Triolein Embedded Cellulose Acetate Membrane as a Tool to Evaluate

Article pubs.acs.org/est

Triolein Embedded Cellulose Acetate Membrane as a Tool to Evaluate Sequestration of PAHs in Lake Sediment Core at Large Temporal Scale Yuqiang Tao,* Bin Xue, Shuchun Yao, Jiancai Deng, and Zhifan Gui State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China S Supporting Information *

ABSTRACT: Although numerous studies have addressed sequestration of hydrophobic organic compounds (HOCs) in laboratory, little attention has been paid to its evaluation method in field at large temporal scale. A biomimetic tool, triolein embedded cellulose acetate membrane (TECAM), was therefore tested to evaluate sequestration of six PAHs with various hydrophobicity in a well-dated sediment core sampled from Nanyi Lake, China. Properties of sediment organic matter (OM) varying with aging time dominated the sequestration of PAHs in the sediment core. TECAMsediment accumulation factors (MSAFs) of the PAHs declined with aging time, and significantly correlated with the corresponding biota-sediment accumulation factors (BSAFs) for gastropod (Bellamya aeruginosa) simultaneously incubated in the same sediment slices. Sequestration rates of the PAHs in the sediment core evaluated by TECAM were much lower than those obtained from laboratory study. The relationship between relative availability for TECAM (MSAFt/MSAF0) and aging time followed the first order exponential decay model. MSAFt/ MSAF0 was well-related to the minor changes of the properties of OM varying with aging time. Compared with chemical extraction, sequestration reflected by TECAM was much closer to that by B. aeruginosa. In contrast to B. aeruginosa, TECAM could avoid metabolism and the influences from feeding and other behaviors of organisms, and it is much easier to deploy and ready in laboratory. Hence TECAM provides an effective and convenient way to study sequestration of PAHs and probably other HOCs in field at large temporal scale.

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INTRODUCTION As the increase in contact time between hydrophobic organic compounds (HOCs) and sediment/soil, they diffuse within solid organic matter1 or become sorbed and entrapped within nano- and micropores of the sediment/soil,2 associated with a decreasing bioavailability, extractability, desorption, and toxicity.3 This process is termed as aging effect or sequestration. Over the past few decades, numerous laboratory studies have addressed sequestration by spiking HOCs in sediment/soil after a certain time.4,5 However, laboratory tests suffer from several problems associated with the interpretation of the data in terms of issues in field.2 Little attention has been paid to its evaluation method in field at large temporal scale.6 Apart from the analysis of partition coefficient between sediment/soil and water (Kd) and the uptake of HOCs by organisms,4,5,7 the extent of sequestration of HOCs is usually expressed as the extractability by mild chemical extraction,8,9 which is called extractable fraction and decreases with the contact time between chemicals and sediment/soil. Meanwhile, another fraction may be released when the residue sediment/ soil is subsequently alkaline hydrolyzed and extracted by organic solvents. This fraction is called bound or nonextractable © 2012 American Chemical Society

fraction, and used to evaluate sequestration of HOCs as well.6,10,11 However, sequestration of HOCs evaluated by methods of chemical extraction is usually time-consuming.12 Different extractant even the same extractant with different extraction conditions will result in various results.9,13 Passive sampling devices (PSDs), such as semipermeable membrane device (SPMD),4,14 solid-phase microextraction fiber (SPME)15,16 and solid-phase extraction disks or cartridges (SPE),17,18 have been used to sample freely dissolved fraction of HOCs in sediment/soil and predict their bioavailability to organisms, which offer several advantages over the chemical methods, including simplifying and speeding up the analysis procedures, using small volumes of solvent or even no solvent at all, and saving costs and labor.19 However, to date, PSDs have seldom been used to evaluate sequestration of HOCs especially in field study.4,20,21 Received: Revised: Accepted: Published: 3851

September 5, 2011 February 27, 2012 February 28, 2012 February 28, 2012 dx.doi.org/10.1021/es203102b | Environ. Sci. Technol. 2012, 46, 3851−3858

Environmental Science & Technology

Article

dried. The treated sediment was measured for content of organic carbon (TOC) with an element analyzer (Euro EA 3000). Black carbon (BC) in the sediment core was analyzed by the method of CTO375 according to Gustafsson et al.,26 which is described in detail in the Supporting Information. 1 mg of each sediment slice was added into 10 mL of 0.05 mol L−1 NaHCO3, treated with ultrasonic wave for 15 min, then placed in the dark for 15 min. The supernatant solution was immediately measured with a UV−vis spectrometer (Shimadzu UV−vis 2450) at 465 and 665 nm wavelengths. 5 mg of each sediment slice were mixed with 125 mg KBr and ground with an agate mortar and pestle. The milled sample was pressed at 7 MPa, then measured at a resolution of 4 cm−1 with 32 scans on a Nicolet Nexus 670 FTIR spectrometer. Spectra were obtained and analyzed with OMNIC 6.0 software. Extractable and Nonextractable Fraction of PAHs in the Sediment Core. 1.0 g of each sediment slice was loaded into a Soxhlet thimble and extracted with 70 mL of n-hexane/ dichloromethane (1:1 v/v) at 60 °C for 24 h. The extract was reduced to about 5 mL with a rotary evaporator, purged to about 1−2 mL under a gentle nitrogen stream, and then cleaned with a Florisil SPE (1 g/6 mL) and eluted with 6 mL of n-hexane/dichloromethane (4:1 v/v). The eluates were evaporated, solvent-exchanged into acetonitrile (0.5 mL) and stored prior to analysis. This fraction is defined as the extractable fraction in this study. After Soxhlet extraction, the pre-extracted sediment was subsequently alkaline hydrolyzed and extracted with dichloromethane for nonextractable fraction according to the methods used by Jin et al.,6 Reddy et al.,10 and Schwarzbauer et al.11 Experiments with Gastropods and TECAMs. Gastropods (B. aeruginosa) were allowed to acclimatize to laboratory conditions for at least 2 weeks and were analyzed for PAHs residues before use. Fifteen active B. aeruginosa with similar weight and size were transferred to a 2 L beaker containing 50 g sediment slice and 500 mL of distilled water, and reared at room temperature. Simutaneously, a piece of TECAM (2 cm × 3 cm × 0.1 mm, 2.5 mg cm−2 after evaporation of acetone) was buried in the same beaker. Half of the water in the beaker was discarded and replaced with fresh water every other day during the exposure period. Oxygen content was monitored weekly. B. aeruginosa and TECAMs were collected from the sediments after 28 days. Previous studies indicated that 28 days was long enough for the equilibrium of PAHs uptake by TECAMs.23 B. aeruginosa was allowed to purge gut contents in distilled water for 24 h before wet-weight analysis. Flesh of B. aeruginosa was then extracted and cleaned with distilled water to remove external sediment particles, freeze-dried, weighed. The dry flesh was cut into small pieces and ground with a mortar and pestle to obtain homogeneous sample, which was used for PAHs and lipid analysis. Calculation of Kd. Kd was calculated by passive sampling with TECAM, which was described in detail in Supporting Information. Chemical Analysis. 1 g of dry flesh of B. aeruginosa was loaded into a Soxhlet thimble and extracted with 100 mL of mixed solvent of chloroform and methanol (2:1 v/v) for 24 h for lipid content analysis. The extract was dried in a rotary evaporator, redissolved in 20 mL of n-hexane, filtered through No. 5 Whatman filter paper into a preweighed glass tube to remove precipitates, and dried to a constant weight. The weight

A new type of lipid-containing integrative sampler, triolein embedded cellulose acetate membrane (TECAM), has recently been developed.22 The greatest advantage of TECAM is the fast exchange kinetics because 1 mL of triolein is uniformly embedded within cellulose acetate with a surface area of approximately 15 000 cm2, resulting in a large contact area between triolein and HOCs.23 Our previous studies indicated that it could be well-used to evaluate sequestration and predict bioavailability of PAHs to earthworms and plants in soil in laboratory.13,20,23 Lake sediment core well records the information of deposition of contaminants, which provides an unique opportunity to investigate sequestration of HOCs in field at large temporal scale. Therefore, to expand on our previous works, TECAM was applied to evaluate sequestration of six PAHs with various hydrophobicity (with values of log Kow from 3.45 to 6.9024) in a well-dated sediment core sampled from Nanyi Lake, China. Sequestration of PAHs in this core and the related mechanisms were explored first. The potential to evaluate sequestration of PAHs in sediment core with TECAM was elucidated by comparison with the results of chemical extraction and the accumulation by gastropod (B. aeruginosa). Additionally, relation between uptake of PAHs by TECAMs and minor changes of the properties of sediment organic matter (OM) varying with aging time was investigated.

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EXPERIMENTAL SECTION Chemicals and Solvents. Naphthalene (Nap), acenaphthene (Ace), phenanthrene (Phe), benzo[a]anthracene (BaA), benzo[a]pyrene (BaP), and benzo[g,h,i]perylene (BghiP) were studied in this study. Anthracene (Ant) and chrysene (Chr) in the sediment core were analyzed additionally for the PAH fingerprints analysis. Standard solution of 16 priority PAHs (100−2000 μg mL−1) with purity >97.5% was purchased from AccuStandard, Inc. and used for identification and quantification. All solvents used, i.e., n-hexane, dichloromethane and acetonitrile were of HPLC grade. TECAMs were prepared according to Xu et al..22 They were made of cellulose acetate (18.0 wt %), acetone (69 wt %), 1,4dioxane (10 wt %), anhydrous magnesium perchlorate (2 wt %), and triolein (1.0 wt %). All the membranes were kept in distilled water before use. Sampling and Dating of the Sediment Core. Sediment cores were collected from the center of the east part of Nanyi Lake (located at a remote rural area in East China (see Figure S1 in the Supporting Information), area, 148.4 km2; water depth of the sampling site, 3.25 m) with a 6.5 cm diameter box corer in August 2009. The water-sediment interface was distinct, which suggested undisturbance of the upper sediments. One core was sectioned at 5 cm intervals to the depth of 50 cm. Each slice was set as one sample. All together ten samples were collected, freeze-dried, passed through a 1 mm sieve and stored for PAHs and physicochemical properties analysis. The other core sampled at the same site was sectioned at 1 cm intervals for sediment chronology. Dating of the sediment core was determined by 210Pb and 137Cs with EG&G Ortec Gamma Spectrometry. 137Cs and 210Pb were measured at 662 and 46.5 Kev, respectively. 226Ra was determined with 295 and 352 Kev γ-rays emitted by its daughter isotope 214Pb.25 Characterization of the Sediment Core. 1 g of each sediment slice was treated with 10 mL of 1:5 HCl (v/v) for 24 h, then washed with distilled water and centrifugated. This procedure repeated until pH appropriate 7.0 and finally freeze3852

dx.doi.org/10.1021/es203102b | Environ. Sci. Technol. 2012, 46, 3851−3858


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Table 1. Sedimentation Rates, Sediment Chronology, and Selected Properties of Sediment Core from Nanyi Lake, Chinaa depth (cm)

sedimentation rate (cm year−1)

year

TOC (%)

BC (mg g−1 d.w.)

E465/E665

CAro/CAli

R−OH

0−5 5−10 10−15 15−20 20−25 25−30 30−35 35−40 40 − 45 45−50

0.56 0.45 0.31 0.33 0.71 0.56 0.56 0.56 0.56 0.56

2000−2009 1989−2000 1973−1989 1958−1973 1951−1958 1942−1951 1933−1942 1924 −1933 1915− 1924 1906−1915

1.057 0.726 0.685 0.729 0.785 0.799 0.610 0.527 0.523 0.520

0.357 0.313 0.364 0.257 0.296 0.337 0.279 0.260 0.322 0.298

1.262 1.417 1.467 1.453 1.140 1.164 1.023 0.921 0.901 0.915

0.035 0.041 0.040 0.049 0.059 0.064 0.066 0.064 0.090 0.194

0.496 0.475 0.474 0.443 0.457 0.431 0.432 0.409 0.411 0.361

a E465/E665: ratio of UV absorbance at 465 and 665 nm; CAro/CAli : ratio of the sum of peak areas for aromatic carbons (3050, 1610 and 1530 cm−1) to that of aliphatic carbons (2925, 2850, 1450, 1150 and 1074 cm−1); R−OH: ratio of peak area for hydroxyl (3430 cm−1) to sum of peak areas of carbons, hydroxyl and carbonyl (1632 cm−1).

Figure 1. Relation between relative availability of PAHs for (a) B. aeruginosa (BSAFt/BSAF0), (b) TECAM (MSAFt/MSAF0) and the aging time.

of the residue was considered as the lipid,27,28 which accounted for 3.45 ± 0.14% of the dry flesh (n = 5). 0.5 g of dry flesh of B. aeruginosa was loaded into a Soxhlet thimble and extracted with 70 mL of n-hexane/dichloromethane (1:1 v/v) at 60 °C for 24 h. The extract was reduced to about 5 mL with a rotary evaporator, purged to about 1−2 mL under a gentle nitrogen stream, and then cleaned with a Florisil SPE (1 g/6 mL) and eluted with 6 mL of n-hexane/ dichloromethane (4:1 v/v). The eluates were evaporated, solvent-exchanged into acetonitrile (1.0 mL) and stored prior to analysis. TECAMs were rinsed with distilled water, wiped with clean filter paper, and dialyzed in 10 mL of n-hexane for 24 h and rinsed with n-hexane (1 mL × 3). The n-hexane solutions were combined, evaporated under a gentle nitrogen stream, solventexchanged into acetonitrile (0.1 mL), and stored prior to analysis. TECAMs were stable in n-hexane, with negligible weight loss of triolein or cellulose acetate during dialysis. PAHs in samples were analyzed by HPLC-FLD (Agilent 1200 Series). Chromatographic separation and resolution were best achieved by using a LiChrospher (Merck, Darmstadt, Germany) reverse-phase C18 column (4.6 × 250 mm, 5 μm particle size) specific for PAH analysis with the mobile phase of

acetonitrile/water (0.75 mL/min, 0−10 min 60:40, 10−50 min from 60:40 to 100:0, post run 5 min). The C18 column was kept at 25 °C. The excitation wavelength was 260 nm. The emission wavelength of Nap, Ace, and Phe was 380 nm, and of BaA, BaP, and BghiP was 420 nm. Quality Control and Statistical Analysis. Calibration standards with seven concentration levels were prepared. Results were obtained from three replicates. Calibration standard and blank were run with each set of analysis, and the blank values were subtracted. Extraction recoveries for Nap, Ace, Phe, BaA, BaP, and BghiP in sediment were 79.3, 88.5, 93.7, 94.3, 96.1, and 94.3%, respectively, which were determined by spiking the standard solutions with seven concentrations into the sediment. Extraction recoveries for PAHs in TECAM were determined by adding the standard solutions into acetone and 1,4-dioxane before the preparation of TECAM, and the recoveries were 85.2, 92.2, 94.6, 95.8, 98.1, and 97.5%, respectively. A standard reference material (SRM 1941b) was analyzed to evaluate the accuracy of the analysis. The average deviations with the reported values of SRM 1941b for Nap, Ace, Phe, BaA, BaP and BghiP were 12.9, 8.1, 7.4, 7.3, 6.7, and 6.9%, respectively. 3853



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Figure 2. Relation between BSAFs and MSAFs of the PAHs in the sediment core.

(constant rate of 210Pb supply) model could not be obtained. Thereby, the CIC model was still used to estimate the sediment accumulation rates for the sediment slices before 1963. Sedimentation rates were calculated with the 137Cs date (using the depth recorded in 1963 and 1986 as the datum levels). The average sedimentation rates of 0−5, 5−10, 10−15, 15−20, 20−25, and 25−50 cm of the sediment core were 0.56, 0.45, 0.31, 0.33, 0.71, and 0.56 cm year−1, respectively (Table 1). Sediment chronology of the ten sediment slices at 5 cm intervals is also listed in Table 1, which ranged from 1906 to 2009. Deposition of PAHs in the Sediment Core. Concentrations (extractable + nonextractable) of Nap, Ace, Phe, and BaA in the sediment core showed no obvious increase trends over time (see Table S1 in the Supporting Information), whereas levels of BaP and BghiP increased dramatically from 1906 to 2009. It may be ascribed to different sources of the PAHs in this area. Nanyi Lake is located at a remote rural area

Averages, standard deviations, and linear regressions were performed with Origin 7.0. Simple t tests were used to evaluate differences in averages between groups and to identify any systematic error in the data. Least square fitting was performed with SPSS 12.0.

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RESULTS AND DISCUSSION Sediment Chronology. Data of 210Pb and 137Cs of the core could be found in the previous work of the coauthors.29 210Pb generally showed an exponential distribution in the core. However, there was a significant discrepancy between the constant initial concentration (CIC) model 210Pb dates and the 1963 date inferred from the 137Cs chronostratigraphy. Corrected 210Pb dates calculated with the 137Cs date as a dating marker using composition model were thereby selected.30 The sediment core used for dating was not long enough to get the 210Pb equilibrium point with 226Ra. Hence the unsupported 210Pb inventory for dating with the CRS 3854



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Figure 3. Relation between relative availability for TECAM (MSAFt/MSAF0) and organic matter properties of the sediment core. E465/E665: ratios of UV absorbance at 465 and 665 nm; CAro/CAli: ratio of the sum of peak areas for aromatic carbons (3050, 1610, and 1530 cm−1) to that of aliphatic carbons (2925, 2850, 1450, 1150, and 1074 cm−1); R−OH: ratios of peak area for hydroxyl to sum of peak areas of carbons, hydroxyl, and carbonyl.

(Table 1). However, Koc (Kd normalized on TOC) of all the studied PAHs in the sediment core increased with the depth (see Figure S4 in the Supporting Information). The results suggest that physicochemical properties varying with depth (aging time) rather than amount of amorphous OM dominated the sequestration of PAHs in this core. Spectroscopical methods were applied to illustrate the mechanisms for the sequstration of PAHs in this core. Ratios of UV absorbance at 465 and 665 nm (E465/E665) for the sediment core are listed in Table 1. Kononova reported that the magnitude of E465/E665 ratio was related to the degree of the condensation of aromatic carbon network, with a low ratio indicative of a relatively high degree of condensation of aromatic humic constitutes. Conversely, a high E465/E665 ratio reflected a low degree of condensation and inferred the presence of relatively large proportions of aliphatic structures.41 Ratios of E465/E665 of the sediment core decreased from surface to bottom, suggesting higher degree of condensation and relatively larger proportion of aromatic structures or higher hydrophobicity of OM with aging time. FTIR spectra of the sediment core are shown in Figure S5 in the Supporting Information. Evident absorption bands appeared at 3430, 2925, 2850, 1632, 1530, 1450, 1150, and 1074 cm−1. Ratio of the sum of peak areas for aromatic carbons (3050, 1610, and 1530 cm−1) to that of aliphatic carbons (2925, 2850, 1450, 1150, and 1074 cm−1), expressed as CAro/CAli, was used to reflect aromaticity of OM in the sediment core.42 Ratios of CAro/CAli of the sediment core increased from 0.035 to 0.194 with aging time (Table 1), which indicates a relatively larger proportions of aromatic structures of OM with aging time. Ratios of peak area for hydroxyl to sum of peak areas of carbons, hydroxyl and carbonyl (expressed as R−OH) of the sediment core declined from 0.496 to 0.361 with aging time (Table 1), which indicates decreasing hydrophilicity of OM with aging time. The results obtained from FTIR suggest increasing proportions of aromatic structures and elevating hydrophobicity of OM with aging time, which agrees well with

embraced with hills with little industry. There is a very long history of combustion of biomass of straw and wood for domestic cooking and agricultural field burning in rural areas of China. To date it is still very common in this area, which is likely the prevalent source of Nap, Ace, Phe, and BaA in this sediment core.31,32 The average ratio of BaP/BghiP of the sediment core is 0.494 ± 0.04, which is the emission characteristic of diesel combustion.33,34 Thereby, the increase of BaP and BghiP may be ascribed to diesel combustion from shipping due to fishing in this lake. The other possible explanation may be higher redistribution of lower molecular weight PAHs throughout the lake as a result of water and sediment transport.35,36 Sequestration of PAHs in the Sediment Core. Apart from BghiP, Kd of the other PAHs in the sediment core generally increased with the depth (see Figure S2 in the Supporting Information). Pure BC has extremely high sorption capacity for HOCs (exceeds sorption in amorphous OM by a factor of about 10−100).37 To test the role of BC in the sequestration of PAHs in the sediment core, content of BC in this core and its correlation with Kd were investigated. Content of BC in this core varied from 0.357 to 0.298 mg g−1 d.w. from surface to bottom. Like Nap, Ace, Phe, and BaA, content of BC in this core showed no significant increase trend over time. Combustion of biomass of straw and wood for domestic cooking and agricultural field burning in this area may dominate the source of BC as well. No significant correlation could be observed between Kd and the content of BC (see Figure S3 in the Supporting Information). Furthermore, sorption to BC in natural environments can be as much as one order magnitude lower than pure BC,37,38 which is caused by amorphous OM or native HOCs competing for or block sorption sites of BC.38−40 Additionally, BC accounts for only 3.4−6.2% of the TOC in this core. Therefore, compared with amorphous OM, BC contributed less to the sequestration of PAHs in this core. Content of TOC of the sediment core generally decreased from 1.06 to 0.52% from surface to bottom 3855


the interpretation from UV−vis absorbance. Although the input of BC in this sediment core may contribute a little to the increased proportions of aromatic structures, no significant positive correlation could be found between aromaticity of OM and the content of BC in this sediment core (Table 1). Furthermore, it is impossible to distinguish the signal of BC in the presence of much higher concentration of humic/fulvic substance.43 Therefore, the increasing aromaticity with depth could be ascribed to the increasing degree of condensation and relatively larger proportion of aromatic structures of humic/ fulvic substance with aging time. Uptake of PAHs by B. aeruginosa is shown in Table S2 in the Supporting Information. After lipid and TOC normalization, uptake of BaP and BghiP by B. aeruginosa significantly increased with the extractable concentrations in the sediment core. While no such trend could be observed for the other PAHs (see Figure S6 in the Supporting Information). It may be ascribed to the overestimation for the bioavailable concentrations of low molecular weight PAHs by chemical extraction. Because of lower hydrophobicity and much higher diffusivities, lowmolecular-weight PAHs move slowly to the inner structure of OM with aging time. During the chemical extraction process, the macromolecular structure or nanopores of the OM may be destroyed, a part of the trapped low-molecular-weight PAHs due to aging effect thereby released. However, because of their higher hydrophobicity and much lower diffusivities, BaP and BghiP have stronger interaction with surface of the solid OM and move extremely slowly to the inner structure of OM with aging time, thereby the extractable concentrations agree well with the bioavailable concentrations and account for much larger proportions of the total concentrations (extractable + nonextractable) in the sediment core (see Table S1 in the Supporting Information). Biota - sediment accumulation factor (BSAF, defined as the ratio of concentration in B. aeruginosa to that in the sediment core) of the PAHs significantly decreased with the aging time (see Figure S7a in the Supporting Information), which supports the viewpoint that aging time dominated the sequestration of PAHs in the sediment core. Quantitive relationship was found between relative bioavailability (BSAFt/BSAF0) and aging time (Figure 1a), which could be well described with the model of first-order exponential decay as

BSAFt/BSAF0: ratio of biota-sediment accumulation factor (BSAF) at aging time t to 0; MSAFt/MSAF0: ratio of TECAM-sediment accumulation factor (MSAF) at aging time t to 0; EPt/EP0: ratio of extractable percentage (EP) at aging time t to 0.

100.0 98.9 97.3 98.4 98.0 96.1 96.9 95.8 95.6 95.3

Article

BSAFt /BSAF0 = aexp( −t /b) + c (n = 10, r 2 = 0.609 − 0.850)

(1)

where BSAFt is the BSAF at aging time t; BSAF0 is the BSAF at aging time 0; t is the aging time (y); a, b, and c are the constants. Biphastic patterns were observed for Nap, Ace, Phe, and BaA with an initial rapid decrease followed by a slower decline. In contrast, this pattern was not observed for BaP and BghiP. Higher affinity to sediment and stronger interaction with OM due to their higher hydrophobicity led them to be sequestrated even at the very initial stage of aging period. The results agree well with our previous work on sequestration conducted in laboratory20 and the review by Semple et al.3 Evaluating Sequestration of PAHs in the Sediment Core with TECAMs. TECAM − sediment accumulation factors (MSAFs, defined as the ratio of concentration in TECAM to that in sediment core after lipid and OC normalization) of PAHs significantly decreased with aging time (see Figure S7b in the Supporting Information), with a decline of 74.7, 58.0, 60.7, 77.0, 6.5, and 12.3% for Nap, Ace,

a

BaP

100.0 99.7 96.8 98.5 92.8 91.9 100.3 100.8 99.9 100.4 100.0 99.6 97.6 100.8 90.9 83.8 86.3 89.6 93.0 87.0

BaA Phe

100.0 98.5 96.1 94.6 94.0 95.2 86.9 92.1 84.0 81.5 100.0 98.3 97.9 96.8 94.3 90.8 86.3 84.4 88.8 83.8

Ace Nap

100.0 92.0 99.5 94.3 97.9 94.4 86.9 86.4 80.0 75.4 100.0 98.1 95.7 97.4 96.7 94.8 92.8 90.7 88.8 88.6

BghiP BaP

100.0 97.7 90.9 94.0 86.7 80.1 82.0 77.4 71.5 66.5 100.0 48.2 40.5 46.2 53.7 70.4 38.6 25.6 22.9 23.8

BaA Phe

100.0 58.7 49.6 68.1 58.4 63.2 32.0 28.5 26.1 38.2 100.0 95.4 95.1 96.3 96. 9 93.0 91.5 88.5 89.6 87.7

Ace Nap

100.0 58.8 22.4 74.3 37.0 46.7 13.8 25.8 13.4 23.4

BghiP BaP

100.0 91.1 97.9 94.6 84.5 71.9 72.4 75.8 68.1 69.7 100.0 52. 4 36.5 43.9 55.1 68.5 34.7 28.7 25.7 23.0

BaA Phe

100.0 55.3 51.1 67.2 60.0 61.1 30.6 27.3 27.0 39.3 0 9 20 36 51 58 67 76 85 94

Ace Nap

100.0 58.4 23.1 69.4 34.1 42.5 14.0 27.6 13.0 25.3

aging time

100.0 54.1 55.3 77.4 40.5 53.8 30.3 25.3 23.7 42.0

EPt/EP0 MSAFt/MSAF0 BSAFt/BSAF0

Table 2. Relative Available Percentages of PAHs in Sediment Core by B. aeruginosa, TECAM and Chemical Extraction (%) with Aging Time (y)a

100.0 57.8 54.0 71.6 43.3 52.9 27.3 24.5 22.4 40.8

BghiP


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higher than the corresponding BSAFt/BSAF0 especially for Nap, Ace, Phe, and BaA (Table 2). Furthermore, as aforementioned except for BaP and BghiP, uptake of the other PAHs by B. aeruginosa was not well correlated with the extractable concentrations in the sediment core (see Figure S6 in the Supporting Information). Therefore, chemical extraction overestimated sequestration of the PAHs in the sediment core. In contrast, MSAFt/MSAF0 of the PAHs was much closer to the corresponding BSAFt/BSAF0 for B. aeruginosa (Table 2), which suggests that TECAM is much more suitable than chemical extraction to assess sequestration of the PAHs in the sediment core at large temporal scale. Compared with B. aeruginosa, TECAM is much easier to deploy. Furthermore, TECAM could avoid metabolism of PAHs and the influences from feeding and other behaviors of organisms. Additionally, TECAM is ready in laboratory, and it requires little solvent and no cleanup step. Therefore, TECAM provides an effective and convenient way to evaluate sequestration of PAHs and probable other HOCs in field at large temporal scale.

Phe, BaA, BaP, and BghiP after 94 years. Our previous study indicated that MSAFs of Nap, Phe, and BaP decreased by 58.9, 47.5, and 53.0% after 150 days’ spiking in soil in laboratory.18 Decreasing rates of these PAHs in laboratory study were much higher than the corresponding values of the present study. Therefore, although availability of PAHs obtained from both laboratory and field studies decreased with aging time, there is difference in the interpretation of sequestration at different temporal scale. After lipid and triolein normalization, significant correlations were found between BSAFs and MSAFs for the PAHs (Figure 2), which could be expressed as BSAF = a MSAF

(2)

where a is the coefficient. BSAFs of Phe, BaA, BaP, and BghiP were a little higher than the corresponding MSAFs. PAHs associated with dissolved organic matter, colloids or sediment ingested by B. aeruginosa may result in the higher BSAFs. Behaviors of B. aeruginosa may facilitate the desorption of PAHs from the surrounding sediment as well, and consequently enhanced their availability to B. aeruginosa. However, in the case of Nap and Ace, BSAFs were much lower than the MSAFs, which may be ascribed to the metabolism of Nap and Ace in B. aeruginosa. Quantitive relation was also found between relative availability of PAHs for TECAM (MSAFt/MSAF0) and aging time t, which could be well described with the model of firstorder exponential decay as

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S Supporting Information *

Additional tables, figures, and information (PDF). This material is available free of charge via the Internet at http://pubs.acs. org/.

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*E-mail: [email protected]; phone: 86-25-86882158; fax: 8625-57714759. (3)

Notes

The authors declare no competing financial interest.

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where MSAFt is the MSAF at aging time t; MSAF0 is the MSAF at aging time 0; t is the aging time (y); a, b, and c are the constants. Like BSAFt/BSAF0, biphastic patterns were observed for Nap, Ace, Phe, and BaA with an initial rapid decrease followed by a slower decline. While this pattern was not found for BaP and BghiP. The results were well-consistent with BSAFt/BSAF0 and those obtained from TECAM in laboratory study.20 MSAFt/MSAF0 of the PAHs significantly increased with ratios of E465/E665 and R−OH, and generally decreased with CAro/CAli of the sediment core (Figure 3), which indicates that sequestration of PAHs increased with the elevating degree of condensation and the enhancing hydrophobicity of OM varying with aging time. It agrees well with the trend refelcted by BSAFt/BSAF0 (see Figure S8 in the Supporting Information), which suggests that TECAM is sensitive to the minor changes of physicochemical properties of OM varying with aging time, and it has the potential to evaluate sequestration of PAHs in the sediment core at large temporal scale. Relative extractability (EPt/EP0) of PAHs was defined as EPt /EP0 =

Cextract, t /(Cextract, t + Cnon, t ) Cextract,0/(Cextract,0 + C non,0)

AUTHOR INFORMATION

Corresponding Author

MSAFt /MSAF0 = aexp(−t /b) + c (n = 10, r 2 = 0.591 − 0.935)

ASSOCIATED CONTENT

ACKNOWLEDGMENTS This work was funded by Natural Science Foundation of China and Jiangsu Province (21107118, BK2010604), National Basic Research of China (2008CB418104), Foundation of Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS2010KXJ01 and NIGLAS2010QD13), and President Scholarship Foundation of Chinese Academy of Sciences.

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REFERENCES

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(4)

where EPt is the extractable percentage at aging time t; EP0 is the extractable percentage at aging time 0; Cextract,t is the extractable concentration at aging time t; Cextract,0 is the extractable concentration at aging time 0; Cnon,t is the nonextractable concentration at aging time t; Cnon,0 is the nonextractable concentration at aging time 0. Although EPt/ EP0 generally decreased with aging time, EPt/EP0 was much 3857



Article 239,240

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Triolein Embedded Cellulose Acetate Membrane as a Tool to Evaluate

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