Combining Leaching and Passive Sampling To Measure the Mobility and Distribution between Porewater, DOC, and Colloids of Native Oxy-PAHs, N-PACs, and PAHs in Historically Contaminated Soil

Abstract

Different methods to quantify soil porewater concentrations of contaminants will provide different types of information. Passive sampling measurements give freely dissolved porewater concentrations (C), while leaching tests provide information on the mobile concentration (C), including contaminants associated with dissolved organic carbon (DOC) and particles/colloids in the porewater. This study presents a novel combination of these two measurements, to study the sorption and mobility of polycyclic aromatic compounds (PACs) to DOC and particulate organic carbon (POC) in 10 historically contaminated soils. The PACs investigated were polycyclic aromatic hydrocarbons (PAHs), oxygenated-PAHs, and nitrogen containing heterocyclic PACs. Observed C was up to 5 orders of magnitude higher than C; implying large biases when C is used to assess bioavailability or soil partitioning. Sorption of PACs to DOC and POC was important for the mobility of compounds with log K > 4. Average DOC/water-partitioning coefficients (K) correlated well with K (log K = 0.89 × log K +1.03 (r = 0.89)). This relationship is likely more accurate for historically contaminated soils than previously published data, which suffer from artifacts caused by problems in measuring C correctly or not using historically contaminated soils. POC/water-partitioning coefficients (K) were orders of magnitude larger than corresponding K suggesting sorption to mobile particles/colloids is the dominant mechanism for PAC mobility.

Analytical progress and challenges for the detection of oxygenated polycyclic aromatic hydrocarbon transformation products in aqueous and soil environmental matrices: A review

“…Nevertheless a few trends in the distribution of oxygenated PAH can be observed. Similar to PAH, highest concentrations of oxygenated PAH in soils are typically associated with contaminated industrial sites including former coking ovens, gasworks, and wood preservation sites, where oxygenated PAH may also be present in pore water, leachate, and groundwater (Arp et al, 2014;Enell et al, 2016;Ohlenbusch et al, 2002). Urban areas which receive atmospheric inputs from traffic or other combustion sources may also be substantially impacted, along with areas such as river deltas and harbours which receive large loads of terrestrial and atmospheric materials.…”

“…Filtration is sometimes performed prior to extraction of aqueous samples and may be applied to organic extracts prior to analysis. However, it has been generally recognised that hydrophobic organic compounds including PAH and many metabolites may adsorb on to filter membrane surfaces, leading to underestimates of analyte content (Enell et al, 2016). Despite this, filtration of samples or organic extracts is commonly overlooked as a source of loss during sample preparation.…”

“…A few studies indicate that nylon may be appropriate for OHPAH prepared in methanol or methanol/DCM (1:1) (Avagyan et al, 2015;Hu et al, 2014) and PVDF may be appropriate specifically for filtering aqueous samples containing naphthoic acids (Boll et al, 2015). In general, however, centrifugation rather than filtration is the recommended approach for separating very wet soil samples or for removing particulate materials from aqueous samples (Enell et al, 2016).…”

“…Where an aqueous sample has large colloid load, e.g. a simulated leachate (shaken aqueous extracts of soils), analysis of centrifuged samples may lead to overestimation of the analytes; sampling protocols may be adapted to avoid this error, for example, through the use of flow-through or recycled leachate collection systems (Enell et al, 2016).…”

Persistent organic pollutants in wood fiber–contaminated sediments from the Baltic Sea

“…The higher log K TOC s of Booij et al (2003), who used passive samplers (low-density polyethylene) that specifically sample the freely dissolved phase (i.e., a similar method as used in this study), is likely a consequence of the more stringent sampling method. A In Kramfors, only fiberbank and fiber-rich sediment samples were collected similar discrepancy between sampling methods has also been observed for PAHs (Enell et al 2016).…”