Comparison of different exhaustive and biomimetic extraction techniques for chemical and biological analysis of polycyclic aromatic compounds in river sediments

The importance of the bioaccessible fractions of particle-bound contaminants is a key feature for the assessment of their likely risks to the aquatic environment. The present study investigated the extractability and potential toxicity of polycyclic aromatic hydrocarbons (PAHs) in river sediments. This study combined chemical with bioanalytical tools to establish a more in-depth insight into the relationship between the extractability of sediment contaminants, the chemodynamic properties of each extraction approach, and resulting toxicity. Sediment samples were treated with different extraction methods, namely Soxhlet extraction with acetone (SOX), membrane dialysis extraction (MDE) with n-hexane, ultrasonic extraction with acetone (USE), and extraction with (2-hydroxpropyl)-beta-cyclodextrin (HBCD). The extracts were analyzed for PAHs using gas chromatography/mass spectrometry and tested using the neutral red retention assay and the ethoxyresorufin-O-deethylase (EROD) induction assay with the permanent fish cell line RTL-W1. The SOX and MDE approaches were comparable in their extraction power regarding PAHs and their cytotoxicity. However, the EROD activity differed between SOX and MDE, possibly due to retardation effects of the polyethylene membrane used in MDE. Thus, macromolecular components of the sediment were not extracted and therefore did not contribute to toxicity. HBCD extraction provided 3.4 % of the total PAH content in the sediments and might be an appropriate approach to predict the bioaccessible fraction. USE showed an extraction power between the HBCD approach and the MDE as well as SOX and MDE method. Hence, USE is neither appropriate for exhaustive extraction nor for biomimetic extraction. MDE and SOX have been approved for the exhaustive extraction of PAHs from sediments for a worst case assessment of effect potentials. The influence of the low-density polyethylene membrane and the experimental conditions on the diffusion of compounds with broad physical-chemical properties, and the establishment of models such as quantitative-structure relationships for the prediction of diffusion behavior of a broad range of compounds require further assessment. HBCD was confirmed as a method providing a certain, putatively bioaccessible, fraction. Mechanistic research is required regarding desorption and uptake kinetics of particularly bound compounds with different physical-chemical properties in the solid phase-water-HBCD system to get more insight in the underlying partitioning processes.