Abstract
The sorption of organic compounds to soil, sediments and dissolved organic matter affects the fate of organic compounds. Given the central role of this process in environmental transport, distribution, and (bio)degradation processes, it needs to be well-understood and represented in risk assessment of chemicals in the environment. In this thesis
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soil-sorption of various organic compounds was studied in order to improve the scientific basis for representing sorption in risk assessment. Chapters 2 to 5 study the sorption of hydrophobic organic chemicals. They are focused on the development and validation of passive sampling techniques to simplify the determination of freely dissolved concentrations and sorption coefficients. Chapters 6 and 7 explore the sorption of ionizable organic antimicrobial agents in relation to the pore water and soil composition.
The sorption of neutral organic (hydrophobic) compounds has been studied intensively for several decades. Difficult determination of freely dissolved concentrations and the heterogeneity of soil organic material can complicate the measurement and modeling of sorption coefficients for these compounds. In this thesis the simple and sensitive solid phase microextraction (SPME) technique using a poly-dimethylsiloxane (PDMS) coated fiber was used. This passive sampling technique can measure (changes in) freely dissolved concentrations in complex matrices such as soil (Chapter 4 and 5), sediment (Chapter 3) and dissolved organic matter solutions (Chapter 2), and should therefore be applied to generate unbiased sorption coefficients. The simplicity and sensitivity of the technique strongly advocates for both generating high quality sorption data for modeling purposes and specific monitoring and risk assessment of contaminated sites.
Contrastingly, there is limited knowledge on the soil sorption of polar ionizable organic compounds such as veterinary pharmaceuticals. Hence, more research is needed on the sorption of these compounds. This thesis has demonstrated that soil properties like organic carbon content, clay content, cation exchange capacity and iron and aluminum oxyhydroxide content (Chapter 7) and pore water properties like pH and ionic strength (chapter 6) significantly influence sorption of these compounds. Modeling the influence of soil properties allows prediction of sorption with limited accuracy. Modeled sorption data should therefore (only) be taken as qualitative indicators of the sorption behavior. Consequently, experimental data are preferred for site-specific risk assessment. Clearly, more research is needed in order to improve our understanding and modeling of the sorption of these compounds.
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