Environ. Sci. Technol. 1984, 18,587-591
(8) Wakeham, S. G.; Schaffner, C.; Giger, W. Geochim. Cosmochim. Acta 1980, 44, 403-413. (9) Epanhouse, R. P.; Kaplan, 1.R. Environ. Sci. Technol. 1981, 1.5, 310-315. (10) Acheson, M. A,; et al. Water Res. 1976, 10, 207-212. (11) MacKenzie, M. J.; Hunter, J. V. Environ. Sci. Technol. 1979, 13, 179-183. (12) Herrmann, R. Water,Air, Soil Pollut. 1981, 16, 445-467. (13) Hoffman, E. J.; Mills, G. L.; Latimer, J. S.; Quinn, J . G. Can. J. Fish. Aquat. Sci. 1983, 40 (Suppl. 2), 41-53. (14) Hoffman, E. J.; Latimer, J. S.; Mills, G. L.; Quinn, J . G. J. Water Pollut. Control Fed. 1982,54, 1517-1525. (15) Hoffman, E. J.; T,atimer, J. S.; Mills, G. L.;Quinn, J. G. Oct 1982, NOAA Quality Assurance Report on Grant NA80RAD00047, pp 1-18. (16) Mackay, D.;Babra, A.; Shiu, W. Y. C'hemosphere 1980,9, 701-711. (17) Prahl, F. G.; Carpenter, R. Geochim. Cosmochim.Acta 1983, 47,1013-1023. (18) Pierce, R. C.; Katz, M. Environ. Sci. Technol. 1975, 9, 347--353. (19) Latimer, J. S., Graduate School of Oceanography, University of Rhode Island, personal communication. (20) Marsalek, J. Proc. Am. SOC.Civ. Eng. 1976, 564.
(21) Litwin, Y. J.;Anthony, S. D. J. Water Pollut. Control Fed. 1978, 50, 2348. (22) Bedient, P. B.; Lambert, J. L.; Springer, N. K. J . Water Pollut. Control Fed. 1980,52, 2396. (23) Whipple, W.; Hunter, J. V.; Yu, S . L. J . Water Pollut. Control Fed. 1977, 49, 2243. (24) Hunter, J. V.; Sabatino, T.; Gamperts, R.; MacKenzie, M. J. J. Water Pollut. Control Fed. 1979, 5 1 , 2129. (25) Belli, G.; et al. Chemosphere 1983, 12, 517-521. (26) Gordon, R. J. Enuiron. Sci. Technol. 1976, 10, 370-373. (27) Katz, M.; Sakuma, T.; Ho, A. Environ. Sci. Technol. 1978, 12, 909-915. (28) Latimer, J. S. MS Thesis, University of Rhode Island, 1984. (29) Hoffman, E. J., unpublished data, 1983. (30) Pruell, R. J., Graduate School of Oceanography, University of Rhode Island, personal communication, 1983. (31) Gschwend, P. M.; Hites, R. A. Geochim. Cosmochim. Acta 1981, 45, 2359-2367.
Received for review May 16, 1983. Revised manuscript received January 12, 1984. Accepted February 23,1984. This work was funded by the U.S. National Oceanic and Atmospheric Administration through the Office of Marine Pollution Assessment (Grant NA80RAD00047).
Solubility of Organic Mixtures in Water Sujlt Banerjee* Life and Environmental Sciences Division, Syracuse Research Corporation, Syracuse, New York 13210 -
.
- --
--
-
--
The solubilities of several chlorobenzenes and other mixtures in water have been determined. The results varied with the phase of the solute mixture and the hydrophilicity of the components and were interpreted through activity coefficients calculated by the UNIFAC equation. It was found that mixtures of structurally related hydrophobic liquids were near ideal in the organic phase; in the aqueous phase the activity coefficient of a component was unaffected by the presence of cosolutes. Increasing hydrophilicity of the solutes led to deviations from ideality in the organic phase, but these could be largely accounted for by the UNIFAC equation. For mixtures of solids which did not interact, the components tended to behave independently of one another, and their solubilities were approximately additive. The behavior of mixtures of liquids and solids was intermediate between that of liquid mixtures and that of mixtures of solids. The application of these results to the toxicity of organic mixtures in water is discussed. -- - - .-- -- --_ I
-_I_----
The growing number of organic compounds under present or potential regulation has prompted extensive work on structure-activity relationships and on environmental models (1, 2). Present techniques for assessing environmental effects from laboratory studies typically rely on data such as solubility and the octanol-water partition coefficient for the calculation of bioconcentration factors ( 3 , 4 ) ,sediment adsorption coefficients (ij),toxicity (6),and biodegradation rates (7,8). Environmental contaminants, however, are frequently encountered as mixtures, and the behavior of a compound in a mixture may not correspond to that predicted from pure component data. The work of Sutton (9)and others (10, 11) on the solubility of hydrocarbons has shown that the interaction of components __
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_.-_
_"I___
*Address correspondence to this author at the Safety and Environmental Protection Division, Rrookhaven National Laboratory, IJpton, NY 11973. 0013-936X/84/0918-0587$01.50/0
in a mixture can cause complex and substantial changes in the solubilities of its constituents. We have measured solubilities in water of mixtures of liquid components, of solid components, and of both liquid and solid components, and in this paper we present our results and identify behavior typical of each category. In addition we discuss the potential application of our conclusions to the toxicity of organic mixtures dissolved in water. Experimental Section
For the solubilitystudies the substrates (50 mg-2 g) were separately weighed into 25-mL glass tubes to each of which 5-15 mL of distilled water was then added. The tubes were shaken in a water bath maintained at 25 f 0.05 OC for at least 48 h, after which the shaking was stopped and the phases were allowed to separate over 24 h. In some of the mixtures containing solid components, partial or complete liquefaction of the solids occurred at equilibrium. For example, in the mixture containing 1,2,3-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, and water, the solids liquefied to various degrees depending upon the composition of the mixture, as shown in Table VIII. Following equilibration, the water in each tube was sampled at least in duplicate, and the solution was diluted with an equal volume of acetonitrile to prevent any deposition of material and then analyzed by high-pressure liquid chromatography (HPLC). A Waters Associate M6000A pump fitted with either a Lichrosorb RP-2 or an Altex Ultrasphere ODS column and a LDC Spectromonitor I11 detector was used, and the mobile phase consisted of various mixtures of acetonitrile and water. Five replicate determinations of the solubility of chlorobenzene yielded a standard error of 5.470,and a similar degree of uncertainty was associated with the other solubility measurements. Pure component solubilities of all the compounds measured in this study are listed in Table I. Activity coefficients were calculated from composition by the UNIFAC method introduced by Prausnitz and
0 1984 American Chemical Society
Environ. Sci. Technol., Vol. 18, No. 8, 1984 587
nent can be expressed as a fraction of its solubility in its pure form as shown in eq 4, where (xiP), and rep-
Table I. Solubilities in Water of Compounds Studied compd
solubility, mg/L
chlorobenzene 1,2-dichlorobenzene 1,3-dichlorobenzene 1,4-dichlorobenzene 1,2,3-trichlorobenzene 1,2,4-trichlorobenzene 1,3,54richlorobenzene 1,2,3,4-tetrachlorobenzene 1,2,4,5-tetrachlorobenzene 1,2,3,5-tetrachlorobenzene toluene benzyl alcohol ethyl acetate
502 137 143 65.3 18.0 3i.3 6.01 5.92 0.465 5.10 524 42 900 80 000
(4)
resent the solubility and activity coefficient in water respectively of the pure ith component. Equation 4 is more conveniently expressed as eq 5 where C, is the equilibrium
_C, -- ( X J o r g ( Y J o r g ( 7 I P ) a q 8,
molar concentration of the ith component in the mixture and S, is the water solubility of that component in its pure form. Now, if interaction in the aqueous phase is small, then (yJaq = (y,P)aq and eq 5 reduces to eq 6. If the
Table I1 chlorobenzene initial mixture, mg material present in aqueous phase, mg material present in organic phase, mg equilibrium mole fraction (organic phase) equilibrium mole fraction (aqueous phase) (Y)organic phsae (UNIFAC) (Y)aqueousphase (UNIFAC)
benzyl alcohol
87.0 1.15
484 182
85.9
302
CJS,= water 5000 4994 6.0
0.197
0.718
0.086
3.693-5
6.053-3
0.994
1.84 1.3034
0.988 482
co-workers (I,13). In this technique, the activity coefficients is divided into two parts, a combinatorial part which reflects the size and shape of the molecules present and a residual portion which depends on group interactions. Data required for the calculations are van der Waal group volume and surface area and group interaction parameters. These were obtained from the listing provided by Gmehling et al. (13))and a computer program written in BASIC was used for the calculation. For our application, the composition of all components in both the aqueous and the organic phase was required. The concentrations of the organic components in the aqueous phase were measured directly. The concentrations of the organic components in the organic phase were then adjusted for the material dissolved in water. The adjustment was negligibly small for hydrophobic compounds such as the chlorobenzenes but was significant for benzyl alcohol and ethyl acetate. The concentration of water in the organic phase was obtained as the inverse of its activity coefficient at infinite dilution. A sample calculation is provided in Table 11.
Results and Discussion When a hydrophobic liquid is equilibrated with water, its solubility is given by eq 1where xaq and xorgrepresent Xaq = XorgYorg/Yaq (1) the mole fraction of the compound in the aqueous and organic phases, respectively, and yaq and yorgare the corresponding activity coefficients. Since the organic phase is essentially the pure liquid, xog and yo%both approximate unity, and eq 1 reduces to eq 2. In the event that the Xaq = l / T a q (2) organic phase constitutes a mixture of hydrophobic liquids, the solubility in water of the ith component can be written as in eq 3. The saturation concentration of this compo-
588
Environ. Sci. Technol., Vol. 18, No. 8, 1984
(5)
(YJaq
(XJorg(YJ0rg
(6)
mixture is ideal, (yJorg= 1 and eq 6 simplifies to eq 7. C,/S, = ( X J o r g (7) Equations 5-7 therefore represent three progressive levels of approximation. Equation 7 is the simplest and applies to near ideal mixtures, eq 6 includes a correction for the activity coefficient in the organic phase, and eq 5 corrects for activity coefficients in both organic and aqueous phases. Liquid-Liquid Mixtures. Sutton (9),Leinonen and Mackay (IO),and (14) measured the solubilities of hydrophobic mixtures in water and found that eq 7 was generally obeyed. Where deviations occurred they were positive; i.e., measured concentration exceeded values calculated from eq 7 by about 10-20%. These deviations which were not much greater than the experimental uncertainty, were attributed by Leinonen and Mackay to a combination of an increase in the activity coefficient of the component in the organic phase and a decrease in the aqueous phase (IO). In our studies, mixtures containing only hydrophobic components, both hydrophobic and hydrophilic components, and only hydrophilic components were used. The data were analyzed by eq 5 and 7, and activity coefficients required for the former equation were calculated from composition with the UNIFAC method developed by Prausnitz and co-workers (12,13). Briefly, the method dissects solvent and solute into their functional groups, calculates the activity coefficients of these groups, and then reassembles them to yield the activity Coefficients of the parent compounds. I t must be kept in mind that the method is an approximation, as is any group contribution technique, since the contribution of a group in one molecule is not necessarily the same as that in another (12). Our solubility results with various chlorobenzene mixtures are listed in Table 111. In all cases, C / S varied linearly with xorg(r > 0.95) as expected, but the observed values were higher than those calculated from eq 7 by an average of 7 % . No improvement was obtained with the use of eq 5, since for these compounds UNIFAC calculations showed that (yJOrg= 1 and (yJaq = ( Y I ~ ) ~and ~ , therefore eq 5 reduced to eq 7. Sutton also showed that mixtures composed of seemingly unrelated compounds such as m-xylene and hexadecane exhibited near ideal behavior, and he concluded that most hydrocarbon mixtures were likely to be near ideal (9). In order to determine the extent to which a similar situation might apply to other compounds, we equilibrated mixtures containing 1,2,4-trichlorobenzene and either hexane or p-cymene with water and measured the water solubility of the trichlorobenzene. Our results are presented in Table IV, and in most cases, concentra-
Table 111. Solubilities in Water of Mixtures of Liquid Chlorobenzenes 1,3-dichlorobenzene
chlorobenzene CIS 0.131 0.194 0.357 0.357 0.718 0.843 0.926 0.902
Xorg
0.121 0.202 0.312 0.357 0.553 0.710 0.793 0.872
1,2,4-trichlorobenzene
chlorobenzene CIS 0.150 0.443 0.399 0.424 0.664 0.697 0.851
Xorg
0.187 0.335 0.407 0.488 0.565 0.722 0.833 chlorobenzene
CIS 0.027 0.155 0.163 0.341 0.713 0.861
xorg
0.051 0.138 0.152 0.369 0.731 0.790
CIS 0.828 0.672 0.611 0.655 0.439 0.268 0.215 0.155
xotg
0.879 0.798 0.688 0.643 0.447 0.290 0.207 0.128
1,3-dichlorobenzene xotg
0.787 0.709 0.196 0.273 0.140 0.176
CIS 0.908 0.718 0.712 0.644 0.423 0.483 0.269
xorg
0.813 0.665 0.593 0.512 0.435 0.278 0.167
CIS 0.825 0.755 0.201 0.287 0.120 0.188
1,2,44richlorobenzene
CIS 0.195 0.181 0.702 0.410 0.143 0.037
xotg
0.162 0.153 0.652 0.358 0.129 0.034
Table IV. Solubility in Water of 1,2,4-Trichlorobenzenein the Presence of Hexane or p-Cymene
XOrS
0.137 0.314 0.320 0.586 0.136 0.321 0.607 0.634
1,2,4-trichlorobenzene (C/S)obd Yotg 2.60 1.64 1.62 1.15 2.28 1.23 1.09 1.08
0.423 0.406 0.585 0.747 0.339 0.356 0.695 0.466
cosolute 0.356 0.512 0.516 0.671 0.176 0.393 0.664 0.685
hexane hexane hexane hexane p-cymene p-cymene p-cymene p-cymene
nFrom ea 6.
tions expected from eq 7 were exceeded in practice, Le., (C/S)o,,d > xorV Activity coefficient calculations showed that the deviations originated from variations in Y~~~ for the trichlorobenzene with composition, while yaqremained constant and equal to yaqP. Values for yorgare included in Table IV, and incorporation of these results into eq 6 provides calculated concentrations which agree with the experimental data within an average of 1% For mixtures containing one or more hydrophilic components, two additional complications arise. The concentration of water in the organic phase becomes appreciable and increases yorgfor the organic solutes, with the most hydrophobic solutes being the most severely affected. Increased interaction in the aqueous phase also occurs as a result of the increased concentration of the hydrophilic components, and yaqvaries with composition. The importance of these effects is illustrated in the data in Table V which lish the solubilities of mixtures of benzyl alcohol with various cosolutes, along with activity coefficients obtained with the UNIFAC equation. In all cases, the
.
solubility of the more hydrophobic cosolute is less sensitive to variations in composition than is benzyl alcohol. For example, in the benzyl alcohol-chlorobenzene-water system, a change in x,,,(chlorobenzene) from 0.411 to 0.741 results in a corresponding change in (C/S)owof from only 0.904 to 1.07. This occurs because water in the organic phase increases yorgfor the cosolute to a greater extent than it does benzyl alcohol. Thus, as benzyl alcohol is added to the cosolute, the decrease in xorgfor the cosolute is partially offset by an increase in y . Incorporation of the various activity coefficients in T a g e V into eq 5 provides calculated values of C / S , and these exceed experimental results by an average of only 0.2%. While the high degree of agreement is probably fortuitous, the UNIFAC method appears to be well suited for solubility calculations for these types of mixtures. For mixtures containing only hydrophilic components, variations in activity coefficient with changes in composition tend to be lower than those encountered in the preceding examples. This follows from the increased compatibility of the solutes. Our results with a mixture of benzyl alcohol and ethyl acetate provide a case in point, and the solubility data in Table VI can be accommodated by eq 7 with an average deviation of 15%. Correction for activity coefficient variations with eq 5 leads to poorer results in that calculated values for C/S exceed those found in practice by an average of 57%. It is likely that the discrepancy originates from an underestimation of the yaq term, since yaqfor either component in the mixture is substantially lower than it is for the pure component. Solid-Solid Mixtures. The behavior of solid-solid mixtures is much more complex and is poorly understood. The solubility of a hydrophobic solid in water is given by eq 8 where a, b, and c are constants (15),and X is a palog S = aX b(mp) + c (8)
+
rameter such as the total surface area (16),molar volume (17,18), the octanol-water partition coefficient (19,20) or the boiling point (21). Since solubility is dependent upon melting point, it follows that impure compounds which generally have lower melting points than those of pure compounds will have correspondingly higher solubilities. In general, all other factors being equal, a 100 "C difference in melting point translates to a 10-fold difference in solubility. The behavior of solid-solid mixtures when equilibrated with water may range between two extreme situations. Mixtures of noninteracting solids represent one extreme where the components behave independently of one another. Our results on the solubility of mixtures of 1,3,5trichlorobenzene exemplify this situation and are presented in Table VII. At the other extreme are interacting mixtures in which the components are solids but which exist as liquids. Commercial PCB formulations are a case in point, and these mixtures are expected to exhibit the same general behavior as liquid-liquid mixtures with one important difference. Since the components in the mixture are solids when pure and the mixture is a liquid, it is inappropriate to relate Cifor a component in a liquid its solubility in its pure form, without cormixture to Si, recting for the difference in phase. This can be done through eq 8 by converting Si,the solubility of the pure solid, to that of the pure supercooled liquid. Intermediate between the two extremes are mixtures which interact to a degree. Eganhouse and Calder (21) have studied the solution behavior of several binary hydrocarbon mixtures in water, and they have noted that both solubility enhancement and depression can occur. For the most part, these variations were small, although in one case a soluEnvlron. Scl. Technol., Vol. 18, No. 8, 1984 589
Table V. Solubilities in Water of Mixtures of Benzyl Alcohol and Various Cosolutes benzyl alcohol
cosolute: chlorobenzene
xorg
Yorg
Yaq
(c/s)oLwd
(C/s)cdcd"
0.246 0.250 0.297 0.541 0.718
1.43 1.42 1.32 1.04 0.988
562 559 553 509 482
0.463 0.479 0.500 0.709 0.851
0.429 0.435 0.486 0.757 1.00
xorg
Yorg
0.741 0.737 0.686 0.411 0.197
1.10 1.10 1.14 1.45 1.84
benzyl alcohol
Yaq 15500 15400 15200 13900 13000
Yorg
Yaq
(C/s)obd
0.338 0.488
1.36 1.14
552 538
0.514 0.577
(c/s)cdcd'
0.572 0.708
Yorg
Yaq
1.60 1.59 1.15 1.09 0.997
550 555 525 479 467
1.07 1.10 1.04 0.904 0.461
xorg
Yorg
78s
0.647 0.482
1.17 1.38
129000 125000
benzyl alcohol xorg
(C/S)cdeda
1.01 1.01 0.988 0.823 0.531
cosolute: 1,2-dichlorobenzene
xotg
0.239 0.242 0.431 0.486 0.690
(c/s)obsd
(C/S)obsd
(c/s)calcd"
1.28 1.20
1.02 0.917
cosolute: toluene
(c/s)obsd
0.511 0.489 0.627 0.859 0.930
(c/s)calcd"
Xorg
Yorg
Yaq
(c/s)obsd
0.476 0.475 0.647 0.758 1.01
0.745 0.742 0.530 0.467 0.222
1.16 1.17 1.43 1.53 2.02
9680 9780 9240 8420 8180
1.06 1.06 0.984 0.786 0.684
(C/s)cdcd'
1.08 1.07 0.992 1.03 0.663
Calculated from ea 5. Table VI. Solubilities in Water of Mixtures of Benzyl Alcohol and Ethyl Acetate benzyl alcohol
a
ethyl acetate
xorg
Yorg
Yaq
(c/s)obe.d
0.196 0.249 0.639 0.698
1.20 1.13 0.974 0.981
402 406 431 448
0.267 0.300 0.678 0.781
(C/s)cdcd"
xorg
Yorg
Yaq
(c/s)obsd
(C/s)cdcd"
0.400 0.475 0.989 1.05
0.795 0.738 0.287 0.214
1.04 1.07 1.35 1.40
109 110 113 116
0.740 0.700 0.327 0.186
1.14 1.07 0.513 0.386
Calculated from ea 5.
Table VII. Solubilities in Water of Mixtures of 193,5-Trichlorobenzeneand 1,2,4,5-Tetrachlorobenzene 1,3,5-trichlorobenzene
1,2,3-trichlorobenzene
1,2,4,5-tetrachlorobenzene
xorg
c/s
Xorg
0.027 0.057 0.479 0.922
1.02 1.03 1.01 1.01
0.973 0.943 0.521 0.078
CIS 1.09 1.15 0.949 1.08
bility depression of 40% was observed. The authors have attributed this behavior to solute-solute interactions or to the formation of solid solutions. We report in Table VI11 an example of interacting solids. In this illustration, the components are solids when pure but form semisolids or liquids when mixed in the presence of water. Liquefaction through mixing has two opposing effects on solubility. The solubility is raised as a result of a melting point depression in accordance with eq 8. On the other hand, since components in liquids interact and < 1, the solubility is depressed. Both components in Table VI11 are low melting, and the solubility enhancement resulting from a melting point depression will be small. Hence, the predominant effect of mixing will be a reduction of solubility, as observed. Liquid-Solid Mixtures. Mixtures of liquids and solids can exhibit complex behavior which varies with the nature and proportion of liquid and solid in the mixture. If the liquid components in the mixture dissolve the solid components, then the mixture behaves as a typical liquidliquid mixture. This is borne out by the data shown in Table IX which represent the solubilities of mixtures of chlorobenzene (liquid) and 1,2,4,5-tetrachlorobenzene 590
Table VIII. Solubilities in Water of Mixtures of 192,3-Trichlorobenzeneand 1,2,3,4-Tetrachlorobenzene
Environ. Sci. Technol., Vol. 18, No. 8, 1984
1,2,3,4-tetrachlorobenzene
Xorg
c/s
xorg
c/s
phase
0.920 0.642 0.535 0.349 0.143
0.907 0.928 1.00 0.680 0.634
0.080 0.358 0.465 0.651 0.857
0.543 0.693 0.475 0.862 0.821
solid liquid liquid semisolid semisolid
~~~~
~~
~
~
Table IX. Solubilities in Water of Mixtures of Chlorobenzene and 1,2,4,5-Tetrachlorobenzene chlorobenzene Xorg C/S 0.9941 0.990 0.977 0.969 0.913 0.836 0.659 0.320 0.127 0.0521
1.00 1.07 0.973 0.957 0.957 0.927 0.900 0.834 0.804 0.797
1,2,4,5-tetrachlorobenzene xorg
CIS
0.0059 0.010 0.023 0.031 0.087 0.164 0.341 0.680 0.873 0.948
0.180 0.397 0.664 1.12
1.24 1.16 1.12 1.00
phase liquid liquid liquid liquid liquid liquid liquid liquid liquid liquid
+ solid + solid
+ solid + solid
+ solid
(solid). For the mixture where the mole fraction of tetrachlorobenzene ranges between 0.0059 and 0.087, the mixture is a homogeneous liquid, and the concentration of tetrachlorobenzene in water increases proportionately with the mole fraction, as expected. However, as the proportion of tetrachlorobenzene in water increases further
in the mixture, phase separation occurs, the concentration of tetrachlorobenzene in water reaches a constant maximum, and the two components tend to behave independently of each other. The liquid mixtures in Table M can be shown to be near ideal if the melting point correction referred to in eq 8 is taken into account. The melting point of the tetrachlorobenzene is 139 "C,and if b in eq 8 is assigned a value of -0.01 (15,16),then the solubility of the supercooled tetrachlorobenzene should be 25 times greater than that of the pure solid. Hence, the C / S values in Table IX should exceed the correspondingly x, terms by a factor of 25 if eq 7 is obeyed. Experimentalfy, a factor of 30 is obtained. Conclusions
Our findings demonstrate that the solubility in water of liquid mixtures is affected by the composition of the mixture, whereas those of solids are relatively independent of composition. Mixtures of structurally related liquids display near ideal behavior, and their solubilities are adequately defined by eq 7. Deviations from ideality occur with mixtures of great diversity, but these may largely be accounted for by the UNIFAC equation. The dependence of the solubilities of mixtures of liquids and solids on composition is complex and varies with the degree of interaction of the components. These conclusions are of particular relevance to toxicity studies in that they can be used to estimate limiting toxicities of mixtures. Consider, for example, a mixture of hydrophobic liquid solutes, only one of which is toxic. The concentration of the toxicant in a saturated solution prepared from the mixture will be lower than that of saturated solution obtained from the pure toxicant. Hence, from a purely physicochemical viewpoint, the toxicity of the mixture-derived solution will also be lower than that obtained from the pure toxicant. In other words, in the absence of biological interaction, the toxicity of a saturated solution derived from a mixture of liquids will be less than that of a corresponding saturated solution obtained from ita most toxic component. The opposite argument applies for solids since their solubilities are roughly additive. For these mixtures, toxicities, should also be additive, and the toxicity of a solution prepared from a mixture of solids will exceed that of a solution obtained from its most toxic component. Preliminary support for these relationships are available and have been described (22). Registry No. Chlorobenzene, 108-90-7; 1,2-dichlorobenzene, 95-50-1; 173-dichlorobenzene, 541-73-1; 1,4-dichlorobenzene,
106-46-7; 1,2,3-trichlorobenzene,87-61-6; 1,2,4-trichlorobenzene, 120-82-1; 1,3,5-trichlorobenzene, 108-70-3; 1,2,3,4-tetrachlorobenzene, 634-66-2; 1,2,4,5-tetrachlorobenzene,95-94-3; 1,2,3,5tetrachlorobenzene, 634-90-2; toluene, 108-88-3;benzyl alcohol, 100-51-6; ethyl acetate, 141-78-6; hexane, 110-54-3; p-cymene, 99-87-6.
Literature Cited Baughman, G. L.; Lassiter, R. ASTM Spec. Tech. Publ. 1978, STP 657. Mackay, D.; Paterson, S. Environ. Sci. Technol. 1981,15, 1006. Neely, W. B.; Branson, D. R.; Blau, G. E. Environ. Sci. Technol. 1974, 8, 1113. Mackay, D. Environ. Sci. Technol. 1982, 16, 274. Karickhoff, S. W.; Brown, D. S.; Scott, T. A. Water Res. 1979, 13, 241. Craig, P. N.; Enslein, K. In "Hazard Assessment of Chemicals"; Saxena, J.; Fisher, F., Eds.; Academic Press: New York 1981. Yonezwa, Y.; Urushigawa, Y. Chemosphere 1979,8, 139. Banerjee, S.; Howard, P. H.; Rosenberg, A.; Dombrowski, A. E.; Sikka, H.; Tullis, D. L. Environ. Sci. Technol. 1984, 18,416-422. Sutton, C. Ph.D. Thesis, Florida State University, 1974. Leinonen, P. J.; Mackay, D. Can. J. Chem. Eng. 1973,51, 230. Eganhouse, R. P.; Calder, J. A. Geochim. Cosmochim. Acta 1976, 41, 55. Fredenslund, Aa.; Jones, R; Prausnitz, J. M. AIChE J. 1975, 21, 1086. Gmehling, J.; Rasmussen, P.; Fredenslund, Aa. Ind. Eng. Chem. Process Des. Dev. 1982, 21, 118. Tewari, Y. B.; Martise, D. E.; Wasik, S. P.; Miller, M. M. J. Solution Chem. 1982, 11, 435. Pearlman, R. S.; Yalkowsky, S. H.; Banerjee, S. J. Phys. Chem. Ref. Data, in press. Yalkowsky, S. H.; Valvani, S. C. J. Chem. Eng. Data 1979, 24, 127. Lindenberg, A. G. C. R. Hebd. Seances Acad. Sci. 1956,243, 2057. Lande, S. S.; Banerjee, S. Chemosphere 1981,10, 751. Hansch, C.; Quinlan, J. E.; Lawrence, G. L. J. Org. Chem. 1968, 33, 347. Banerjee, S.; Yalkowsky, S. H.; Valvani, S. C. Environ. Sci. Technol. 1980,14, 1227. Almgren, M.; Griesser, F.; Powell, J. R.; Thomas, J. K. J. Chem. Eng. Data 1979,24, 285. Sugatt, R. H.; O'Grady, D. P.; Banerjee, S. Chemosphere 1984, 13, 11.
Received for review May 19,1983. Revised manuscript received November 7, 1983. Accepted February 27, 1984. Research supported by U.S. EPA Grant R808613.
Environ. Sci. Technol., Vol. 18, No. 8, 1984 591
