Desorption of Hydrophobic Compounds from Laboratory-Spiked Sediments Measured by Tenax Absorbent and Matrix Solid-Phase Microextraction

Abstract

Tenax extraction and matrix solid-phase microextraction (matrix-SPME) were used to study desorption of hydrophobic contaminants (HOC) from sediments. 14C-labeled hexachlorobiphenyl, DDE, permethrin, chlorpyrifos, and phenanthrene were individually spiked into sediments differing in physical characteristics. Sequestration of the HOCs into sediment was observed for all compounds, and desorption was described by rapid, slow, and very slow rates. The freely dissolved HOC concentration in the sediment porewater was estimated by matrix-SPME, and serial sampling was used to ensure equilibrium was achieved among sediment, porewater and matrix-SPME fiber. Differences in partitioning of the HOCs between sediment and porewater for the different sediments were reduced by replacing the HOC concentration in sediment with the rapidly desorbing fraction. The significantly lower porewater concentration determined from matrix-SPME, than predicted from equilibrium partitioning theory (EPT), showed that only a small fraction of sediment HOCs were available for equilibrium and the predictability of EPT can be improved with the consideration of sequestration in sediment. A good correlation was noted between sediment concentration in the rapidly desorbing fraction measured by Tenax extraction, and SPME fiber concentration as determined by matrix-SPME. Thus, the two methods both tracked the readily desorbed contaminant equally well though Tenax extraction measures the accessible pool, and matrix-SPME measures the chemical activity of the HOCs.

Addition of contaminant bioavailability and species susceptibility to a sediment toxicity assessment: Application in an urban stream in China

“…where, C free and C fiber were the freely-dissolved chemical concentration and SPME fiber concentration, respectively, and K OC and K fw were the partition coefficients between OC or fiber and water, respectively, and their values were taken from the literature (Laskowski, 2002;You et al, 2007). The OC normalized LC50 was used to calculate TU bioavailable due to the lack of Tenax-and SPME-based LC50 values.…”

“…One of the reasons for this discrepancy is that contaminants have distinct sorption capacities to different types of OC, but the understanding of OC classification and the partitioning processes of contaminants within OC is still quite limited . In addition, other factors may also affect bioavailability and toxicity of sediment-associated contaminants, including sediment grain size (Mehler et al, 2011b), sediment aromaticity and planarity (Lyytikainen et al, 2003), niches of the test organisms (Wang et al, 2004), and chemical properties (You et al, 2007). Thus, it is beneficial to incorporate bioavailability measurements into risk assessments to improve the accuracy of sediment toxicity estimates .…”

Bioavailability of Hydrophobic Organic Contaminants in Sediment with Different Particle-Size Distributions

“…Consecutive Tenax extraction was performed in triplicate to measure desorption rates of HOCs from sediments, and six sampling time points were used (3,6,24,72,168, and 336 h) (You et al 2007b). In brief, 5 g wet sediment, 5 ng NaN 3 , 45 ml MHW, and 0.5 g Tenax beads were added into a 50-ml screw-cap glass tube.…”

“…The fibers were sampled at five time points (72,168,240,336, and 672 h) to ensure that the HOCs had reached equilibrium between the sediment porewater and the fibers. Matrix-SPME experiments were performed according to previously published procedures (You et al 2007b). The fibers were protected with a 2 9 2-cm envelope made of stainless steel mesh with 110-lm openings.…”

“…Non-exhaustive chemical extraction has been shown to be a more accurate method for predicting bioavailability and toxicity of sediment-associated HOCs compared with exhaustive extraction methods because it estimates only the bioavailable fractions within the system (Conder et al 2004;You et al 2006;Jonker et al 2007;You et al 2007b;Styrishave et al 2008;van der Heijden and Jonker 2009;Oleszczuk 2009), and it has been effective in evaluating bioavailability of various classes of HOCs in sediment with different OC Jonker et al 2007) and black carbon contents (Cornelissen et al 2005;Yang et al 2008). However, relatively few studies have examined whether non-exhaustive extraction techniques can accurately predict the bioavailable fractions of HOCs when differing physical factors, such as particle-size distribution, occur.…”