influence of black carbon and chemical planarity on bioavailability of sediment-associated...

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INFLUENCE OF BLACK CARBON AND CHEMICAL PLANARITY ON BIOAVAILABILITY OF SEDIMENT-ASSOCIATED CONTAMINANTS SARI PEHKONEN, yz JING YOU,*§ JARKKO AKKANEN, z JUSSI V.K. KUKKONEN, z and MICHAEL J. LYDYy yFisheries and Illinois Aquaculture Center and Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901, USA zFaculty of Biosciences, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland §State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People’s Republic of China (Submitted 5 December 2009; Returned for Revision 1 February 2010; Accepted 13 April 2010) Abstract 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 0 ,4,4 0 -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 0 ,4,4 0 ,5,5 0 -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. Environ. Toxicol. Chem. 2010;29:1976–1983. # 2010 SETAC Keywords —Black carbon Planarity Matrix solid-phase microextraction Bioavailability INTRODUCTION When hydrophobic organic contaminants (HOCs) reach aquatic systems, they tend to bind to sediment organic carbon (OC). A recent study showed sediment OC was not homo- geneous, but composed of various compartments (i.e., amor- phous and condensed compartments) where the sorption of HOCs varied [1]. Amorphous materials, such as amino acids, lipids, lignins, and humic and fulvic substances, show linear and noncompetitive sorption [1]. However, carbonaceous geosorbents such as black carbon (BC), kerogen, and coke are included in the condensed domain of OC, and exhibit extensive, nonlinear and competitive sorption [2]. Soot and charcoal are two types of BC that are products of incomplete combustion of vegetation and fossil fuels [3,4]. These pyrogenic carbon particles are ubiquitous in the aquatic environment, accounting for 1 to 22% of total OC (TOC) in sediment [5]. Although soot and charcoal are derived from wood, they possess different structures and physicochemical properties, such as TOC content, specific surface area, and pore volume. The structure of soot particles is coarse and boulder- like [6], whereas charcoal maintains a wood-like structure containing deep narrow pores [7]. Compared to soot, charcoal has relatively higher specific surface area and pore volume [6]. The narrow pores and relatively rigid, planar, and aromatic surface of carbonaceous geosorbents represent major sorption sites [1,6]. As a result, higher sorption of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) has been observed with charcoal than with soot [6]. In addition to sediment characteristics, planarity, polarity, and molecular size also play an important role in HOC sorption. Strong sorption to BC has been observed for compounds with a planar structure, such as PAHs [6] and planar PCBs [8,9]. The planar compounds may penetrate narrow pores where they interact with aromatic pore walls by pp interactions, and similar interactions also enable sorption of planar compounds to the geosorbent surface. Conversely, the size of nonplanar compounds may exceed the average geosorbent pore size and impair electronic interactions between the compound and the geosorbent surface. Therefore, the steric hindrance caused by bulky atoms, like chlorine in highly chlorinated PCBs, reduced sorption of nonplanar compounds to the geosorbent [1,10,11]. However, BC may strongly sorb some nonplanar compounds, for example, the pesticide diuron. The dipole interactions between diuron and BC may provide diuron a better ability to attain planar conformation, which enhanced its sorption to the BC [12]. Although several studies have been conducted on the bioavailable potential of HOCs in sediment amended with activated carbon [13–15], the influence of naturally originated BC in sediment on the bioavailability of HOCs with differing chemical properties to aquatic species has not been thoroughly studied. The complexity of the interactions between different types of HOCs and BC also requires more research. The objectives of the current study were to determine the effect of different types of BC including charcoal and soot, at various environmentally relevant concentrations on bio- accumulation potential of HOCs in sediment; the effect of HOCs’ characteristics, including planarity and molecular size, on their bioaccumulation potential; and the applicability of using matrix-solid phase microextraction (matrix-SPME) as an indicator for bioavailability of HOCs in sediment with different BC content. Four HOCs were studied, including two Environmental Toxicology and Chemistry, Vol. 29, No. 9, pp. 1976–1983, 2010 # 2010 SETAC Printed in the USA DOI: 10.1002/etc.260 * To whom correspondence may be addressed ([email protected]). Published online 28 May 2010 in Wiley Online Library (wileyonlinelibrary.com). 1976

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Environmental Toxicology and Chemistry, Vol. 29, No. 9, pp. 1976–1983, 2010# 2010 SETAC

Printed in the USADOI: 10.1002/etc.260

INFLUENCE OF BLACK CARBON AND CHEMICAL PLANARITY ON BIOAVAILABILITY OF

SEDIMENT-ASSOCIATED CONTAMINANTS

SARI PEHKONEN,yz JING YOU,*§ JARKKO AKKANEN,z JUSSI V.K. KUKKONEN,z and MICHAEL J. LYDYyyFisheries and Illinois Aquaculture Center and Department of Zoology, Southern Illinois University, Carbondale, Illinois 62901, USA

zFaculty of Biosciences, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland

§State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640,People’s Republic of China

(Submitted 5 December 2009; Returned for Revision 1 February 2010; Accepted 13 April 2010)

* T(youjin

Pub(wileyo

Abstract—Black carbon (BC) and chemical properties may play a significant role in defining the bioavailability of hydrophobic organiccompounds (HOCs) in sediment. In the current study, bioavailability of four HOCs with differing planarity was determined in sedimentsamended with two types of BC (soot and charcoal) at different concentrations by matrix solid-phase microextraction (matrix-SPME) andbioaccumulation testing using the freshwater oligochaete Lumbriculus variegatus. Furthermore, the applicability of the matrix-SPMEmethod to bioavailability estimation in BC-amended sediment was tested. The charcoal treatment significantly reduced thebioaccumulation of the planar compounds (3,30,4,40-tetrachlorobiphenyl and benzo[a]pyrene) in L. variegatus, and the matrix-SPMEmethod showed a similar trend as contaminant bioaccumulation in L. variegatus. Conversely, manipulation of sediment with soot had noeffect or slightly increased bioavailability of the planar compounds in both bioaccumulation and matrix-SPME tests. Little if any affectwas noted in bioavailability of the nonplanar compounds (2,20,4,40,5,50-hexachlorobiphenyl and permethrin) with the soot and charcoalamendments. Results showed that the role of BC in defining bioavailability of HOCs depends not only on the type and concentrations ofBC present, but also the planarity of the HOCs. Environ. Toxicol. Chem. 2010;29:1976–1983. # 2010 SETAC

Keywords—Black carbon Planarity Matrix solid-phase microextraction Bioavailability

INTRODUCTION

When hydrophobic organic contaminants (HOCs) reachaquatic systems, they tend to bind to sediment organic carbon(OC). A recent study showed sediment OC was not homo-geneous, but composed of various compartments (i.e., amor-phous and condensed compartments) where the sorption ofHOCs varied [1]. Amorphous materials, such as amino acids,lipids, lignins, and humic and fulvic substances, show linearand noncompetitive sorption [1]. However, carbonaceousgeosorbents such as black carbon (BC), kerogen, and cokeare included in the condensed domain of OC, and exhibitextensive, nonlinear and competitive sorption [2].

Soot and charcoal are two types of BC that are products ofincomplete combustion of vegetation and fossil fuels [3,4].These pyrogenic carbon particles are ubiquitous in the aquaticenvironment, accounting for 1 to 22% of total OC (TOC) insediment [5]. Although soot and charcoal are derived fromwood, they possess different structures and physicochemicalproperties, such as TOC content, specific surface area, and porevolume. The structure of soot particles is coarse and boulder-like [6], whereas charcoal maintains a wood-like structurecontaining deep narrow pores [7]. Compared to soot, charcoalhas relatively higher specific surface area and pore volume [6].The narrow pores and relatively rigid, planar, and aromaticsurface of carbonaceous geosorbents represent major sorptionsites [1,6]. As a result, higher sorption of polycyclic aromatichydrocarbons (PAHs) and polychlorinated biphenyls (PCBs)has been observed with charcoal than with soot [6].

o whom correspondence may be [email protected]).lished online 28 May 2010 in Wiley Online Librarynlinelibrary.com).

1976

In addition to sediment characteristics, planarity, polarity,and molecular size also play an important role in HOC sorption.Strong sorption to BC has been observed for compounds witha planar structure, such as PAHs [6] and planar PCBs [8,9]. Theplanar compounds may penetrate narrow pores where theyinteract with aromatic pore walls by p–p interactions, andsimilar interactions also enable sorption of planar compoundsto the geosorbent surface. Conversely, the size of nonplanarcompounds may exceed the average geosorbent pore size andimpair electronic interactions between the compound and thegeosorbent surface. Therefore, the steric hindrance caused bybulky atoms, like chlorine in highly chlorinated PCBs, reducedsorption of nonplanar compounds to the geosorbent [1,10,11].However, BC may strongly sorb some nonplanar compounds,for example, the pesticide diuron. The dipole interactionsbetween diuron and BC may provide diuron a better abilityto attain planar conformation, which enhanced its sorption tothe BC [12]. Although several studies have been conducted onthe bioavailable potential of HOCs in sediment amended withactivated carbon [13–15], the influence of naturally originatedBC in sediment on the bioavailability of HOCs with differingchemical properties to aquatic species has not been thoroughlystudied. The complexity of the interactions between differenttypes of HOCs and BC also requires more research.

The objectives of the current study were to determine theeffect of different types of BC including charcoal and soot,at various environmentally relevant concentrations on bio-accumulation potential of HOCs in sediment; the effect ofHOCs’ characteristics, including planarity and molecularsize, on their bioaccumulation potential; and the applicabilityof using matrix-solid phase microextraction (matrix-SPME)as an indicator for bioavailability of HOCs in sediment withdifferent BC content. Four HOCs were studied, including two

Black carbon and chemical planarity on bioavailability Environ. Toxicol. Chem. 29, 2010 1977

planar compounds, 3,30,4,40-tetrachlorobiphenyl (TCBP, PCB77) and benzo[a]pyrene (BaP, a PAH), and two nonplanarcompounds, 2,20,4,40,5,50-hexachlorobiphenyl (HCBP, PCB153) and permethrin (PERM, a pyrethroid insecticide).

MATERIALS AND METHODS

Chemicals

Radiolabeled [14C]HCBP (specific activity 12.6 Ci/mol),[14C]TCBP (12.5 Ci/mol), [14C]PERM (10.9 Ci/mol), and[3H]BaP (50 Ci/mmol) were purchased from Sigma ChemicalCompany. Chemicals were tested for purity using high-performance liquid chromatography (HPLC, Agilent Techno-logies) followed by liquid scintillation counting (LSC) using aPackard TriCarb 2900TR liquid scintillation analyzer (PackardInstrument), and purity was >95%. The HPLC separations andLSC quantification followed the previously developed methods[16,17] with a C18 column and a mobile phase of a mixtureof acetonitrile and water. Isotopic dilutions were made usingthe nonlabeled compounds, which were purchased fromChemService. The molecular weights were 292.0, 252.3,360.9, and 391.3 g/mol for TCBP, BaP, HCBP, and PERM,respectively.

All experiments were conducted under red light to minimizethe photodegradation of BaP. Mercuric chloride was purchasedfrom Supelco and was used to inhibit microbial degradationin the matrix-SPME and partitioning tests. All solvents werepesticide or HPLC grade (Fisher Scientific). Scintillationcocktail (Scinti Safe Plus 50%) was purchased from FisherScientific. Moderately hard water (MHW) was preparedfollowing U.S. Environmental Protection Agency methods [18].

Disposable SPME fibers coated with 10mm of polydime-thylsiloxane were used and had a phase volume of 0.069ml/cm(FiberGuide). Stainless steel screen envelopes (110mm) wereused to protect the fragile fibers [17].

Sediment amendments and analysis

Two types of BC sorbents were used in the current study andincluded soot and charcoal. Soot was donated by Chuck’sChimney Sweep and Masonry, and was collected from privatedomestic wood burning fires. Charcoal, with a mesh size of100mm, was purchased from Columbus Chemical Industries.The BC sorbents were gently grounded, and passed througha 65-mm sieve. This fraction (<65mm) was washed with a0.01-mol/L CaCl2 solution by shaking the suspension in anadjustable reciprocating orbital shaker (Barnstead Interna-tional) with daily water changes [6]. After 14 d of washing,the sorbents were centrifuged and dried at 608C. The TOC andBC content of the sorbents and sediment were measured on an1106 Elemental analyzer (Carlo Erba Strumentazione) using achemothermal oxidation method described by Gustafsson et al.[19] after removing the carbonates by acidification [20]. TheTOC content of soot and charcoal was 51.28� 0.25% and72.38� 0.69%, respectively.

Reference sediment was collected from the Touch of NatureField Station located 15 km south of Carbondale, Illinois, USA,and sieved with a 500-mm sieve. The sediment TOC was0.41� 0.02%, and no BC was detected in the sediment. Char-coal and soot were added to the sediment to obtain 0.618 mgBC/g dry sediment in the A amendments, and 1.230 mg BC/gdry sediment in B amendments. After addition of sorbents,sediments were thoroughly mixed using a stainless steel paddledriven by an overhead motor for 4 h. The BC amended sedi-ments were stored at 48C overnight, and then spiked with

appropriate quantities of the test compounds. After chemicalspiking, sediments were thoroughly mixed, aged at 48C for 30 d,and homogenized again prior to use. Sediment for the matrix-SPME tests was spiked with radiolabeled chemicals, whereassediment for the bioaccumulation tests was spiked with anisotopic mixture of radiolabeled and nonradiolabeled chemi-cals. Although sediments for bioaccumulation and matrix-SPME testing were spiked separately, the total sediment con-centrations were the same.

The HOC concentrations in sediment were quantified intriplicate prior to and after each experiment. Approximately0.05 g wet sediment was placed into a scintillation vial, digestedwith 0.5 ml of Scintigest tissue solubilizer, 10 ml of scintillationcocktail was added, and the solution counted by LSC after a24-h extraction period. Background radioactivity was sub-tracted using control sediment. Potential biodegradation of[3H]BaP and [14C]PERM was measured in the sediments,whereas biodegradation was not expected for the PCBs.Sediment (2 g wet wt) was dried with anhydrous Na2SO4,and extracted three times with a total of 20 ml (10 ml and2� 5 ml) of an acetone:hexane (1:1, v/v) solution. Extractswere decanted, combined and evaporated to near dryness,solvent exchanged to acetonitrile, and filtered through a 45-mm filter. Degradation of PERM and BaP was quantified in thesediment extract using LSC after separating the parent com-pound from the metabolites on HPLC as described in the puritystudies.

Bioaccumulation test

A 28-d sediment bioaccumulation test was carried outwith L. variegatus using an automatic water delivery system.Lumbriculus variegatus were obtained from stock culturesmaintained in the Fisheries and Illinois Aquaculture Center,Southern Illinois University. Each 500-ml beaker contained300 ml of MHW and either 50 g sediment (dry wt) for theTCBP test or 100 g sediment (dry wt) for the PERM test or theexperiment simultaneously spiked with HCBP and BaP. Afterthe sediment settled for 24 h, L. variegatus (10 worms for TCBPand 20 worms for the remaining tests) were randomly trans-ferred into each beaker, and tests were performed at 23� 18Cwith a 16:8 h light:dark photoperiod. Overlying water (100 ml)was renewed automatically three times daily. Temperature,dissolved oxygen, and conductivity were monitored daily,whereas ammonia and pH of the overlying water were measuredweekly. At predetermined times (3, 7, 14, and 28 d), wormswere removed from the sediment by sieving through a 500-mmsieve, and placed in clean MHW to depurate their gut contentsfor 6 h. After depuration, L. variegatus were blotted dry andweighed using a Mettler H18 microbalance. One worm fromeach replicate was used for lipid determinations following thespectrophotometric method of van Handel [21], whereas theremaining worms were used for analyzing body residues andbiotransformation (PERM and BaP only) after extraction. Inshort, L. variegatus were homogenized with 2 ml of acetone,washed with three additional aliquots of acetone (1 ml each),and extracts were combined. A portion of the extracts (2 ml) wasused for tissue residue analysis on LSC after mixing with 10 mlof scintillation cocktail. The remaining extracts among thereplicates were combined, and used to analyze biotransforma-tion of PERM and BaP. The extracts were evaporated to neardryness and solvent exchanged to 0.25 ml of acetonitrile. Afterfiltering the extract through a 45-mm filter, the extract wasinjected into the HPLC to separate the parent compound and themetabolites as that previously discussed for analyzing chemical

1978 Environ. Toxicol. Chem. 29, 2010 S. Pehkonen et al.

purity. For the PCBs, L. variegatus were directly sonicated with10 ml scintillation cocktail for 40 s using a Tekmar model501sonic processor and radioactivity was measured by LSCafter a 24-h extraction period.

Water concentrations were measured prior to the experimentand at each sampling event by mixing 3 ml of water with 10 mlof scintillation cocktail and counting on LSC.

Matrix-SPME test

Matrix-solid phase microextraction (matrix-SPME) experi-ments were conducted following methods outlined in You et al.[17]. Screw-cap glass vials (20 ml) were filled with 2-g drysediment, 3 mg HgCl2, and 10 ml of overlying MHW. Twoenvelopes with 10 cm of fibers were inserted into the sediment.Vials were capped and gently shaken with an adjustable recip-rocating orbital shaker throughout a 28-d exposure. Multiplesampling times were used to ensure that equilibrium wasattained among the fiber, pore water, and sediment. At 3, 7,14, and 28 d fibers were removed from the sediments, andsonicated for 10 min with 1 ml of acetonitrile. Extraction ofthe fibers with acetonitrile was repeated twice, the extracts werecombined, and 10 ml of scintillation cocktail was added. Thesolution was then counted on LSC after a 24 h extractionperiod. Water concentrations were determined similarly as inthe bioaccumulation tests. Concentrations and degradation ofcontaminants in the sediment were analyzed at the beginning ofthe experiment and after each sampling event as describedabove.

Modeling and data analysis

Data from the bioaccumulation test was modeled using afirst-order one-compartment kinetic model as follows:

Cb;t ¼ Cbð1 � e�ke�tÞ (1)

whereCb,t andCb represent HOC concentrations in L. variegatusat time t (d) and at equilibrium, respectively. The elimination rateconstant was expressed as ke. Degradation of BaP was observedin sediment after the 28 d of exposure; thus, only 3-, 7-, and 14-ddata were used for modeling for this compound. Data were fitusing GraphPad Prism1 4.03 software. The uptake of HOCs bythe matrix-SPME fibers was estimated by fitting data from thematrix-SPME experiment using the same model as was used forthe bioaccumulation data, where concentrations in the organism(Cb,t and Cb) were replaced with concentrations of contaminantson the fiber (Cf,t and Cf), respectively.

Calculations and modeling were based on concentrations ofthe parent compounds.

Because steady-state concentrations were achieved, tissueand fiber concentrations at the end of the test were usedto calculate bioaccumulation factors (BAF), biota-sedimentaccumulation factors (BSAF), and freely dissolved concentra-tions of HOCs in sediment pore water (Cpw). Time when 90% ofthe steady-state tissue or fiber concentration was reached (t90,days) was determined using the following equation.

t90 ¼ lnð10Þke

(2)

Bioavailability of the contaminants from the sediment wasexpressed as BAF and BSAF:

BAF ¼ Cb

Cs

(3)

where Cb is the concentration of contaminant in L. variegatus atsteady state and Cs is the concentration of the contaminant insediment.

BSAF ¼Cb ðlipid normalizedÞCs ðOC normalizedÞ

(4)

where Cb and Cs were normalized with mean lipid content ofthe L. variegatus and with organic carbon content of sediment,respectively.

Freely dissolved concentrations of HOCs in sediment porewater (Cpw) were calculated from the Cf at the end of the testsand the partition coefficients between the water and fiber (Kfw)using the following equation:

Cpw ¼ Cf

Kfw

(5)

The Kfw was calculated using the following equation derivedfrom You et al. [17], whereas the log KOW values were adoptedfrom the previously published data [22–25].

Log Kfw¼ 1:03 � log KOW � 0:90 (6)

Statistical comparisons among amendments were conductedwith a Tukey’s honestly significant difference test and p< 0.05was indicative of significant effect using SPSS version 14.0software.

RESULTS

Bioaccumulation test

Bioavailability of the HOCs was measured using a bio-accumulation test with L. variegatus from sediment withand without BC amendments. During the tests, the dissolvedoxygen, pH, and conductivity were 6.99� 0.57 mg/L, 7.72�0.08, and 386� 21ms/cm, respectively. The ammonia concen-tration held constant between 0.8 to 1.0 mg/L throughout thetests. No mortality or avoidance of sediment was observed forL. variegatus during any of the bioaccumulation experiments.No statistically significant difference in lipid content was foundfor L. variegatus among treatments and the mean value was1.84� 0.26%. No degradation of TCBP, HCBP, and PERMoccurred in sediment throughout the tests; however, BaP diddegrade with 69� 8% of the parent compound remaining insediment after the 28-d exposure; thus, only 14-d exposure data(95� 1% of the parent compound remaining in sediment) wasused to model BaP bioaccumulation. Sediment HOC concen-trations were measured in triplicate prior to testing and atevery sampling event and showed no statistically significantdifference, so sediment concentrations were presented asthe mean of all measurements (Table 1). Because of theirhigh hydrophobicity, the tested compounds strongly bondedto sediment; therefore, no detectable quantities of chemicalswere measured in the overlying water.

Bioaccumulation kinetics for L. variegatus exposed tosediment spiked with the four compounds and amendedwith two concentrations of charcoal and soot are shown inFigure 1a. Steady-state HOC concentrations in L. variegatuswere achieved within 14 d for all compounds (Fig. 1a). Thecharcoal amendment decreased body residues of the planarcompounds (TCBP and BaP), whereas the accumulation ofthe nonplanar compounds (PERM and HCBP) was not affectedby the charcoal amendment (Fig. 1a). The soot amendment didnot affect body residues at steady state except for BaP, whose

Table 1. Mean sediment (Cs), Lumbriculus variegatus (Cb), and solid-phase microextraction (SPME) fiber (Cf) concentrations of 3,30,4,40-tetrachlorobiphenyl(TCBP), benzo[a]pyrene (BaP), 2,20,4,40,5,50-hexachlorobiphenyl (HCBP) and permethrin (PERM) in the tests

Bioaccumulation test Matrix-SPME test

Csa (nmol/g dry wt) Cb (nmol/g wet wt) BSAF (g lipid/g OC)b Cs (nmol/g dry wt) Cf (nmol/ml) Cpw (nmol/L)

TCBP Unamended 0.519� 0.006 4.03� 0.09A 1.91� 0.04A 0.503� 0.035 16.55� 1.90A 0.050� 0.006ACharcoal A 0.517� 0.006 3.11� 0.07B 1.58� 0.03B 0.473� 0.044 12.55� 0.47A 0.038� 0.001ACharcoal B 0.517� 0.008 2.20� 0.04B 1.22� 0.02B 0.464� 0.061 10.43� 1.32B 0.031� 0.004BSoot A 0.514� 0.005 3.74� 0.21B 1.77� 0.10B 0.486� 0.040 17.97� 2.69A 0.054� 0.008ASoot B 0.515� 0.007 4.10� 0.17A 1.96� 0.08A 0.512� 0.053 19.35� 1.47B 0.058� 0.004B

BaP Unamended 1.189� 0.002 3.76� 0.10A 0.70� 0.02A 1.189� 0.001 4.07� 0.18A 0.021� 0.001ACharcoal A 1.189� 0.001 3.14� 0.22A 0.68� 0.05A 1.189� 0.001 2.90� 0.35B 0.015� 0.002BCharcoal B 1.189� 0.002 2.61� 0.08B 0.60� 0.02B 1.188� 0.001 2.83� 0.12B 0.014� 0.001BSoot A 1.189� 0.001 4.40� 0.07B 0.88� 0.02B 1.188� 0.001 4.56� 0.44B 0.023� 0.002BSoot B 1.189� 0.004 3.54� 0.15B 0.79� 0.03B 1.189� 0.002 5.30� 0.80B 0.027� 0.004B

HCBP Un-amended 0.547� 0.036 4.00� 0.40A 1.61� 0.16A 1.023� 0.068 9.60� 1.52A 0.007� 0.0004ACharcoal A 0.551� 0.028 3.34� 0.29A 1.57� 0.13A 1.027� 0.095 10.02� 0.48A 0.007� 0.0004ACharcoal B 0.568� 0.026 3.00� 0.12A 1.45� 0.06A 1.056� 0.110 11.91� 1.01A 0.009� 0.001ASoot A 0.557� 0.024 3.43� 0.29A 1.46� 0.12A 0.997� 0.104 9.99� 1.01A 0.007� 0.0007ASoot B 0.574� 0.033 3.17� 0.38A 1.47� 0.18A 1.109� 0.100 10.89� 1.78A 0.008� 0.001A

PERM Unamended 0.776� 0.016 0.84� 0.06A 0.23� 0.02A 0.694� 0.036 14.63� 1.05A 0.080� 0.006ACharcoal A 0.779� 0.012 0.75� 0.08A 0.23� 0.02A 0.739� 0.032 16.27� 1.21A 0.089� 0.007ACharcoal B 0.756� 0.025 0.74� 0.01A 0.25� 0.003A 0.761� 0.075 14.72� 2.10A 0.081� 0.011ASoot A 0.790� 0.025 0.96� 0.12B 0.28� 0.04B 0.758� 0.137 13.94� 1.62A 0.076� 0.009ASoot B 0.776� 0.020 0.85� 0.06A 0.27� 0.02A 0.752� 0.045 12.15� 2.99A 0.067� 0.016A

aCs and Cf were based on three replicates, whereas Cb was calculated using four replicates. Biota-sediment accumulation factors (BSAF), and porewaterconcentrations (Cpw) in unamended control and black carbon (BC, including soot and charcoal) amended sediments. Amendments A were spiked at 0.618 mgBC/g dry sediment, and amendments B were spiked at 1.230 mg BC/g dry sediment. Data were presented as mean� standard deviation.

b OC¼ organic carbon. Capital letters A and B indicated significant difference from unamended.

Black carbon and chemical planarity on bioavailability Environ. Toxicol. Chem. 29, 2010 1979

concentration in the worm exposed in soot-amended sedimentwas slightly higher than that in unamended sediment.

Table 1 showed tissue concentrations based on parentcompound at the end of testing. The tissue concentrationof TCBP, BaP, and HCBP ranged from 2.20� 0.04 to4.40� 0.17 nmol/g wet worm, whereas PERM concentrationswere <1 nmol/g wet worm due to extensive biotransformation.After a 14-d exposure, 7.3 to 11.7% of BaP biotransformedin L. variegatus, and a greater biotransformation rate wasobserved for PERM. The fraction of PERM in parent formdecreased with increasing exposure time. The parent fractionwas approximately 45% at day 3, and reduced to approximately15% after 28 d.

Figure 2 showed the BAFs of all amendments and thestatistically significant differences from controls. The BAFvalues ranged from 4.26� 0.07 to 7.95� 0.34, from 2.20�0.07 to 3.70� 0.06, from 0.96� 0.10 to 1.21� 0.16 and from5.29� 0.23 to 7.32� 0.73 g wet worm/g dry sediment forTCBP, BaP, PERM, and HCBP, respectively. The charcoalamendments significantly (p< 0.05) reduced bioavailability ofthe planar compounds TCBP and BaP. Conversely, BaP-spikedsediment amended with soot at low concentration significantlyincreased its bioavailability compared to controls. Other sootamendments had no statistically significant effects. The in-fluence of BC varied for the two nonplanar HOCs. Additionof charcoal and soot at high concentrations decreasedHCBP bioaccumulation; however, BC did not affected PERMbioavailability. The higher concentration charcoal treatmentsignificantly decreased TCBP bioavailability compared to thelower concentration treatment. Conversely, the TCBP BAF forthe soot B amendment was significantly greater than that ofsoot A (Table 1). No statistically significant differences wereobserved for the other amendments though the similar trend waspresent (Fig. 2).

The BSAFs for the two PCBs ranged from 1.22� 0.03 to1.96� 0.04 g lipid/g OC, with the majority being close to 1.6,

whereas BSAFs for BaP and PERM were less than 1 due tobiotransformation and strong sorption of BaP to sediment(Table 1). Overall, BSAF values followed a similar trend asthe BAF values; statistically significant reduction in BSAFs wasnoticed for the planar compounds in sediment after addingcharcoal.

Matrix-SPME

The SPME fiber uptake kinetics for the four HOCsfrom unamended and amended sediments is presented inFigure 1b. Similar to L. variegatus uptake, addition of charcoalreduced fiber concentrations for the planar compounds (TCBPand BaP), whereas no statistically significant effect was foundin SPME uptake of the nonplanar compounds (PERM andHCBP) by adding BC. The Cf for TCBP, HCBP, and PERMranged from 9.60� 1.52 to 19.35� 1.47 nmol/ml, and the Cf

for BaP ranged from 2.90� 0.35 to 5.30� 0.80 nmol/ml(Table 1). A longer time was required for the HOCs to reachequilibrium in the fibers than in L. variegatus. For example, ittook 7 to 11, 21 to 28, 23 to 37, and 30 to 50 d for BaP, TCBP,HCBP, and PERM to reach equilibrium in the fibers for alltreatments, respectively. It should be noted that the order ofthe four compounds to reach equilibrium is the same as theirmolecular weight, which is different from the order of chemi-cals to reach steady state in the worms where hydrophobicitywas the key factor.

Freely dissolved chemical in sediment pore water (Cpw) wasconsidered an effective indicator of bioavailability and could beestimated from the measured Cf when equilibrium was reachedamong sediment, pore water, and fiber [26]. In the current study,Cpw was calculated using Cf values at 28 d with the exceptionof BaP, whose 28-d data were excluded because of observeddegradation in sediment (94.7� 1% and 69� 8% parentcompound left at 14 and 28 d, respectively). As shown inTable 1, Cpw decreased significantly (p< 0.05) in the charcoalB-amended sediments compared to control sediment for the

Fig. 1. Kinetic curves for Lumbriculus variegatus (Cb, nmol/g wet wt) (a) and solid phase microextraction fibers (b) exposed to 3,30,4,40-tetrachlorobiphenyl(TCBP), benzo[a]pyrene (BaP),2,20,4,40,5,50-hexachlorobiphenyl (HCBP), and permethrin (PERM) in unamended(control) (*), charcoal (CC) A (5), CC B (!),soot A (&), and soot B (&) amended sediments. The lines were modeled using a first-order one-compartment kinetic model.

1980 Environ. Toxicol. Chem. 29, 2010 S. Pehkonen et al.

planar compounds TCBP and BaP. The Cpw was alsoreduced for TCBP and BaP in sediments with charcoalA treatments (0.038� 0.001 and 0.015� 0.002 nmol/L, respec-tively) compared with unamended sediment (0.050� 0.006 and0.021� 0.001 nmol/L, respectively), but the difference wasnot statistically significant. On the other hand, soot Baddition significantly increased Cpw for BaP. Neithercharcoal nor soot amendments significantly changed Cpw for

the nonplanar compounds compared to those in the unamendedsediment.

DISCUSSION

Effects of BC characteristics and concentration on bioavailability

In the current study, the effects of the addition of two typesof BC at different concentrations on the bioavailability of HOCs

Fig. 2. Bioaccumulation factors (BAF) for 3,30,4,40-tetrachlorobiphenyl (TCBP), benzo[a]pyrene (BaP), 2,20,4,40,5,50-hexachlorobiphenyl (HCBP), andpermethrin (PERM) in unamended (control) and charcoal (CC) A, CC B, soot A, and soot B amended sediments. Charcoal and soot were added to the sediment toobtain 0.618 mg BC/g dry sediment in the A amendments, and 1.230 mg BC/g dry sediment in B amendments. Error bars represent standard deviations and stars (�)denote significant differences (p< 0.05) from the unamended treatment.

Black carbon and chemical planarity on bioavailability Environ. Toxicol. Chem. 29, 2010 1981

were evaluated by measuring HOC bioaccumulation inL. variegatus and HOCs in sediment pore water. The additionof charcoal and soot not only changed the sediment TOCcontent, but also supplied additional active sorption sites insediment, thereby potentially affecting bioaccumulation ofHOCs [27]. In addition, the native PAHs, which existed inthe BC, may have played a role on the bioaccumulation ofHOCs by competitive sorption [28]. The influence BC had in thesystem was quantified by comparing HOCs’ BAFs and Cpw insediments with and without treatment. A potential complicatingfactor in these measurements is the fact that L. variegatus iscapable of biotransforming BaP and PERM, and biotransfor-mation was observed in the current study as well as other studies[29,30]. Although biotransformation occurred for BaP andPERM, the percent parent compound remaining was similarfor individual compounds among treatments; therefore, bio-transformation did not affect the differences noted among BCtypes and concentrations.

Charcoal decreased bioavailability of the planar HOCs moreeffectively than soot as measured by the BAF and Cpw values(Table 1 and Fig. 2), and this can be explained by the differentcharacteristics of the two sorbents. Jonker and Koelmans [6]stated that structure and pore size may be different for charcoaland soot though both originated from wood. Charcoal containsnarrow pores [7] that can act as possible active sorption sites forHOCs [1,6]. Conversely, the pore diameter in soot was greaterthan in charcoal, which resulted in less surface area and lesscontact of contaminant to the aromatic pore wall. Thus, charcoalhad a greater sorptive ability than soot [6]. Besides the narrowpores, the rigid, planar, and aromatic nature of the BC surfacehas been reported as another strong sorption site for thearomatic HOCs, such as PAHs by p–p interaction; however,this sorption mechanism was less important than the poresorption for PCBs [1].

The concentration of charcoal also played an important roleon the bioavailability of HOCs, with the higher concentrationproviding more sorption sites, and thus decreasing bioavail-

ability (Fig. 1 and Table 1). However, adding soot to thesediment decreased bioavailability of TCBP but increase bio-availability of BaP and PERM. Although the lower OC contentof soot (51.28� 0.25% compared to 72.38� 0.69% in charcoal)may partially explain the lower sorption of soot-amendedsediment to HOCs, this cannot solely explain the absenceof effects, because the TOC content of the sediment amendedwith a high concentration of soot was greater than that insediment with the low concentration of charcoal. Normalizingthe sediment concentration to TOC effectively removesvariation in TOC as a confounding factor among treatmentsin the BSAF calculation. Similar to the trend noticed for BAFs,adding charcoal to sediment significantly reduced BASFsfor the planar contaminants after normalization for sedimentTOC and lipid levels in the tissue. It has been suggestedthat most of the OC measured by elemental analysis aftercombustion is located deep inside BC materials and may notbe accessible to HOCs [6,31]; thus, the BSAF values mightbe overestimated in BC-amended sediments [10]. The sootused in the current study was supplied from a chimneysweep, and it may contain native PAHs, which may competewith the spiked HOCs for active sites in sediment; thus, theeffect of the added soot on the sorption of HOCs maybe underestimated. The other components of condensedorganic matter such as nonhydrolysable organic matter mayalso play a role in bioavailability of HOCs as well [2,32–34].At the same time, adding BC to sediment may cause detrimentaleffects on the worms. A reduction in lipids has been reportedfor organisms exposed to soot-amended sediment [10].Milward et al. [14] also noticed that although activated carboncould stabilize HOCs and reduce their bioavailability, itmay cause benthic organisms to lose weight. No significantdifference in lipid concentrations among treatments wasreported in the current study. Deviation in the lipid measure-ments was high, however, which may be the reason for theloss of significance in bioavailability reduction for BaP andHCBP.

1982 Environ. Toxicol. Chem. 29, 2010 S. Pehkonen et al.

Impact of compound planarity on bioavailability

In addition to BC characteristics, the planarity of a com-pound also impacts HOC bioavailability [11,12]. Addition ofcharcoal significantly reduced bioavailability of the planarcompounds TCBP and BaP. Both charcoal and soot additionhad no effect on Cpw for the nonplanar compounds (HCBP andPERM), but surprisingly the BAF values for HCBP weresignificantly reduced in the charcoal amendments as well asthe soot B amendment. Several studies have shown that planarcompounds have a stronger affinity to BC than nonplanarcompounds even though the planar compounds may be lesshydrophobic [6,10,11]. A possible explanation for this findingmight be that the planar compounds more easily approach theBC surface due to their flat conformation, and this enables themto come into contact with the BC through p–p interactions[1,6]. The placement of chlorine substitutes in the benzene ringalso affects PCB sorption, and non-ortho-substituted PCBsshowed higher affinities toward the BC than their nonplanarcounterparts that have a more rigid and bulkier conformation[8]. Our previous study [9] showed the degree of chlorinationand planarity affected both desorption and bioaccumulation ofsediment-associated PCBs, and the higher chlorine substitutedand planar PCBs showed less bioavailability. The steric hin-drance of the nonplanar compounds prevented their interactionwith the surface of the sorbent or the pore walls. Sorption to thenarrow pores of the charcoal was also hindered by the sub-stituted atoms, and this effect was more notable for the largermolecules; thus, the nonplanar PERM showed no preference insorption to the charcoal. This is consistent with the resultsreported by Yang et al. [35], who found that permethrin boundto BC to the same extent as to OC. It was surprising to find astatistically significant difference in BAFs for the nonplanarHCBP, whereas BC addition showed no effect on Cpw. Becauseof the capability of attaining a planar conformation, somenonplanar compounds such as diuron may strongly sorb toBC as well [12]. However, this could not explain the observedsignificant effect of BC on HCBP bioavailability. The HCBPmolecule cannot change to a planar structure; thus, the statisti-cally significant difference in BAFs between unamended andBC-amended sediments might be due to the higher tissueconcentration and the larger standard deviation noted in theunamended sediment noted at the 14-d sampling point (Fig. 1a).

Predicting bioavailability with matrix-SPME

In addition to the bioaccumulation testing with L. variegatus,bioavailability was also estimated using matrix-SPME [26,36].A previous study [16] reported that SPME fibers reflect the bodyresidues of various classes of HOCs in benthic organismsexposed to sediments with different characteristics, whichsuggests that matrix-SPME is a promising tool for assessingbioavailability. In the current study, the effect of the BC-amendment showed a similar trend for BAFs measured bybioaccumulation testing and Cpw measured by the matrix-SPMEalthough chemicals reached a steady state concentration fasterin L. variegatus than in the SPME fibers. The correlation wasnot only true for a single compound in the five sediments with orwithout BC amendment, but also across chemicals. Due to theextensive biotransformation of permethrin in L. variegatus, itwas excluded from the correlation. Body residues in the bio-accumulation testing correlated well with the SPME fiberconcentrations (r2¼ 0.58) for HCBP, TCBP, and BaP in thefive sediments. In addition, a strong relationship (r2¼ 0.93) wasobserved for the two planar compounds (TCBP and BaP). As

mentioned previously, the order of the chemicals to reachequilibrium in the fibers was the same as the order of molecularweights. This steric hindrance might contribute to the sloweruptake kinetics in the fibers. Conversely, the behavior ofL. variegatus (i.e., feeding and active movement) may speedtheir uptake of the contaminants, because several uptake routesare available and therefore reach steady-state levels early [27].Thus, matrix-SPME could be used to measure bioavailabilityfor planar and nonplanar HOCs from sediments amendedwith different types of BC; but, it takes longer to reachequilibrium than for the organisms. Further study is neededto reduce equilibrium times for the matrix-SPMEs to expand itsapplications.

Acknowledgement—The authors wish to thank M. Noponen and R. Kelley. J.You thanks the Hundred Talents Program of the Chinese Academy ofSciences (KZCX2-YW-BR-05) and the National Natural Science Founda-tion of China (40971263) for support. This research was partially funded bythe Maj and Tor Nessling foundation.

REFERENCES

1. Cornelissen G, Gustafsson O, Bucheli TD, Jonker MTO, Koelmans AA,van Noort PCM. 2005. Extensive sorption of organic compounds to blackcarbon, coal, and kerogen in sediments and soils: Mechanisms andconsequences for distribution, bioaccumulation, and biodegradation.Environ Sci Technol 39:3881–3895.

2. Huang W, Peng P, Yu Z, Fu J. 2003. Effects of organic matterheterogeneity on sorption and desorption of organic contaminants bysoils and sediments. Appl Geochem 18:955–972.

3. Carcaillet C, Almquist H, Asnog H, Bradshaw RHW, Carrion JS,Gaillard MJ, Gajewski K, Haas JN, Haberle SG, Hadorn P, Muller SD,Richard PJH, Richoz I, Rosch M, Sanchez GMF, von Stedingk H,Stevenson AC, Talon B, Tardy C, Tinner W, Tryterud E, Wick L, WillisKJ. 2002. Holocene biomass burning and global dynamics of carboncycle. Chemosphere 49:845–863.

4. Cochrane MA. 2003. Fire science for rainforest. Nature 421:913–919.5. Accardi-Dey A, Gschwend PM. 2003. Reinterpreting literature sorption

data considering both adsorption into and adsorption onto black carbon.Environ Sci Technol 37:99–106.

6. Jonker MTO, Koelmans AA. 2002. Sorption of polycyclic aromatichydrocarbons and polychlorinated biphenyls to soot and soot-likematerials in the aqueous environment: Mechanistic considerations.Environ Sci Technol 36:3725–3734.

7. Zicherman JB, Williamson RB. 1981. Microstructure of wood char.Wood Sci Technol 15:237–249.

8. Bucheli TD, Gustafsson O. 2003. Soot sorption of nonortho and ortho-substituted PCBs. Chemosphere 53:515–522.

9. You J, Landrum PF, Trimble TA, Lydy MJ. 2007. Availability ofpolychlorinated biphenyls in field-contaminated sediment. EnvironToxicol Chem 26:1940–1948.

10. Jonker MTO, Hoenderboom AM, Koelmans AA. 2004. Effects ofsedimentary sootlike materials on bioaccumulation and sorption ofpolychlorinated biphenyls. Environ Toxicol Chem 23:2563–2570.

11. Cornelissen G, Elmquist M, Groth I, Gustafsson O. 2004. Effect ofsorbate planarity on environmental black carbon sorption. Environ SciTechnol 38:3574–3580.

12. Cornelissen G, Haftka J, Parsons J, Gustafsson O. 2005. Sorption to blackcarbon of organic compounds with varying polarity and planarity.Environ Sci Technol 39:3688–3694.

13. Zimmerman JR, Gosh U, Millward RN, Bridges TS, Luthy RG. 2004.Addition of carbon sorbents to reduce PCB and PAH bioavailability inmarine sediments: Physicochemical tests.EnvironSciTechnol38:5458–5464.

14. Millward RN, Bridges TS, Ghosh U, Zimmerman JR, Luthy RG. 2005.Addition of activated carbon to sediments to reduce PCB bioaccumu-lation by a polychaete (Neanthes arenaceodentata) and an amphipod(Leptocheirus plumulosus). Environ Sci Technol 39:2880–2887.

15. Sun X, Ghosh U. 2007. PCB bioavailability control in Lumbriculusvariegatus through different modes of activated carbon addition tosediments. Environ Sci Technol 41:4774–4780.

16. You J, Landrum PF, Lydy MJ. 2006. Comparison of chemicalapproaches for assessing bioavailability of sediment-associated con-taminants. Environ Sci Technol 40:6348–6353.

Black carbon and chemical planarity on bioavailability Environ. Toxicol. Chem. 29, 2010 1983

17. You J, Pehkonen S, Landrum PF, Lydy MJ. 2007. Desorption ofhydrophobic compounds from laboratory-spiked sediments measured byTenax absorbent and matrix solid-phase microextraction. Environ SciTechnol 41:5672–5678.

18. U.S. Environmental Protection Agency. 2000. Methods for measuringthe toxicity and bioaccumulation of sediment-associated contaminantswith freshwater invertebrates. 600/R-99/064. Washingon, DC, pp 63–71.

19. Gustafsson O, Haghseta F, Chan C, MacFarlane J, Gschwend PM. 1997.Quantification of the dilute sedimentary soot phase: Implications forPAH speciation and bioavailability. Environ Sci Technol 31:203–209.

20. Kukkonen JVK, Landrum PF, Mitra S, Gossiaux DC, Gunnarsson J,Weston D. 2003. Sediment characteristics affecting desorption kineticsof select PAH and PCB congeners for seven laboratory spiked sediments.Environ Sci Technol 37:4656–4663.

21. van Handel E. 1985. Rapid determination of total lipids in mosquitoes.J Am Mosq Control Assoc 1:302–304.

22. Verschueren K. 1983. Handbook of Environmental Data on OrganicChemicals, 2nd ed. Van Norstrand Reinhold, New York, NY, USA.

23. Laskowski DA. 2002. Physical and chemical properties of pyrethroids.Rev Environ Contam Toxicol 174:151–170.

24. Mackay D, Shiu WY, Ma KC. 1992. Illustrated Handbook of Physical–Chemical Properties and Environmental Fate for Organic Chemicals,Vol II. Lewis, Boca Raton, FL, USA.

25. Hawker DW, Connell DW. 1988. Octanol–water partition coefficients ofpolychlorinated biphenyl congeners. Environ Sci Technol 22:382–387.

26. Mayer P, Vaes WHJ, Wijnker F, Legierse KCHM, Kraaij RH, Tolls J,Hermens JLM. 2000. Sensing dissolved sediment porewater concen-trations of persistent and bioaccumulative pollutants using disposablesolid-phase microextraction fibers. Environ Sci Technol 34:5177–5183.

27. Lyytikainen M, Hirva P, Minkkinen P, Hamalainen H, Rantalainen AL,Mikkelson P, Paasivirta J, Kukkonen JVK. 2003. Bioavailability ofsediment-associated PCDD/Fs and PCDEs: Relative importance ofcontaminantand sediment characteristics andbiological factors.EnvironSci Technol 37:3926–3934.

28. Cornelissen G, Gustafsson O. 2006. Effects of added PAHs andprecipitated humic acid coatings on phenanthrene sorption to environ-mental black carbon. Environ Pollut 141:526–531.

29. Leppanen MT, Kukkonen JVK. 2000. Fate of sediment-associatedpyrene and benzo[a]pyrene in the freshwater oligochaete Lumbriculusvariegatus (Muller). Aquat Toxicol 49:199–212.

30. You J, Brennan AA, Lydy MJ. 2009. Bioavailability and biotransfor-mation of sediment-associated pyrethroid insecticides in Lumbriculusvariegatus. Chemosphere 75:1477–1482.

31. Bucheli TD, Gustafsson O. 2000. Quantification of the soot–waterdistribution coefficients of PAHs provides mechanistic basis forenhanced sorption observations. Environ Sci Technol 34:5144–3151.

32. Xiao B, Yu Z, Huang W, Song J, Peng P. 2004. Black carbon and kerogenin soils and sediments. 2. Their roles in equilibrium sorption of less-polarorganic pollutants. Environ Sci Technol 38:5842–5852.

33. Ran Y, Sun, Yang Y, Xing B, Zeng E. 2007. Strong sorption ofphenanthrene by condensed organic matter in soils and sediments.Environ Sci Technol 41:3952–3958.

34. Ran Y, Sun K, Xing B, Shen C. 2009. Characterization of condensedorganic matter in soils and sediments. Soil Sci Soc Am J 73:351–359.

35. Yang Y, Hunter H, Tao S, Gan J. 2009. Effects of black carbon onpyrethroid availability in sediment. J Agric Food Chem 57:232–238.

36. Kraaij R, Mayer P, Busser FJM, van het Bolscher M, Seinen W, Tolls J.2003. Measured pore-water concentrations make equilibrium partition-ing work–A data analysis. Environ Sci Technol 37:268–274.