Prediction of Ecotoxicity of Heavy Crude Oil - American Chemical

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Prediction of Ecotoxicity of Heavy Crude Oil: Contribution of Measured Components Hyun-Joong Kang,† So-Young Lee,†,‡ Ji-Yeon Roh,† Un Hyuk Yim,§ Won Joon Shim,§ and Jung-Hwan Kwon†,* †

Division of Environmental Science and Ecological Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Republic of South Korea ‡ Department of Environmental Engineering, Ajou University, Woncheon-dong, Yeongtong-gu, Suwon 443-749, Republic of South Korea § Oil and POPs Research Group, Korea Institute of Ocean Science and Technology, 391 Jangmok-myon, Geoje 656-834, Republic of South Korea S Supporting Information *

ABSTRACT: A prediction model for estimating the ecotoxicity of the water-accommodated fraction (WAF) and watersoluble fraction (WSF) of heavy crude oil is proposed. Iranian heavy crude oil (IHC), one of the major components of the Hebei Spirit oil spill in Korea in 2007, was used as a model crude oil for the preparation of the WAF and the WSF. Luminescence inhibition of Vibrio f ischeri was chosen as the model ecotoxicity test for evaluating the baseline toxicity of aromatic hydrocarbons in the IHC. The measured concentration of each chemical species in WAF and WSF agreed well with the predicted soluble concentration calculated using Raoult’s law from the measured amount in the IHC. This indicates that the toxic potential of an oil mixture can be evaluated from the dissolved concentration of each species, which in turn, may be predicted from the composition of the crude or weathered oils. In addition, the contribution of each species in the mixture to the apparent luminescence inhibition by the WAF and the WSF was assessed using a concentration-addition model. The relative contributions of benzene, toluene, ethylbenzene, xylenes (BTEX), polycyclic aromatic hydrocarbons (PAHs), and alkylated PAHs in luminescence inhibition were estimated to be 76%, 2%, and 21%, respectively. It was further identified that C3and C4-naphthalenes were the most important aromatic hydrocarbons responsible for baseline toxicity. This indicates that alkylated PAHs would be the major components of oil-spill residue. Further research is needed to evaluate the fate and ecotoxicity of alkylated PAHs.

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INTRODUCTION

accumulation is useful in explaining the results of laboratory ecotoxicity tests using either the critical body burden or target lipid model, especially for single chemicals. It must be pointed out that none of these hydrocarbons, individually, is likely to be present at concentrations high enough to cause baseline toxicity after an oil spill although chemical analyses of residual oil components using bioassays revealed that the aromatic fractions containing many mono- and polycyclic aromatic hydrocarbons are the most important fractions in terms of ecotoxicity of oil-spill residues.14,15 Furthermore, it is believed that the mode of toxic action of each aromatic hydrocarbon is similar and does not interfere with that of the other hydrocarbons.12,13 The cumulative toxicity can help explain

Marine oil spills are some of the most serious environmental problems worldwide. The adverse ecological effects caused by oil-spill residues have been studied for decades.1−7 However, linking the observed environmental effects at many different levels to the components of oil-spill residue is still a very challenging problem, because oil is a complex mixture of numerous chemicals, whose chemical composition changes with time because of weathering processes. Among the various ecotoxicological end points applied to assess the impact of oil spills on the ecosystem, narcotic effect or baseline toxicity is regarded as one of the most important toxic modes of action. This effect has been intensively studied to explain the effects of oil mixtures.8−13 Petroleum oils are mainly composed of many hydrophobic hydrocarbons such as straight-, branched-, cyclic-aliphatic hydrocarbons, and various mono- and poly cyclic aromatic hydrocarbons that accumulate in the lipid tissues of the bodies of living organisms. This lipid © 2014 American Chemical Society

Received: Revised: Accepted: Published: 2962

September 29, 2013 January 24, 2014 February 3, 2014 February 3, 2014 dx.doi.org/10.1021/es404342k | Environ. Sci. Technol. 2014, 48, 2962−2970

Environmental Science & Technology

Article

⎡ ΔSm,i ⎛ Tm,i ⎞⎤ L = Si exp(−KS,i[salt]tot )exp⎢ − 1⎟⎥ Ssw,i ⎜ ⎠⎦ ⎣ R ⎝ T

the gaps between the chemical analysis results of oil-spill residues and the overall observed toxicity.13,16−18 Thus, a few mixture toxicity models have been built based on the dissolution of individual components in water and the additivity of toxic effects by each component.9,13 However, contribution of each chemicals in a mixture still need to be evaluated because identified components are often not enough to explain the overall ecotoxicological effects.7,19,20 In this study, we propose a predictive model for luminescence inhibition of Vibrio f ischeri as a model ecotoxicological end point resulting from the dissolved species of heavy crude oil and evaluated the mixture effects of heavy crude oil by taking into account the contribution of individual chemicals identified. This is possible because the V. f ischeri test is a well-established ecotoxicity test,21 the EC50 values for individual hydrocarbons are well-documented, and quantitative structure−activity relationships for them are available.22−25 Iranian heavy crude oil (IHC) was chosen as the model crude oil because it was one of the main components of the Hebei Spirit oil spill, which occurred in 2007.26,27 The mass concentrations of chemical species such as benzene, toluene, ethylbenzene, xylenes (BTEX), polycyclic aromatic hydrocarbons (PAHs), and alkylated PAHs were measured in the IHC. The water-accommodated fraction (WAF) and watersoluble fraction (WSF) of IHC were prepared in the laboratory and subjected to chemical analyses and luminescence inhibition tests. The measured concentration of each species in the WAF and WSF was compared with the predicted dissolved concentration using Raoult’s law. The overall luminescence inhibition caused by the WAF and WSF was compared with the sum of the contributions of the identified individual species using a concentration-addition model. The relative contribution of the various chemical groups in IHC to the inhibition of luminescence was compared in order to identify the major species responsible for marine ecotoxicity after an oil spill.

where [salt]tot is the total salt concentration in artificial seawater (0.5 mol L−1). For evaluating the overall effects of baseline toxicants using a concentration-addition model, it is useful to express the toxicity of a chemical species using the concept of toxic units (TU) (eq 4). TUi = C i /EC50i

TU =

∑ i

TUi

(5)

Thus, we can estimate the overall toxic unit of a mixture by eqs 1−5 once we know the mole fractions of each chemical species, their relevant physicochemical properties, and the toxicological end point values for the individual chemicals (EC50 in this study).

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EXPERIMENTAL SECTION Materials and Chemicals. Artificial seawater was prepared at 3.5% (w/w) by dissolving the artificial sea salt obtained from Sigma-Aldrich (St. Louis, MO, U.S.). Polydimethylsiloxane (PDMS) tubing used for the preparation of the WSF was purchased from Dong-Bang Silicone Inc. (Gimpo, Republic of Korea). GC 2 -grade dichloromethane and hexane were purchased from Burdick & Jackson (Morristown, NJ, U.S.). ACS-grade sodium sulfate and silica gel were purchased from Fisher Scientific (Seoul, Republic of Korea). PAH surrogate standards (naphthalene-d8, acenaphthene-d10, phenanthrened12, chrysene-d12, and perylene-d12) and o-terphenyl used for a surrogate standard for total petroleum hydrocarbons (TPHs) were purchased from Supelco (Bellefonte, PA, U.S.). pTerphenyl-d14 used as a GC internal standard for PAHs and 5-α-androstane used as a GC internal standard for TPHs were also purchased from Supelco. The IHC collected on-board before harbor unloading to prevent mixing with other crude oils was obtained from SGS Korea Co. (Seoul, Republic of Korea). Preparation of WAF and WSF of IHC. The WAF of IHC was prepared by gently stirring 1 L of artificial seawater for 24 h using a 2.54-cm stir bar at 200 rpm in the dark with 5, 10, 20, and 40 g of IHC, minimizing the vortex according to Singer et al.29 The WAF solution for chemical analysis and toxicity assay was taken from the bottom of the vessel to separate it from the floating oil film. Because we needed to evaluate the toxicity of the hydrophobic aromatic hydrocarbons, the WSF was also prepared by saturating the water with the hydrophobic chemical species of IHC, which are highly permeable through PDMS. To prevent the direct contact of the oil phase with water, a PDMS tube (ID = 2 mm, OD = 3 mm) containing 5 g of IHC in the lumen was submerged in 1 L of artificial seawater (Figure 1). The solution was stirred at 200 rpm for a designated time, in dark, again using a 2.54-cm stir bar. The contact surface area was 160 cm2, which is approximately twice the contact area of the oil−water interface for the preparation of the WAF. Freshly prepared WAF and WSF solutions were immediately subjected to a luminescence inhibition test and liquid−liquid extraction for chemical analyses.

THEORY Dissolution of a chemical species i from a mixture is described by Raoult’s law, which states that the maximum dissolved concentration (Ci) is the product of the mole fraction of the species in the mixture (xi) and the subcooled liquid solubility in seawater (SLsw,i), assuming an ideal mixture. (1)

Many organic chemicals in crude oil are solids in their pure form at ambient temperature and pressure. For substances existing as solids, SLsw,i is estimated from fusion entropy (ΔSm,i) and melting point (Tm,i) using the relation,28 ⎡ ΔSm,i ⎛ Tm,i ⎞⎤ SiL = Si exp⎢ − 1⎟⎥ ⎜ ⎠⎦ ⎣ R ⎝ T

(4)

Using this expression, the contribution of the toxicity of the mixture can be calculated as the sum of the contributions of the individual chemicals (eq 5).

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L C i = x iSsw,i

(3)

(2)

where SLi and Si are the subcooled liquid solubility of species i and the solubility of pure solid, respectively, R is the gas constant (8.314 J mol−1K−1), and T is temperature in K. The increased chemical activity of hydrophobic solutes in an electrolyte solution such as seawater (i.e., the “salting out” effect) is empirically modeled by the Setschenow equation. Including the Setschenow constant (KS,i), eq 2 is rewritten to calculate the value of subcooled liquid solubility in seawater (SLsw,i): 2963

dx.doi.org/10.1021/es404342k | Environ. Sci. Technol. 2014, 48, 2962−2970


Article

adjusted to an accurate preinjection volume of 1.00 mL for GC/FID and GC/MS analyses. Analyses for n-alkane distribution and TPH were performed on an Agilent 7890 gas chromatograph equipped with a flame-ionization detector (FID) (Agilent Technologies, Inc., Santa Clara, CA, U.S.). Analyses of PAH compounds were performed on Agilent 5890 GC equipped with Agilent 5972 mass selective detector (MS). In the case of BTEX, IHC was dissolved in pentane and directly analyzed using GC/MS.30 System control and data acquisition were achieved with HP G1034C MS ChemStation. The detailed analytical procedure, chromatographic conditions, analysis quality control, and quantification methodology have been described in literature.27,32 Luminescence Inhibition of Vibrio f ischeri. The acute ecotoxicity of WAF and WSF of IHC was assessed by the luminescence inhibition of V. f ischeri (strain NRRL B-11177) using Microtox Model 500 (Strategic Diagnostics Inc., Newark, DE, U.S.). Freeze-dried bacterium was purchased from the supplier (Strategic Diagnostics Inc.). The TU of the sample prepared after dilution of the WAF and WSF was calculated after processing the data using Microtox Omni software (Strategic Diagnostics Inc.), according to the test protocol provided by the manufacturer. The results after 15 min of exposure were used to quantitatively compare the toxicity. Prediction of Dissolved Concentration and Luminescence Inhibition of Identified Species. As stated in the Theory section, the dissolved concentration of each species in the solution was predicted using Raoult’s law. The mole fraction of each species was calculated from the measured content and the number average molecular weight (MWn). Because the MWn for the IHC used in this study has not been reported, the MWn for West Texas crude oil estimated as 375 g mol−1 was used for calculating the mole fractions of the chemical species33 because MWn ranged from 295 to 400 g mol−1.33−35 The TU of the measured chemical species was calculated as described earlier (eq 5). Because the sample solution was subjected to the luminescence inhibition assay according to the standard test protocol,21 dilution and partitioning of chemicals between V. f ischeri and the solution lowers the free concentration of the chemicals from their concentrations measured by chemical analysis. Thus, the free concentration of chemical species i was calculated from the measured (or estimated) concentration in the WAF or WSF as follows:25

Figure 1. Schematic diagram of the preparation method for watersoluble fraction (WSF) of IHC.

Extraction of Chemicals from IHC, WAF, and WSF. For the analysis of chemical concentrations in IHC, the crude oil sample was first dissolved in n-hexane, followed by cleanup using a silica-gel column and fractionation. The oil solution was spiked with appropriate surrogates (100 μL of 200 μg mL−1 oterphenyl and 100 μL of a mixture of naphthalene-d8, acenaphthene-d10, phenanthrene-d12, chrysene-d12, perylened12, 10 μg mL−1 each). The spiked oil samples were transferred to 3 g of activated silica gel column topped with ∼1 cm anhydrous granular sodium sulfate layer for sample cleanup and fractionation. The column was eluted with 15 mL of n-hexane (F1), followed by 30 mL of n-hexane/dichloromethane (50:50) solution (F2). Half of the F1 fraction was used for the analysis of saturates, and half of the F2 fraction was used for the analysis of alkylated PAH homologues and other target PAHs. The remaining halves of F1 and F2 were combined to form F3 and used for the determination of total GC-detectable TPHs, GCresolved peaks, and the GC-unresolved complex mixture (UCM) of hydrocarbons. The detailed procedure of the fractionation for the analysis of aromatic hydrocarbons is described in literature.27,30 Freshly prepared WAF and WSF were extracted by liquid− liquid extraction using dichloromethane. First, 500 mL of the aqueous sample, spiked with 30 μL of 10 μg mL−1 of the TPH surrogate standard (o-terphenyl) and 100 μL of 20 μg mL−1 PAHs surrogate standards (naphthalene-d8, acenaphthene-d10, phenanthrene-d12, chrysene-d12, perylene-d12) were extracted with 50 mL dichloromethane three times by a modified EPA method 3510C.31 In short, the dichloromethane extract was evaporated using a rotary evaporator and the solvent was exchanged with approximately 20 mL of n-hexane. After concentrating the n-hexane solution to ∼2 mL, the extract was fractionated using the same fractionation method described for IHC for the instrumental analysis. Instrumental Analyses. Instrumental analyses were performed according to target analytes. After fractionation, three fractions were concentrated to appropriate volumes, spiked with internal standards (5-α-androstane, p-terphenyl-d14, and 5-α-androstane for F1, F2, and F3, respectively), and then

Cfree, i =

1 Ci 1 + Klipw,iflip (MV . fischeri /Vw )

(6)

where Klipw,i is the lipid−water partition coefficient of i, f lip is the lipid content of V. f ischeri (assumed as 0.01 kg kg−1), and MV.fischeri is the mass of V. f ischeri in the test vessel. The values of K lipw,i used are present in the literature (Supporting Information, SI, Table S1); however, if literature values are not available, they were estimated using the following equation:36 log Klipw,i = 1.01 log Kow,i + 0.12

(7)

Because the baseline toxicity is related to the hydrophobicity of aromatic hydrocarbons, a quantitative structure−activity relationship derived in our previous study25 was used to derive the EC50 value of the individual chemicals without using the measured values. 2964



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Table 1. Comparison of the Measured Concentrations in WAF and WSF Solutions by Different Preparation Methods measured concentration (μg L−1) −1

chemical

WAF (40 g L )

WSF 3 h

WSF 8 h

WSF 24 h

naphthalene acenaphthylene acenaphthene fluorene phenanthrene anthracene fluoranthene pyrene benz[a]anthracene chrysene benzo[b]fluoranthene benzo[k]fluoranthene benzo[a]pyrene indeno[1,2,3-cd]pyrene dibenz[a,h]anthracene benzo[ghi]perylene ∑ EPA priority 16 PAHs biphenyl benzo[e]pyrene perylene dibenzothiophene 1-methylnaphthalene 2-methylnaphthalene C2-naphthalene C3-naphthalene C4-naphthalene C1-fluorene C2-fluorene C3-fluorene 1-methylphenanthrene 2-methylphenanthrene 3-methylphenanthrene 4/9-methylphenanthrene C2-phenanthrene C3-phenanthrene C4-phenanthrene 1-methyldibenzothiophene 2-/3-methyldibenzothiophene 4-methyldibenzothiophene C2-dibenzothiophene C3-dibenzothiophene C1-chrysene C2-chrysene C3-chrysene ∑ alkylated PAHs TPH

19 ± 3 ND 0.16 ± 0.01 0.77 ± 0.03 0.53 ± 0.02 0.026 ± 0.002 0.0019 ± 0.0002 0.0066 ± 0.0003 0.0029 ± 0.0003 0.0032 ± 0.0002 ND ND ND ND ND 0.00099 20 ± 3 0.67 ± 0.03 0.00020 ND 0.87 ± 0.02 17 ± 2 18 ± 2 21 ± 1 8.6 ± 0.3 2.2 ± 0.1 0.49 ± 0.04 0.28 ± 0.00 0.13 ± 0.00 0.13 ± 0.01 0.12 ± 0.01 0.11 ± 0.00 0.18 ± 0.01 0.25 ± 0.01 0.093 ± 0.005 0.022 ± 0.003 0.20 ± 0.00 0.28 ± 0.00 0.36 ± 0.01 0.45 ± 0.02 0.13 ± 0.01 0.0031 ± 0.0006 ND ND 71 ± 5 1397 ± 98

14 ± 1 ND 0.15 ± 0.00 0.81 ± 0.02 0.55 ± 0.01 0.013 ± 0.001 0.0018 ± 0.0003 0.0072 ± 0.0005 0.0029 ± 0.0001 0.0035 ± 0.0003 ND ND ND ND ND 0.00050 16 ± 1 0.64 ± 0.01 ND ND 0.89 ± 0.04 14 ± 0 16 ± 0 21 ± 0 8.6 ± 0.2 2.0 ± 0.0 0.51 ± 0.01 0.32 ± 0.01 0.15 ± 0.00 0.14 ± 0.00 0.13 ± 0.00 0.12 ± 0.00 0.20 ± 0.00 0.26 ± 0.00 0.082 ± 0.012 0.027 ± 0.003 0.22 ± 0.01 0.30 ± 0.02 0.38 ± 0.02 0.50 ± 0.02 0.13 ± 0.00 0.0028 ± 0.0001 0.00018 ND 65 ± 1 945 ± 10

12 ± 4 ND 0.17 ± 0.01 0.89 ± 0.02 0.58 ± 0.01 0.015 ± 0.001 0.0025 ± 0.0002 0.0068 ± 0.0004 0.0038 ± 0.0008 0.0034 ± 0010 ND ND ND ND ND 0.00027 13 ± 4 0.70 ± 0.02 ND ND 0.87 ± 0.15 14 ± 2 15 ± 2 23 ± 1 10 ± 0 2.4 ± 0.0 0.60 ± 0.02 0.37 ± 0.01 0.16 ± 0.01 0.14 ± 0.00 0.14 ± 0.00 0.12 ± 0.00 0.20 ± 0.00 0.28 ± 0.01 0.097 ± 0.019 0.021 ± 0.004 0.21 ± 0.04 0.28 ± 0.06 0.37 ± 0.06 0.45 ± 0.09 0.13 ± 0.02 0.0033 ± 0.0006 ND ND 68 ± 6 720 ± 96

16 ± 1 ND 0.16 ± 0.01 0.83 ± 0.01 0.60 ± 0.01 0.016 ± 0.001 0.0017 ± 0.0002 0.0073 ± 0.0001 0.0025 ± 0.0003 0.0041 ± 0.0001 ND ND ND ND ND ND 18 ± 1 0.63 ± 0.02 ND ND 0.79 ± 0.08 16 ± 1 17 ± 1 22 ± 1 9.0 ± 0.2 2.2 ± 0.1 0.61 ± 0.01 0.34 ± 0.01 0.13 ± 0.01 0.15 ± 0.00 0.14 ± 0.00 0.12 ± 0.00 0.22 ± 0.00 0.29 ± 0.02 0.092 ± 0.033 0.019 ± 0.002 0.18 ± 0.02 0.23 ± 0.03 0.33 ± 0.03 0.39 ± 0.04 0.11 ± 0.01 0.0033 ± 0.0007 ND ND 69 ± 2 933 ± 56

log(1/EC50) = 1.36 log Kow − 2.75

log Kow.25 The TUi for aromatic hydrocarbons with log Kow greater than 5.0 was not taken into account.

(8)

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For all chemicals except for BTEX, the measured concentration in the WSF solution prepared for 24 h was used to calculate TUi. Because BTEX are highly volatile in aqueous solution with high Henry’s law constants, the corresponding TUi for BTEX was calculated using the predicted aqueous concentration. In addition, the luminescence inhibition of V. f ischeri showed a log Kow cutoff of approximately 5.0 due to the partitioning between the organism and the solution and a decreased fugacity ratio with increasing

RESULTS AND DISCUSSION

Comparison of Methods for Preparing WAF and WSF. As shown in Table 1, concentrations of PAHs and alkylated PAHs in the WAF and WSF solutions prepared at varying times did not significantly differ. This suggests that the method used for the preparation of the WAF did not result in a significant difference in the dissolved concentration of hydrophobic aromatic hydrocarbons. In addition, the V. f ischeri luminescence inhibition assay using the WSF solutions prepared at varying 2965



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Table 2. Comparison of Measured Chemical Concentrations in WAF and WSF, and Those Predicted by Eqs 1 and 2

chemical benzene toluene ethylbenzene p-xylene m-xylene o-xylene naphthalene acenaphthylene acenaphthene fluorine phenanthrene anthracene fluoranthene pyrene benz[a]anthracene chrysene benzo[b]fluoranthene benzo[k]fluoranthene benzo[a]pyrene indeno[1,2,3-cd]pyrene dibenz[a,h]anthracene benzo[ghi]perylene biphenyl benzo[e]pyrene perylene dibenzothiophene 1-methylnaphthalene 2-methylnaphthalene C2-naphthalene C3-naphthalene C4-naphthalene C1-fluorene C2-fluorene C3-fluorene 1-methylphenanthrene 2-methylphenanthrene 3-methylphenanthrene 4/9-methylphenanthrene C2-phenanthrene C3-phenanthrene C4-phenanthrene 1-methyldibenzothiophene 2-/3-methyldibenzothiophene 4-methyldibenzothiophene C2-dibenzothiophene C3-dibenzothiophene C1-chrysene C2-chrysene C3-chrysene

molar mass (g mol−1) 78.11 92.14 106.17 106.17 106.17 106.17 128.17 152.19 154.21 166.22 178.23 178.23 202.25 202.25 228.29 228.29 252.31 252.31 252.31 276.33 278.35 276.33 154.21 252.31 252.31 184.26 142.20 142.20 156.22 170.25 184.28 180.25 194.27 208.30 192.26 192.26 192.26 192.26 206.28 220.31 234.34 198.28 198.28 198.28 212.31 226.34 242.32 256.34 270.37

Tm (°C)a 5 −95 −95 13 −48 −25 80 92 93 115 99 216 110 151 161 256 168 217 181 162 270 273 69 181 278 98 −30 35 112 63 72q 87 101q 94q 123 94q 65 54 109q 116q 128q 112q 112q 112q 117q 128q 173 154q 165q

ΔSm (J mol−1 K−1)b 35.4 37.2 51.4 59.8 51.4 54.9 53.8 42.4 58.6 50.5 44.8 60.1 48.9 43.4 49.2 55.5 56.5h 56.6h 42.4 49.4 58.3 31.3 54.8 36.5h 67.9 56.4n 49.3 58.9 65.4 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p 56.5p

KS (L mol−1)c d

0.20 0.21d 0.23d 0.25d 0.25d 0.23d 0.26d 0.35 0.24d 0.27d 0.38 0.35 0.36 0.35 0.36 0.37 0.35 0.35 0.35 0.35 0.34 0.29 0.28d 0.35 0.35 0.35 0.44d 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35

aqueous solubility (mg L−1, at 25 °C) S

SswL

concentration in IHC (μg g−1)

1789 580e 187e 214e 160e 221e 30.60f 16.10g 4.16g 1.57f 0.82f 0.044f 0.20g 0.086f 0.017g 0.00070f 0.0015i 0.00080i 0.0015f 0.00019i 0.0025j 0.00014i 6.71k 0.0050l 0.00040m 1.47j 31.70e 21.50f 1.00o 2.10m 1.39r 1.092k 0.15r 0.10r 0.27s 0.28t 0.28t 0.27u 0.071r 0.021r 0.0059r 0.33r 0.33r 0.33r 0.095r 0.027r 0.013r 0.0037r 0.0011r

1429 455 143 160 120 170 75.21 33.75 15.92 7.19 2.028 3.013 0.70 0.52 0.16 0.080 0.026 0.043 0.014 0.0020 0.53 0.0023 12.90 0.034 0.27 5.20 6.34 18.05 6.62 3.34 2.72 3.00 0.56 0.33 1.68 0.89 0.47 0.34 0.32 0.11 0.041 1.60 1.60 1.60 0.52 0.19 0.26 0.047 0.017

1469 3623 1208 2468 825 1536 172 0.28 4.64 27.3 50.9 3.38 0.56 3.64 1.99 8.85 1.17 0.15 1.05 0.22 0.49 0.64 13.7 2.20 0.15 88.8 451 540 1226 1265 682 207 114 132 41.8 44.2 36.6 66.0 250 167 82.4 76.5 129 165 553 477 14.7 21.4 20.9

e

mole fraction (x) in IHC 7.1 1.5 4.3 8.7 2.9 5.4 5.0 6.8 1.1 6.2 1.1 7.1 1.0 6.7 3.3 1.5 1.7 2.2 1.6 3.0 6.6 8.7 3.3 3.3 2.2 1.8 1.2 1.4 2.9 2.8 1.4 4.3 2.2 2.4 8.2 8.6 7.1 1.3 4.5 2.8 1.3 1.4 2.4 3.1 9.8 7.9 2.3 3.1 2.9

× × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × × ×

10−3 10−2 10−3 10−3 10−3 10−3 10−4 10−7 10−5 10−5 10−4 10−6 10−6 10−6 10−6 10−5 10−6 10−7 10−6 10−7 10−7 10−7 10−5 10−6 10−7 10−4 10−3 10−3 10−3 10−3 10−3 10−4 10−4 10−4 10−5 10−5 10−5 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−5 10−5 10−5

Cpre (μg L−1) 1.0 6.7 6.1 1.4 3.5 9.2 3.8 2.3 1.8 4.4 2.2 2.1 7.3 3.5 5.3 1.2 4.5 9.3 2.2 5.9 3.5 2.0 4.3 1.1 6.0 9.4 7.53 25.7 19.5 9.30 3.77 1.29 1.2 7.9 1.4 7.7 3.3 4.4 1.5 3.1 5.4 2.3 3.9 5.0 5.0 1.5 5.9 1.5 5.1

× × × × × × × × × × × × × × × × × × × × × × × × × ×

104 103 102 103 102 102 101 10−2 10−1 10−1 10−1 10−2 10−4 10−3 10−4 10−3 10−5 10−6 10−2 10−7 10−4 10−6 10−1 10−4 10−5 10−1

× × × × × × × × × × × × × × × × ×

10−1 10−2 10−1 10−2 10−2 10−2 10−1 10−2 10−3 10−1 10−1 10−1 10−1 10−1 10−3 10−1 10−4

a

Ref 47. bRef 48. cRef 49. dRef 50. eRef 51. fRef 52. gRef 53. hRef 54. iRef 55. jRef 56. kRef 57. lRef 58. mRef 59. nRef 60. oRef 61. pEstimated value using Walden rule, ref 62. qEstimated value using MPBPVP v1.43.63 rEstimated value using WSKOW v1.42.63 sRef 64. tRef 65. uRef 66.

times up to 117 h showed consistent TU values of approximately 2.1 after 6 h (SI Figure S1). This indicates that almost all of the chemical species that exert toxic effects on V. f ischeri were, in fact, released from the IHC to the seawater solution. Furthermore, 24-h duration appears to be sufficient for most of the hydrophobic chemicals of the IHC that can permeate the PDMS membrane to complete the process. There was no noticeable difference in the concentrations of aromatic

hydrocarbons between the WAF and WSF solutions. This suggests that most of the hydrophobic aromatic hydrocarbons in the WAF solution are likely to be present in the dissolved state, i.e., in the solution prepared using the method that minimized physical agitations. Unlike the case of aromatic hydrocarbons, TPH concentration measured in the WAF solution prepared at the oilloading rate of 40 g L−1 was approximately 40% greater than 2966



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each chemical in the oil mixture. This information can then be used to evaluate the resulting ecotoxicological effects of each chemical species. Because the MWn of a crude oil mixture is a critical parameter that determines the mole fraction of the individual species, an accurate value of MWn is needed for a good prediction. In most studies, the MWn of crude oils was estimated by comparing the measured vs predicted concentration of major species, and ranged from 295 to 400 g mol−1.33−35 Researchers have found that weathering of crude oils may increase their ecotoxicity, primarily because of the increase in toxic transformation products such as oxygenated hydrocarbons,6,7,38,39 in spite of the evaporation loss of smaller chemicals. These polar compounds are mostly not included in monitoring of oil residues and need to be studied to fill gaps between observed ecotoxicity and chemically identified components. Another possible reason in need of consideration is the increased mole fraction of heavier, and subsequently, more toxic components. Because chemicals with lower molecular weights tend to have a higher vapor pressure, the MWn of spilled oil is likely to increase because of weathering and the mole fraction of less volatile aromatic hydrocarbons increases. Although further validation of the toxic potentials for these more persistent chemicals is needed, their increased mole fraction may explain the increased ecotoxicity of weathered oils. Prediction of Luminescence Inhibition and Comparison with Measured Data. The TU values of individual species were calculated as described above (detailed results are presented in SI Table S3). As shown in Figure 3, the TU for the

that in the WSF solutions (Table 1). Mass fractions of asphaltenes and resins of IHC were reported as 5.6 and 5.6%, repectively.27 These fractions may contain polar organic chemicals such as phenols that have much higher water solubility than the hydrocarbons of similar size. Dissolution of polar organic chemicals may significantly decrease the mole fraction in the oil mixture, as they dissolve in water due to their relatively high water solubility. This is in contrast to the highly hydrophobic aromatic hydrocarbons, for which the initial mole fraction changes only negligibly because of their limited water solubility. It has been shown that the depletion of soluble species in the nonaqueous phase liquid (NAPL) induces decreased concentration in water as the water/NAPL ratio increases.37 Prediction of Dissolved Concentration of Chemicals in Artificial Seawater. Table 2 shows the initial concentration and the mole fraction of each chemical in the IHC. The table also shows the predicted concentration (Ci) in the artificial seawater and the physicochemical properties necessary to calculate Ci (molar mass, Tm, ΔSm, KS, S, and SLsw). For alkylated PAHs, physicochemical properties were taken from representative compounds listed in SI Table S2. The predicted values in Table 2 agree very well with the measured ones in Table 1, as shown in Figure 2. The differences between the measured and

Figure 2. Comparison of predicted and measured concentrations in water-accommodated fraction (WAF) and water-soluble fraction (WSF). Open circles and open diamonds denote substances in WAF and WSF, respectively. Solid and dotted lines indicate 1:1 and 2:1 (or 1:2) lines, respectively.

predicted values were within a factor of 2 for more than 60% of the hydrocarbons evaluated. Relatively larger deviations were found for chemicals with lower measured concentrations, such as benzo[a]anthracene, probably because of the larger experimental errors in quantification. Similarly, Sterling et al.34 showed that the measured soluble concentrations of PAHs agreed well with the predicted ones, especially for those with higher mole fractions when a best-fit value of MWn was used. Because it is much easier to measure chemical composition in crude or weathered oils than in aqueous solutions, the estimation method proposed in this study could be used to evaluate the freely dissolved concentrations of each chemical species in the WAF or WSF by measuring the mole fraction of

Figure 3. Toxic unit (TU) measured for WAF and WSF solutions. Error bars denote the standard errors (n = 3).

WSF was the lowest and that for the WAF showed an increasing trend with increasing oil-loading rate. These do not agree with the negligible changes in the measured concentrations of hydrophobic aromatic hydrocarbons (Table 1). Because PDMS is a nonpolar polymeric phase, highly polar organic compounds and inorganic species cannot easily penetrate through the PDMS layer (Figure 1). Thus, the 2967



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Figure 4. Contribution of the measured chemical species to the overall toxicity in toxic unit (TU). Values in parentheses represent the contribution of chemically identified components to TU using eqs 1−5.

limited number of studies and were comparable to, or even greater than, that of the parent PAHs.43−46 This suggests that further studies are required to study the fate and toxicity of individual alkylated PAHs and their mixtures in the environment.

differences in TU between the WSF and WAF solutions with varying oil-loading rates may be attributed to the presence of polar organic compounds and/or inorganic chemicals. As discussed above, the dissolved concentration of these chemicals may increase with increasing oil-loading rate if they are present in a limited amount in the mixture. Crude oils are known to contain a substantial fraction of inorganic substances such as sulfur, vanadium, nickel, and copper compounds,40,41 which may be toxic to V. fischeri. However, the extremely high oilloading rates used for the preparation of WAF in this study (5− 40 g L−1) are not likely to occur at oil-spill sites. Thus, the potential contribution of these species to ecotoxicity from spilled oil residues under field conditions should be limited. Figure 4 summarizes the comparison of TU measured for the WAF using various oil-loading rates and for the WSF using the estimated contribution due to aromatic hydrocarbons. The contributions of the PAHs and alkylated PAHs were calculated based on the measured concentration in the 24-h WSF, whereas that of the BTEX compounds was based on the predicted concentration, because their actual concentrations were not measured in the WAF and WSF solutions. The relative contribution of BTEX compounds, PAHs, and alkylated PAHs in luminescence inhibition was estimated at 76%, 2%, and 21%, respectively. Although the estimated contribution by BTEX is the highest, the actual contribution might be lower than calculated, because the BTEX compounds evaporate during the experiment owing to their high Henry’s law constants.42 Interestingly, C3- and C4-naphthalenes and other alkylated PAHs were identified as the most important aromatic hydrocarbons responsible for baseline toxicity, with the exception of BTEX as suggested by earlier literature.8−12 Meanwhile, the contribution of the 16 priority PAHs designated by the US EPA was only approximately 2%. The toxic potentials of alkylated PAHs have been reported in a

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ASSOCIATED CONTENT

S Supporting Information *

Literature values of Klipw,i used in this study are summarized in Table S1, and TU values of each chemical species are summarized in Tables S1 and S2. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +82 2 3290 3041; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was a part of the project entitled “Oil Spill Environmental Impact Assessment and Environmental Restoration (PM57431)” funded by the Ministry of Oceans and Fisheries, Korea, and the National Research Foundation of Korea (NRF) grant (No. 2012R1A1B4000841).

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Prediction of Ecotoxicity of Heavy Crude Oil - American Chemical

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