Environ. Sci. Technol. 1988,22,382-387
Octanol-Water Partition Coefficients of Polychlorinated Biphenyl Congeners Darryl W. Hawker” and Des W. Connell School of Australian Environmental Studies, Griffith University, Nathan, Queensland, Australia 4 1 11 Octanol-water partition coefficients (KO,) for 13 polychlorinated biphenyl (PCB) congeners were accurately determined by the generator column technique. These values were used to confirm a highly significant linear relationship between log KO, and the logarithm of the relative retention time on a nonselective gas chromatographic stationary phase. The total surface areas (TSA) for all the PCB congeners were determined by assuming planar molecules, van der Waal’s radii for component atoms, and appropriate values for solvent radius, bond angles, and distances. The TSA was highly significantly correlated with log KO,and the relationship used to calculate log KO,values for all the PCB congeners. Further development of these relationships gave an expression for aqueous solubility which can be used to calculate the solubility for those PCB’s where appropriate data are available.
Introduction Polychlorinated biphenyls (PCB’s) were recognized as significant environmental contaminants in 1966, and since that time, their ubiquitous presence in biotic adipose tissues has been established (1,2). There is now considerable interest in evaluating the potential environmental behavior of the PCB’s, and other compounds, by utilization of their physicochemical characteristics. A key parameter in assessing the potential environmental behavior of such lipophilic chemicals is the octanol-water partition coefficient Wow)(3). The determination of KO,is recommended in the OECD chemical hazard evaluation program (4), and it has been used with considerable success in estimating bioconcentration factors, soil and sediment organic carbon-water partition coefficients, toxicities, and aqueous solubilities (5-11). The use of KO,with the PCB’s is limited because inconsistent values have been reported for some PCB congeners while for many of the compounds these values have not been determined. A number of techniques have been used to measure KO, values. The first was the shake-flask method in which the concentrations of the compound are measured in octanol and water, shaken together until equilibrium is attained. However, the water concentrations may be inaccurate due to formation of molecular aggregates and the analytical difficulties inherent in the measurement of the extremely low aqueous equilibrium concentrations (12). Measurements and estimates based upon reverse-phase high-performance liquid chromatography and thin-layer chromatography (RP-HPLC and RP-TLC) have achieved moderate success for other groups of lipophilic compounds but require the use of empirical correction factors in the case of PCB’s (12-17). Reliable and consistent KO,values for a number of PCB congeners have been obtained by the generator column technique, which obviates problems such as colloidal suspensions, absorption, and volatilization of the solute (18,19). With this technique an octanol solution of the compound is sorbed to a solid support in a column, and the quantity of the compound in a mobile phase of water or octanol-saturated water which is passed through is determined (20). The log KO,values of some PCB’s determined by this technique have been shown to be lin382 Environ. Sci. Technol., Vol. 22, No. 4, 1988
early related to the logarithms of their relative retention times (a)on GC analysis with a nonselective (C-87) stationary phase (18) by log KO, = 1.40 log a + 5.54 (1) Although the compounds employed were all ortho substituted except for biphenyl, it would be expected that a and KO,would generally increase with chlorine substitution number, and so this relationship provides a possible means of estimation of KO,values for all 209 PCB congeners, as well as biphenyl. Octanol-water partition coefficients have been correlated with molecular properties such as molar refraction, parachor, and connectivity indices (21-23) and also indirectly estimated from a base value with additive fragmental constants for chlorine or separate constants for chlorine in the ortho, meta, and para positions. Such approaches with PCB congeners have proven relatively unsuccessful. However, some success has been recently achieved in relating log KO,to calculated molar volumes (24). Also, total surface area (TSA), which is a function of molar volume, has been found to have a linear relationship with log KO,for compounds such as polyaromatic hydrocarbons and alkyl- and halobenzenes (23-26). Thus the aims of our work were as follows: first, to measure KO,values for some PCB congeners by the generator column method and to confirm the linear relationship between log KO, and log a;second, to determine a relationship between TSA and log KO,and to use this to predict the log KO,values of all the remaining PCB isomers and congeners.
Materials and Methods The l-octanol used was purchased from Sigma Chemical Co., St. Louis, MO, with a stated purity of >99%. The PCB congeners were obtained from Ultra Scientific Inc., Hope, RI, and the purity as determined by GC analysis was >95%. Water was deionized and then distilled while the n-hexane employed was twice fractionally distilled through a helice-filled glass column of approximately 10 theoretical plate efficiency. The KO,determinations was made with both modified and nonmodified generator column techniques (19, 20). The mobile phase was pumped with a Waters Associates Model 510 HPLC pump at a flow rate of 0.2 mL min-’ connected with stainless steel tubing, 0.051-cm id., to the generator column constructed from stainless steel (48 cm X 0.4 cm id.) and half filled with solid support. The column eluant was collected in a preweighed receiving flask, reweighed, and extracted (efficiency >go%) with a Waters Associates (3-18 reverse-phaseSep-Pak column (19, 27). Aqueous concentrations were then determined by injection of an aliquot (10 pL) of the hexane eluant (5 mL) from the Sep-Pak column into a Tracor Model 560 GC equipped with an electron capture detector (63Ni,350 “C) and linearizer. Peak areas were quantified on a HP 3390A integrator, and concentrations were determined by comparison with the peak areas of standard hexane solutions of the congener of interest. To ensure the highest possible accuracy, fresh standard solutions were regularly made up. Relative retention times (2,4,5-trichlorobiphenyl= 1) of a series of PCB congeners were measured on a 3 % (w/ w)
0013-936X/88/0922-0382$01.50/0
0 1988 American Chemical Society
-
Table I. Logarithms of Octanol-Water Partition Coefficients and Relative Retention Times of Polychlorinated Biphenyls compound 2,2’,6,6’-tetra 2,2’,5,6’-tetra 2,2’,3,3’-tetra 2,3,5,6-tetra 2,3,4,5-tetra 2,3’,4,4’-tetra 3,3’,4,4’-tetra 2,2’,4,6,6’-penta 2,3,3’,4,4’-penta 2,2‘,3,3‘,6,6‘-hexa 2,2’,3,3’,4,5’,6,6’-octa 2,2’,3,3’,4,4’,5,5’-octa 2,2’,3,3‘,4,4‘,5,6,6’-nona
log KO,
log a4
5.48 5.46 5.55 5.94 6.18 6.31 6.21 5.37 5.82 5.76 7.21 7.67 7.52
0.02 0.08 0.24 0.19 0.32 0.35 0.39 0.18 0.63 0.54 0.75 1.00 1.13
8.0
7.0
-D0
6.0
-
5.0
C-87 hydrocarbon (Alltech Associates, Deerfield, IL) on Chromosorb W (SO/lOO mesh) glass column (2.75 m X 0.3 cm id.), isothermally at 270 “C. The series of 13 PCB’s was selected so as to contain a great deal of structural variation and cover a wide range of lipophilicity (see Table I). It included seven tetrachlorobiphenyls with from zero (3,3’,4,4’-) to four (2,2’,6,6’-) ortho-substituted chlorines and also two substituted on one ring only, together with six other congeners containing five, six, eight, and nine chlorine substituents.
Results Table I contains the log Kowand log a values determined for our selected PCB congener series. The reference compound, 2,4,5-trichlorobiphenyl,for the relative retention time data is the same as was used by Miller (18). This compound was not available to us, but its retention time under our gas chromatographic conditions was calculated by utilizing the presence of 2,2/,3,3/,6,6/-hexachlorobiphenyl in both experimental sets of compounds. A plot of log KO,against log a for the experimental data from Table I and Miller’s data is presented in Figure 1. The linear regression equation is log KO,= 1.47 log a + 5.52 (2) r = 0.951 Sy,z= 0.332 This equation is very similar to that derived from Miller’s data (18) (eq 1) and demonstrates a highly significant relationship betwen log KO,and log a. Figure 2 contains the above log KO,data, together with further PCB generator column derived data from Woodburn (19) for a total of 46 congeners (37individual compounds), plotted against the TSA of the molecules with a 0’ dihedral angle between the phenyl rings, on the basis of calculations by Armstrong (28,29). Regression analysis yields
r = 0.959
-
-
Relative to 2,4,5-trichlorobiphenyl.
log KO,= (3.41X 10-’)TSA - 2-20
-
(3)
Sy,x= 0.319
Discussion The theoretical basis for a linear relationship between log KO,and log a has been developed by Wasik et al. (30). The high significance ( r = 0.951, Sy,x= 0.332,n = 30) of the relationship between these parameters with our experimental results for selected diverse PCB congeners suggests that log KO,values for other PCB’s could be estimated with reasonable precision from such a relationship. It must be emphasized however that it would be expected
-
4.0
-1.0
-1.5
0 log
-0.5
0.5
1.5
1.0
2.0
rx
Figure 1. Plot of log KO, versus log a using our experimental data (A)and that of Miller (0)(78) and showing the linear regression line
represented by eq 2.
0
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
Table 11. log KO,Values for PCB Congeners
congener no.
substitution patterna
~ 1 0 - 2 0m2
log KO,
0 1 2 3 4 5 6 7 8 9
biphenyl 2342,2’2,32,3’2,42,4‘2,52,63,3’3,43,4‘3,54,4‘2,2’,32,2’,42,2’,52,2’,62,3,3’2,3,42,3,4’2,3,52,3,62,3‘,42,3’,52,3’,62,4,4’2,4,52,4,62,4’,52,4’,62,3’,4’2,3‘,5’3,3‘,43,3’,53,4,4’3,4,53,4’,52,2’,3,3’2,2’,3,42,2’,3,4’2,2’,3,52,2‘,3,3‘2,2‘,3,62,2’,3,6’2,2‘,4,4’2,2’,4,52,2’,4,5’2,2’,4,62,2’,4,6’2,2’,5,5’2,2’,5,6’2,2’,6,6’2,3,3’,42,3,3’,4’2,3,3’,52,3,3’,5’2,3,3’,62,3,4,4’2,3,4,52,3,4,62,3,4’,52,3,4’,62,3,5,62,3’,4,4‘2,3‘,4,52,3‘,4,5‘2,3’,4,62,3’,4’,52,3’,4’,62,3’,5,5’2,3’,5’,62,4,4’,5-
184.43 195.45 201.95 202.12 200.80 210.34 212.97 213.14 213.14 212.97 206.46 219.47 217.73 219.64 219.47 219.81 215.69 218.50 218.32 211.82 227.86 226.11 228.03 227.86 221.35 230.66 230.49 223.99 230.83 228.74 224.16 230.66 224.16 228.75 230.49 235.25 236.99 235.42 233.33 237.16 230.58 231.47 233.38 233.21 233.21 226.71 223.71 236.19 234.10 236.01 229.51 229.51 235.84 229.34 217.18 243.63 243.63 245.38 245.38 238.87 243.80 241.72 237.13 245.55 239.04 236.24 246.44 246.26 248.18 241.68 246.26 239.76 248.01 241.50 246.43
4.09 4.46 4.69 4.69 4.65 4.97 5.06 5.07 5.07 5.06 4.84 5.28 5.22 5.29 5.28 5.30 5.16 5.25 5.24 5.02 5.57 5.51 5.58 5.57 5.35 5.67 5.66 5.44 5.67 5.60 5.44 5.67 5.44 5.60 5.66 5.82 5.88 5.83 5.76 5.89 5.66 5.69 5.76 5.75 5.75 5.53 5.53 5.85 5.78 5.85 5.63 5.63 5.84 5.62 5.21 6.11 6.11 6.17 6.17 5.95 6.11 6.04 5.89 6.17 5.95 5.86 6.20 6.20 6.26 6.04 6.20 5.98 6.26 6.04 6.20
10
11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 384
TSA,b
Environ. Sci. Technol., Vol. 22, No. 4, 1988
congener no.
substitution patterna
X ~ O - ~ m2 O
log KO,
75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
2,4,4’,62,3’,4’,5’3,3’,4,4’3,3’,4,53,3’,4,5’3,3’,5,5’3,4,4’,52,2’,3,3’,42,2’,3,3‘,52,2’,3,3’,62,2’,3,4,4’2,2’,3,4,52,2’,3,4,5’2,2’,3,4,62,2’,3,4,6’2,2’,3,4’,52,2‘,3,4‘,62,2’,3,5,5’2,2’,3,5,62,2’,3,5,6’2,2‘,3,5‘,62,2‘,3,6,6’2,2’,3,4’,5’2,2’,3,4’,6’2,2’,4,4’,52,2’,4,4’,62,2’,4,5,5’2,2’,4,5,6’2,2’,4,5’,62,2’,4,6,6’2,3,3’,4,4’2,3,3’,4,52,3,3’,4’,52,3,3’,4,5’2,3,3’,4,62,3,3’,4’,62,3,3’,5,5’2,3,3’,5,62,3,3’,5’,62,3,4,4’,52,3,4,4’,62,3,4,5,62,3,4‘,5,62,3’,4,4’,52,3’,4,4’,62,3‘,4,5,5‘2,3’,4,5’,62,3,3’,4’,5’2,3,4,4’,5’2,3’,4’,5,5’2,3’,4’,5’,63,3‘,4,4‘,53,3‘,4,5,5‘2,2’,3,3’,4,4’2,2’,3,3’,4,52,2’,3,3’,4,5’2,2’,3,3’,4,62,2’,3,3’,4,6’2,2’,3,3’,5,5’2,2’,3,3’,5,62,2’,3,3’,5,6’2,2’,3,3’,6,6’2,2’,3,4,4’,52,2’,3,4,4’,5’2,2’,3,4,4’,62,2’,3,4,4’,6’2,2’,3,4,5,5’2,2’,3,4,5,62,2’,3,4,5,6’2,2’,3,4,5’,62,2’,3,4,6,6’2,2’,3,4’,5,5’2,2‘,3,4‘,5,62,2‘,3,4‘,5,6‘2,2’,3,4’,5’,6-
241.85 244.35 251.02 250.85 252.77 254.51 251.02 246.36 248.10 241.60 249.16 247.07 248.99 242.48 242.48 250.90 244.40 250.73 241.60 244.23 244.23 232.06 248.99 244.40 251.79 247.20 251.62 254.12 247.03 234.87 259.41 259.24 261.15 261.15 254.65 254.65 262.90 253.76 256.39 259.41 254.82 250.10 253.93 262.04 257.45 263.78 259.20 259.24 262.04 261.87 255.37 266.63 268.37 262.13 261.96 263.88 257.37 257.37 265.62 256.49 259.12 246.95 264.76 264.76 260.18 260.18 264.59 255.46 258.09 260.00 247.84 266.51 259.29 261.92 260.00
6.05 6.13 6.36 6.35 6.42 6.48 6.36 6.20 6.26 6.04 6.30 6.23 6.29 6.07 6.07 6.36 6.13 6.35 6.04 6.13 6.13 5.71 6.29 6.13 6.39 6.23 6.38 6.16 6.22 5.81 6.65 6.64 6.71 6.71 6.48 6.48 6.76 6.45 6.54 6.65 6.49 6.33 6.46 6.74 6.58 6.79 6.64 6.64 6.74 6.73 6.51 6.89 6.95 6.74 6.73 6.80 6.58 6.58 6.86 6.55 6.64 6.22 6.83 6.83 6.67 6.67 6.82 6.51 6.60 6.67 6.25 6.89 6.64 6.73 6.67
100
101 102 103 104 105 106 107 108 109 110 111 112 113
114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149
TSA,b
Table I1 (Continued) congener no. 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179
substitution pattern‘ 2,2’,3,4’,6,6’2,2’,3,5,5’,62,2’,3,5,6,6’2,2’,4,4’,5,5’2,2’,4,4’,5,6’2,2’,4,4’,6,6’2,3,3‘,4,4‘,52,3,3‘,4,4‘,5’2,3,3’,4,4’,62,3,3’,4,5,5’2,3,3’,4,5,62,3,3’,4,5’,62,3,3’,4’,5,5’2,3,3‘,4’,5,62,3,3’,4’,5’,62,3,3’,5,5’,62,3,4,4‘,5,62,3‘,4,4’,5,5‘2,3’,4,4’,5’,63,3’,4,4’,5,5’2,2’,3,3’,4,4’,52,2‘,3,3‘,4,4’,62,2’,3,3’,4,5,5’2,2’,3,3’,4,5,62,2’,3,3’,4,5,6’2,2’,3,3’,4,5’,62,2’,3,3’,4,6,6’2,2’,3,3’,4,5’,6’2,2’,3,3’,5,5’,62,2’,3,3’,5,6,6’-
TSA: X ~ O - ~ m2 O
249.76 259.12 246.95 267.39 262.81 252.56 275.01 275.01 270.64 276.76 267.62 272.17 276.76 296.54 270.25 271.28 267.79 277.64 273.06 282.23 277.74 273.15 279.48 270.35 272.98 274.89 262.73 272.26 274.01 261.84
1% KO, 6.32 6.64 6.22 6.92 6.76 6.41 7.18 7.18 7.02 7.24 6.93 7.08 7.24 6.99 7.02 7.05 6.93 7.27 7.11 7.42 7.27 7.11 7.33 7.02 7.11 7.17 6.76 7.08 7.14 6.73
congener no. 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209
substitution pattern’ 2,2’,3,4,4’,5,5’2,2’,3,4,4’,5,62,2‘,3,4,4‘,5,6‘2,2’,3,4,4’,5’,62,2’,3,4,4’,6,6’2,2’,3,4,5,5’,62,2’,3,4,5,6,6’2,2’,3,4’,5,5’,62,2’,3,4’,5,6,6’2,3,3’,4,4’,5,5’2,3,3’,4,4’,5,62,3,3’,4,4’,5’,62,3,3’,4,5,5’,62,3,3’,4’,5,5’,62,2’,3,3’,4,4’,5,5’2,2’,3,3’,4,4’,5,62,2’,3,3’,4,4’,5,6’2,2’,3,3’,4,4’,6,6’2,2’,3,3’,4,5,5’,62,2’,3,3’,4,5,6,6’2,2’,3,3’,4,5’,6,6’2,2’,3,3’,4,5,5’,6’2,2’,3,3’,5,5’,6,6’2,2’,3,4,4’,5,5’,62,2’,3,4,4’,5,6,6’2,3,3‘,4,4’,5,5’,62,2’,3,3’,4,4’,5,5’,62,2’,3,3’,4,4*,5,6,6’2,2’,3,3’,4,5,5’,6,6’-
decachlorobiphenyl
TSA: ~ 1 0 - 2 0m2
log KO,
280.37 273.15 275.78 275.78 265.53 272.98 260.81 274.89 264.64 290.61 283.40 286.03 285.14 285.14 293.34 286.12 288.75 278.50 287.87 275.70 277.62 287.87 276.73 288.75 278.50 299.00 301.73 291.48 290.59 304.45
7.36 7.11 7.20 7.20 6.85 7.11 6.69 7.17 6.82 7.71 7.46 7.55 7.52 7.52 7.80 7.56 7.65 7.30 7.62 7.20 7.27 7.62 7.24 7.65 7.30 8.00 8.09 7.74 7.71 8.18
‘Using the numbering system of Zell et al. (40). *With planar molecules.
because it is nonselective and can be operated at high temperatures (31). For small values of log a there is a close correspondencebetween experimental log a values on C-87 and those calculated for Apiezon L (which has McEEeynolds constants close to those of C-87). But with larger log a values there is an increasing disparity (32). Retention times of all PCB congeners on (2-87 are thus difficult to predict from results obtained with Apiezon L and more difficult with more diverse stationary phases. Therefore, the relationship expressed by eq 2 can only be effectively used for estimation of unknown log KO,values, where the relative retention time is measured directly on (2-87 stationary phase. Partition coefficients are related to the free-energy change on transfer between two phases. Also for groups of chemically similar compounds there is much empirical evidence to suggest that log KO,values are related to the aqueous solvent cavity size or the size of the solute molecule (23,33-35). For example, a linear relationship between molar volume (cm3 mol-’) and log KO, has been found for 17 ortho-substituted PCB congeners (27). However, the molar volumes were calculated by the Le Bas method with a constant increment for chlorine regardless of position. Such calculations cannot account for variations in substitution patterns between isomers that have been observed to have marked effect on log KO,(see Table I). Pearlman (36)has indicated that there is in general, little difference between the use of surface area and the use of volume for these correlations. Surface area computations with a range of compounds have proven reliable estimates of log KO,values and are also sensitive to structural variation (24, 26, 35, 37). The experimental log KO,determinations for a series of tetrachlorobiphenyls (Table I) reveal that the values are smallest for the fully ortho substituted isomers and greatest for the isomer with no o-chlorines and extend over
almost 1order of magnitude. To facilitate the comparison of TSA with log KO,and encompass such variation, it is appropriate to accentuate the difference in TSA between these isomers. This was achieved by consideration of the surface areas of PCB molecules in a planar configuration, with a Oo dihedral angle between the phenyl rings. In this configuration, much of the exposed surface area of ortho substituents, particularly chlorine, is reduced by mutual occlusion. It is emphasized that for most PCB congeners this planar conformation is a hypothetical one that cannot exist in reality because of excessive steric ortho-ortho interactions. Surface areas of all PCB congeners have been calculated by Armstrong ( 2 4 2 9 )on the basis of a computer program using the van der Waals radii of component atoms, zero solvent radius, and appropriate bond distances and angles. The interplanar angle can be arbitrarily specified, and thus, an accurate computation of the TSA for all congeners in a planar configuration can be obtained (see Table 11). In addition, we have found using a program originally written by Hermann (QCPE No. 225) (35)that areas comparable to those listed in Table TI are obtained with similar input data. A plot of geherator column derived log KO, values against TSA, in a planar configuration, is shown in Figure 2, yielding a significant linear relationship, expressed by eq 3 (r = 0.959, S,,% = 0.320, n = 46), for PCB’s ranging from the parent biphenyl to decachlorobiphenyl and containing all levels of ortho substitution. The outlying points in Figure 2 do not always represent those congeners for which forced planarity is a poor model. This suggests that this relationship could be used to provide reasonable estimates of previously unknown log KO,values of PCB congeners. The calculated log KO,values of all the PCB congeners are shown in Table 11. It is noteworthy that these data include values for non-ortho-substituted PCB’s, Ehviron. Sci. Technol., Vol. 22, No. 4, 1988 385
which are not present to any significant extent in commercial products but have been shown to be the most toxic (38). The inadequacy of the fragmental constant approach to prediction of log KO,values is revealed by consideration of the TSA data. For example, TSA increases on substitution in the 2-, 3-, and 4-positions of biphenyl are 11.0 X 17.5 X and 17.7 X m2,respectively, and with 2,2’-dichlorobiphenyl, TSA takes into account ochlorine overlap and is not merely the sum of biphenyl and two ortho contributions. In addition, allowance is made for overlap with adjacent chlorine substituents (e.g., 3,4dichlorobiphenyl). However, there are few examples of systematic increases in surface area with chlorine substitution, one being biphenyl, 3-chlorobiphenyl, 3,3’-dichlorobiphenyl, 3,3’,5-trichlorobiphenyl,and 3,3’,5,5‘tetrachlorobiphenyl. TSA calculations thus provide for a greater precision in recognizing subtle variations between PCB congeners. Of the experimentally determined log KO,values, only those for 2,3,4,5-tetra- (6.18) and 2,2’,3,3’,6,6’-hexachlorobiphenyl (5.76) have been measured before, and the values obtained in that study were 5.72 and 6.63, respectively (33). There is little reliable partition coefficient data concerning most PCB’s, and much of that we have used in deriving our correlation. In order to judge the validity and predictive utility of eq 3, however, the calculated log Kowvalue of 4,4‘-dichlorobiphenyl (5.30) may be compared with published values of 5.58 (IO),4.82 (12),4.92 (14),5.36 (In, and 5.33 (19) and that of decachlorobiphenyl (8.18) with previous values of 8.26 (18) and 8.20 (19). Agreement is quite reasonable considering that the partition coefficients differ by 3 orders of magnitude. The aqueous solubility of these compounds is also of interest. Knowledge or reliable estimates of log Kowprovide a method for determination of maximum aqueous solubilities. Relationships between the logarithm of maximum aqueous solubility [log S (mol L-l)] and partition coefficient were originally theorized to be of an inverse linear form (11,24,39). Including a term to account for the crystal lattice interactions of solids, equations of the following general form were proposed: log KO, = -log
”-(
s + 2.303R
1-
%)
- log yo* - log
vo* (4)
where AS, is the entropy of fusion (J K-l mol-l), R is the gas constant (8.314 J K-l mol-l), T M is the melting point (K) of the solid solute, T i s the system temperature (K), yo* is the activity coefficient in water-saturated octanol, and Vo*is the molar volume of water-saturated octanol L mol-’) (33). (126.6 X These derivations, possessing a negative unitary slope, assume a constant value of log yo*. Recently, it has been found that for PCB’s and chlorobenzenes log yw (the aqueous activity coefficient) and hence log S together with log yo* are linearly related to solute molar volume due to increasing size and nonideality (33). On this basis, it has been proposed that log KO,to log S correlations should have a slope slightly greater than -1, in agreement with experimental correlations where the slope is commonly of the order of -0.8 (11,24). Using PCB solubility data from Miller (I@, log KO,is related to log S for these compounds by log KO, = -0.795
2.303R
(1 -
%)]+
0.960 (5)
388
Environ. Sei. Technol., Vol. 22, No. 4, 1988
For compounds that are liquid at the system temperature, the melting point T M is set equal to T and hence the entropic term (ASf/2.303R)(l - TM/T) reduces to zero. Correlating these log S - (ASf/2.303R)(1- TM/T)data with TSA values from Table 11, an expression for solubility in terms of TSA results (r = 0.949, S,,x = 0.464, n = 17): log S = (-4.13 X 10-’)TSA
+(1 - $) + 3.48 2.303R (6)
Assuming the entropy of fusion to be approximately 54.8 J K-l mol-l (18),then the maximum aqueous solubility of a PCB congener can be estimated from its melting point and TSA (Table 11) with eq 6. Calculated solubilities compare favorability to published data. The value for 4,4’-dichlorobiphenyl (1.95 X mol L-l) is in good agreement with literature solubilities of 2.78 X (IO),2.51 X (41),and 3.59 X mol L-l (42). There is similar agreement between the calculated solubility of decachlorobiphenyl (1.62 X mol L-l) and (18), 3.21 X 10-l’ (41),and published values of 1.49 X 8.02 X mol L-I (43).
Conclusions These results indicate that there is a direct linear relationship between log KO,and log a,when a nonselective gas chromatographic stationary phase is used, expressed by eq 2. It is suggested that this relationship could be used to obtain the KO,values for all the PCB congeners if the relative retention times are available. Also, a relationship between log KO,and TSA has been established for a diverse group of PCB congeners by calculating TSA for molecules in which the two phenyl rings are coplanar, Le., eq 3. This equation has been used to calculate the log KO,values for all of the PCB congeners. On the basis of this and other relationships, an expression for water solubility of the PCB’s was developed, Le., eq 6. In addition, it is suggested that this method could be used for prediction of log KO,values for other groups of compounds such as polybrominated biphenyls and polyhalodibenzodioxins and -furans. However, constants for the appropriate equation need to be established initially from experimental log KO,values for a small number of compounds from each group. Acknowledgments We gratefully acknowledge the helpful assistance of David Armstrong, University of Wisconsin, for providing PCB surface area data. Registry No. 1, 2051-60-7; 2, 2051-61-8; 3, 2051-62-9; 4, 13029-08-8; 5, 16605-91-7; 6, 25569-80-6; 7, 33284-50-3; 8, 34883-43-7; 9, 34883-39-1; 10, 33146-45-1; 11, 2050-67-1; 12, 2974-92-7; 13, 2974-90-5; 14, 34883-41-5; 15, 2050-68-2; 16, 38444-78-9; 17, 37680-66-3; 18, 37680-65-2; 19, 38444-73-4; 20, 38444-84-7; 21, 55702-46-0; 22, 38444-85-8; 23, 55720-44-0; 24, 55702-45-9; 25, 55712-37-3; 26, 38444-81-4; 27, 38444-76-7; 28, 7012-37-5; 29, 15862-07-4; 30, 35693-92-6; 31, 15862-07-4; 32, 38444-77-8; 33, 38444-86-9; 34, 37680-68-5; 35, 37680-69-6; 36, 38444-87-0; 37, 38444-90-5; 38, 53555-66-1; 39, 38444-88-1; 40, 38444-93-8; 41, 52663-59-9; 42, 36559-22-5; 43, 70362-46-8; 45, 70362-45-7; 46, 41464-47-5; 47, 2437-79-8; 48, 70362-47-9; 49, 41464-40-8; 50, 62796-65-0; 51, 68194-04-7; 52, 35693-99-3; 55, 74338-24-2; 56, 41464-43-1; 57, 70424-67-8; 58, 41464-49-7; 59, 74472-33-6; 60, 33025-41-1; 62, 54230-22-7; 63, 74472-34-7; 64, 52663-58-8; 67, 73575-53-8; 68, 73575-52-7; 69, 60233-24-1; 70, 32598-11-1; 71, 41464-46-4; 72, 41464-42-0; 73, 74338-23-1; 74, 32690-93-0; 75, 32598-12-2; 76, 70362-48-0; 78, 70362-49-1; 79, 41464-48-6; 80, 33284-52-5; 81, 70362-50-4; 82, 52663-62-4; 83, 60145-20-2; 84, 52663-60-2; 85, 65510-45-4; 86, 55312-69-1; 87,
38380-02-8; 88, 55215-17-3; 89, 73575-57-2; 90, 68194-07-0; 91, 68194-05-8; 92, 52663-61-3; 93, 73575-56-1; 94, 73575-55-0; 95, 38379-99-6; 96, 73575-54-9; 97, 41464-51-1; 98, 60233-25-2; 99, 38380-01-7; 100,39485-83-1;101,37680-73-2;102,68194-06-9;103, 60145-21-3; 106,70424-69-0;107,70424-68-9;108,70362-41-3; 109, 74472-35-8; 110,38380-03-9; 111,39635-32-0; 112,74472-36-9; 113, 68194-10-5; 114,74472-37-0;115,74472-38-1;116,18259-05-7; 117, 68194-11-6; 118,31508-00-6;119,56558-17-9; 120,68194-12-7;121, 56558-18-0; 122,76842-07-4;123,65510-44-3;124,70424-70-3;125, 74472-39-2; 126,57465-28-8;127,39635-33-1;128,38380-07-3; 129, 55215-18-4;130,52663-66-8;131,61798-70-7; 132,38380-05-1;133, 35694-04-3; 134,52704-70-8; 135,52744-13-5; 137,35694-06-5;138, 35065-28-2; 139,56030-56-9;140,59291-64-4;141,52712-04-6;142, 41411-61-4; 143,68194-15-0;144,68194-14-9;145,74472-40-5; 146, 51908-16-8; 147,68194-13-8; 148,74472-41-6; 149,38380-04-0;150, 68194-08-1; 151,52663-63-5;152,68194-09-2;153,35065-27-1; 154, 60145-22-4; 155,33979-03-2;156,38380-08-4;157,69782-90-7;158, 74472-42-7; 159,39635-35-3;160,41411-62-5;161,74472-43-8; 162, 39635-34-2; 163,74472-44-9;164,74472-45-0; 165,74472-46-1; 166, 41411-63-6; 167,52663-72-6;168,59291-65-5; 169,32774-16-6;170, 35065-30-6; 171,52663-71-5;172,52663-74-8; 173,68194-16-1;174, 38411-25-5; 175,40186-70-7;176,52663-65-7;177,52663-70-4;178, 52663-67-9; 179,52663-64-6;180,35065-29-3;181,74472-47-2;182, 60145-23-5; 183,52663-69-1;184,74472-48-3;185,52712-05-7;186, 74472-49-4; 187,52663-68-0;188,74487-85-7;189,39635-31-9; 190, 41411-64-7; 191,74472-50-7;192,74472-51-8;193,69782-91-8; 195, 52663-78-2; 196,42740-50-1;197,33091-17-7;198,68194-17-2;199, 52663-73-7; 201,52663-75-9; 202, 2136-99-4; 203,52663-76-0; 204, 74472-52-9;205,74472-53-0;206,40186-72-9;208,52663-77-1; 209, 2051-24-3; BP, 92-52-4; 2,2‘,6,6‘-CB, 15968-05-5; 2,2‘,5,6‘-CB, 41464-41-9; 2,2’,3,3’-CB, 38444-93-8; 2,3,5,6-CB, 33284-54-7; 2,3,4,5-CB, 33284-53-6; 2,3’,4,4’-CB, 32598-10-0; 3,3’,4,4’-CB, 32598-13-3; 2,2’,4,6,6’-CB, 56558-16-8; 2,3,3’,4,4’-CB, 32598-14-4; 2,2’,3,3‘,6,6‘-CB, 38411-22-2; 2,2‘,3,3‘,4,5‘,6,6‘-CB, 40186-71-8; 2,2‘,3,3’,4,4‘,5,5’-CB, 35694-08-7;2,2’,3,3’,4,4’,5,6,6’-CB,52663-79-3; 1-octanol, 111-87-5.
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Received for review March 3,1987. Revised manuscript received September 21,1987. Accepted November 11,1987. Wegratefully acknowledge the receipt of an Australian Marine Sciences and Technology grant to carry out this work.
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