water partition coefficients of a series of mixed halogenated dimethyl bipyrroles

Chemosphere 57 (2004) 1373–1381 www.elsevier.com/locate/chemosphere

Vapour pressures, aqueous solubilities, HenryÕs Law constants, and octanol/water partition coefficients of a series of mixed halogenated dimethyl bipyrroles Sheryl A. Tittlemier a,*, Eric Braekevelt b, Thor Halldorson b, Christopher M. Reddy c, Ross J. Norstrom a,d,1 a

c

Centre for Analytical and Environmental Chemistry, Carleton University, Ottawa, Ont., Canada K1S 5B6 b Department of Fisheries and Oceans, Freshwater Institute, Winnipeg, Man., Canada R3T 2N6 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA d National Wildlife Research Centre, Environment Canada, Hull, Que., Canada J8Y 1V9 Received 4 December 2003; received in revised form 9 August 2004; accepted 23 August 2004

Abstract Basic physical–chemical properties of five bromine and chlorine containing mixed halogenated dimethyl bipyrroles (HDBPs) were determined using established methods. Subcooled liquid vapour pressures ðP oL;25 Þ, aqueous solubilities (Sw,25), and octanol/water partition coefficients (Kow) were determined using the gas chromatography-retention time, generator column, and slow-stirring methods, respectively. HenryÕs Law constants (H25) were estimated using experimentally-derived P oL and Sw,25 data. Values of all four properties were generally similar to those reported for other polyhalogenated aromatic compounds [P oL;25 ¼ ð7:55–191Þ
106 Pa; Sw,25 = (1.0–1.9) · 105 g/l; log Kow=6.4–6.7; H25 = 0.0020–0.14 Pa m3/mol]. The effect of replacing a chlorine with a bromine atom significantly decreased P oL;25 (log P oL;25 ¼ 0:4197 (# bromine atoms)  2.643, p < 0.01) and H25 (log H25 = 0.508 (# bromine atoms) + 0.394, p < 0.02). There were no significant effects of bromine/chlorine substitution on Sw,25 or Kow. A simple Level I equilibrium partitioning model predicted the environmental behaviour of HDBPs to be similar to a tetrabrominated diphenyl ether. Only slight differences in behaviour amongst HDBP congeners were predicted since substitution of a bromine for a chlorine (Cl/Br substitution) atom had less effect than H/Cl or H/Br substitution on P oL;25 , Sw,25, H25, and Kow. Crown Copyright
2004 Published by Elsevier Ltd. All rights reserved. Keywords: Organohalogen; Naturally-produced; Physical–chemical properties; Equilibrium partition model

1. Introduction *

Corresponding author. Present address: Food Research Division, Health Canada, Ottawa, Ont., Canada K1A 0L2. Tel.: +1 613 941 5603; fax: +1 613 941 4775. E-mail address: [email protected] (S.A. Tittlemier). 1 Present address: Ottawa, Ont., K1A 0H3.

Halogenated organic compounds are present throughout the environment and are found in virtually every location and sample matrix studied. The vast majority of organohalogens routinely monitored are anthropogenic in nature and are either exclusively chlorinated or exclusively brominated. Polychlorinated

0045-6535/$ - see front matter Crown Copyright
2004 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2004.08.061

1374

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381

biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polybrominated diphenyl ethers (PBDEs) are examples of such compounds. These compounds have been detected in many environmental media, including sediments (Sellstro¨m et al., 1998; Mu¨ller et al., 1999), water (Tanabe and Tatsukawa, 1980; Iwata et al., 1993), air (Rappe et al., 1988; Halsall et al., 1995), and biota (Watanabe et al., 1987; Muir et al., 1992). Organohalogens have been found in samples obtained from locations worldwide, including areas considered to be pristine environments, such as the Arctic (Muir et al., 1992) and Antarctica (Bacci et al., 1986). Detection in remote areas indicates that these compounds undergo long-range transport. Their transport and fate are governed by physical–chemical properties such as vapour pressure, aqueous solubility, HenryÕs Law constant, and the octanol/water partition coefficient (Kow). These fundamental physical–chemical properties have been well characterized for most classes of commonly analyzed organohalogens. In addition to exclusively chlorinated or brominated organic compounds present in the environment, there exist a number of mixed halogenated compounds that contain both bromine and chlorine. Many of these compounds are formed as incineration (Mu¨ller and Buser, 1986; Heeb et al., 1995) or water disinfection by-products (Suzuki and Nakanishi, 1995). A large number of mixed halogenated organic compounds are also formed by marine organisms (Gribble, 1998). A series of mixed hexahalogenated dimethyl bipyrroles (HDBPs) has recently been observed in sediment, zooplankton, Arctic cod, and seabirds (Tittlemier et al., 1999; Tittlemier et al., 2002b). They have also been detected in many pinnipeds and cetaceans sampled from over 25 locations, including sites in the North and South Pacific, Atlantic, Arctic, and Indian Oceans, and the Mediterranean, Wadden, Kara, and White Seas (Tittlemier et al., 2002a). Structural similarity to a known marine bacterial product (Andersen et al., 1974), a geographic distribution different from that of anthropogenic PCBs, and a radiocarbon signal indicative of a recent source of carbon (Reddy et al., 2004), suggest that HDBPs are naturally-produced. Irrespective of the nature of their source, they are widespread and most likely undergo extensive transport. HDBPs are bioaccumulative persistent compounds that have been observed to biomagnify in marine food webs to a similar extent as recalcitrant PCB congeners, such as CB-153 (Tittlemier et al., 2002b). They have displayed some in vitro dioxin-like ability (Tittlemier et al., 2003b), but did not elicit any reproductive effects when administered to a captive population of raptors (Tittlemier et al., 2003a). The fundamental physical–chemical properties affecting the movement of HDBPs have not been character-

ized. In this study, the vapour pressures, aqueous solubilities, and Kows of five HDBP congeners (ranging from trichlorinated/tribrominated to hexabrominated species found in nature) were determined using the gas chromatography-retention time technique, generator column technique, and slow-stirring method. HenryÕs Law constants were estimated using the experimentally determined vapour pressures and aqueous solubilities. The effects of substitution of bromine for chlorine atoms on these four physical–chemical properties were also examined.

2. Materials and methods 2.1. Chemicals HDBP congeners were synthesized and characterized according to the methods outlined in Gribble et al. (1999). Three congeners used in this study were of known structure-1,1 0 -dimethyl-3,3 0 ,4,4 0 -tetrabromo-5,5 0 dichloro-2,2 0 -bipyrrole (DBP-Br4Cl2); 1,1 0 -dimethyl-3,3 0 , 4,4 0 ,5-pentabromo-5 0 -chloro-2,2 0 -bipyrrole (DBP-Br5Cl); and 1,1 0 -dimethyl-3,3 0 ,4,4 0 ,5,5 0 -hexabromo-2,2 0 -bipyrrole (DBP-Br6). The two remaining congeners were hypothesized to be 1,1 0 -dimethyl-3,3 0 ,4-tribromo-4,5,5 0 -trichloro-2,2 0 -bipyrrole (DBP-Br3Cl3a) and 1,1 0 -dimethyl3,4,4 0 -tribromo-3 0 ,5,5 0 -trichloro-2,2 0 -bipyrrole (DBP-Br3 Cl3b) based on their presence as by-products in the electrophilic substitution formation of DBP-Br4Cl2. All HDBP congeners used were > 99% pure. Four of these congeners (DBP-Br3Cl3a, DBP-Br4Cl2, DBP-Br5Cl, and DBP-Br6) are environmentally-relevant compounds found in biota (Tittlemier et al., 2001). Mirex, t-chlordane, octachloronaphthalene, and PCB congeners used as method calibration external standards, instrument performance internal standards, and recovery internal standards were obtained from Accustandard (New Haven, CT, USA). Purity of octachloronaphthalene was 98%; purities of all other standards were greater than or equal to 99%. Isotopically labeled 13 C12-CB-138 was purchased from Cambridge Isotope Laboratories (Andover, MA, USA). Both solvents used in the slow-stirring experiment (1octanol and water) were HPLC grade (Fisher Scientific, Ottawa, ON, Canada). 2.2. Vapour pressures The gas chromatographic-retention time (GC-RT) technique described in Hinckley et al. (1990) was used to determine subcooled liquid vapour pressures ðP oL Þ of the HDBPs. The GC-RT method estimates the subcooled liquid vapour pressure as opposed to vapour pressure (Bidleman, 1984), defined as the equilibrium partitioning of a chemical between its pure condensed

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381

and gaseous states (Schwarzenbach et al., 1993). The subcooled liquid vapour pressure is the equilibrium partitioning of a chemical between its subcooled liquid and gaseous states. The subcooled liquid is a hypothetical state in which molecules behave as in a liquid, and is used to act as a reference state for compounds that are solids at the experimental temperatures. The GC-RT method relates P oL of a compound to its retention time (relative to a reference compound) obtained during an isothermal GC run according to the following equations:  log

t



tref

log P oL ¼

   DH vap ¼ 1 log P oL;ref  C DH vap;ref



DH vap DH vap;ref



log P oL;ref þ C

ð1Þ

ð2Þ

where DHvap and DHvap,ref are the enthalpies of vaporization of the test and reference compounds, respectively. Eq. (1) assumes the infinite dilution activity coefficients of the test and reference compounds are identical, the ratio of the test and reference compound enthalpies is constant over the experimental temperature range, and that the P oL of the reference compound is accurate. The GC-RT method also assumes that the partitioning of the compounds between the GC carrier gas and the column stationary phase is driven solely by a compoundÕs volatility. Relative retention times are obtained over a range of temperatures and plotted versus P oL of the reference compound using Eq. (1) to determine DHvap and the constant C. P oL of the test compound is then calculated using DHvap/DHvap,ref and C in Eq. (2). Mirex, t-chlordane, and the PCB congeners CB-4, CB-15, CB-118, CB-153, CB-180, CB-187, CB-194, CB-202, CB-206, and CB-209 were used as standards for the GC-RT method. These compounds, whose P oL s are reported in the literature, were selected to represent a range of vapour pressures. Solutions of all standards and HDBPs were made in isooctane in the 50–100 pg/ll range and spiked with the reference compound p,p 0 -DDT. The instrumentation used was the same as that described in Tittlemier et al. (2002c). Retention times for all compounds on a DB-1 column (2 m · 0.250 mm i.d., film thickness 0.25 lm, J&W Scientific, Folsom, CA, USA) were determined during six isothermal runs performed at oven temperatures ranging from 140 C to 165 C at 5 C intervals. The HDBP P oL;25 values were derived by using a calibration curve to correct vapour pressure values obtained directly from the GC-RT method (designated PGC). This correction is performed in an attempt to reduce systematic errors in PGC values caused by inequalities of the test and reference compound activity in the stationary phase. The calibration curve was constructed from the

1375

correlation between PGC and literature values of subcooled liquid vapour pressures ðP oL;lit Þ of the standard compounds. In the past, PGC values have been corrected by using a calibration curve constructed from P oL values derived from other methods to remove the systematic error caused by the GC-RT method (Bidleman, 1984; Hinckley et al., 1990; Lei et al., 1999). In this study, the P oL;lit Õs used were values obtained from other GCRT studies and thus were themselves previously corrected by comparison to P oL derived from other methods (Bidleman, 1984; Foreman and Bidleman, 1985; Shiu et al., 1987; Hinckley et al., 1990; Falconer and Bidleman, 1994). Vapour pressures for HDBPs (PGC) were corrected using the following regression equation obtained from the P oL;lit –P GC correlation of the standard compounds: log P oL;lit ¼ 0:931ðlog P GC Þ  0:250

ð3Þ

Values of DHvap for the HDBP congeners were determined from DHvap,DDT = 89.9 kJ/mol and the slope of the line described by Eq. (1). The coefficients B and A were calculated from the integrated form of the Clausius–Clapeyron equation (4), which describes the change in vapour pressure of a compound with temperature. log P oL ¼ 

B þA T

ð4Þ

where B¼

DH vap 2:303R

ð5Þ

The coefficients A and B were calculated using the corrected HDBP P oL;25 values. 2.3. Aqueous solubility Aqueous solubilities at 25 C (Sw,25) of the five HDBPs were measured using the generator column technique (May et al., 1978). Three PCB congeners (CB-28, CB-101, and CB-136) were selected to encompass a range of aqueous solubilities and act as standards to monitor the effectiveness of the technique. The experimental apparatus used is described in Tittlemier et al. (2002c). Briefly, approximately 5 mg of crystals of an HDBP congener were dissolved in acetone and sorbed onto pre-cleaned 60–80 mesh glass beads. Two precleaned stainless steel HPLC columns (250 · 3.9 mm; 100 · 3.9 mm) were then packed with the HDBP-coated glass beads. The larger column was connected to an HPLC pump using only stainless steel tubing and flushed with HPLC grade water at a flow rate of 1 ml/ min to create an aqueous solution saturated with HDBP. An external column heater was used to maintain the column at a temperature of 25 ± 1 C. To ensure that all active sites within the column, fittings, and tubing

1376

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381

had been coated with compound, water was pumped through the packed column for 1 h prior to collecting the first samples. Three replicates of HDBP-saturated water (10.0 ml each) were collected in volumetric flasks after 1 h of equilibration. A second smaller HPLC column similarly packed with HDBP-coated beads was connected in series after the first column to ensure that the aqueous eluate was saturated. An additional three eluate samples were collected after water was pumped through the two columns to coat all active sites. Collected samples were spiked with recovery internal standard (CB153) and extracted with 1:1 dichloromethane/hexane (3 · 8 ml). Pure HPLC grade water was used as a method blank with every six eluate samples collected. Organic fractions were combined; dried using activated Na2SO4, and reduced on a rotary evaporator. Instrument performance internal standard (mirex) was added to all samples and external standards prior to analysis by GC-ECD. The eluate was deemed saturated if the concentrations of HDBP in water samples collected from one and two columns did not differ significantly from each other. 2.4. Henry’s Law constants HenryÕs Law constants (H) were estimated at 25 C using the following equation: H¼

P oL;25 S L;25

ð6Þ

where P oL;25 and SL,25 are the respective subcooled liquid vapour pressures and aqueous solubilities at 25 C. SL,25 was calculated from Sw,25 using Eq. (7) since experimental values obtained from the generator column method are for the solid, rather than subcooled liquid, phase. Eq. (7) uses melting point (Tm) to calculate and correct for the entropy of fusion required to move from the solid to the subcooled liquid phase. It is derived from the ratio of the fugacity of the pure solid to that of the subcooled liquid (Kan and Tomson, 1996), and assumes that HDBP molar entropies of fusion are similar to rigid aromatic hydrocarbons (56.5 J mol1 K1) (Yalkowsky, 1979). S L;25 ¼

S w;25 e0:023ðT m 25Þ

ð7Þ

Tm values used in Eq. (7) were taken as the midpoint of the melting range using a Laboratory Devices MelTemp apparatus (Holliston, MA, USA).

octanol-saturated water were prepared by gently stirring HPLC grade water and 1-octanol continuously for 72 h. Approximately 50 mg each of the five HDBPs and a series of PCB congeners used as standards (CB-153, CB180, CB-202, CB-206, CB-209) were dissolved in 200 ml of water-saturated octanol. Octanol-saturated water (3.5 l) and organohalogen octanol solution (20 ml) were added to four pre-cleaned and dried Erlenmeyer flasks. The mixture was gently stirred with a Teflon stir bar so that a vortex no greater than 1 cm in height was formed. On Days 2, 4, 7, 10, and 14 of the slow-stirring experiment, 1 ml of the octanol and 500 ml of the water phases were collected using a volumetric pipette and flask, respectively. The initial preparation of water-saturated octanol and octanolsaturated water plus the slow-stirring experiment were performed in a controlled environment room at a constant temperature of 25 ± 1 C. The water samples were spiked with recovery standard (octachloronaphthalene) and extracted with 1:1 dichloromethane/hexane (3 · 50 ml). NaCl (10 g) was added to the water phase to facilitate extraction of the organohalogens. The dichloromethane/hexane fractions were combined, dried over anhydrous Na2SO4, and reduced to 1 ml. Octanol phase samples were diluted by a factor of 1000 with hexane. Prior to analysis, the water extracts and 1ml aliquots of the diluted octanol samples were spiked with performance standard (13C12-CB-138). Organohalogens were quantitated by gas chromatography-electron capture negative ionization-mass spectrometry in the selected ion mode using the method outlined in Tittlemier et al. (2002b).

3. Results 3.1. Vapour pressures Table 1 lists values of P oL;25 , DHvap, and the coefficients of the integrated Clausius–Clapeyron equation for HDBPs. Uncertainty in P oL;25 is given as the 95% confidence interval of the distribution of log P oL;lit values at each level of log PGC. Uncertainty in PGC would mainly arise from variations in GC retention times. This confidence interval is the range that would be expected to cover 95% of the log P oL;lit values. Fig. 1 shows the relationship between P oL;25 and bromine content of the HDBP congeners. There was a statistically significant decrease in P oL;25 with an increase in bromine content [analysis of variance (ANOVA): p < 0.01].

2.5. Octanol/water partition coefficients 3.2. Aqueous solubilities Octanol/water partition coefficients of the five HDBPs were evaluated using the slow-stirring method (de Bruijn et al., 1989). Water-saturated octanol and

The experimentally determined Sw,25 values for the five HDBP congeners are given in Table 2. Sw,25 values

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381

1377

Table 1 Halogenated dimethyl bipyrrole (HDBP) enthalpies of vaporization, integrated Clausius–Clapeyron integers (B, A from Eq. (5)), and subcooled liquid vapour pressures at 25 C ðP oL;25 Þ HDBP

DHvap (kJ/mol)

B

A

P oL;25 (Pa)

Estimated P oL;25 95% population CIa (Pa)

DBP-Br3Cl3a DBP-Br3Cl3b DBP-Br4Cl2 DBP-Br5Cl DBP-Br6

96.1 99.6 104 109 113

5020 5204 5442 5696 5910

13.13 13.44 13.87 14.34 14.71

0.000191 0.0000942 0.0000411 0.0000168 0.00000755

0.00010–0.00023 0.000051–0.00011 0.000023–0.000051 0.0000093–0.000021 0.0000042–0.0000094

a The 95% confidence interval (CI) of P oL;25 was estimated from the 95% confidence interval of log P oL;lit in the log P oL;lit versus log PGC correlation.

-3.0

-3.5

log PoL,25 (Pa)

DBP-Br3Cl3a -4.0

DBP-Br3Cl3b DBP-Br4Cl2

-4.5 DBP-Br5Cl -5.0

DBP-Br6 log PoL,25= -0.4197 (# bromine atoms) - 2.643 R2 = 0.9548

-5.5 2

3

4

5

6

7

number of bromine atoms

Fig. 1. Effect of bromine/chlorine substitution on the subcooled liquid vapour pressure at 25 C (P oL;25 ) of halogenated dimethyl bipyrroles. The error bars on the graph represent the 95% confidence interval of the distribution of log P oL;lit values from the correlation described in Eq. (3).

of CB-28, CB-101, and CB-136 (1.01 · 104, 9.78 · 106 and 7.84 · 106 g/l, respectively) used to evaluate the generator column technique were well correlated with literature values (1.63 · 104, 6.74 · 106 and 6.03 · 106 g/l, respectively) (Mackay et al., 1999).

For comparative purposes, estimated Sw,25 values were also derived using an equation that exploits the relationship between Sw,25 and Kow. The equation was constructed using a data set of 90 compounds from mixed classes, including polychlorinated hydrocarbon insecticides, PCBs, polychlorinated diphenyl ethers, polynuclear aromatic hydrocarbons, and nitrogen-containing hetereocyclics (Kenaga and Goring, 1980). Estimation of Sw,25 in this manner only requires input of Kow. The Kow values used in the generation of the estimated values are the experimental values listed in Table 2. The experimentally determined and estimated Sw,25 values did not differ by more than a factor of 2. No significant trend of log Sw,25 or log SL,25 with bromine content was observed (ANOVA: p = 0.8, p = 0.3, respectively). 3.3. Henry’s Law constants The melting points used to calculate H25 from Eqs. (6) and (7) were taken as the midpoint of the ranges given in Table 2. There was a significant (ANOVA: p < 0.02) decrease in H25 with increasing bromine content of the HDBP congeners [log H25 = 0.508 (# bromine atoms) + 0.394, R2 = 0.866].

Table 2 Halogenated dimethyl bipyrrole (HDBP) experimentally determined and estimated aqueous solubilities at 25 C (Sw,25), melting points (Tm), HenryÕs Law constants at 25 C (H25), experimentally determined and estimated octanol/water partition coefficients at 25 C (Kow) HDBP

Experimental Sw,25 (g/l)

Estimateda Sw,25 (g/l)

Tm (C)

H 25 b (Pa m3/mol)

Experimental log Kow

Estimatedc log Kow

DBP-Br3Cl3a DBP-Br3Cl3b DBP-Br4Cl2 DBP-Br5Cl DBP-Br6

(1.1 ± 0.3) · 105 (2.2 ± 0.3) · 105 (9 ± 1) · 106 (2.7 ± 0.2) · 105 (1.4 ± 0.3) · 105

1.6 · 105 1.9 · 105 1.6 · 105 1.3 · 105 1.0 · 105

203.0–203.5 210.0–210.5 209.0–210.0 197–200 247–248

0.14 ± 0.04 0.030 ± 0.004 0.036 ± 0.004 0.0068 ± 0.0005 0.0020 ± 0.0004

6.5 ± 0.3 6.4 ± 0.2 6.5 ± 0.3 6.6 ± 0.3 6.7 ± 0.3

6.9 6.9 7.0 7.2 7.3

a b c

Estimated using log S = 0.922log Kow + 4.184 (Kenaga and Goring, 1980) and experimental log Kow values. Uncertainties were derived from the standard deviations of the Sw,25 values. Estimated using the fragment constant method (Lyman, 1982).

1378

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381

3.4. Octanol/water partition coefficients The HDBP Kows determined by the slow-stirring experiment are listed in Table 2, alongside values estimated using the fragment constant method (Lyman, 1982). The means and standard deviations were calculated from the Day 14 aliquots for the four replicate flasks. Concentrations of HDBPs in the aqueous phase did not significantly change after Day 10 measurements, indicating that the phases were in equilibrium at the end of the experiment. log Kows of the five PCB congeners used as standards were well correlated with literature values [literature log Kow = 1.17 (experimental log Kow)  0.761; R2 = 0.788]. The log Kow values determined for HDBPs are approximately 0.4–0.6 log units lower than those predicted by the fragment constant method. No significant trend of log Kow with bromine content was observed (ANOVA: p = 0.997).

4. Discussion 4.1. Vapour pressures The values obtained for P oL;25 s of the five HDBP congeners studied were comparable to those for hepta- to decachlorinated PCBs (Mackay et al., 1999; Li et al., 2003) and tetra- to hexabrominated PBDEs (Wania and Dugani, 2003). The relative amounts of chlorine and bromine on the HDBP molecule significantly affected P oL;25 . Replacement of a chlorine with a bromine atom resulted in a 2.6-fold decrease in P oL;25 (Fig. 1). The magnitude of this decrease is less than for hydrogen/chlorine (approximately 4-fold decrease) (Ballschmiter and Zell, 1980; Falconer and Bidleman, 1994; Drouillard et al., 1998) or hydrogen/ bromine substitution (approximately 7-fold decrease) (Wong et al., 2001; Tittlemier et al., 2002c). The smaller effect of chlorine/bromine substitution is consistent with the effects of size on vapour pressure. In general, compounds occupying larger molar volumes have lower vapour pressures than those which are smaller due to stronger intermolecular attractions in the liquid phase. Substitution of a chlorine for a bromine atom results in a smaller volume change than substitution of a hydrogen for either a bromine or chlorine atom. 4.2. Aqueous solubility The HDBP aqueous solubilities are comparable to values for other halogenated environmental contaminants such as adjusted values for di- and tribrominated PBDEs (Wania and Dugani, 2003) and di- and trichlorinated PCBs (Li et al., 2003). The smaller molar volumes of the hexahalogenated bipyrroles (LeBas molar volumes: 333.5–340.4 cm3/mol) may render these com-

pounds more soluble than the larger PBDEs (361.8 cm3/mol) and PCBs (340.6 cm3/mol) containing the same number of halogen atoms. Electronic effects related to the ability of the heterocyclic nitrogen atoms to interact energetically more favourably with water may also play a role in the relatively high solubility of the HDBPs. There appears to be no significant effect on Sw,25 when a chlorine is exchanged for a bromine substituent. This suggests that for HDBPs, molecular size does not play as large a role in governing the magnitude of Sw,25 as with P oL;25 . This reduced effect of molecular size is also observed for some organobromine compounds. In the case of PBDEs, substitution of a bromine for a hydrogen atom (H/Br substitution) has a more pronounced effect on P oL (6.9–9.2-fold decrease) (Wong et al., 2001; Tittlemier et al., 2002c) than Sw (2.8-fold decrease) (Tittlemier et al., 2002c). However, for organochlorines, the difference in effects of H/Cl substitution on P oL and Sw are reversed (4.3 versus 6.8-fold decrease, respectively, for PCDEs) (Kurz and Ballschmiter, 1999) or non-existent (4.5 versus 4.8-fold decrease, respectively, for PCBs) (Bidleman, 1984; Miller et al., 1984). 4.3. Henry’s Law constants The estimated HDBP HenryÕs Law constants are all approximately 10–1000 times lower than those reported for all PCBs (Li et al., 2003) and PCDEs. The values for the tri- and tetrabrominated HDBPs are on the same order of magnitude as hepta- to decabrominated PBDEs (Wania and Dugani, 2003). The penta- and hexabrominated HDBP H25 values are lower than those reported for BDE-209. This occurs because SL,25 (the denominator in Eq. (3)) is higher, whereas P oL;25 (the numerator), is lower as compared to values for PCBs and PCDEs of equivalent halogenation. In a similar fashion to P oL , H25 significantly decreased with an increase in the amount of bromine in an HDBP congener. The magnitude of decrease of H25 with bromine content (3.2-fold decrease for each Cl/Br substitution) is similar to that for P oL . This is expected since only changes in P oL are driving the decrease in H25; Sw,25 did not significantly change with Cl/Br substitution. A somewhat larger decrease of H25 occurs with PBDEs (4.3-fold decrease for each additional H/Br substitution) (Tittlemier et al., 2002c). As with HDBPs, the decrease in PBDE H25 with bromine content is driven by decreases in P oL . 4.4. Octanol/water partition coefficients The log Kow values determined for HDBPs are similar to log Kows obtained for penta- and hexachlorinated PCBs and polychlorinated diphenyl ethers (PCDEs) using generator column and retention indices techniques

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381

(Hawker and Connell, 1988). The values of HDBP log Kows obtained is also comparable to the range determined for adjusted values for tetra- and hexabrominated diphenyl ethers (Wania and Dugani, 2003). The HDBP log Kows are consistent with their biomagnification observed in an Arctic marine food web. HDBPs increased in concentration over trophic levels to a similar extent as CB-153, a compound with a similar log Kow (Tittlemier et al., 2002b). The degree of biomagnification of hydrophobic organochlorines in invertebrates and fish has been shown to be related to Kow in a freshwater food web (Kidd et al., 1998). There was a slight increase in HDBP log Kow with an increase in bromine content of the congener. However, the increase was not statistically significant (p = 0.997). This lack of a significant increase is not entirely unexpected since the value of the octanol/water partition coefficient for organic compounds is generally correlated with solubility in water, rather than solubility in octanol (Schwarzenbach et al., 1993). As discussed above, no significant effect of bromine content on Sw,25 was observed. 4.5. Environmental significance of HDBP physical properties It is well known that physical–chemical properties govern the behaviour of contaminants in the environment. Values of basic physical–chemical properties such as vapour pressure and water solubility, plus the octanol/water partition coefficient and HenryÕs Law constant can thus be used to model and predict the movement, distribution, and fate of contaminants. The distribution of the four environmentally-relevant HDBPs (DBPBr3Cl3a, DBP-Br4Cl2, DBP-Br5Cl, and DBP-Br6) in a simple four compartment environment at equilibrium (Mackay et al., 1996) was estimated using physical– chemical property data determined in this work. The equilibrium distributions of selected aromatic anthropogenic organohalogens (p,p 0 -DDT, CB-138, CB-194, CB209, BDE-28, BDE-47, BDE-85, and BDE-183) were also estimated. Physical–chemical property data for anthropogenic organohalogens were directly measured values obtained from Mackay et al. (1999), Tittlemier et al. (2002c), Braekevelt et al. (2003), and adjusted or extrapolated values from Wania and Dugani (2003) and Li et al. (2003). The model environment consisted of air (1000 m · 1000 m · 6000 m), soil (1000 m · 300 m · 0.15 m, 2% organic content by volume), water (1000 m · 700 m · 10 m), and sediment (1000 m · 700 m · 0.03 m, 5% organic content by volume) at 25C. The equilibrium distributions of the four HDBP congeners most resembled the distribution of CB-194 and CB-209, two highly chlorinated PCB congeners, and BDE-47, a tetrabrominated PBDE. Greater than 99% of CB-194, CB-209, BDE-47 and each HDBP was dis-

1379

tributed in the soil and sediment compartments. Approximately 0.2–0.3% of each HDBP congener was present in the water compartment as compared to less than 0.02% of the two PCB congeners. Less than 0.01– 0.0005% of the total amount of HDBPs in the simplified environment was present in the air compartment. The variations in physical properties observed with changes in chlorine and bromine content of HDBPs indicate that there may be some differences in their distribution and fate. However, because the substitution of bromine for a chlorine atom affected P oL and Kow less than hydrogen/halogen substitution, the differences in HDBP congener distributions are not expected to be as large as for PCB or PBDE homologues. As anticipated, only slight differences in distribution between the HDBP congeners were predicted by the model.

5. Conclusions The characterization of fundamental physical–chemical properties and the results of the simple modeling exercise suggest that the majority of HDBPs would be present in relatively immobile environmental media such as suspended particulate matter and sediment. Based on similarity of physical–chemical properties, HDBPs appear to behave similar to a tetrabrominated PBDE congener in their potential for global distribution. Differences in behaviour among the HDBP congeners are small compared to differences among PCB or PBDE homologues, since substitution of a bromine for a chlorine atom has less effect than H/Cl or H/Br substitution on P oL , Sw,25, H25, and Kow.

Acknowledgments This study was funded by the Canadian Chlorine Coordinating Committee and the Canadian Chemical Producers Association. The authors would like to thank Jennifer Pranschke (National Wildlife Research Centre) and Gregg Tomy (Freshwater Institute) for help with the determination of aqueous solubilities, and David Blank and Gordon Gribble (Dartmouth College) for providing melting point data.

References Andersen, R.J., Wolfe, M.S., Faulkner, D.J., 1974. Autotoxic antibiotic production by a marine Chromobacterium. Mar. Biol. 27, 281–285. Bacci, E., Calamari, D., Gaggi, C., Faneli, R., Focardi, S., Morosini, M., 1986. Chlorinated hydrocarbons in lichens and moss samples from the antarctic peninsula. Chemosphere 15, 747–754.

1380

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381

Ballschmiter, K., Zell, M., 1980. Analysis of polychlorinated biphenyls (PCB) by glass capillary gas chromatography. Fres. Zeit. Anal. Chem. 302, 20–31. Bidleman, T.F., 1984. Estimation of vapor pressures for nonpolar organic compounds by capillary gas chromatography. Anal. Chem. 56, 2496–2500. Braekevelt, E., Tittlemier, S.A., Tomy, G.T., 2003. Determination of octanol/water partition coefficients of some brominated flame retardants by the slow-stirring method. Chemosphere 51, 563–567. de Bruijn, J., Busser, F., Seinen, W., Hermens, J., 1989. Determination of octanol/water partition coefficients for hydrophobic organic chemicals with the ‘‘slow-stirring’’ method. Environ. Toxicol. Chem. 8, 499–512. Drouillard, K.G., Tomy, G.T., Muir, D.C.G., Friesen, K.J., 1998. Volatility of chlorinated n-alkanes (C10–C12): vapor pressures and HenryÕs Law constants. Environ. Toxicol. Chem. 17, 1252–1260. Falconer, R.L., Bidleman, T.F., 1994. Vapor pressures and predicted particle/gas distributions of polychlorinated biphenyl congeners as functions of temperature and orthochlorine substitution. Atmos. Environ. 27, 547–554. Foreman, W.T., Bidleman, T.F., 1985. Vapor pressure estimates of individual polychlorinated biphenyls and commercial fluids using gas chromatographic retention data. J. Chromatogr. 330, 203–216. Gribble, G.W., 1998. Naturally occurring organohalogen compounds. Acc. Chem. Res. 31, 141–152. Gribble, G.W., Blank, D.H., Jasinski, J.P., 1999. Synthesis and identification of two halogenated bipyrroles present in seabird eggs. Chem. Commun., 2195–2196. Halsall, C.J., Lee, R.G.M., Coleman, P.J., Burnette, V., Harding-Jones, P., Jones, K.C., 1995. PCBs in U.K. urban air. Environ. Sci. Technol. 29, 2368–2376. Hawker, D.W., Connell, D.W., 1988. Octanol–water partition coefficients of polychlorinated biphenyl congeners. Environ. Sci. Technol. 22, 382–387. Heeb, N.V., Dolezal, I.S., Bu¨hrer, T., Mattrel, P., Wolfensberger, M., 1995. Distribution of halogenated phenols including mixed brominated and chlorinated phenols in municipal waste incineration flue gas. Chemosphere 31, 3033–3041. Hinckley, D.A., Bidleman, T.F., Foreman, W.T., Tuschall, J.R., 1990. Determination of vapor pressures for nonpolar and semipolar organic compounds from gas chromatographic retention data. J. Chem. Eng. Data 35, 232–237. Iwata, H., Tanabe, S., Sakai, N., Tatsukawa, R., 1993. Distribution of persistent organochlorines in the oceanic air and surface seawater and the role of ocean on their global transport and fate. Environ. Sci. Technol. 27, 1080– 1098. Kan, A.T., Tomson, M.B., 1996. UNIFAC prediction of aqueous and nonaqueous solubilities of chemicals with environmental interest. Environ. Sci. Technol. 30, 1369– 1376. Kenaga, E.E., Goring, C.A.I., 1980. Relationship between water solubility, soil sorption, octanol–water partitioning, and bioconcentration of chemicals in biota. In: Eaton, J.G. (Ed.), Aquatic Toxicology––Third Conference STP 707, American Society for Testing & Materials. Kidd, K.A., Hesslein, R.H., Ross, B.J., Koczanski, K., Stephens, G.R., Muir, D.C.G., 1998. Bioaccumulation of

organochlorines through a remote freshwater food web in the Canadian Arctic. Environ. Pollut. 102, 91–103. Kurz, J., Ballschmiter, K., 1999. Vapour pressures, aqueous solubilities, HenryÕs Law constants, partition coefficients between gas/water (Kgw), n-octanol/water (Kow) and gas/noctanol (Kgo) of 106 polychlorinated diphenyl ethers (PCDE). Chemosphere 38, 573–586. Lei, Y.D., Wania, F., Shiu, W.-Y., 1999. Vapor pressures of the polychlorinated naphthalenes. J. Chem. Eng. Data 44, 577– 582. Li, N., Wania, F., Lei, Y.D., Daly, G.L., 2003. A comprehensive and critical compilation, evaluation, and selection of physical–chemical property data for selected polychlorinated biphenyls. J. Phys. Chem. Ref. Data 32, 1545– 1590. Lyman, W.J., 1982. Octanol/water partition coefficient. In: Lyman, W.J., Reehl, W.F., Rosenblatt, R.H. (Eds.), Handbook of Chemical–Physical Property Estimation Methods. McGraw-Hill, New York, NY, USA. Mackay, D., Di Guardo, A., Paterson, S., Cowan, C.E., 1996. Evaluating the environmental fate of a variety of types of chemicals using the EQC model. Environ. Toxicol. Chem. 15, 1627–1637. Mackay, D., Shiu, W.-Y., Ma, K.-C., 1999. Physical–Chemical Properties and Environmental Fate Handbook. CRC, Boca Raton, FL, USA. May, W.E., Wasik, S.P., Freeman, D.H., 1978. Determination of the aqueous solubility of polynuclear aromatic hydrocarbons by a coupled column liquid chromatographic technique. Anal. Chem. 50, 175–179. Miller, M.M., Ghodbane, S., Wasik, S.P., Tewari, Y.B., Martire, D.E., 1984. Aqueous solubilities, octanol/water partition coefficients, and entropies of melting of chlorinated benzenes and biphenyls. J. Chem. Eng. Data 29, 184– 190. Muir, D.C.G., Wagemann, R., Hargrave, B.T., Thomas, D.J., Peakall, D.B., Norstrom, R.J., 1992. Arctic marine ecosystem contamination. Sci. Tot. Env. 122, 75–134. Mu¨ller, J.F., Haynes, D., McLachlan, M., Bo¨hme, F., Will, S., Shaw, G.R., Mortimer, M., Sadler, R., Connell, D.W., 1999. PCDDs, PCDFs, PCBs and HCB in marine and estuarine sediments from Queensland, Australia. Chemosphere 39, 1707–1721. Mu¨ller, M.D., Buser, H.-R., 1986. Halogenated aromatic compounds in automotive emissions from leaded gasoline additives. Environ. Sci. Technol. 20, 1151–1157. Rappe, C., Kjeller, L.O., Bruckman, P., Hackhe, K.H., 1988. Identification and quantification of PCDDs and PCDFs in urban air. Chemosphere 17, 3–20. Reddy, C.M., Xu, L., OÕNeill, G.W., Nelson, R.K., Eglinton, T.I., Faulkner, D.J., Fenical, W., Norstrom, R.J., Ross, P., Tittlemier, S.A., 2004. Radiocarbon evidence for a naturally-produced, bioaccumulating halogenated organic compound. Environ. Sci. Technol. 38, 1992–1997. Schwarzenbach, R.P., Gschwend, P.M., Imboden, D.M., 1993. Environmental Organic Chemistry. John Wiley & Sons, New York, NY, USA. Sellstro¨m, U., Kierkegaard, A., de Wit, C., Jansson, B., 1998. Polybrominated diphenyl ethers and hexabromocyclododecane in sediment and fish from a Swedish river. Environ. Toxicol. Chem. 17, 1065–1072.

S.A. Tittlemier et al. / Chemosphere 57 (2004) 1373–1381 Shiu, W.Y., Gobas, F.A.P.C., Mackay, D., 1987. Physical– chemical properties of three congeneric series of chlorinated aromatic hydrocarbons. In: Kaiser, K.L.E. (Ed.), QSAR in Environmental Toxicology––II. D. Reidel Publishing Company, Dordrecht, The Netherlands, pp. 347–362. Suzuki, N., Nakanishi, J., 1995. Brominated Analogues of MX (3-chloromethyl)-5-hydroxy-2(5H)-furanone) in chlorinated drinking water. Chemosphere 30, 1557–1564. Tanabe, S., Tatsukawa, R., 1980. Chlorinated hydrocarbons in the North Pacific and Indian Oceans. J. Ocean. Soc. Jpn. 36, 217–236. Tittlemier, S.A., Simon, M., Jarman, W.M., Elliott, J.E., Norstrom, R.J., 1999. Identification of a Novel C10H6N2Br4Cl2 heterocyclic compound in seabird eggs. A bioaccumulating marine natural product?. Environ. Sci. Technol. 33, 26–33. Tittlemier, S.A., Blank, D.H., Gribble, G.W., Norstrom, R.J., 2001. Structure elucidation of four possible biogenic organohalogens using isotope exchange mass spectrometry. Chemosphere 46, 511–517. Tittlemier, S.A., Borrell, A., Duffe, J., Duignan, P.J., Hall, A., Hoekstra, P., Kovacs, K., Krahn, M.M., Lebeuf, M., Lydersen, C., Fair, P., Muir, D., OÕHara, T.M., Olsson, M., Pranschke, J.L., Ross, P., Stern, G.A., Tanabe, S., Norstrom, R.J., 2002a. Global distribution of halogenated dimethyl bipyrroles in marine mammal blubber. Arch. Environ. Contam. Toxicol. 43, 244–255. Tittlemier, S.A., Fisk, A.T., Hobson, K.A., Norstrom, R.J., 2002b. Examination of the bioaccumulation of halogenated

1381

dimethyl bipyrroles in an arctic marine food web using stable nitrogen isotope analysis. Environ. Pollut. 116, 85–93. Tittlemier, S.A., Halldorson, T., Stern, G.A., Tomy, G.T., 2002c. Vapour pressures, aqueous solubilities, and HenryÕs Law constants of some brominated flame retardants. Environ. Toxicol. Chem. 21, 1804–1810. Tittlemier, S.A., Duffe, J., Dallaire, A., Bird, D.M., Norstrom, R.J., 2003a. Reproductive and morphological effects of the proposed natural products halogenated dimethyl bipyrroles on captive American kestrels (Falco sparverius). Environ. Toxicol. Chem. 22, 1497–1506. Tittlemier, S.A., Kennedy, S.W., Hahn, M.E., Reddy, C.M., Norstrom, R.J., 2003b. Naturally-produced halogenated dimethyl bipyrroles bind to the aryl hydrocarbon receptor and induce cytochrome P4501A and porphyrin accumulation in chicken embryo hepatocytes. Environ. Toxicol. Chem. 22, 1622–1631. Wania, F., Dugani, C.B., 2003. Assessing the long-range transport potential of polybrominated diphenyl ethers: a comparison of four multimedia models. Environ. Toxicol. Chem. 22, 1252–1261. Watanabe, I., Kashimoto, T., Tatsukawa, R., 1987. Polybrominated biphenyl ethers in marine fish, shellfish and river and marine sediments in Japan. Chemosphere 16, 2389–2396. Wong, A., Lei, Y.D., Alaee, M., Wania, F., 2001. Vapor pressures of the polybrominated diphenyl ethers. J. Chem. Eng. Data 46, 239–242. Yalkowsky, S.H., 1979. Estimation of entropies of fusion of organic compounds. Ind. Eng. Chem. Fundam. 18, 108–111.