Mass solubility and aqueous activity coefficients of stable organic chemicals in the marine environment: polychlorinated biphenyls

41

Marine Chemistry, 6(1978) 41--53 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

MASS SOLUBILITY AND AQUEOUS ACTIVITY COEFFICIENTS OF STABLE ORGANIC CHEMICALS IN THE MARINE ENVIRONMENT: POLYCHLORINATED BIPHENYLS 1,2

R. N. D E X T E R 3 and S. P. P A V L O U 3'4

Department of Oceanography, University of Washington, Seattle, Wash. 98195 (U.S.A.) (Received March 2, 1977; revision accepted July 7, 1977)

ABSTRACT Dexter, R. N. and Pavlou, S. P., 1978. Mass solubility and aqueous activity coefficients of stable organic chemicals in the marine environment: polychlorinated biphenyls. Mar. Chem., 6: 41--53. The solubilities and aqueous activity coefficients of polychlorinated biphenyls were measured m distilled and sahne water (30/0o sahmty). Solubilities in distilled water ranged from 3 • 10 -4 g/l for dichlorobiphenyls to 6 • 10 -6 g/1 for heptachlorobiphenyls; values in artificial seawater were about five times lower than the corresponding values in distilled water. In both cases, the solubilities decreased regularly with increasing degree of chlorination. The corresponding activity7 coefficients are inversely proportional to the chlorine content and range from 4 • 10 to 4 • 109 in distilled water and from 3 • 108 to 1.5 • 101° in saline water. Both the solubilities and activity coefficients agree well with those predicted from additivity considerations. The physical chemical aspects discussed in this paper can be applied in determining the solubility behavior of other stable organic molecules in the marine environment. .

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INTRODUCTION

Although organic pollution of marine ecosystems is continuously increasing on a global scale, little effort is made to determine the physical chemical processes that effect the distribution of stable but potentially hazardous chemicals in these systems. One of the primary considerations in assessing the extent to which man-made organic compounds accumulate in the marine environment is the characterization of their interaction with seawater. 1 Contribution No. 982 of the Department of Oceanography, University of Washington. This work was supported by the U.S. Environmental Protection Agency, Grant No. R--800362. 2 Abstracted in part from the Ph.D. thesis of R. N. Dexter, University of Washington, Seattle, Wash., 1976. 3 Present address: URS Company, Fourth and Vine Building, Seattle, Wash. 98121, U.S.A. 4 Author to whom inquiries about the paper should be addressed.

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This paper presents a detailed physical chemical framework for computing the solubilities and aqueous activity coefficients of an environmentally significant class of compounds, the polychlorinated biphenyls (Lee and Falk, 1972; Hutzinger et al., 1974; U.S. Congressional Research Service, 1975). T H E O R E T I C A L CONSIDERATIONS

The polychlorinated biphenyls (C12Hm-nCln with n = 1--10) are normally encountered in the aquatic environment as complex assemblages, reflecting their origin from the commercial mixtures. Only a few of the individual components identified in the mixtures are available as pure isomers. In addition, they are all sparingly soluble and tend to form gravitationally stable aggregates in aqueous solutions. As a result of these characteristics, determination of their solubilities is not a trivial problem. Evidence of this is the wide variability in the values reported by previous studies. Solubilities of individual isomers in distilled water have been determined by Wallnofer et al. (1973) and ranged from a high of 1800 pg/1 for a dichlorobiphenyl to 8.8 pg/1 for a hexachlorobiphenyl. Although the magnitude for isomers of the same degree of chlorination, especially at low values, varied considerably, the solubilities showed a fairly uniform decrease with increasing chlorine substitution. A study by Haque and Schmedding (1975) showed similar trends in the solubilities of pure isomers determined in distilled water, but the values were from 3 to 10 times lower than the ones reported b y Wallnofer et al. A typical example of the prevailing inconsistency in the published data is provided by the measurements of the solubility of the commercial PCB mixture, Aroclor 1254. Zitko (1970) measured values ranging between 0.3--3.0 mg/1, while SSdegren (1971), Nisbet and Sarofim (1972) and Haque et al. (1974) reported 4 pg/1, 50 gg/1 and 56 pg/1 respectively. Although the solubilities of chlorobiphenyls would be expected to decrease in seawater due to the "salting o u t " effect, Zitko (1970) did not observe a significant change in magnitude for Aroclor 1254 (0.3--1.5 mg/1). It should be apparent that what has been termed "solubility" by the latter investigators is actually an effective distribution of as many as fifty distinct compounds between an aqueous phase and an organic phase comprised of the chlorobiphenyl mixture. In fact, the " m i x t u r e " concept is inherently misleading; the behavior of each chlorobiphenyl in any system, laboratory or natural, is a function of the physical chemical characteristics of that individual compound. Consequently, it is more appropriate to determine the true solubilities of these individual components, and then use them to calculate the equilibrium total mass concentration of any given chlorobiphenyl mixture. In this manner the thermodynamic significance of the aqueous behavior of each c o m p o n e n t is retained. In practice, their aqueous activity coefficients and mass solubilities can be derived from the equilibrium water concentration of a given Aroclor mixture as follows.

43

The mass concentration of any of the chlorobiphenyl (CB) c o m p o n e n t s in an aqueous solution in equilibrium with liquid PCB mixture can be converted to the corresponding mole fraction. By definition: e Xi-CB(w)

=

e

Ni-CB(w) ~ N ie- C B ( w ) + N ew

(1)

l

where X is the mole fraction and N refers to the number of moles. The subscript i--CB denotes the ith CB c o m p o n e n t and i is an integer. The w denotes water or the aqueous solution and the superscript e refers to the equilibrium values. e Since the solution is dilute in CB, N e >~ .E Ni_CB(w ) and eq.1 can be reduced to the form: e

e Ni-CB(w) Xi_CB(w ) = Nw

(2)

By definition: e

e

m i - CB(w)

Ni-CB(w) = Mi-CB

Y w

and Nw = ~ww

(3), (4)

therefore the equilibrium mole fraction can be expressed in a final form as: e

e

X i _ CB(w ) =

m i - CB(w)

Yw

Vw

Mi-CB

(5)

where m e_ CB(w)/Vw is the equilibrium concentration expressed in units of mass (m) per volume (V). Vw is the molar volume of the water and Mi-CB is the molecular weight of the ith CB component. Following standard physical chemical convention for liquid-liquid interactions (Lewis and Randall, 1961; Tsonopoulos and Prausnitz, 1971) at equilibrium, the activity, a, of the ith CB c o m p o n e n t in the water and PCB phase must be equal; i.e., a/ecB(w) _ a ei-CB(PCB) -

(6)

or, e e e e ~/i- C B ( w ) X i - CB(w) = )' i - CB(PCB)Xi - CB(PCB)

(7)

where 7i-CB e is the equilibrium activity coefficient. The subscripts (PCB) and (w) refer to the values of the standard PCB mixture and aqueous solution, respectively. Since the aqueous and PCB phases are essentially immiscible and the PCB mixture constitutes a nearly ideal CB solution, 7 ie- C B ( P C B ) = 1. The equilibrium activity coefficient can then be expressed as:

44 e

"Yi-CB(w)

xie- CB(PCB) - e X i - CB(w)

(8)

For low solubility compounds, "Yi-CB(w) is a constant at any system temperature and pressure, independent of Xi_CB(w ) (Tsonopoulos and Prausnitz, 1971; McKay and Wolkoff, 1973), i.e., e

~/i-CB(w) = ~/i-CB(w) = constant

(9)

Therefore the mole fraction ratio on the right hand side of eq.8 is also a constant applicable to any system at equilibrium. For Xi_CB(PCB ) = 1, which applies to a pure i--CB phase, the corresponding Xi-CB(w) is b y definition the solubility of the i--CB expressed as the mole fraction: Xiecs(w) =__1 0 Xi-CB(w) = - e Xi_ CB(PCB) ~/i- CB(w)

(10)

0 Conversion of X i_ CB(w) to the eorresponding mass concentration via eq.5, gives: 0

0

mi-CB(w) = X i - C B ( w ) M i - c B - solubility

Yw

(11)

Vw

EXPERIMENTAL Pure commercial PCB mixtures were used for the solubility determinations. Approximately 1.0-ml aliquots of standard Aroclor 1242 were added to 200 ml of prefiltered (glass fiber, Reeve Angel 934AH) distilled water and to 200 ml of artificial seawater of 30 ~ salinity (Kester et al., 1967). Similar aliquots of Aroclor 1254 were added to 2000 ml of distilled water and seawater, respectively. The flasks were stoppered with ground glass stoppers and placed in a cold r o o m at 11.5 + I°C for between 2 weeks and 3 months. The flasks were swirled periodically at a rate sufficient to produce considerable water movement b u t not to disrupt the PCB globule in the b o t t o m of the flask. At the end o f the equilibration period, aliquots of the solutions were removed with pre-wetted glass pipets and rapidly filtered through 2 layers of glass fiber filters to remove any suspended aggregates. The filtered aliquots were extracted with triplicate volumes of 6% ethyl ether in hexane. The filter flasks were also extracted, first with acetone and then with duplicate volumes of 6% ethyl ether in hexane. The solvents were combined and prepared for GC analysis. The filters were separated, freeze-dried and extracted separately by refluxing first in acetone and then in hexane. The solvents were again combined and prepared for analysis. All analyses were performed on a Tracor MT-220 gas chromatograph equipped with a pulse energized high-temperature 6aNi electron-capture detector. The column consisted of a 1.8 m x 2 mm ID Pyrex U-tube packed with 1.5% SP2250/1.95% SP-2401 on 1 0 0 / 1 2 0 mesh Supelcon AWDMCS

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(Supelco, Inc., Bellafonte, Pa.} and was operated isothermally at 200°C. The carrier gas was 5% methane in argon. Inlet and detector temperatures were 225°C and 300°C, respectively. Spectra were recorded on a Westronics MT-22 strip chart recorder and the resolved c o m p o n e n t s quantified by the technique of Dexter and Pavlou (1976). This technique involves the generation of response factors for each spectral c o m p o n e n t based on their responses from precalibrated PCB standards. Values of Xi-CB(PCB)were obtained from flame ionization gas chromatography of the standard Aroclor mixtures, and the Mi_CB quantities were determined from gas chromatography-mass spectrometry (Dexter, 1976). RESULTS

Typical gas chromatographic spectra of Aroclor 1 2 4 2 and 1 2 5 4 are shown in Fig.1. Analysis of the glass fiber filter pairs after filtration showed variable quantities of chlorobiphenyls on the upper filter, but no detectable residues on the lower. Therefore, no correction to the data were made for agglomeration effects. PCB residues were not detected on the flask walls. The equilibrium mass concentrations of the chlorobiphenyl components measured in both distilled and salt water are shown in Table I. The corresponding values for the mixtures, determined simply as the sum of all the c o m p o n e n t values, are also included. The mass solubilities, calculated from

i 0~

c

A [D

o L~ CO Z 0 O~ LU 13::

B 1

16

14

12

10

I

I

6

4

~

TIME (minutes)

Fig.1. Typical gas chromatographic spectra for polychlorinated biphenyl mixtures. A, Axoclor 1242; B, Aroclor 1254. The numbers above the spectral peaks designate the ith chloribiphenyl component.

46 TABLE I Summary of the equilibrium mass concentrations of the components o f A r o c l o r s 1 2 4 2 a n d 1 2 5 4 in d i s t i l l e d w a t e r a n d a r t i f i c i a l s e a w a t e r at o 1 1 . 5 C ( C o n c e n t r a t i o n x 1 0 -5 g/l) Distilled water

Artificial seawater

i

n

1242

1242

4--5 6 7--10 11--12 13--14 15--16 17--18 19--22 23--24 25--27 28 29--31 32--33 34 35 36 37

2 2 3 3 3 4 4 4 ** 5 5 5 6 5 6 7 7

19.1 34.1 29.0 19.4 10.2 5.7 7.0 6.0 2.4

Aroclor 1242 Aroclor 1254

1254 + 0.8 -+ 1 . 2 -+ 1 . 3 -+ 1.1 +- 0 . 6 + 0.3 + 0.5 + 0.4 + 0.2

3.24 2.35 5.60 4.12 1.91 2.93 1.84 0.53 0.75 0.76 0.09 0.11

1 3 2 . 9 +- 8 . 6 2 4 . 2 +- 2 . 9

+ 0.47 + 0.26 + 0.48 -+ 0 . 4 1 -+ 0 . 2 9 + 0.31 + 0.30 -+ 0 . 1 0 + 0.12 + 0.13 +- 0 . 0 2 + 0.02

1.95 5.53 5.36 2.04 1.47 0.82 0.88 0.48 0.16

1254 + 0.12 + 0.20 + 0.38 + 0.12 + 0.12 + 0.09 -+ 0 . 0 7 + 0.06 -+ 0 . 0 2

0.74 0.33 0.83 0.67 0.30 0.51 0.35 0.12 0.14 0.18 0.02 0.03

+ 0.24 -+ 0 . 0 8 + 0.24 + 0.16 + 0.09 + 0.15 + 0.08 -+ 0 . 0 4 +- 0 . 0 5 + 0.07 -+ 0 . 0 1 + 0.02

1 8 . 6 +- 2 . 4 4 . 3 4 -+ 0 . 6 3

* T h e v a l u e s a r e p r e s e n t e d as t h e m e a n s a n d s t a n d a r d d e v i a t i o n s c o m p u t e d from four determinations. * * C o m p o n e n t 2 3 - - 2 4 is a t e t r a c h l o r o b i p h e n y l in 1 2 4 2 a n d a p e n t a c h l o r o b i p h e n y l in 1 2 5 4 .

these data are summarized in Table II. Good consistency and a relatively uniform decrease in solubility with increasing chlorine content are shown. From the information presented in Table II, the total mass of chlorobiphenyls in the aqueous solutions at equilibrium corresponded roughly to the solubility of the median c o m p o n e n t of the source mixture. The aqueous activity coefficients for each c o m p o n e n t in distilled and artificial seawater are presented in Table III. To compare the solubilities and activity coefficients as a function of the degree of chlorination, average values were obtained at each chlorine number, n, by summing the equilibrium concentrations of all chlorobiphenyl c o m p o n e n t s of the same n. Together with the corresponding mole fractions, the n--CB values were calculated similar to the i--CB quantities and are given in Table IV.

47 T A B L E II S u m m a r y o f t h e solubilities o f t h e c o m p o n e n t s o f Aroclors 1242 and 1254 in distilled w a t e r and artificial s e a w a t e r at 11.5°C * (Solubility x 10 -6 g/l) Distilled w a t e r i

n

1242

4--5 6 7- 10 11--12 13--14 15--16 17-18 19--22 23--24 25--27 28 29--31 32--33 34 35 36 37

2 2 3 3 3 4 4 4 ** 5 5 5 6 5 6 7 7

347 +-14 310 +11 128 + 6 115 -+ 6 104 +- 6 58.8-+ 3.2 6 7 . 3 + 4.4 63.8 + 3.8 72.7 + 4.6

Artificial s e a w a t e r 1254

37.47 + 5 . 4 3 67.21+7.39 39.21 + 3.33 24.25+2.43 22.19 + 3.44 20.78 + 3.14 18.78 -+ 2.15 10.13 + 1.92 12.00 + 1.92 9.82 + 1.67 6.92 -+ 1.49 5.79 + 1.48

1242 35.4 -+ 2.13 50.27 +-1.76 23.61+-3.41 12.14-+0.73 15.00+-1.28 8.45+0.89 8.46+-0.68 5.11 +- 0.59 4.85+0.70

1254

7.73+1.24 9.36+-1.10 5.33 + 0.78 3.89+-0.47 3.55 -+ 0.54 3.62 + 0.75 3.52 + 0.29 2.21 +- 0.42 2.25 +- 0.43 2.25 +- 0.43 1.85 -+ 0.62 1.47 -+ 1.09

* The values are p r e s e n t e d as t h e m e a n s and s t a n d a r d deviations c o m p u t e d f r o m four d e t e r m i n a t i o n s . * * C o m p o n e n t 23--24 is a t e t r a c h l o r o b i p h e n y l in 1242 and a p e n t a c h l o r o b i p h e n y l in 1254.

DISCUSSION

The data presented in Tables II and IV show the expected decrease in solubility with increasing degree of chlorination of the solute and ionic strength of the medium. The values for distilled water are compared with those reported in the literature in Table V. The overall agreement is good, indicating the accuracy of the data. In addition, the range of values exhibited by the components with the same n in the Aroclor mixtures is small compared to the corresponding pure isomers. This is consistent with the way the mixtures are manufactured, i.e., the process favors the formation of a limited number of isomers (Sisson and Welti, 1971; Hutzinger, et al., 1974). As a result, both the number of isomers at each n as well as the variations in their physical chemical properties are small. Good support to this argument is given by the fact that the solubilities of the dichlorobiphenyl isomers in distilled water varied by over 2000%

,18 T A B L E III S u m m a r y of the activity coefficients of the c o m p o n e n t s of Aroclors ] 242 a n d 1 2 5 4 in distilled w a t e r a n d artificial s e a w a t e r at 1 1 . 5 ° C * ( A c t i v i t y c o e f f i c i e n t , ~/i-cB(w) × 108) Distilled w a t e r i

n

1242

4--5 6 7--10 11--12 13--14 15--16 17--18 19--22 2 3 - 24 25--27 28 29--31 32--33 34 35 36 37

2 2 3 3 3 4 4 4 ** 5 5 5 6 5 6 7 7

0 . 3 6 + 0.01 0 . 4 0 -+ 0.01 1.11 + 0 . 0 5 1 . 2 4 +- 0.07 1.37 + 0 . 0 8 2.74 + 0.15 2.39 + 0.16 2.53 + 0 , 1 5 2.22+0.14

Artificial s e a w a t e r 1254

4.35 + 0.63 2 . 4 0 +- 0 . 2 6 4.11 + 0 . 3 5 7.24-+0.74 8.11 -+ 1.20 8.66 ± 0.63 9.58 ± 2.28 19.63 ± 3.72 15.00 ± 2.40 20.25 + 3.44 31.47 ± 6.78 70.10 ± 9.60

1242 3.48 + 0.21 2.45 + 0 . 0 9 6 . 0 2 + 0.87 11.72 + 0.70 9.48 + 0.81 19.07 + 2.01 1 9 . 0 4 + 1.53 31.53 + 3.64 33.22±4.79

1254

20.84 + 03.34 17.21 + 0 1 . 0 6 30.23 + 04.42 46.27-+05.59 50.70 ± 07.71 49.72 ± 05.05 51.13 + 08.84 8 9 . 9 9 -+ 1 7 . 1 0 8 0 . 0 0 -+ 1 5 . 8 5 88.40 + 16.89 117.70 ± 19.04 148.10 ± 94.00

* V a l u e s are p r e s e n t e d as t h e m e a n s a n d s t a n d a r d d e v i a t i o n s c o m p u t e d f r o m f o u r determinations. ** C o m p o n e n t 2 3 - - 2 4 is a t e t r a c h l o r o b i p h e n y l in 1 2 4 2 a n d a p e n t a c h l o r o b i p h e n y l in 1 2 5 4 .

(Wallnofer, et al., 1973), while the values for similar components in the 1242 mixture differed by less than 50%. The variations tend to decrease with increasing chlorine substitution, most likely because the number of significantly different isomeric forms is reduced as the available sites for C1 addition are utilized. In most studies, including this one, it is cumbersome to resolve and identify completely all of the c o m p o n e n t s in a sample. However, reasonably accurate n values can be assigned to the c o m p o n e n t s which are separated by the particular GC system utilized (Webb and McCall, 1973, Dexter and Pavlou, 1976). All c o m p o n e n t s of the same n can then be combined to establish the dependence of the behavior of the CB in the sample as a function of the degree of chlorination. Due to the low isomeric variability, this m e t h o d of data reduction is not only expedient b u t retains most of the significant information since the degree of chlorination is the primary molecular variable responsible for the observed behavior of the CB solubilities. The dependence of both the solubility and the activity coefficients on n are presented in Table IV.

49 T A B L E IV S u m m a r y of t h e solubilities a n d a c t i v i t y c o e f f i c i e n t s of t h e n - - C B in distilled w a t e r and artificial s e a w a t e r at 11.5°C * S o l u b i l i t y (x 10 -6 g/l) n

Distilled w a t e r

Artificial s e a w a t e r

2 3 4 5 6 7

3 3 2 . 0 0 -+ 14.0 1 1 9 . 0 0 ± 6.00 5 3 . 3 0 ± 3.90 2 0 . 7 0 ± 2.10 9.94+- 1.44 6.25-+ 1.50

4 5 . 3 0 -+ 2.30 1 8 . 0 0 +- 2.60 7.43+1.05 3.48+0.45 2.23+0.23 1.54±1.03

")'n--CB(w) X l 0 s n

Distilled w a t e r

Artificial s e a w a t e r

2 3 4 5 6 7

0.38 -+ 0.02 1.20+0.06 3.02+0.22 8.70+0.88 20.10+-2.90 3 4 . 8 0 + 8.40

2.72 + 0 0 . 1 4 7.90+ 1.14 2 1 . 7 0 + 3.10 51.70-+ 6.70 89.20+- 9.20 141.00 + 73.00

* T h e values are p r e s e n t e d as t h e m e a n s a n d standard deviations computed from four d e t e r m i n a t i o n s . Values for n = 4 were averaged over t h e t w o s t a n d a r d s . TABLE V C o m p a r i s o n of t h e solubilities of the c o m p o n e n t s of A r o c l o r s 1 2 4 2 a n d 1 2 5 4 w i t h t h o s e o f s o m e p u r e isomers in distilled water* ( S o l u b i l i t y x 10 6 g/l) n

This s t u d y

Wallnofer et al. (1973)

Haque and Schmedding (1975)

2 3 4

3 1 0 - - 3 4 7 (2) 1 0 4 - - 1 2 8 (3) 3 7 - - 7 3 (7)

8 0 - - 1 8 8 0 (4) 78--85 (2) 3 4 - - 1 7 5 (7)

6 3 7 . 0 0 (1) 2 3 8 . 0 0 (1) 26.50(1)

5

12--24 (5)

6 7

9 . 8 - - 1 0 (2) 5.8--6.9 (2)

22--31

(2)

10.30 (1)

8.8

(1)

0.95(1)

* T h e d a t a are p r e s e n t e d as t h e range of o b s e r v e d values. Values in p a r e n t h e s i s i n d i c a t e t h e n u m b e r o f c o m p o n e n t s or isomers measured.

5O loOt

i

\x I0~

10-I

>; 10,2 I-_] Z)

_j

0

I0-~

104¸¸ i

10-61 0 I00

, 'c

200

3 0 400

5 0 600

700

PARACHOR Fig.2. Plots of solubilities versus parachor for some homologous series of hydrocarbons. o, saturated n-alkanes (C~-8 ) ; ' , monounsaturated n-alkenes (C s -7); ~, saturated cycloalkanes (C 5 -8); A, mono-unsaturated cycloalkenes (C 5 -7), ~, chlorinated aromatics (the individual compounds according to decreasing order of the solubility are: monochlorobenzene, 1,2- and 1,3-dichlorobenzene, and p , p ' - - D D T ) , . , polychlorinated biphenyls (n = 2--7); ×, aromatics (listed in order of decreasing solubility are: benzene, toluene, o-xylene, ethylbenzene, 1,2,4-trimethylbenzene, isopropylbenzene, 1,2,3,4-tetrahydronapthalene, 1-methylnapthalene, 2-methylnapthalene, butylbenzene, 2-ethylnapthalene, biphenyl, and 2,4-dephenyl-4-methyl-2-pentene).

The overall accuracy of these values can be assessed by comparing them to what would be anticipated from correlations with data for similar non-polar hydrocarbons. In general, the solubilities for this type of compounds show a logarithmic dependence on the molar volume of the solute within a homologous series (MacAuliff, 1966). This behavior is demonstrated for a number of representative saturated and mono-unsaturated alkanes and cycloalkanes (MacAuliff, 1966), aromatics (Deno and Berkheimer, 1960; MacAuliff, 1966; Eganhouse and Calder, 1976), and chlorinated aromatics (Bowman et al, 1960; Deno and Berkheimer, 1960) in Fig.2. The values for n--CB solubilities obtained for distilled water in this study are also included for comparison. The data are plotted against the parachor, P, which is essentially an effective molar volume corrected to account for solute-solute interactions. This parameter can be quite accurately predicted for most organic c o m p o u n d s from the additive contributions of the constituent molecular moieties (Quayle,

51

II

I0

Q 0 0

9 rn 0 I r"

0 __1

•

0

8 7 6~

`50

I

I

I

2

L

:5

L

n

4

l

,5

I

6

l

7

Fig.3. Plots of the logarithm of the activity coefficients versus chlorine number for the chlorobiphenyls, o, values in distilled water; o, values in artificial seawater. The solid line represents the behavior predicted by additivity considerations.

1953). The linearity of these data within a h o m o l o g o u s series is evident as are the effects on the solubility due to changes in molecular structure. Of particular interest here are the data for the chlorinated aromatic hydrocarbons; despite the paucity of the data, t h e y do describe a similar logarithmic correlation with P. The observed solubilities of the n--CB agree well with this relationship, at least at low values of n. T s o n o p o u l o s and Prausnitz {1971) described similar linear relationships between th e logarithms of the activity coefficients and molecular structure for aromatic c o m p o u n d s . This study included a quantitative estimate of the additive changes in t he value of the activity coefficient as a function of the n u m b e r o f chlorine atoms added to a parent aromatic molecule. Plots of the logarithms of the activity coefficients of biphenyl and the n--CB are shown in Fig.3. The data in b o t h distilled and saline water are nearly linear. For low n, th e distilled water values agree well with those predicted from the computations o f T s o n o p o u l o s and Prausnitz (1971); their data is represented in t he figure by a solid line.

52

F o r b o t h t h e solubility and activity c o e f f i c i e n t data, t h e increasing devia t i o n f r o m linearity at high n p r o b a b l y reflects the high incidence o f chlorine a t o m a d j a c e n c y w h i c h partially masks t h e effects o f t h e a d d i t i o n a l c h l o r i n e atoms. While the solubilities a n d activity c o e f f i c i e n t s o f the CB c o m p o u n d s vary u n i f o r m l y with t h e degree o f c h l o r i n a t i o n , t h e a q u e o u s c o n c e n t r a t i o n o f a n y individual c o m p o n e n t o f a c o m m e r c i a l m i x t u r e d e p e n d s b o t h o n t h e s e parameters and o n its c o n c e n t r a t i o n in the PCB m i x t u r e (Table I). The ranges in the latter c o n c e n t r a t i o n s are usually m u c h greater t h a n the c o r r e s p o n d i n g solubility differences. Thus e q u i l i b r a t e d a q u e o u s solutions, while relatively e n r i c h e d in l o w e r c h l o r i n a t e d CB, have c o m p o n e n t distributions w h i c h still e x h i b i t t h e characteristic PCB spectral p a t t e r n or " f i n g e r p r i n t " . REFERENCES Bowman, M. C., Acree, Jr. F. and Corbett, M. K., 1960. Solubility of carbon-14 DDT in water. J. Agr. Food Chem., 8: 406--408. Deno, N. C. and Berkheimer, H. E., 1960. Activity coefficients as a function of structure and media. J. Chem. Eng. Data, 5: 1--5. Dexter, R. N., 1976. An application of Equilibrium Adsorption Theory to the Chemical Dynamics of Organic Compounds in Marine Ecosystems. Thesis, Dept. of Oceanography, Univ. Washington, Seattle, Wash., 181 pp. Dexter, R. N. and Pavlou, S. P., 1976. Characterization of polychlorinated biphenyl distribution in the marine environment. Bull. Environ. Contam. Toxicol., 16: 477--482. Eganhouse, R. P. and Calder, J. A., 1976. The solubility of medium molecular weight aromatic hydrocarbons and the effects of hydrocarbon co-solutes and salinity. Geochim. Cosmochim. Acta, 40: 555--561. Haque, R. and Schmedding, D., 1975. A method of measuring the water solubility of hydrophobic chemicals: solubility of five polychlorinated biphenyls. Bull. Environ. Contam. Toxicol., 14: 13--18. Haque, R., Schmedding, D. W. and Freed, V. H., 1974. Aqueous solubility, adsorption, and vapor behavior of polychlorinated biphenyl Aroclor 1254. Environ. Sci. Technol., 8: 139--142. Hutzinger, O., Safe, S. and Zitko, V., 1974. The Chemistry of PCB. CRC Press, Cleveland, 269 pp. Kester, D. R., Duedall, I. W., Conners, D. H. and Pytkowicz, R. M., 1967. Preparation of artificial seawater. Limnol. Oceanogr., 12: 176--178. Lee, D. H. K. and Falk, H. L. (Editors), 1972. Perspectives on PCB. Environmental Health Perspective, Experimental Vol. 1. Natl. Inst. Environ. Health Sci, U.S. Dep. Health, Educ. Welfare. U.S. Government Printing Office, No. 1972 0-455-263, pp. 21--38. Lewis, G. N., and Randall, M., 1961. Thermodynamics. (Revised by K. S. Pitzer and L. Brewer.) McGraw-Hill, New York, N.Y., pp. 242--267. MacAuliff, C., 1966. Solubility in water of paraffin, cycloparaffin, olefin, acetylene, cycloolefin, and aromatic hydrocarbons. J. Phys. Chem., 70: 1267--1275. McKay, D. and Wolkoff, A. W., 1973. Rate of evaporation of low-solubility contaminants from water bodies to atmosphere. Environ. Sci. Technol., 7: 611--614. Nisbet, C. T. and Sarofim, A. F., 1972. Rates and routes of transport of PCBs in the environment. In: D. H. Lee and H. L. Falk (Editors), Environmental Health Perspectives, Experimental Vol.1. Natl. Inst. Environ. Health Sci. U.S. Dep. Health, Educ. Welfare. U.S. Government Printing Office, No, 1972 0-455-263, pp. 21--38.

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Quayle, O. R., 1953. The parachors of organic compounds. Chem. Rev., 53: 439--589. Sisson, D. and Welti, D., 1971. Structural identification of polychlorinated biphenyls in commercial mixtures by gas-liquid chromatography, nuclear magnetic resonance and mass spectrometry. J. Chromatogr., 60: 15--32. SiSdegren, A., 1971. Accumulation and distribution of chlorinated hydrocarbons in cultures of Chlorella pyrenoidosa (chlorophyceae). Oikos, 22: 215--220. Tsonopoulos, C. and Prausnitz, J. M., 1971. Activity coefficients of aromatic solutes in dilute aqueous solution. Ind. Eng. Chem. Fundam., 10: 593--600. U.S. Congressional Research Service, 1975. Effects of chronic exposure to low-level pollutants in the environment. Prepared for the Subcommittee on the Environment and the Atmosphere of the Committee on Science and Technology, U.S. House of Representatives. Ninety-Fourth Congress. U.S. Government Printing Office, Washington, D.C., 401 pp. Wallnofer, P. R., Koniger, N. and Hutzinger, O., 1973. Analabs Research Notes, 13: 14--17. Webb, R.G. and McCall, A. C., 1973. Quantitative PCB standards for electron capture gas chromatography. J. Chromatogr. ~ci., 11: 366--373. Zitko, V., 1970. Polychlorinated biphenyls (PCB) solubilized in water by nonionic surfactants for studies of toxicity to aquatic animals. Bull. Environ. Contain. Toxicol., 5:279--285