Freely Dissolved Concentrations of PAHs in Soil Pore Water:  Measurements via Solid-Phase Extraction and Consequences for Soil Tests

Abstract

Freely dissolved pore water concentrations are difficult to assess in complex matrixes such as soils or sediments. In this study, a negligible-depletion partitioning-based sampling technique was applied to measure freely dissolved pore water concentrations. A poly(dimethylsiloxane) (PDMS)-coated glass fiber was exposed to a slurry of a soil spiked with several PAHs at concentrations ranging from 2 to 2000 mg/kg. PAH-concentrations in the PDMS coating increased linearly with the total soil concentration until a certain maximum was reached. Freely dissolved pore water concentrations were calculated using PDMS-water partition coefficients, and the calculated maximum pore water concentrations corresponded with the aqueous solubility of the tested compounds. Furthermore, the sampling technique is very sensitive because it can detect freely dissolved pore water concentrations in the ng/L range for the tested PAHs. Freely dissolved pore water concentrations are an important parameter for the exposure of organisms in soil. Saturation of the pore water with increasing soil concentrations should therefore be considered in soil toxicity testing. Sorption coefficients that were calculated from freely dissolved concentrations were slightly higher than estimates based on octanol-water partition coefficients. These differences are discussed in relation to the effects of dissolved organic matter in soil pore water on the determination of sorption coefficients.

Polycyclic Aromatic Hydrocarbons Degradation Techniques: A Review

“…Ter-Laak, Agbo, Barendregt, and Hermens (2006) examined the use of solid-phase extraction (SPE) in measuring freely dissolved concentrations of PAHs in soil pore water. Some researchers have suggested that solid-phase microextraction (SPME) with gas chromatographic/mass spectrometric (GC/MS) analysis can achieve detection limit as low as nanograms per litre of PAHs and alkyl PAHs in sediment pore water (Hawthorne, Grabanski, Miller, & Kreitinge, 2005).…”

Modeling Uptake of Hydrophobic Organic Contaminants into Polyethylene Passive Samplers

“…1 Single-phase, polymeric passive samplers are increasingly used for measuring HOC concentrations in water, 2−4 air, 5,6 and sediment pore water. 7−14 The most widely used polymers for passive samplers include polyoxymethylene (POM), polydimethylsiloxane (PDMS) and polyethylene (PE).…”

Uptake and toxicity of polycyclic aromatic hydrocarbons in terrestrial springtails—studying bioconcentration kinetics and linking toxicity to chemical activity

“…It is well established that nominal or total measured concentrations of HOCs in soil are not sufficient to define exposure due to the numerous interactions between the HOCs and the heterogeneous soil matrix [1,2]. The freely dissolved concentration (C free ) takes sorption into account and is therefore frequently perceived as the effective concentration for bioconcentration and toxicity [3][4][5], and the concept is clear and straightforward for aqueous media and sediments. However, it seems more challenging to define the exposure of HOCs in soils, particularly in unsaturated soils, where only limited free water is present or when the target organism mainly inhabits the interstitial pore space.…”