and the field with respect to chemical exposure and toxicity to benthic organisms. In this work, we developed both experimental and computational approaches to better understand the actual chemical exposure of test organisms in laboratory toxicity testing. A mechanistically based mass transport model was established that accounted for diffusion, sorption, dilution, and colloid-facilitated transport of chemicals in the spiked-sediment exposure system. The model successfully reproduced experimental concentration data and was used to quantitatively estimate the influences of chemical, sediment, and system properties on the mass distributions of chemicals. Comparison of the model and experimental results indicated a crucial role of dissolved organic matter (DOM) in the transport of hydrophobic chemicals. In addition, the passive dosing method using polymer meshes was developed and optimized to set up a consistent exposure condition. Toxicity tests with a set of chemicals with varying properties proved the robustness, repeatability, and applicability of the method. The influences of DOM in water on the toxicity of hydrophobic chemicals to a benthic invertebrate species were confirmed using the developed method. The result suggests that DOM plays an important role and should be considered when assessing toxicity to benthic organisms.