Environ. Sci. Techno/. 1995, 29, 1401- 1406
Partition of Nottpolar Organic Pollutants from Water to Soil and Sediment Organic Matters DANIEL E. KILE AND CARY T. CHIOU* U S . Geological Survey, Box 25046, MS 408, Denver Federal Center, Denver, Colorado 80225
HUAIDONG ZHOU Water Quality Research Center, Ministry of Water Resources, Beijing 100044, People’s Republic of China
H U I LI A N D OUYONG XU Department of Environmental Science and Engineering, Nanjing University, Nanjing 21 0093, People’s Republic of China
The partition coefficients (KO,)of carbon tetrachloride and 1,2-dichlorobenzene between normal soil/sediment organic matter and water have been determined for a large set of soils, bed sediments, and suspended solids from the United States and the People’s Republic of China. The KO, values for both solutes are quite invariant either for the soils or for the bed sediments; the values on bed sediments are about twice those on soils. The similarity of KO, values between normal soils and between normal bed sediments suggests that natural organic matters in soils (or sediments) of different geographic origins exhibit comparable polarities and possibly comparable compositions. The results also suggest that the process that converts eroded soils into bed sediments brings about a change in the organic matter property. The difference between soil and sediment KO, values provides a basis for identifying the source of suspended solids in river waters. The very high KO, values observed for some special soils and sediments are diagnostic of severe anthropogenic contamination.
Introduction Sorption to soils and sediments is probably the most influential factor on the transport and fate of organic contaminants in the environment (1). The organic matter and mineral matter in soil and sediment are known to exhibit distinct contributions to the sorption of nonionic organic compounds (2-14); the soillsediment organic matter (SOM) functions as a partition medium, and the mineral matter functions as an adsorbent (2-7). For relatively nonpolar solutes in soillsediment-water systems, where a significant SOM content is present, the solute partition in SOM predominates over adsorption on mineral matter because of strong suppression by water of solute adsorption on polar mineral surfaces (2-7). In such systems, the solute sorption isotherm exhibits a high linearity over a wide range of relative concentrations (ratios of equilibrium solute concentrations to solute water solubilities). For polar solutes, where mineral adsorption may be less effectively suppressed by water, the partition to SOM may not predominate at very low relative concentrations because one cannot exclude the possibility of significant unsuppressed mineral adsorption (15). Because of the predominance in sorption of relatively nonpolar solutes by partition to SOM, the partition coefficient of a nonpolar solute between SOM and water (Kom)would depend on SOM composition and particularly on its polarity. An alternative partition coefficient commonly used is KO,,which is based on the soil/sediment organic carbon content instead of the SOM content. In light of the expected dependence of Komor &, on SOM composition and polarity, it is essential to determine the variability in SOM medium properties between soils and between sediments that affect the partition coefficient. The degree of variation in Grn or &,will reveal whether the sorptive behavior of individual soils (or sediments) needs to be studied separately. Although some information is available in the literature on the variability of soil &, values for selected solutes (16, 13, the KO,data for given solutes are taken from a relatively small combined set of soil samples analyzed by different experimental procedures. On the basis of the combined literature KO,data for some solutes, Kenaga and Goring (16) concluded that the &, variation between soils is generally less than a factor of 3-4. Mingelgrin and Gerstl (I 7 ) indicated that the&, could vary by as large as a factor of 10, based on the selected &, values of some pesticides on soils. In studying the effect of organic matter compositionlpolarity on KO,of nonpolar solutes, Rutherford et al. (18) estimated the &, variation between soils to be less than a factor of 3 on the assumption that the (0 N) /Cratio in SOM of ordinary soils does not vary widely. Because different experimental procedures contribute to KO, variation, especially in studies involving very low SOM contents (It?), measurements ofthe sorption data from a large set of soils and sediments with significant SOM contents by use of consistent and rigorous analytical methods are essential to the determination of &, variation. Moreover, since no comprehensive studies have been conducted previously to compare soil and sediment KO, values, it would be of considerable interest to determine whether a significant difference in SOM medium properties
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VOL. 29, NO. 5, 1995 I ENVIRONMENTAL SCIENCE &TECHNOLOGY
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(i.e., composition and polarity) exists between soils and sediments. The partition data of nonpolar solutes with SOM should facilitate the detection of this difference, if any, because the solubility of nonpolar solutes is sensitive to SOM medium polarity (18)and because the adsorption of such solutes on soil/sediment minerals should be most effectivelysuppressed bywater (15). The latter findingwill reveal whether soils and sediments can be treated indiscriminately in their sorption of organic contaminants. With the preceding consideration, we measured the I(Oc values of two relatively nonpolar solutes, carbon tetrachloride (CT) and 1,2-dichlorobenzene(DCB),on32 normal soils and 36 bed sediments collected from widely diverse geographicregions in both the United States and the People's Republic of China. To reduce the uncertainty of the sorption coefficients, only soils and sediments with organic carbon contents greater than 0.1%were used. The resulting GCdata are analyzed statistically to obtain the average KO, values and their standard deviations between soils and between sediments. Also determined are the values of these two solutes on several river-suspended solids and hydrocarbon-contaminatedsoils and sediments. The latter values are compared with the averages of normal soil and sediment GCvalues for identifying the likely source of suspended solids in river water and for illustrating the influence of severe hydrocarbon contamination in soils/ sediments on solute partition behavior.
Experimental Section Materials. Carbon tetrachloride (CT) (reagent grade, with a purity of 99.9%) and 1,2-dichlorobenzene (DCB) (HPLC grade, 99%) were purchased from Aldrich Chemical Co. and used as received. All U.S. soils and some Chinese soils (soils 18-21) were taken from the A horizon of the soil profile. All other Chinese soils were taken from regions about 1 m below the land surface to minimize the impact of agricultural practice; no record of the soil-layer classification was established. Bed sediments were taken from the top 0-20 cm of the sediment surface. Sediment samples include those from rivers, freshwater lakes, and marine bay/ harbors. Soil and sediment samples were dried, ground, and homogenized to pass a 35-mesh sieve (U.S. samples) or a 200-mesh sieve (Chinese samples). A list of sample sources and their organic carbon (OC) contents is given in Table 1. The OC contents of studied soils and sediments, except those indicated below, were measured by a hightemperature oxidation method using a Leco instrument (19). The OC contents of a few Chinese soils (soils 18-21) and bed sediments (sediments 16, 18,19,21,and 22) were analyzed by the dichromate oxidation method (20).Both analyses gave results reproducible within f 5 % . Soil and sediment samples with OC < 0.1% were excluded from being used in sorption experiments. Five river-suspended solids were also collected for sorption experiments. Suspended solids were collected in June 1989 from the Illinois River (Hardin, IL) during a lowto-normal river flow and from the Missouri River (Herman, MO) during a moderately high flow. Suspendedsolids from the Mississippi River (Thebes, IL, and Saint Louis, MO) were collected during a high river flow in June 1990. The samples were collected at regular intervals across the channel at a depth of 5 m or one-half of the water depth, whichever was smaller, by a discharge-weightedpumping method (211, where the volume of water with suspended solids at a given vertical below the water surface was 1402 m ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 5,1995
pumped in proportion to the fraction of total water discharge at that vertical. The collected water was processed by filtration through a 63-pm sieve to remove the sand fraction, followed by continuous-flow centrifugation at 15 000 rpm in a 10.5 cm diameter x 71.1 cm long stainless steel cylinder, with a flow rate of 2 Llmin (22). This procedure was calculated to give a particle size cutoff of 0.2 ,um based on the density of hydrated minerals (23). The samples were dried and homogenized. The suspended solid from the Yellow River, near Zhengzhou, Henan, People's Republic of China, was collected in August 1991 during the high-flow season from a depth of 0.5 m below the water surface using a cylindrical sampling bucket (about 2 L in volume) at three different sites that were nearly evenly distributed across the river channel. The water samples from the three sites were pooled, and the suspended solids were separated by gravitational settling over night. The supernatant was then filtered by a 0.45-pm sieve, and the solids collected were combined with those from the earlier separation. The solid sample was dried and ground to pass a 200-meshsieve. The OC contents of all suspended solids were analyzed by the high-temperature oxidation method (19).
The surface areas of soil and bed sediment sampleswere measured by standard BET-(N*)method, using a Gemini 2360 surface area analyzer (Micromeritics, Norcross, GA), The results are shown in Table 1. Sorption Experiments. In sorption experiments, 2-5 g of soils or sediments was added to 20-24 mL of 0.005 M CaCI2aqueous solution. Various quantities of CT or DCB in stock methanol solutions were introduced by a syringe into soillsediment-water slurries;the amount of methanol in the slurries ranged from 5 to 50 pL and was assumed to have a negligible effect on solute equilibrium behavior. The slurries were mixed on a mechanical mixer for 2-3 days to attain equilibrium at room temperature (24f 1"C);separate studies showed that the solutes reached equilibriumwithin 2 days. After equilibrium, solid and aqueous phases were separated by centrifugation at 3000g (18). Solutes in aqueous phase were extracted with hexane and quantified by gas chromatography using either a flame ionization detector or an electron capture detector. Solid-phase solute concentrations were achieved by extracting the solid samples with 1:4 acetone/hexane mixtures for 1-2 days and similarly quantified by gas chromatography. A correction was made for the amount of solute retained by residual water in the solid sample. The amount of solute sorbed per unit weight of solid (Q) was plotted against the equilibrium solute concentration (CJ in water to construct the isotherm. The organic carbon-based sorption coefficient (Koc)of the solute was obtained by normalization of the slope of the isotherm (&) to the organic carbon fraction (foe) of the solid. Isotherms for both carbon tetrachloride and 1,2-dichlorobenzeneon most samples were extended to C, values near or greater than half of solute solubility in water (&I. Sorption experiments were performed in both the U.S. Geological Survey laboratory in Arvada, CO, and in the laboratory of Department of Environmental Science, Nanjing University, using essentially the same procedures and analyticalmethods. The sorption data generated in Nanjing University are those of the four Chinese soils and five sediments mentioned previously, with the rest established in the U.S. Geological Survey.
TABLE 1
Studied Soils and Sediments, Respective Surface Areas (SA) (m2/g), Organic Carbon Contents (OC), and Measured Partition Coefficients (&J of Carbon Tetrachloride (CT) and 1,2=Dichlorobenzene (DCB) no.
source
SA
Yo oc
Lo CT
7.85
52 53 63 58 57 67 61 53 45 65 49 65 59 68 74 68 54 67 53 61 55 53 64 70 61 62 59 66 66 64 55 62
263 277 319 248 230 308 261 263 223 318 252 296 340 344 407 383 262 288 327 236 253 257 306 313 315 295 264 31 5 275 293 257 304
66 103 116 90 94 87 91 109 119 119 112 105 107 106 106 117 93 103 94 101 95 112 101 106 112 92 116 92 96 112 91 108 103 107 101 93
30 1 476 572 444 44 1 370 387 534 499 549 536 516 532 532 551 553 420 557 554 455 545 589 477 599 542 437 555 451 47 4 535 466 584 499 526 539 487
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Soils Burleigh County, ND (U.S. EPA ref soil 2) Oliver County, ND (U.S. EPA ref soil 3) Pierre, SD (US. EPA ref soil 7) west-central Iowa (US. EPA ref IO) Manchester, OH (US. EPA ref soil 12) Columbus, KY (US. EPA ref soil 19) Anoka, M N Piketon, OH Marlette soil, East Lansing, MI Spinks soil, East Lansing, MI Elliot, IL (International Humic Substances Society ref soil) Woodburn soil, Corvallis, OR Renslow soil, Kittitas County, W A Sanhedrin soil, Mendocino County, CA Cathedral soil, Fremont County, CO Wellsboro soil, Otsego County, NY Fangshan District, Beijing, China Anda, Heilongjiang, China Jinxian County, Jiangxi, China Nanjing, Jiangsu, China Changshu, Jiangsu, China Xuyi County, Jiangsu, China Jinhu County, Jiangsu, China Hongze County, Jiangsu, China Dushan County, Guizhou, China Gangcha County, Qinghai, China Xinghai County, Qinghai, China Luochuan County, Shanxi, China Yishan County, Guangxi, China Yangchun County, Guangdong, China Xuwen County, Guangdong, China Qiongzhong County, Hainan, China
4.85
2.40 1.43 2.21 2.04 2.25 1.73 1.08 1.49 1.80 1.03 2.90 1.26 2.40 6.09 3.12 3.47 5.61 2.83 0.34 1.08 1.77 0.67 4.02 0.81 2.54 1.12 0.16 0.46 0.66 0.83 0.64 0.34
1 2 3 4 5 6 7 8 9 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
Bed Sediments lsaacs Creek at Ohio River, near Ripley, OH (US. EPA ref sediment 11) 20.2 Mississippi River near Columbus, KY (US. EPA ref sediment 18) 22.1 Illinois River, near Lacon, IL (US. EPA ref sediment 22) 3.39 Kaskaskia River, IL ( U S . EPA ref sediment 25) 7.60 Mississippi River (pool 2), St. Paul, M N 5.90 Mississippi River (pool 111, Guttenburg, IA 4.86 Mississippi River (pool 261, Alton, IL 15.5 Mississippi River, Helena, AR 12.8 Yazoo River, Vicksburg, MS 19.7 Mississippi River, St. Francisville, LA 8.09 Lake Charles, adjacent t o the Calcasieu River, Lake Charles, LA 13.3 Marine sediment from Suisin Bay, site 408.1, northern San Francisco Bay15.7 Marine sediment from Suisin Bay, site 416, northern San Francisco Bay 21.6 Marine sediment from Suisin Bay, site 433, northern San Francisco Bay 21.3 Tangwang River, Yichun, Heilongjiang, China 12.8 Songhuajiang River, Majiadukou, Jiling, China Tumen River, Helong County, Jiling, China 4.93 Xuanwu Lake, Nanjing, Jiangsu, China Guchen Lake, Gaochun County, Jiangsu, China Lake Hongze, Sihong County, Jiangsu, China 29.9 Zhujiang River, Guangzhou, Guangdong, China Yellow River, Zhengzhou, Henan, China Yinghe River, Lushan County, Henan, China 1.85 Ziya River, Ci County, Hebei, China 5.83 Ganjiang River, Ruijin County, Jiangxi, China 5.32 Zishui River, Chengbu County, Hunan, China 8.97 Liuyanghe River, Liuyang County, Hunan, China Youshui River, Xuanen County, Hubei, China 11.9 Niqu River, Louhuo County, Sichuan, China 4.84 Huaihe River, Bengbu, Anhui, China 17.6 Huaihe River, Huainan, Anhui, China 8.21 Jinghe River, Jingyuan County, Ningxia, China 12.1 Sangonghe River, Fukang County, Xinjiang, China 4.00 Yaluzangbu River, Lazi County, Tibet, China 4.94 Lake Pumo, Langkazi County, Tibet, China 3.87 Niyanghe River, Gongbujiangda County, Tibet, China 3.12
1.50 0.79 2.20 0.99 1.50 1.13 1.40 1.60 0.58 0.40 1.97 1.17 1.48 1.78 4.73 1.12 1.99 4.12 1.24 1.04 3.37 0.11 0.11 2.19 0.70 2.82 0.29 1.22 0.39 0.50 0.45 0.73 0.38 0.45 1.94 0.54
22.4 8.84 9.38 3.75 1.07 7.77 3.99 1.51 9.79 11.2 11.6 7.88 5.58 5.73 4.96
54.0 22.8 8.20 4.21 2.86 40.2
&c,
VOL. 29, NO. 5, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
DCB
1
1403
8 1800
I
r
I
A
-
140
I
I
Sed.21 l4
0 1400
1.
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1200
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200
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600
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0 200
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oooo
t
40
k
0
1
2
3
4
5
6
7
800
Percent Organic Carbon (foe x I 0 0 ) Equilibrium Concentration, C, ( m g / L )
FIGURE 1. Sorption isotherms of CT on representative soils and bed sediments.
FIGURE 3. rC, values of CT on 32 normal soils and 36 bed sediments plotted against the organic carbon contents of the samples. ann
4
E 2000 -
-
0
f
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Soil 14
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Sed.21 Sed 8 SOll 12 soli 20 Sed 10
. -
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0
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150
Equilibrium Concentration, Ce ( m g l L )
FIGURE 2. Sorption isotherms of DCB on representative soils and bed sediments.
Results and Discussion Plots of carbon tetrachloride (CT)and 1,2-dichlorobenzene (DCB)sorbed per unit mass of soil or sediment (Q)against the equilibrium concentration in water (C,) on representative soils and bed sediments are shown in Figures 1 and 2. The linearity of sorption isotherms as noted for CT and DCB is typical of the partition of nonionic organic solutes in SOM (2, 4, 6, 11, 18). The KO,values for CT and DCB on all soils and bed sediments are presented in Table 1. The uncertainty of the ZC,, values is about f8% based on results of repeated experiments. When this uncertainty is combined with that of the organic carbon mass fraction in soill sediment,f,, (f5%),the observed differences between the individual soil ZC,, values for both CT and DCB become relatively small. The mean KO,for CT on 32 "normal" soils is 60 (SD = f71, and the mean IC,, for DCB is 290 (SD = f 4 2 ) . The Ko,'s for both CT and DCB on 36 normal bed sediments are generally higher and show about the same variation as the &,'s with soils. The mean &, with bed sediments for CT is 102 (SD = f11) and for DCB is 502 (SD = f66); they are greater by a factor of 1.7 than the mean &,'s for CT and DCB with soils. This difference is more than the deviation of the means and is illustrated in Figures 3 and 4 by the sorption data of CT and DCB. The finding that the &,'s for DCB are a factor of 4-6 greater than respective Ko,'s for CT on all soils and sediments is about 1404
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 5, 1995
1
2
3
4
5
6
7
Percent Organic Carbon ( f o c x I O 0 )
FIGURE 4. L v a l u e s of DCB on 32 normal soils and 36 bed sediments plotted against the organic carbon contents of the samples.
what one would expect from the difference in water solubility of CT (800 mglL) and DCB (154 mglL) and the similarity of their solubilities in SOM (18). The high degree of invariance of the KO,values of CT and DCB between most soils or between most bed sedimentsis striking, since these samples came from widely dispersed locations in the United States and the People's Republic of China. As illustrated, the normalized sorption coefficients (ZC,,'s) for both solutes show little dependence on the soil or sediment OC contents (e.g., 0.16-6.09% for soils) and on the surface areas of the (dry)soils or sediments giveninTable 1 (e.g., 1.07-54.0 m2/gforsoils). This finding reveals the comparability of SOM polaritylcomposition between soils and between bed sediments and the predominance of solute partition in SOM over mineral adsorption; if mineral adsorption were important, the sorption coefficient would be affected by the sorbent's surface area. The range of variation for the soils is much smaller than that reported in earlier studies,which are based on a small set of combined sorption data acquired by different procedures and analytical techniques (16,17). In this study, the extreme GCvalues for soils (or sediments) differ by less than a factor of 2. The relative invariance in KO,suggests that the properties of the (humified)SOM that control nonpolar solute solubility are quite similar for a wide variety of uncontaminated shallow soils and also likely for relatively pristine surficial bed sediments. It appears that there may not be much variability in the SOM polarity
and composition between soils of relatively shallow depths from diverse geographic locations worldwide. This speculation will be further tested. The question of how much the SOM properties vary between shallow and deep soils as influenced by weathering is another subject to be investigated. While different experimental procedures contribute to the variability of &, values, another reason for the lower &, variability between soils in this study as compared to that from the combined data of other studies may be the solute polarity and equilibrium concentration. The present sorption experiments were confined to low-polaritysolutes at relatively high relative concentrations and to soils with significant SOM contents. For such systems, the solute partition to SOM clearly predominates over adsorption on mineral matter, with the results reflecting closely the SOM medium property. Studies with solutes of higher polarities (and therefore generally higher solubilities in water) frequently extend into a much lower range of relative concentrations, where unsuppressed mineral adsorption may become a significant contribution (15). The greater the relative importance of mineral adsorption versus partition to SOM, the higher will be the apparent %, value. This speculated complication will be the subject of future investigations. The fact that most soil Koc’s are distinct from bed sediment &,Is suggests that the process that turns eroded soils into bed sediments brings about a noticeable change in the property of the organic constituent. Apossible cause for this change is that the sedimentation process fractionates soil organic constituents such that the more polar and more water-soluble organic components in soil organic matter (e.g., fulvic and humic acid fractions) or soil particles with more polar organic components are separated out to form dissolved organic matter and colloids in water, and hence the less polar organic constituents in soils are preserved in the bed sediment. The time scale to bring about a complete soil-to-sediment conversion should be a function of hydrodynamics. Another possible cause for this change would be the influence of biological inputs. However, this effect, if any, must be small since the difference between bed sediment and soil KO,values, while statistically significant, is not large. Part of the variation in KO,within bed sediments may reflect the extent of conversion of the eroded soils to bed sediments. Consider, for example, the relatively low KO, values of CT and DCB with sediment 1, sediment 6, and sediment 7. Sediment 1 is a U.S. EPA sample taken from the mouth of Isaacs Creek at junction with the Ohio River near Ripley, OH. That the KO,values on sediment 1 are significantlylower than the rest but are very similar to soil Ko,’s suggests that this sample could be a recently eroded soil which retains most of its soil organic composition. The somewhat lower KO,values with sediments 6 and 7 relative to the average sediment KO, may again be a result of incomplete conversion of eroded soils to bed sediments. Our KO,data suggest that bed sediments from most large rivers and lakes are quite comparable in their SOM polarity/ composition, possibly because they are more aged and contain less recently eroded soils. The difference between soil and bed sediment %,values as detected by relatively nonpolar solutes lends a basis for identifylng the source of suspended solids in rivers. In this study, the suspended solids from the Mississippi River, the Missouri River, and the Yellow River were collected during
TABLE 2
River=Suspended Solids and Contaminated Bed Sediments and Soils, Respective Organic Carbon Contents (OC), and Measured Partition Coefficients (KJ of Carbon Tetrachloride (CT) and 1,2-Dichlorobenzene (DCB) no.
source
%OC
Koc.
Koc.
CT
DCB
60 58 89 49 63
296 283 423 231 300
3.22
155
189
3.68
133
662
5.27
226
978
1.56
665
2910
Suspended Solids Mississippi River, Thebes, IL Mississippi River, St. Louis, MO Illinois River, Hardin, IL Missouri River, Herman, MO Yellow River, Zhengzhou, Henan, China
1.82 1.78 2.60 2.87 0.38
Contaminated Bed Sediments and Soils sediment from an industrial wastewater outfall at Bayou d’lnde, feeding the Calcasieu River, downstream from Lake Charles, near Lake Charles, LA sediment from the mouth of Bayou d’lnde at the Calcasieu River, downstream from Lake Charles, LA marine sediment from Fort Point Channel, Boston Harbor, MA soil from a crude oil spill site near Bemidji, MN
high river flows, and the sample from the Illinois River was collected during alow-to-normal river flow. The K cvalues of CT and DCB are typical of those for soils in the former but are more representative of bed sediments in the latter (Table2). One may infer from these data that the suspended solids during high water flows in these three rivers consist mainly of newly eroded soils, and the suspended solid from the Illinois River under low-to-normal water flow consists largely of resuspended bed sediment. The Yellow River suspended solid, which shows its origin as an eroded soil, is in keeping with the river’s high carrying load of eroded soils during the high-flow season. In contrast, a bed sediment collected from the Yellow River (sediment 22) gives K,,, values typical of those for other bed sediments. Thus, the sorption data serves as a simple indicator of the source and time histo of the suspended solids. We now turn to the%, data for contaminated soils and sediments in Table 2. The marine bed sediment from the Fort Point Channel of Boston Harbor is known to be severely contaminated by hydrocarbons (24);bed sediments from the Bayou d’Inde, which drains industrial wastewaters into the Calcasieu River downstream from Lake Charles, Louisiana, are contaminated by chlorinated hydrocarbons (25); the soil from Bemidji, MN, is contaminated by an oil spill. In comparison with the KO,values with normal soils and sediments, the Bayou d’Inde sediments yield noticeably higher &, values, and the sediment from Fort Point Channel of Boston Harbor and the soil from Bemidji exhibit exceptionallyhigh KO,values. Thus the KO,data reflect the different extents of hydrocarbon contamination of the samples. A similar effect was reported by Sun and Boyd (26)that nonpolar solutes exhibit unusually high KO,values on soils contaminated by petroleum and/ or polychlorinated biphenyl (PCB) oils. Here, the sorption data may serve as an effectivesensor for relatively high levels of contamination in soils and sediments. In aquatic systems, the sorption data can thus be used as a simple tool to monitor the “sediment quality” of streams, rivers, and lakes susceptible to pollution by high loads of relatively nonpolar organic wastes. VOL. 29, NO. 5,1995 / ENVIRONMENTAL SCIENCE &TECHNOLOGY
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In summary, the KO,data of both CT and DCB on most normal soils from shallow depths are shown to be quite invariant,suggestingthat soil organic matters at such depths from diverse geographic sources maintain a comparable polar-to-nonpolar balance and possibly a comparable composition. A similar effect is observed for the natural organic matter in relatively pristine surficial bed sediments. The average KO,values for nonpolar solutes on sediments are about twice those on soils, suggesting that sediment organic matter is in general less polar in nature than soil organic matter. This difference suggests that the process that converts eroded soils into bed sediments brings about a change in the composition of the organic constituent. The comparability of &, values either for the soils or for the bed sediments provides a basis for identifymg the likely source of suspended solids in riverwaters and for detecting severe soillsediment contamination by hydrocarbons. In view of the relative invariance in &, between soils or between sediments from this study, the use of average soil (or sediment) KO, values for assessment of contaminant sorption to different soils (or sediments) would appear to be sufficient in most environmental applications. However, it would be prudent to take into account the difference between soil and sediment &, values for relatively nonpolar organic pollutants.
Acknowledgments We thank G. W. Bailey for providing U.S. EPA reference soils and bed sediments; R. L. Pullman and L. A. Pytlik for soils from Colorado,Washington, and New York S. A. Boyd for soils from Michigan;G. R. Aiken for an oil-contaminated soil from Bemiji, MN; C. E. Rostad and L. M. Bishop for bed sediments from the Mississippi River; W. E. Pereira for bed sediments from the San Francisco Bay; C. R. Demas for bed sediments from Bayou d’Inde at the Calcasieu River, Louisiana; J. A. Moody and J. A. Leenheer for suspended solidsfrom the MississippiRiver, MissouriRiver, and Illinois River; and S. E. McGroddy for a bed sediment from Fort Point Channel, Boston Harbor. We also thank D. W. Rutherford for assistance in determining the surface areas of many of the soils and sediments. The use of trade and product names in this article is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.
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Received for review January 6, 1995. Accepted January 17, 1995. ES940522C
@Abstractpublished in Advance ACS Abstracts, March 15, 1995.
