Matrix Solid-phase Microextraction Research Articles

DDT and related compounds in pore water of shallow sediments on the Palos Verdes Shelf, California, USA

Abstract For nearly two and a half decades following World War II, production wastes from the world's largest manufacturer of technical DDT (1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene) were discharged into sewers of Los Angeles County. Following treatment, the wastes were released via a submarine outfall system to nearshore coastal waters where a portion accumulated in shallow sediments of the Palos Verdes Shelf (PVS). An investigation of the pore-water geochemistry of DDT-related compounds (DDX) was undertaken in an effort to understand factors controlling the rate of reductive dechlorination (RDC) of the major DDT degradate, 4,4′-DDE (1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene). Equilibrium matrix-solid phase microextraction (matrix-SPMEeq) combined with automated thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) was used to determine freely dissolved concentrations of ten DDX analytes in sediment cores collected from three locations on the PVS (stations 3C, 6C, 8C, which are 7 km, 2 km, and 0 km, respectively, downcurrent from the outfall system). Pore-water concentrations (pM) of the principal DDX compounds involved in RDC were: 3C-DDE: 6.0–24, DDMU (1-chloro-4-[2-chloro-1-(4-chlorophenyl)ethenyl]benzene): 11–160, DDNU (1-chloro-4-[1-(4-chlorophenyl)ethenyl]benzene): 1.8–68; 6C-DDE: 5.6–170, DDMU: 5.6–177, DDNU: 1.7–87; 8C-DDE: 27–212, DDMU: 31–403, DDNU: 5.5–89. Variations in the spatial distribution of DDX analytes in pore water reflect several factors including proximity to the outfalls, RDC reaction rates, and natural variability in sedimentation and post-depositional transport processes. A comparison of pore-water data produced using matrix-SPMEeq/TD-GC/MS and whole-core squeezing/solvent extraction/liquid injection-GC/MS indicates that the majority of the DDE in the upper sediment column (≤about 10 cm) is associated with dissolved/colloidal organic matter. Below that depth, freely-dissolved DDE predominates. The principal organic geochemical phase controlling sorption of DDE in PVS sediments are residual hydrocarbons, the vast majority of which originated from petroleum refinery wastes. Organic carbon-normalized sediment-water distribution coefficients (KOC) were calculated from solid-phase and pore-water concentrations of DDX and organic carbon. Log KOC values (L/kg) were relatively invariant across the shelf and with depth in the sediment column. Shelf-wide compound-specific coefficients (log KOC) were: DDE: 7.5 ± 0.11, DDMU: 6.92 ± 0.13, DDNU: 6.37 ± 0.19. The spatial uniformity of KOC means that biological exposure and availability of the DDX compounds can, in principle, be estimated from solid-phase chemical measurements.

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

Sediments collected from an urban creek in China exhibited high acute toxicity to Hyalella azteca with 81.3% of sediments being toxic. A toxic unit (TU) estimation demonstrated that the pyrethroid, cypermethrin, was the major contributor to toxicity. The traditional TU approach, however, overestimated the toxicity. Reduced bioavailability of sediment-associated cypermethrin due to sequestration explained the overestimation. Additionally, antagonism among multiple contaminants and species susceptibility to various contaminants also contributed to the unexpectedly low toxicity to H. azteca. Bioavailable TUs derived from the bioavailability-based approaches, Tenax extraction and matrix-solid phase microextraction (matrix-SPME), showed better correlations with the noted toxicity compared to traditional TUs. As the first successful attempt to use matrix-SPME for estimating toxicity caused by emerging insecticides in field sediment, the present study found freely dissolved cypermethrin concentrations significantly improved the prediction of sediment toxicity to H. azteca compared to organic carbon normalized and Tenax extractable concentrations.

Assessing bioavailability and toxicity of permethrin and DDT in sediment using matrix solid phase microextraction

Matrix solid phase microextraction (matrix-SPME) was evaluated as a surrogate for the absorbed dose in organisms to estimate bioavailability and toxicity of permethrin and dichlorodiphenyltrichloroethane (DDT) in laboratory-spiked sediment. Sediments were incubated for 7, 28, and 90 days at room temperature to characterize the effect of aging on bioavailability and toxicity. Sediment toxicity was assessed using two freshwater invertebrates, the midge Chironomus dilutus and amphipod Hyalella azteca. Disposable polydimethylsiloxane fibers were used to estimate the absorbed dose in organisms and to examine bioavailability and toxicity. The equilibrium fiber concentrations substantially decreased with an increase in sediment aging time, indicating a reduction in bioavailability. Based on median lethal fiber concentrations (fiber LC50), toxicity of permethrin was not significantly different among the different aging times. Due to the substantial degradation of DDT to dichlorodiphenyldichloroethane (DDD) in sediment, sediment toxicity to C. dilutus increased, while it decreased for H. azteca with extended aging times. A toxic unit-based fiber LC50 value represented the DDT mixture (DDT and DDD) toxicity for both species. Significant linear relationships were found between organism body residues and the equilibrium fiber concentrations for each compound, across aging times. The study suggested that the matrix-SPME fibers mimicked bioaccumulation in the organisms, and enabled estimation of body residues, and could potentially be used in environmental risk assessment across matrices (e.g. sediment and water) to measure bioavailability and toxicity of hydrophobic pesticides.

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

Few studies have been conducted examining the distribution of different-sized particles in sediment and its potential impact on bioavailability of sediment-associated contaminants. In the current study, three sediments composed of different particle sizes, i.e., fine (0-180 μm), combined (0-500 μm), and coarse (180-500 μm), were used to evaluate the bioaccumulation potential and toxicokinetic rates of four hydrophobic organic contaminants (HOCs) including two polychlorinated biphenyls (PCB-101 and PCB-118), a metabolite of an organochlorine insecticide (p,p'-DDE), and a polybrominated diphenyl ether (BDE-47) to the benthic oligochaete Lumbriculus variegatus. Two chemical approaches, Tenax extraction and matrix-solid phase microextraction (SPME), were also used to measure bioavailability of the sediment-associated HOCs. The uptake and elimination rates of HOCs by L. variegatus from coarse sediment were greater than those from fine sediment, although the biota-sediment accumulation factors (BSAFs) were not significantly different among sediments with different particle sizes. The freely dissolved HOC concentrations measured by matrix-SPME were greater in coarse sediment, however, no difference was found in uptake and desorption rates for the matrix-SPME and Tenax extraction measurements. Although BSAFs in L. variegatus were the same among sediments, kinetic rates of HOCs for organisms and freely dissolved HOC concentrations were lower in fine sediment, suggesting that sediment ingestion may also play a role in organism uptake, especially for HOCs in fine sediment.

Influence of black carbon and chemical planarity on bioavailability of sediment‐associated contaminants

Black carbon (BC) and chemical properties may play a significant role in defining the bioavailability of hydrophobic organic compounds (HOCs) in sediment. In the current study, bioavailability of four HOCs with differing planarity was determined in sediments amended with two types of BC (soot and charcoal) at different concentrations by matrix solid-phase microextraction (matrix-SPME) and bioaccumulation testing using the freshwater oligochaete Lumbriculus variegatus. Furthermore, the applicability of the matrix-SPME method to bioavailability estimation in BC-amended sediment was tested. The charcoal treatment significantly reduced the bioaccumulation of the planar compounds (3,3',4,4'-tetrachlorobiphenyl and benzo[a]pyrene) in L. variegatus, and the matrix-SPME method showed a similar trend as contaminant bioaccumulation in L. variegatus. Conversely, manipulation of sediment with soot had no effect or slightly increased bioavailability of the planar compounds in both bioaccumulation and matrix-SPME tests. Little if any affect was noted in bioavailability of the nonplanar compounds (2,2',4,4',5,5'-hexachlorobiphenyl and permethrin) with the soot and charcoal amendments. Results showed that the role of BC in defining bioavailability of HOCs depends not only on the type and concentrations of BC present, but also the planarity of the HOCs.

Degradation of fipronil in anaerobic sediments and the effect on porewater concentrations

The current study measured the degradation of fipronil in laboratory-spiked silt loam sediment under anaerobic conditions at different aging times. The half-life of fipronil in anaerobic sediments spiked at 5.8 ± 0.049 and 21 ± 1.4 μg/kg dry weight (dw) was 21 ± 0.22 and 15 ± 0.11 d, respectively. Fipronil-sulfide was the primary degradation product with fipronil-sulfone detected at lower concentrations. No degradation occurred to fipronil-sulfide and fipronil-sulfone over 200 d in separate systems. A concurrent decline in sediment concentrations resulted in a decline of fipronil in sediment porewater with an increase in fipronil-sulfide and fipronil-sulfone measured by matrix–solid phase microextraction (matrix-SPME). Equilibrium among sediment, porewater, and matrix-SPME fiber occurred within 138 d for fipronil and fipronil-sulfone; however, fipronil-sulfide did not reach equilibrium during the test, and modeling predicted upwards of 1083 d to reach equilibrium. Regardless of the time to reach equilibrium, the rapid degradation of fipronil has little ecological significance given that fipronil-sulfide and fipronil-sulfone have equal or greater toxicity, and exhibit greater environmental stability in both the sediment and porewater, thereby becoming bioavailable.

Using Matrix Solid-Phase Microextraction (Matrix-SPME) to Estimate Bioavailability of DDTs in Soil to Both Earthworm and Vegetables

This study was conducted to find an appropriate approach for the assessment of bioavailability of DDTs in soil to both earthworm and vegetables. Four chemical approaches--Soxhlet extraction with n-hexane, n-butanol agitation extraction, water agitation extraction, and matrix solid-phase microextraction (matrix-SPME)--were used to assess the relationships between the extractability of 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (p,p'-DDE), 1,1,1-trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl) ethane (o,p'-DDT), 1,1-dichloro-2,2-bis(p-chlorophenyl) ethane (p,p'-DDD), and 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (p,p'-DDT) in soil and their amounts uptaken by the earthworm (Eisenia foetida), Chinese cabbage (Brassica campestris L. spp.), and cole (Brassica napus L.). These results indicated that the extractability and bioavailability of DDTs in soil decreased with time of aging. Correlation analysis showed that n-butanol extraction or 12-h matrix-SPME could be used to assess the bioavailability of DDTs to the earthworm, and Soxhlet extraction, n-butanol extraction, or 12-h matrix-SPME could be used to predict the bioavailability of DDTs to both Chinese cabbage and cole. As a solventless, time-efficient, and negligible-depletion technique, it could be concluded that matrix-SPME is a better approach to predict the bioavailability of DDTs to both the earthworm and vegetables, compared with Soxhlet extraction, n-butanol extraction, and water extraction.

Matrix solid-phase microextraction for measuring freely dissolved concentrations and chemical activities of PAHs in sediment cores from the western Baltic Sea

Sediment-pore water partitioning of polycyclic aromatic hydrocarbons (PAHs) was studied in sediment cores of a dumping area in the western Baltic Sea and compared to a reference site. Freely dissolved concentrations ( C free) of nine PAHs were measured in sediment samples using solid-phase microextraction (SPME), a cost and time-efficient method with detection limits in the lower ng L −1 range. Elevated levels of C free were measured at the dumping site, where concentration peaks in the core correlated with the presence of the dumped material, which was conspicuous in its color and consistency. Sediment concentrations of PAHs were three orders of magnitude higher at the dumping site than at the reference site, whereas C free was only one order of magnitude greater. Chemical activities of the PAHs in the sediment cores were calculated from C free to predict the baseline toxic potential of the contaminant mixture. Finally, gradients in C free and chemical activity were used to determine the direction of diffusion within the sediment and to obtain a spatial characterization of the PAH exposure. C free and chemical activity are important exposure parameters for the prediction of bioconcentration and toxicity in sediment organisms, and their measurement should be included in risk-assessment and pollution-management strategies.

Bioavailability of PCBs from field-collected sediments: Application of Tenax extraction and matrix-SPME techniques

Two chemical approaches, Tenax extraction and matrix solid phase microextraction (matrix-SPME), were evaluated for their potential to improve the prediction of bioavailability by equilibrium partitioning theory (EPT) across sediments with various characteristics. Biota-sediment accumulation factors (BSAFs) and body residues were quantified by exposing Lumbriculus variegatus to three PCB-contaminated field sediments. The concentration of PCBs in biota was positively correlated to the total PCB sediment concentration, the PCB concentration in the rapidly desorbing fraction estimated using Tenax extraction, and the PCB concentration on the SPME fibers. Results showed EPT was acceptable for estimating bioavailability from the tested sediments with sum PCB BSAFs of 1.18–2.47; however, it overestimated PCB bioavailability from sandy sediment. Both Tenax extraction and matrix-SPME, which take sequestration into account, reduced variability in prediction of PCB bioavailability across sediments, including the sandy sediment, and could be used as cost- and time-efficient alternatives for bioassay. Matrix-SPME was considered the better technique due to its ability to directly predict PCB body residues in the exposed biota and its potential use with in situ applications in the field.

Availability of polychlorinated biphenyls in field‐contaminated sediment

Two chemical approaches, Tenax extraction and matrix solid phase microextraction (matrix-SPME), were evaluated as surrogates to estimate bioavailability of polychlorinated biphenyls (PCBs) from field-contaminated sediment. Aroclor 1254 was the primary contaminant found in sediment from Crab Orchard Lake in Marion, Illinois, USA, and a total of 18 PCB congeners were selected for study. Bioaccumulation was determined by exposing the freshwater oligochaete, Lumbriculus variegatus, to the sediment for 28 d. Differences in the rapidly desorbing fraction of PCBs and fraction desorbed within 6 h, defined by Tenax extraction, accounted for 39 and 31% of the differences among biota-sediment accumulation factor values, respectively. A better relationship (r2 = 0.95) was found between the oligochaete PCB body residues and the concentration of PCBs in the rapidly desorbing fraction of sediment. The degree of chlorination and planarity of the PCB congeners affected both desorption and bioaccumulation. The higher chlorine substituted and planar PCBs showed less chemical and biological availability, due to their stronger sorption to sediment, compared to the lower chlorinated and nonplanar PCBs. Accumulation of PCBs by L. variegatus correlated well (r2 = 0.88) with matrix-SPME fiber concentrations. The ratio of measured body residue to estimated body residue from the pore water concentration measured by matrix-SPME ranged from 0.4 to 1.3 with an average of 0.9. Overall, both Tenax and matrix-SPME approaches were useful surrogates of bioaccumulation for a field-contaminated sediment.

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

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.

Comparison of Chemical Approaches for Assessing Bioavailability of Sediment-Associated Contaminants

Two chemical approaches, Tenax extraction and matrix solid-phase microextraction (matrix-SPME), were compared to assess the bioavailability of hydrophobic contaminants from sediment. Hexachlorobiphenyl, DDE, permethrin, chlorpyrifos, and phenanthrene were individually spiked into two sediments differing in physical characteristics. Bioaccumulation was determined by exposing the oligochaete, Lumbriculus variegatus, to the spiked sediments. The rapidly desorbing fraction from Tenax extraction at 6 h and fiber concentration at 14 d from the matrix-SPME were compared for predicting bioaccumulation. Further, a comparison between laboratory-spiked and field-contaminated sediments was conducted. A regression between the rapidly desorbed sediment concentration at 6 h and the amount bioaccumulated across compounds and sediments described 94% of the variation in the data when phenanthrene was excluded. Phenanthrene was excluded because of complications due to a combination of biotransformation and rapid elimination during the sampling process. Contaminant accumulation by L. variegatus also correlated well with matrix-SPME fiber concentrations, accounting for 92% of the variation in the data, again excluding phenanthrene. Both chemical methods provided matrix- and chemical-independent estimations of bio-accumulation for hydrophobic contaminants without extensive biotransformation.

Biomimetic measurement of allelochemical dynamics in the rhizosphere

Polydimethylsiloxane (PDMS) materials were used to quantify levels of the photosynthesis inhibitor sorgoleone in the undisturbed rhizosphere of sorghum plants. The materials used included stir bars coated with PDMS (stir bar sorptive extraction), technical grade optical fiber coated with a thin film of PDMS (matrix-solid phase microextraction), and PDMS tubing. PDMS tubing retained the most sorgoleone. As analyzed by high performance liquid chromatography, amounts of sorgoleone retained on the PDMS materials increased with time. Other materials tested (polyurethane foam plugs, C18 and Tenax disks, and resin capsules) proved less suitable, as they were subject to sometimes extensive penetration by fine root hairs. These results demonstrate the potential for PDMS-based materials to monitor the release of allelochemicals in the undisturbed rhizosphere of allelopathic plants. Unlike extraction procedures that recover all available compounds present in the soil, PDMS functions in a manner more analogous to plant roots in sorbing compounds from soil solution or root exudates. Information on chemical dynamics in the rhizosphere is crucial for evaluating specific hypotheses of allelopathic effects, understanding allelopathic mechanisms, and assessing the importance of allelopathic processes in plant communities.

Sensing Dissolved Sediment Porewater Concentrations of Persistent and Bioaccumulative Pollutants Using Disposable Solid-Phase Microextraction Fibers

Polymer coated glass fibers were applied as disposable samplers to measure dissolved concentrations of persistent and bioaccumulative pollutants (PBPs) in sediment porewater. The method is called matrix solid-phase microextraction (matrix-SPME), because it utilizes the entire sediment matrix as a reservoir for an equilibrium extraction: a glass fiber with a 15 μm coating of poly(dimethylsiloxane) (PDMS) was placed in a sediment sample until the PBPs reached their equilibrium distribution between the PDMS and the sediment matrix (1−30 days). PBP concentrations in the PDMS were determined by gas chromatography, and they were divided by PDMS water partition coefficients to derive at dissolved porewater concentrations. This approach was applied to measure porewater concentrations of spiked as well as field sediment, and several hydrophobic organic substances (log KOW 5.2−7.5) were measured with high precision in the pg to ng/L range. Simple equilibrium partitioning is the basis for the substantial concentration factors that are built into matrix-SPME and for the low demands in materials and operation time. Matrix-SPME was in this study directed at the determination of dissolved porewater concentrations in sediment, and it is further expected to be applicable to other environmental media, to field sampling, and to the sensing of fugacity.