Environ. Sci. Technol. 1982, 16, 10-14
Kuber, M. V.; Kulkmi, S. B.; Biswas, A. B. 2.Phys. Chem. (Frankfurt am Main) 1958, 17, 155. Voitovich, B. A.; Lozovskaya, N. F. Izv. Akad. Nauk SSSR Met. 1966, 31. Hill, A. E.; Macy, R. J . Am. Chem. SOC.1924, 46, 1132. Leo, A.; Hansch, C.; Jow, P. Y.C. J. Med. Chem. 1976,19, 611. Gross, P. M.; Saylor, J. H. J. Am. Chem. SOC.1931,53,1744. Gross, P. M.; Saylor, J. H.; Gorman, M. A. J . Am. Chem. SOC.1933, 55, 650. Andrews, L. J.; Keefer, R. M. J.Am. Chem. SOC.1949, 71, 3644.
(44) Bohon, R. L.; Claussen, W. F. J. Am. Chem. SOC.1951, 73, 1571. (45) Kurihara, N.; Uchida, M.; Fujita, T.; Nakajima, M. Pestic. Biochem. Physiol. 1973, 2, 383.
Received for review September 18, 1980. Revised manuscript received June 9,1981. Accepted September 28,1981. This work was supported by US.Public Health Grants ES-02400 and ES-00210 from NIEHS and by EPA Cooperative Research CR808046 through the EPA Environmental Research Laboratory at Corvallis, OR.
Prediction Method for Adsorption Capacities of Commercial Activated Carbons in Removal of Organic Vapors Kohel Urano," Shigeakl Omori, and Eijl Yamamoto
Department of Safety and Environmental Engineering, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama-shi, 240 Japan Adsorption isotherms for vapors of 13 organic solvents on 7 commercial granular activated carbons were studied. The isotherms were analyzed by the Dubinin-Polanyi equation, and relationships between the parameters of the Dubinin-Polanyi equation, Woand K,, and properties of the activated carbons were investigated. It was found that W, was approximately equal to 0.055 mL plus the micropore volume, ~ 3 . 2(smaller than 3.2 nm in diameter), and K , of benzene could be approximated to 2.8 X mo12/J2 for various types of commercial activated carbons. From the above results, a prediction method for adsorption capacities of organic vapors on commercial activated carbons was introduced, and the method was confirmed for various conditions. W
Emission of organic vapors from industrial and commercial sources is a cause of photochemical smog and nuisance odors. This certainly needs to be controlled. Recovery of organic vapors can contribute to the conservation of petroleum resources. There are several methods such as condensation, absorption, adsorption, contact oxidation, and incineration for removal and/or recovery of organic vapors. The adsorption method using granular activated carbon possesses many advantages for removal and recovery of organic vapors in low concentrations. Although there are many theories (1-5) concerning adsorption of vapor on activated carbon, the Dubinin-Polanyi equation (1,2)is a simple and practically useful equation for estimation of adsorption capacity for the organic vapor from waste gas on activated carbon. Dubinin (1, 2) reported that the adsorbed amount in liquid volume per unit weight of microporous adsorbent, W, could be shown by the following equation from Polanyi's adsorption potential theory: In ( W / W o )= -KA' A = RT In (Po/P) (1) Here, Wois an apparent limiting amount of adsorption for each adsorbent, K is a parameter for each system of adsorbent and adsorbate, A is an adsorption potential, R is the gas constant, and T is the absolute temperature of adsorption. Po and P are saturated vapor pressure and adsorbed vapor pressure, respectively. Since eq 1 for a standard adsorbate was replaced by eq 2, eq 1 could be In ( W / Wo)= - K , A , ~ (2) 10 Environ. Scl. Technol., Vol. 16, No. 1, 1982
rewritten as eq 3 for any adsorbates on an adsorbent. In ( W / W o )= - ( K , / ~ ~ ) A
K,/K
= A 2 / A,2 = p2 (3)
Consequently, the logarithmic adsorbed amount (In W) could be given by eq 4. Dubinin (2) also reported that In W = In Wo- ( K , / ~ ' ) ( RIn T (P0/P))'
(4)
the affinity coefficient p for adsorption on activated carbon could be approximated by the ratio of molar volumes ( V / V , ) or parachors (P/P,) of an adsorbate to the standard adsorbate, regardless of the activated carbon. Reucroft et al. (6) reported that p could be approximated by the ratio of polarities (ala3 for polar organic adsorbates better than parachors. Therefore, it was thought that the adsorption capacity for a vapor could be calculated from K , and Woof the standard vapor and P and Po of the adsorbed vapor. However, it has not clearly been confirmed that the values of p do not change with the kinds of activated carbon. Relationships between the properties of activated carbon and the values of Woand K , have not been shown either. In this study, adsorption isotherms for various systems of granular activated carbon and organic solvent were investigated. The applicability of the Dubinin-Polanyi equation, eq 1,for various commercial activated carbons was tested. The relationships between the observed values of the parameters, Wo,K,, and p, and the properties of the organic adsorbate and activated carbon are discussed. Further, a practical method of predicting the adsorption capacities for single-solvent vapor under any conditions of temperature and concentration of vapor was introduced by the application of the Dubinin-Polanyi equation. Materials and Methods Seven kinds of commercial granular activated carbons, which had been made from coconut shell, coal, or oil pitch by the steam activation method, were used in this study. Their properties are shown in Table I. Their pore-size distributions were calculated from the adsorption isotherms of nitrogen, and the curves are shown in Figure 1 as relations between pore diameter, d, and cumulative volume of pores smaller than d, ud. Carbon F had been made for use in liquid-phase adsorption, but the other carbons had been made for use in gas-phase adsorption.
0013-936X/82/0916-0010$01.25/0
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Table I. Properties of Commercial Granular Activated Carbons Used sample A B C commercial name
Tsurumi
raw material
coal and coconut shell 1170 0.43 0.82 0.430
Tsurumi HC-8 coconut shell 1270 0.44 0.70 0.470
4GS-S .~
surface area, m*/g packed density, g/cm3 total pore vol, cm3/g micropore vol, cm3/g
Takeda sx coconut shell 1090 0.41 0.94 0.405
Table 11. Properties of Organic Solvents Used As Adsorbates sample no. compd Ma ab 1 2 3 4 5 6 7 8 9 10 11 12 13 a
benzene toluene o-xylene nitrobenzene methyl alcohol ethyl alcohol formic acid ethyl acetate acetone methyl ethyl ketone chloroform carbon tetrachloride trichloroethylene
Molecular weight.
78 92 106 123 32 46 46 88 58 72 119 154 131
6.906 6.955 6.999 7.545 7.879 8.045 6.945 7.098 7.024 6.974 6.903 6.934 6.770
Parameter of Antoine equation.
D
E
F
G
Hokuetsu Y-20 coconut shell 1098 0.45 0.57 0.385
Fujisawa B-CG coconut shell 1240 0.43 0.65 0.440
Fujisawa A coal
Kureha G-BAC oil pitch
840 0.42 0.97 0.325
1000 0.51 0.56 0.380
bb
Cb
doC
1211 1345 1475 2064 1473 1554 1295 1239 1161 1210 1163 1242 1150
221 220 214 230 230 223 21 8 217 224 216 227 230 210
0.900 0.885 0.897 1.223 0.810 0.806 1.244 0.925 0.813 0.826 1.526 1.633 1.497
Parameter of density.
% -
1 0 3 ~ ~ Pled 1.00 1.06 1.19 0.93 1.39 0.84 1.15 0.99 0.45 0.93 0.64 0.85 0.49 1.24 1.06 1.20 0.77 1.10 0.97 1.03 0.89 1.86 1.07 1.92 1.03 1.66
Ratio of parachors. I
?0,6
FOS5 U
c
2 0,4
-
a, L
E 0,3
-52
a,
I
0.2
a,
a 0
,
N2
3
0,l
Air
0
Pore diorneter,d (nm) Figure 1. Pore-size distribution curves of carbon samples.
Thirteen kinds of typical organic solvents whose properties are shown in Table I1 were used for adsorption tests in this study. The adsorption capacities were measured by the gravimetric method with an apparatus shown in Figure 2. An activated-carbon sample of 100-300 mg was put in a mesh basket, and it was then hung with a quartz spring. Gas containing a solvent vapor was introduced to the adsorption part at a flow rate of 1L/min. The concentrations of vapor were controlled with f 2 % accuracy by mixing nitrogen gas and solvent vapor from an evaporator in a water bath. Weight increase of the activated carbon with adsorption of the vapor was detected by a differential transformer, and it was recorded automatically with a precision of f O . l mg.
Results and Discussion Parameters of Dubinin-Polanyi Equation. If eq 1 can be applied for adsorptions of solvent vapors on com-
Flgure 2. Apparatus for adsorption tests by gravimetric method: (1) quartz spring, (2) differential transformer, (3) sample basket, (4) solvent evaporator.
0,2
340 330 320 310
- 60 :0 +-
50
40
+
MO
30 20
Figure 3. Adsorption isotherms of benzene at various temperatures: (0,$, 0)60 'C, (A)40 O C , (Jf, 0)30 'C. (Lower part is a nomograph for obtaining A* from tand PIP,).
mercial granular activated carbons, the logarithmic adsorbed amount (log W) will decrease proportionally with A2 independent of adsorption temperature as shown by Environ. Sci. Technoi., Vol. 10, No. 1, 1982
11
Table 111. Parameters of Eq 1 Determined Experimentally for Various Systems o f Activated Carbon and Organic Solvent carbon 1 0 9 ~ ,mo12/J2 , wo,mL/g P benzene toluene o-xylene nitrobenzene methyl alcohol ethyl alcohol formic acid ethyl acetate acetone methyl ethyl ketone chloroform carbon tetrachloride trichloroethylene
A 2.9 0.485 1.00 1.27 1.42 1.18 0.39 0.62 0.97 1.04 0.82 1.00 0.93 1.09 1.17
n c
"'"I
B
C
D
E
F
2.7 0.525
2.4 0.455
2.9 0.440
3.0 0.495
2.6 0.375
1.00
1.00
1.21 1.37 1.13 0.38 0.61
1.26
1.00 1.25 1.40
0.40 0.63
1.00 1.26 1.44 1.15 0.39 0.61
1.25
0.81 0.97 0.91 1.08 1.16
0.37 0.60 0.93 1.01 0.80 0.99 0.85 1.09 1.10
0.95 0.78 0.96 0.88 1.09 1.14
G 2.6 0.430
mean
1.00 1.25
1.00 1.30 1.37
0.38 0.62
0.39 0.63 0.99 0.98 0.83 1.02 0.89 1.08
1.00 1.26 1.40 1.15 0.39 0.62 0.96 1.00 0.81 0.99 0.89 1.08 1.15
2.73
1.09
I
4
'
2'
'
4'
' 6' ' ~2 ( 1 0 7 J~AIOI~)
8'
'
IO '
'
12 I
'
Flgure 5. Adsorption isotherms for several systems of activated carbon and organic solvent 11: (0)ethyl acetate, (4)acetone, methyl ethyl ketone, (#) chloroform, (#) carbon tetrachlorlde, trichloroethylene; (-) carbon A, (- - -) carbon G.
(8
Flgure 4. Adsorption isotherms for several systems of activated toluene, (A)xylene, (0) nitrocarbon and organic solvent I: (0) benzene, (0)methyl alcohol, (A)ethyl alcohol,) . ( formic acid: (-) carbon A, (- - -) carbon F.
eq 4. The relationships of log W vs. A2 for adsorption of benzene on the several activated carbons were studied at different temperatures, and they are shown in Figure 3. The lower part of Figure 3 shows a nomograph for obtaining A2 from the values of adsorption temperature (t ("C)) and relative pressure (PIP,) of solvent vapor. The slant lines in this nomograph were drawn as relationships of A2 vs. (273 t ) 2for various PIP,, because A2 is proportional to P as constant P/P,, as shown by eq 1. By using this nomograph, one can easily obtain the value of A2from the cross point of the lines for desired t and P/P@ The relationships of log W and A2 seemed to be one straight line for each activated carbon independent of temperature. Consequently, the simple Dubinin-Polanyi equation, eq 1,without correction for adsorption in transitional pores (2) can apparently be applied for the adsorption of benzene vapor on various commercial activated carbons. The linear relationships for adsorptions of the other solvent vapors were also confirmed, as shown representatively in Figures 4 and 5. Benzene was selected as the standard adsorbate in this , /3 for all of the systems study, and the values of W,, K ~ and of activated carbon and organic solvent were obtained from graphs similar to Figures 3-5. They are summarized in Table 111. The limiting adsorbed amount, Wo,seemed to be an approximate constant value for each activated carbon regardless of solvents. Dubinin (2) reported that the value of W,was related to the volume of a "micropore", which was defined as a pore of activated carbon smaller than 3.2
+
12
Envlron. Sci. Technot., Vol. 16, No. 1, 1982
nm in diameter. Here, the relationships of Woand pore volumes of the activated carbons were investigated, and they are shown in Figure 6. It was empirically found that the values of W, were approximately equal to 0.055 mL plus the volume of pores smaller than 3.2 nm in diameter, ~ 3 . 2 for , all of the activated carbons used. Therefore, the values of Wocan be practically predicted from the micropore volume, 113.2, for any activated carbon. Dubinin (2) reported that the values of K~ for benzene to 2.7 X lo4 mo12/J2, would usually range from 1.1 X and they were influenced by the pore-size distribution pattern of micropores of activated carbon. However, the apparent values obtained in this study, without correction for adsorption in transitional pores, were in the range of mo12/J2,namely, (2.7 f 0.3) X 2.4 X 10-"3.0 X mo12/J2. Further, the difference was negligibly small for all of the carbons except only for carbon C, which was made by a specific process for control of surface oxides, and K, was about (2.8 f 0.2) X moI2/J2. This value is slightly larger than those values reported in Dubinin's study with complicated corrections. Nevertheless, the values of K , for many commercial activated carbons can practically be approximated to 2.8 X lo4 mo12/J2without the complicated corrections. The values of /3 were slightly different for the various kinds of activated carbon. However, the differences in 0 were negligible with regard to the actual adsorption process of vapor. In other words, the values of /3 can be approximated by the ratio of parachors of a vapor to the standard vapor, P / P 8 ,for many organic solvents. The value of P, is 204.6 (mL/m~l)(dyn/cm)l/~ for benzene in this study. From the above results, the adsorption capacities for any solvent vapor on any activated carbon, whose pore-size distribution is known, can be predicted under any conditions of temperature and concentration. For example, we can easily obtain the volumetric adsorption capacities,
Table IV. Agreement between Predicted Adsorption Capacities and Observed Data carbon B adsorbate benzene toluene o-xylene nitrobenzene methyl alcohol ethyl alcohol formic acid ethyl acetate acetone methyl ethyl ketone chloroform carbon tetrachloride trichloroethylene
carbon E
adsorption temp, "C
C, g/m3
Q(calcd), g/g
Q(obsd), g/g
C, dm3
Q(calcd1, g/g
Q(obsd), g/g
30 30 30 70 30 30 30 30 30 30 30 30 30
81 32 6.0 4.0 72 47
0.43 0.43 0.44 0.57 0.33 0.37
0.43 0.44 0.44 0.56 0.33 0.38
19 11 10
0.35 0.39 0.42
0.36 0.39 0.42
91 86 18 7.2 62 34
0.44 0.35 0.35 0.40 0.72 0.67
0.45 0.34 0.34 0.39 0.70 0.69
51 33 28 62 44 26 14 31 68
0.27 0.33 0.57 0.40 0.30 0.34 0.44 0.63 0.67
0.28 0.33 0.55 0.40 0.32 0.34 0.43 0.64 0.66
b, c, and a are parameters which can be obtained from handbooks (8-10). From eq 4-8, eq 9 can be obtained. log Q = log W + log dt
+
= log Wo - 2.3(~,//3~)R~TL(Iog ( P o / P ) ) ~log (do - at) I I
.R
/
-
I
I
0.3
I
L
vd
0,4
0,5
(crn3/g)
Flgure 6. Relationshipsof W, and pore volume vdof activated carbon (v, means volume of pore smaller than d nm in diameter).
W , from a graph similar to Figure 3 by the following procedures, if the micropore volume 113.2 is known and the relative pressure PIPo is calculated: (1)Draw a line of log W vs. A2 with a slope of -2.8 X 10-9/p2from a point of log ( I I ~ . ~0.055) on the ordinate intercept. (2) Obtain the value of A2 from t and PIPo by using the nomograph as shown in the lower part of Figure 3. (3) Obtain the value of W from the line of log W vs. A2 and the value of A2. Further, the adsorbed capacities can be predicted merely by calculation, as discussed in the following section. Calculation Method of Adsorption Capacities. In actual vapor removal, the concentration C is usually given in units of g/m3, and the adsorption capacity Q in g/g of carbon. However, in the Dubinin-Polanyi equation, eq 1, the concentration and the adsorption capacity have been given by the vapor pressure P (torr) and the adsorbed volume as liquid, W (mL/g), respectively. The vapor pressure P is given by eq 5 from the ideal gas law, and the P = 0.062(273 + t)C/M (5) saturated vapor pressure Po is given approximately by the Antoine equation (eq 6) at t. The relation between gralog Po E a - b / ( c + t ) (6) vimetric adsorption capacity and volumetric adsorption capacity is given by eq 7. Further, the density of liquid (7) Q = Wd, adsorbate dt (g/mL) at t can be approximated by eq 8. dt II do - at (8) Here, M is the molecular weight (g/mol) of adsorbate, do is the density of adsorbate at 0 "C,and the values of a,
+
+
(9)
t
0.3 5 0.1
+
log ( 1 4 ~0.055)(do- at) - ((4.6 X lo-') X (273 t)2/p2){a - b / ( c + t ) - log 0.062(273 + t)C/IM)'
E
Namely, from the micropore volume ~3.2of activated carbon and from M, a, b, c, do, a, and p of the solvent, the adsorption capacity Q can be calculated by eq 9 for any system of activated carbon, solvent, and temperature. The values of M, a, b, c, do,a,and 9, of all of the organic solvents used are shown in Table 11. From these values, the adsorption capacities were calculated at various conditions by eq 9, and they are compared with observed data in Table IV, representatively. The calculated values agree closely with the observed data. Sansone et al. (11) reported a prediction method of breakthrough time for column adsorption of organic vapor from eq 4 and a pseudo-first-order adsorption rate equation. They concluded that the adsorption rate influenced the breakthrough time when a small amount of activated carbon was used. However, the amount of vapor adsorption in the case of using enough activated carbon could be approximated by the adsorption capacity at equilibrium. Therefore, the maximum adsorption amount for activated carbons in removal of organic vapors could be predicted by eq 9 under various conditions without experiments. In other words, we can evaluate maximum abilities of the activated carbons in the removal of organic vapors without experiments. Further, the maximum treatable volume of waste gas containing an organic vapor, V (m9/kg of carbon), and the minimum amount of activated carbon needed, G (kg of carbon/m3), can also be calculated easily from Q and C by eq 9 and 10. V = 1 / G = lOOOQ/C (10)
Literature Cited (1) Dubinin, M. M.; Zaverina, E. D.; Radushkevich, L. V. Zh. Fiz. Khim. 1947,21, 1351. 1
Dubinin, M. M. "Chemistry and Physics of Carbon"; Walker, P. L., Jr., Ed.; Marcel Dekker: New York, 1966; Vol. 2, p 51. Bering,B. P.; Dubinin, M. M.; Serpinsky, V. V. J. Colloid Interface Sci. 1966, 21, 378. Astakhov, V. A.; Dubinin, M. M.; Romankov, P. G. Teor. Osn. Khim. Tekhnol. 1969, 3, 292. Hasz, J. W.; Barrere C. A., Jr. Chem. Eng. B o g . , Symp. Ser. 1969, 65, 48. Environ. Sci. Technol., Vol. 16, No. 1, 1982
13
Environ. Sci. Technol. 1982, 16, 14-19
Reucroft, P.J.; Simpson, W. H.; Jonus, L. A. J.Phys. Chern. 1971, 75, 3526. Dubinin, M. M.; Plavnik, G. M. Carbon 1968, 6, 183. Lange, N. A. “Handbook of Chemistry”;McGraw-Hik New
York, 1961. Timmermans, J. “Physico-Chemical Constants of Pure Organic Compounds”; Elsevier: Amsterdam, Netherlands,
1950.
(10) Washburn, E. W. “International Critical Tables”; McGraw-Hill: New York, 1926;Vol. 3. (11) Sansone, E. B.; Tewari, Y. B.; Jonas L. A. Environ. Sci. Technol. 1979,13, 1511.
Received for review October 6,1980. Revised manuscript received February 17, 1981. Accepted September 25, 1981.
Empirical Test of the Association between Gross Contamination of Wells with Toxic Substances and Surrounding Land Use Mlchael Greenberg,* Rlchard Anderson, Jennifer Keene, Annye Kennedy, G. William Page, and Sandy Schowgurow
Departments of Urban Studies and Urban Planning, Rutgers University, New Brunswick, New Jersey 08903
To begin to understand where particular groups of toxics are found in the environment, the 10 groundwater wells most contaminated with light chlorinated hydrocarbons were identified from a 408-well sample in New Jersey. Thirty other wells were selected: ten each with the highest levels of pesticides and heavy metals and, as a control group, a clean group of ten wells with nondetectable or the minimum detectable levels of 45 toxic pollutants. Twenty-one categories of land use drawn from aerial photographic surveys were measured for the 10 mi surrounding each site. The pesticide wells showed a relative excess of mixed and evergreen forests and agricultural land uses within 1 mi of the well sites. The light chlorinated hydrocarbon wells exhibited a surfeit of urban land uses within 1 mi of the well sites. The land-use profiles of the heavy-metal wells were not distinct from the clean group. W
Introduction The combination of the failure to consider the long-term impacts of using the environment for a dumping ground for hazardous substances and deliberate criminal activity has become the most serious environmental problem of the 1980s ( I ) . The USEPA and the states are trying to cope with this legacy and at the same time plan for future acceptable sites. Included among USEPA actions are a “cradle-to-grave”hazardous-waste tracking and regulatory process under the Resource Conservation and Recovery Act, litigation under the “imminent-hazard” provision of existing Federal environmental laws, a “Superfund” to provide monies for the cleaning up of the many dangerous sites that have been uncovered, and implementation of emergency control of toxic chemicals threatening navigable waters. At the state level, government activities to combat illicit dumping, particularly when criminal prosecution results, command wide publicity. New Jersey, the study area for the research reported in this paper, exemplifies state government activity against illegal dumpers. A multigovernment strike force has been set up to aid in the detection, investigation, and prosecution of violators (2). This program, which has received heavy USEPA funding because it is viewed as a model for the remainder of the nation, uses numerous legal and scientific methods, including photographic surveillance to detect buried drums and to catch midnight dumpers. Cutting into illicit dumping is a necessary, but not sufficient, means of accounting for all cases of gross hazardous waste contamination. To get a broader perspective on the spatial distribution of hazardous substances in the 14
Environ. Sci. Technol., Vol. 16, No. 1, 1982
Table I. Forty-Five Chemical Substances Identified in Groundwater Samples light chlorinated heavy chlorinated heavy hydrocarbons (17 ) metals ( 9 ) hydrocarbons (19) arsenic methylene chloride BHC-a beryllium methyl chloride BHC-B’ cadmium lindane methyl bromide aldrin copper chloroform chromium dieldrin bromoform heptachlor nickel bromodichloromethane + lead heptachlor 1,1,2-trichloroethylene selenium epoxide 1,1,2,2-tetrachloroethane zinc 1,1,2-trichloroethane toxaphene dibromochloromethane trifluoromethane carbon tetrachloride 1,2-dibromoethane p,p’-DDT meth y oxychlor 1,2-dichloroethane 1,1,1drichloroethane mirex vinyl chloride endrin 1,1,2,2-tetrachloroethylene y -chlordane polychlorinated dichlorobenzene biphenyls trichlorobenzene diiodomethane
environment, it is necessary to step back from the highly visible dumping cases and to explore the relationship between land use and the presence of hazardous substances in the environment. This paper follows this broad-perspective approach and tests three hypotheses: (1)gross organic pesticide contamination of groundwater is associated with agricultural, forest, and horticultural land uses; (2) gross light chlorinated hydrocarbon pollution of groundwater will be found in industrial and commercial areas; and (3) gross heavy-metal contamination of groundwater is found in industrial, commercial, and agricultural areas. To the best of our knowledge this is the first reported attempt to test empirically these hypotheses over a large geographical area.
Data and Methods Two data sets were available from the New Jersey Department of Environmental Protection. The toxic-substances data were selected from a 408-well sample ( 3 , 4 ) . Briefly, the 408 samples are distributed relatively uniformly across the state’s 21 counties. Each county has about 20 samples. Forty-five chemicals were sampled including nineteen heavy organic substances (pesticides), seventeen light chlorinated hydrocarbons (LCHs), and nine heavy metals (Table I). Statistical analyses (factor analyses) of the data disclosed that the chemicals strongly associated by type and each
0013-936X/82/0916-0014$01,25/0
0 1981 American Chemical Society
