Environ. Sci. Technol. 1992,26,2517-2523
(34) Norwood, D. M.; Wainman, T.; Lioy, P. J.; Waldman, J. M.Arch. Environ. Health, in press. (35) Huntzicker, J. J.; Cary, R. A.; Ling, C. S. Environ. Sci. Technol. 1980, 14, 819.
Received April 6,1992. Revised manuscript received August 17, 1992. Accepted August 24,1992. The field study was funded by the Electric Power Research Institute (EPRT) under Contracts
RP1630-59 and RP-3009-04. Information in this document also has been funded in part by the United States Environmental Protection Agency (EPA) under Cooperative Agreement CR816740 to the Harvard School of Public Health. It has been subjected to the Agency’s peer and administrative review, and it has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
Seasonal Variations and Modes of Riverine Input of Organic Pollutants to the Coastal Zone: 1. Flux of Detergent-Derived Pollutants to Tokyo Bay Hldeshlge Trkada, * g t Norlo Ogura,? and Ryoshl Ishlwatarlt Tokyo University of Agriculture & Technology, Faculty of Agriculture, Fuchu, Tokyo 183,Japan, and Tokyo Metropolitan University, Faculty of Science, Hachioji, Tokyo 192-03, Japan
In order to discuss seasonal variations and modes of riverine input of organic pollutants to the coastal zone, linear alkylbenzenesulfonates (LAS) and linear alkylbenzenes (LABs)were determined for the Tamagawa River water at 2-week intervals for 2 years. The sampling site, Chofu Dam, is located at the boundary between freshwater and brackish zones. LAS flux was ca. 5 times higher in winter than in summer. LAS with longer homologues and external isomers were more depleted in summer. The LAB isomer distribution also showed a clear seasonal trend in that external isomers were more depleted in summer, while LAB flux had a small seasonal variation. These seasonal variations are due to higher microbial degradation activity of in-stream LAS and LABs at higher water temperatures in summer months. A continuous supply of LAS to the estuary was relatively more important (96% of the annual supply) than an intermittent supply. However, a major portion of the LABS (67% of the annual supply) were intermittently transported to the coastal zone by flush during/after rainfall. Despite the LABS’ highly hydrophobic nature, 1040% of total LABSwere transported as the dissolved form. This may be due to association of LABs with colloidal material and/or solubilization by surfactants. The annual suspended CLAB flux to Tokyo Bay via the Tamagawa River is estimated at 110 kg/yr, which comprises 6.4% of the CLABs accumulated in Tokyo Bay sediment. Annual CLAS flux is estimated at 320 ton/yr. This is much greater than the amount of CLAS accumulated in the bay sediment (0.4 ton/yr), indicating that more than 99.9% of the LAS are degraded in the estuary and the bay.
Introduction Various pollutants are supplied to coastal environments via riverine transport. To estimate the impact of the pollutants on the coastal zone, it is important to understand the quantity and modes of the riverine input. Seasonal variation in the riverine input, form of entry (i.e., dissolved or suspended form), and timing of input (e.g., continuous or intermittent input) are key considerations for reliable prediction of behavior of the pollutants in a coastal environment. In this study, we focus on the riverine inputs of two detergent-derived pollutants [Le., linear alkylbenzenesulfonates (LAS) and linear alkylbenzenes (LABS)]. Tokyo University of Agriculture & Technology. t Tokyo Metropolitan University. 0013-936X/92/0926-2517$03.00/0
LAS are widely used surfactants in synthetic detergents for household and industrial use. Their toxicity to aquatic biota has been cited, and chronic toxicity occurs at concentrations greater than 0.1 mg/L (1). There are reports on the monitoring of LAS in freshwater (e.g., refs 2-7) and in coastal environments (2,8-10). The transport processes of LAS in the aquatic environment (e.g., LAS removal by biodegradation and/or adsorption) have been studied (7, 9,11,12). However, the flux of LAS from freshwater to a coastal environment has not been studied. LABs are the raw materials in LAS production. A small amount of LABs are not sulfonated and are contained in commercial LAS detergents (13). The LABS are discharged to rivers associated with the usage of LAS detergents, which causes LAB pollution in aquatic environments (14). The occurrence of LABs in coastal environments has been reported by others (10, 15-17). A few reports on LABs in freshwater environments are available (14, 18). The properties of LABS are quite different from those of LAS, although both are discharged to the aquatic environment from the same source. LABs are hydrophobic and considerably resistant to biodegradation, while LAS are hydrophilic and easily biodegraded. Therefore, the differences in the behaviors of LABS and LAS reflect differences in their physicochemical properties. Comparison of the modes of riverine inputs will give us insight into relationships between the modes of riverine inputs of pollutants and their physicochemical properties. Such relationships are useful for predicting the behavior of pollutants with a wide range of physicochemical properties in coastal zones. The Tokyo metropolitan area is one of the biggest urbanized areas, with 23 million inhabitants, supplying large amounts of pollutants to Tokyo Bay via rivers. Previously we have reported the detailed distribution of LABs and LAS in Tokyo Bay sediments and calculated the deposition rate of both compounds (10). Data on input of LABs and LAS from rivers will allow us to discuss the relationship between their input and distribution, especially a mass balance calculation. The Tamagawa River is one of the major rivers flowing into Tokyo Bay. There are several reports on the concentrations of LAS (2,5,19) and LABs (14) in the Tamagawa River water. However, frequent measurements over an extended period of time are necessary to calculate the flux of LAS and LABs from the river to Tokyo Bay. Therefore, we measured LAS and LAB concentrations at
0 1992 American Chemical Soclety
Environ. Sci. Technol., Vol. 26, No. 12, 1992 2517
139015'
30'
50
L5 '
1l.0000'
15'E
N * LO'
30' 0
10
20
..
Aug
Nov
Feb
May
Aug
Figure 2. Suspended CLAB (0) and total CLAS (0)concentratlons in the Tamagawa Rhrer water at Chofu Dam. Arrows lndkxte highflow samples.
Figure 1. Sampling location.
2-week interval for 2 years at Chofu Dam, which separates a freshwater region from a brackish water region. At the dam, the flow rate of water is monitored every hour all year round by the Tokyo Metropolitan Bureau of Waterworks, which enabled us to calculate the flux of the pollutants from the Tamagawa River to Tokyo Bay. The purposes of the present study are the following: (1) to determine the flux of LABs and LAS from the Tamagawa River to Tokyo Bay and (2) to understand the modes of riverine input of LABs and LAS (i.e., seasonal variation, form of entry, and timing of input).
Experimental Section Site Description/Sampling. The Tamagawa River is 140 km in length with a mean flow of approximately 15 m3/s at Chofu Dam (Figure 1). The population and area of its drainage basin are approximately 3.0 X lo6 people and 1240 km2, respectively (20). Both untreated and treated wastes are discharged to the river. About 60% of the people inhabiting this drainage basin are served by municipal sewerage treatment (activated sludge). Untreated domestic wastes from the remaining 40% of the people in the drainage basin are directly discharged to the river. Both wastes are introduced to the river through many tributaries and effluents widely distributed in upper and middle stream of the drainage. Water samples were collected from Chofu Dam, located just above the upper limit of the tidal zone of the Tamagawa River (Figure 1). Most of the samples were taken at 2-week intervals from June 1984 to August 1985. Additional samples were collected in 1983 and 1986, and a total of 48 samples were taken for this study. The detailed sampling data are listed in Table I. Grab water samples of 200-600 L were in-situ filtered by a glass fiber filter (Toyo Roshi GB 100R; nominal pore size 0.6 pm) which had been previously baked at 400 OC for 5 h to remove organic contaminants. The glass fiber filters on which the suspended particles were collected were wrapped with aluminum foil and stored at -20 "C. Filtrates for LAB analysis were taken in organic-free glass bottles and immediately (within 30 min) brought back to the laboratory for the subsequent extraction. HC1 was added to filtrates for LAS analysis to suppress LAS biodegradation during transportation. Analytical Procedures. (a) Alkylbenzenes. LABS in suspended solids were determined for all 48 samples, while LABSin filtrates were analyzed for 8 samples, which are indicated in Table 11. The analytical procedure used for determination of alkylbenzenes was essentially the same as reported previously (21). Briefly, LABS in suspended particles were Soxhlet-extracted from the freezedried glass fiber filters containing suspended particles. Dissolved LABS were liquid-liquid extracted from 32 L 2518
Envlron. Scl. Technol., Vol. 26, No. 12, 1992
of the filtrates. The organic solvent extracts were purified and fractionated by column chromatography. LABs were quantified by capillary gas chromatography. All LAB concentrations were corrected for recovery using the recovery efficiency of l-CI1AB (spiked recovery standard). (b) Linear Alkylbenzenesulfonates (LAS). Dissolved LAS and suspended LAS were determined for all 48 samples. The analytical procedure for LAS was essentially the same as reported previously (21). Dissolved LAS were liquid-liquid extracted from the filtrate after formation of the LAS-methylene blue complex by adding methylene blue solution. Suspended LAS were Soxhletextracted from the freeze-dried glass fiber filters. Purified extracts were analyzed by HPLC with a fluorometric detector. LAS concentrations were not corrected for recovery. Recovery tests by spiking with dodecylbenzenesulfonates indicated recovery was 81.2 f 4.5% for filtrate analyses and 100 f 11% for particulate analyses. (c) Carbon Content. Organic carbon contents for the suspended particles were determined by a dry combustion method using a Yanagimoto MT-3 CHN analyzer. Freeze-dried filters containing suspended particles were cut into small pieces, put into a nickel combustion boat, and introduced to the CHN analyzer.
Results and Discussion (1) Seasonal Change in Suspended LAB Input to the Estuary. LABS consist of 26 isomers, and the sum of all the isomers is referred to as CLABs. LAB data as well as physical characteristics for the river water samples are given in Table I. The normal water flow at Chofu Dam was 25 m3/s in 1985 (20).Water samples are categorized into two groups: the samples collected when the river flow was below 25 m3/s (referred to as "low flow") and those collected at a flow above 25 m3/s (referred to as "high flow"). Suspended CLAB concentrations in the river water on a volume basis range from 34 to 942 ng/L. The annual (September 1984-August 1985) average CLAB concentration is 179 f 115 ng/L. The measured river water concentrations are significantly higher than the concentrations measured in the effluents from a municipal wastewater treatment plant (8.1-55.9 ng/L) in the drainage area and lower than CLAB concentrations for untreated domestic wastewater [1040-5560 ng/L (14)l. This is consistent with our previous hypothesis that untreated domestic wastewater is the dominant contributor of LABs to the rivers in Tokyo (14). Figure 2 shows seasonal variations in suspended LAB concentrations in the river water. For low-flow samples, CLAB concentrations in winter months were slightly higher than those in summer months. The CLAB flux shows a similar trend (Table I). At low flow, the average LAB flux for winter months (December-February) and
2.0 1
Aug.
Nov,
Feb.
May
Aug.
Flgure 3. I/E LAB ratlo of suspended matter in the Tamagawa River water at Chofu Dam. I/E LAB ratio: the sum of 66,*AB 4- 5612 AB relative to the sum of 4-C,2 AB 4- 3-c12 AB 4- 2-CI2 AB.
Aug.
1985 Nov. Feb.
May
Aug.
Figure 4. Suspended CLAB flux in the Tamagawa River at Chofu Dam. Arrows indicate high-flow samples.
summer months (July-September) is 211 f 110 and 143 f 67 g/day, respectively. LAB isomers with externally substituted phenyl groups (i.e., external isomers) were more depleted in summer samples than in winter samples. The seasonal trend in the isomer distribution as an I/E LAB ratio (ratio of the s u m of the concentration of 6-C12 AB and 5-C12AB relative to that of 4-c12 AB, 3-c12 AB, and 2-C12 AB) is shown in Figure 3. The I / E LAB ratio shows a marked seasonal trend, being lower in winter months (1.0 & 0.1; n 13) and higher in summer months (1.4 f 0.2;n = 19). The external isomers are more susceptible to microbial degradation than the internal isomers (18,22),and higher I / E LAB ratios indicate more extensive LAB degradation (21). This seasonal trend indicates that in-stream LAB degradation is more active in summer and depressed in winter. The higher water temperatures of the river in summer increase bacterial metabolic activity. This is consistent with the result of our incubation experiments (21). The I/E LAB ratio has been quantitatively related to the degree of LAB degradation (21). An annual average I/E LAB ratio of 1.2 f 0.2 for the river water samples indicates 20% degradation compared with untreated domestic wastes. The seasonal change in the I/E LAB ratio indicates that the degree of LAB degradation ranges from 0% in winter months to 40% in summer months. This is consistent with the fact that the flux of suspended LABS in summer months (143 f 67 g/day) was slightly lower than that in winter months (211 f 110 g/day). (2) Intermittent LAB Supply to the Estuary. As shown in Figure 2, when the river flow increased during/after rainfall, in most cases, the suspended LAB concentration significantly increased. As a result, the flux of suspended LAB increased up to 100 times that of the flux at low flow (Figure 4), indicating an intermittent supply of LABs to the coastal zone. This increase in LAB flux at high flow is probably caused by resuspension of the
310
‘
1
10 1o2 Water Flow I m3/s)
103
Flgure 5. Relationship between flux of suspended CLABs and water flow in the Tamagawa River at Chofu Dam. The solid line and dotted lines indicate the regression line and the 95% confidence intervals, respectively.
sediments containing LABs. It has been demonstrated that sediments from the Tamagawa River contain significant amounts of LABs (14). LABs supplied to the river would be temporarily stored in the river bed sediment, and under high-flow conditions, the LABS would be resuspended and increase the LAB concentration in the river water. The annual flux of LABS in the Tamagawa River at Chofu Dam can be estimated. Generally the relationship between water flow and flux of a constituent in river water can be expressed by the following equation flux = K(water flow)” (1) where K and n are constants (23).Then, the flux of suspended LABS is regressed against the water flow for all samples examined. As shown in Figure 5, a clear linear relationship can be seen between log [flux of suspended CLABs] (g/day) and log [water flow] (m3/s) (IC = 0.89). K and n are 11.9 and 1.08, respectively. The 95% confidence interval of K ranges from 3.5 to 40.7. The daily average water flow is available from the data monitored by the Tokyo Metropolitan Bureau of Waterworks, and the daily flux of suspended LABS can be calculated by using eq 1. The annual flux of suspended LABS is calculated by the summation of the daily flux of suspended LABs. The annual (September 1984-August 1985) flux of suspended CLABs in the Tamagawa River is calculated to be 161 kg/yr, with the range from 48 to 560 kg/yr based on the 95% confidence interval of K in eq 1. This annual flux is approximately 3 times as large as the suspended CLABs flux at low flow of 54 kg/yr (147 g/day X 365 days; Table I). Therefore, the amount of suspended CLABs carried to the estuary at flood is estimated to be 107 kg/y (Le., 161 - 54 kg/yr), corresponding to 67% of the annual flux of suspended LABS. It is evident from the present results that a major fraction of LABs are supplied to Tokyo Bay intermittently (Le., flush at rainfall) rather than by continuous supply. The estimated LAB flux in the Tamagawa River can be compared to the amount of LABS accumulated in Tokyo Bay sediments. LABS are expected to be degraded as they travel from the river to the bay Sediments. A degradation correction is made as follows. The degree of degradation and LABs remaining in the river water is estimated at 20% and 80% compared to untreated domestic wastes by use of the I/E LAB ratio (21). Likewise, the degree of degradation and LABs remaining in the bay sediments is estimated at 45% and 55% compared to untreated domestic wastes (10). The LABS remaining in Tokyo Bay sediments compared to the river water can be calculated Environ. Sci. Technoi., Vol. 26, No. 12, 1992 2518
Table I. LABs and LAS in the Tamagawa River Water at Chofu Dam
ss
suspended CLAB concn (ng/L) flux (g/day)
total CLAS
water temp ("C)
water flow (m3/s)
(mg/L)
(% of SS)
nd" 9.0 9.0 5.3 5.1
19.0 13.5 9.2 9.2 13.3
4.6 4.1 5.4 nd 5.7
nd nd nd nd 31.3
287 207 184 278 400
471 242 145 220 458
nd nd 313 410 nd
nd nd 248 324 nd
nd nd 97.6 97.6 nd
6.0 20.2 25.8 21.3 28.2 nd 27.4 22.9 20.6 16.5 17.1 15.9 10.2 9.7 8.0
8.8 10.2 20.9 160.5 10.4 9.8 10.3 10.3 10.4 41.2 9.4 5.5 10.4 6.4 9.8
5.2 10.0 9.5 455.0 10.5 14.5 14.8 4.1 6.4 18.4 4.3 4.8 13.1 3.8 5.7
43.9 23.0 25.0 3.0 29.9 34.5 29.1 28.6 20.7 26.6 19.7 26.8 15.4 37.1 27.3
272 177 107 412 64 150 198 151 159 526 96 146 179 206 143
206 155 192 5710 58 127 176 135 143 1874 78 69 161 114
nd nd 79 33 49 67 nd 77 142 208 140 325 257 334 352
nd nd 142 462 44 57 nd 69 127 741 114 154 230 186 297
nd nd 98.2 72.3 97.9 96.4 nd 98.0 98.3 91.9 99.0 98.8 98.3 98.2 97.8
6.9 5.0 5.9 5.0 9.3 8.2 12.4 11.0 17.2 19.0 19.5 23.0 15.0 17.5 17.2 27.0 28.9 30.0 29.0 25.9 12.2
5.7 5.8 5.8 14.1 14.6 26.6 20.5 111.8 45.5 15.5 15.3 10.4 159.1 910.0 99.8 26.9 14.7 14.7 9.8 77.3 10.6
3.1 6.9 6.1 7.3 4.6 20.9 10.6 89.1 7.7 7.3 25.7 7.5 95.2 956.0 27.3 5.7 9.6 10.6 12.8 51.8 6.2
35.3 27.0 36.4 25.7 31.6 11.3 13.6 8.5 12.1 22.7 8.2 34.1 3.2 1.6 2.5 22.7 22.1 25.0 25.0 5.6 20.4
124 266 283 286 164 201 156 485 98 122 130 190 160 288 34
321 318 484 408 217 89 138 106 117
65 105 104 62 202
61 132 141 349 207 460 276 4689 384 164 172 171 2196 22622 289 165 82 133 89 418 186
158 159 241 498 274 203 243 1027 459 147 274 222 333 3084 411 214 70 63 152 120
98.5 96.6 96.9 97.6 98.4 98.3 98.3 92.8 98.2 98.3 97.9 98.3 93.8 91.0 99.2 99.1 98.6 97.3 98.3 98.1 97.1
10.1
61.0 170.6
7.6 13.3 61.5 420.2 6.9 5.6 5.4 50.9 178.9
28.3 23.6
SD'
6.0 7.2 18.4 nd 23.8 26.0 24.8 16.2 7.7
19.3 19.4 14.1 20.6 10.7
295 380 942 383 129 112 126 179 115
258 293 7363 6254 454 147 229 1282 4291
363 47 1 153 14 16 36 29 177 130
318 363 1194 220 58 47 52 363 574
95.8 96.4 87.9 59.5 93.5 98.1 98.2 97.4 2.2
low-flow samplesd annual mean SD
15.7 8.5
11.0 4.2
8.1 5.2
25.4 7.8
162 62
147 71
222 131
187
98.1 0.6
sampling date 1983 Nov 30 Dec 8 Dec 14 Dec 21 Dec 28 1984 Jan 11 Jun 22 Ju16 Jul 20 Aug 3 Aug 17 Aug 31 Sep 13 Sep 28 Oct 12 Oct 26 Nov 9 Nov 21 Dec 7 Dec 21 1985 Jan 4 Jan 18 Feb 1 Feb 15 Mar 7 Mar 15 Mar 29 Apr 12 Apr 26 May 10 May 24 Jun 7 Jun 21 Jul 1 Jul 5 Jul 19 Aug 2 Aug 16 Aug 30 Aug 31 Nov 29 1986 Feb 6 Feb 14 Jun 30 Aug 5 Aug 19 Aug 22 Aug 25 annual meanb
8.9 90.4 189.0 40.7 15.2 21.1
POC
11.0 2.1
71
121
concn (rg/L)
110
207 247 24 39 48 92 55 17 74 23 130
21
110
"Not determined. bArithmetic mean computed by weighting each measurement equally; For samples from Sep 13, 1984 to Aug 31,1985. Standard deviation. Water flow was below 25 m3/s.
at 70% (dividing 55% by 80%). Therefore, 30% of the LABS in river water are degraded as they pass from the river to the bay sediments. The estimated suspended CLAB flux from the Tamagawa River of 160 kg/yr (48-560 kg/yr) is reduced to 110 kg/yr (34-390 kg/yr) in Tokyo Bay by degradation. The amount of CLABs deposited in the total area of the bay has been estimated at 1700 kg/yr (IO). Therefore, the degradation-corrected LAB flux from the Tamagawa River comprises 6.4% (2.8-33%) of the LABs deposited in Tokyo Bay sediment. 2520
Environ. Sci. Technoi., Vol. 26, No. 12, 1992
The population in the drainage basin of the Tamagawa River (3 million) is 13% of that for Tokyo Bay (23 million). The contribution of suspended LABSfrom the Tamagawa River (i.e., 6.4%)is somewhat lower than the population distribution (i-e., 13%). However, the contribution of dissolved LABS has been ignored in the above discussion. As described in the following section, considerable amounta of LABs were found in the dissolved phase. Incorporation of dissolved LABs into the bay sediment makes the contribution of the Tamagawa River higher.
Table 11. Suspended and Dissolved LABs in the Tamagawa River Water at Chofu Dam sampling date 1985 Nov 29 1986 Feb 6 Feb 14 Jun 30 Aug 5 Aug 19 Aug 22 Aug 25 average SDn
sus
DISS/
(ng/L)
ELAB concn DISS (ng/L)
sus
sus
1.3
202
426
2.10
1.19
1.00
2.2 3.1 6.8 8.8 1.3 1.1 0.8
295 380 942 383 129 112 126 321 274
1001
3.39 2.19 0.36 0.14 0.98 1.94 1.31 2.18 0.77
0.96 1.02 1.14 1.09 1.31 1.20 1.14 1.13
0.91 0.90 1.08 1.00 1.31 1.38 1.11 1.09 0.18
water flow (m3/s)
POC (mg of C/L)
10.6 10.1 8.9 90.4 189 40.7 15.2 21.1
834 343 52 126 217 165 395 346
I/E LAB ratio DISS
0.11
Standard deviation ~~~~~~
Table 111. Average Apparent log Koc of LAB Isomers in the Tamagawa River Water at Chofu Dam averagen
SDb
average”
SDb
5.60 5.58 5.63 5.56 5.55 5.30 5.61 5.55 5.61 5.36 5.36 5.36
0.38 0.26 0.31 0.25 0.28 0.16 0.37 0.32 0.28 0.19 0.24 0.23
“Arithmetic mean of eight observations indicated in Table 11. Standard deviation.
(3) Dissolved LABs. The dissolved LAB concentrations at low flow were 2-3 times higher than the suspended LAB concentration (Table 11). At high flow, dissolved CLAB was not so significant relative to suspended CLAB. Their homologous distributions were similar to those observed in the suspended phase. In addition, I/E LAB ratios (i.e., isomeric composition of LABS) showed no significant differences between suspended and dissolved phases (Table 11). LABS are fairly hydrophobic compounds [KO, = 6.90-9.29 (24,25)]. It seems difficult to explain the high concentrations of dissolved LABS by simple two-phase partitioning. Apparent partition coefficients on an organic carbon basis (K,’) are calculated for LABS by use of the following equation. Koel = C,/(CdfOJ (2)
where C, is the solid-phase concentration calculated on a dry weight basis (ng/g), Cdis equal to the concentration of LABS in the dissolved phase (ng/mL), and f, is the organic carbon weight fraction in the solids. The observed log KW’sof individual LAB isomers are listed in Table 111. The average apparent log KW’sof individual LAB isomers determined for eight samples range from 5.36 f 0.23 to 5.73 f 0.48. They show no systematic differences between homologues or isomers. Sherblom et al. (24) experimentally determined the octanol-water partition coefficient (K,J of LABS by an HPLC technique. The experimentally determined log KO@ range from 6.90 for 5-cloAB to 9.29 for 2-CI4AB. These values can be converted to log Ko,s of 6.69-9.08 by use of
the relationship between KO,and KO,reported by Karickhoff et al. (26). K,’ values observed in the river water are 1-4 orders of magnitude lower than the experimentally determined values, indicating that higher concentrations of LABS were present in the “dissolved phase” than predicted from KO,. This may be due to colloid-LAB association and/ or solubilization of LABS by surfactants. Many workers (e.g., refs 27-30) have experimentally demonstrated that the association of hydrophobic compounds with colloidal organic matter increases the apparent dissolution of the compounds and, as a result, lowers their apparent sorption coefficient. Brownawell and Farrington (31)demonstrated a lower apparent K i of PCBs in pore water than the experimentally calculated Kd and indicated the colloid-PCB association. Baker et al. (32)provided the field evidence of colloidal association of PCBs based on detailed field observation in Lake Superior. DOC concentrations were not measured for our samples. Ogawa and Ogura (33) reported that DOC concentration for the river water at the same station was 5.2 f 1.3 mg of C/L. The POC concentration was 0.8-3.1 mg of C/L for the samples at low flow (Table II). Therefore, assuming that the partition coefficients of LABS are the same between POC and DOC, it seems reasonable that LABs are present in the dissolved phase in similar or twice higher concentrations than in the suspended phase. It has also been reported that surfactanta enhance the apparent water solubility of hydrophobic pollutants (34, 35). As is described below, considerable amounts of surfactant (i.e., LAS) were found in the water sample. The ratio of dissolved CLABs relative to suspended CLABs was 2.2 f 0.8 (Table 11); the annual flux of total (i.e., suspended + dissolved) CLABs in the Tamagawa River is roughly estimated to be 510 kg/yr [160 X (2.2 + l)]. This is probably an overestimation, because the proportion of dissolved CLABs to suspended CLABs is smaller for high-flow samples (0.14-0.98) than the average (i.e., 2.2) and the major fraction of suspended LABs is transported at high flow. The fate of dissolved LABS in the estuary and the bay is quite unknown. Some mechanisms (e.g., coagulation of dissolved organic matter, degradation of surfactants in estuaries) may transport LABS to estuarine and bay sediments. Moreover, LABS associated with DOC may be transported to the open sea. (4) Seasonal Variation in LAS Input to the Estuary. LAS having ClO-Cl4 alkyl carbons with phenyl positional isomers were detected from the river water. The s u m of all 26 isomers is referred to CLAS. Dissolved LAS represent 95.8-99.0% (average 97.4%) of the total LAS at low flow (Table I). This is reasonable because of the Environ. Sci. Technol., Vol. 26, No. 12, 1992 2521
70'1 I
@
"
884 Aug
1985 Nov Feb
May
Aug
Flgure 6. I/E LAS ratio In the Tamagawa River water at Chofu Dam. I/E LAS ratio: the sum of &C12 LAS !!J-C,~LAS 44& LAS relative to the sum of 3412 LAS 2-C12LAS.
+
+
+
hydrophilic nature of LAS. Dissolved LAS are enriched in Cll and C12homologues, while suspended LAS are enriched in CI2and C13 homologues. Also, suspended LAS have high concentrations of external isomers relative to dissolved LAS. These results are consistent with the results of laboratory experiments on the adsorption equilibrium of LAS reported by previous workers (36). Total CLAS concentrations in the river water range from 14 to 484 pg/L (Table I). The annual (September 1984-August 1985) average of the concentrations is 177 f 130 pg/L (n = 28). LAS concentrations in the Tamagawa River water have been reported by some workers (2,5,19, 37). The previously reported values are comparable to the LAS concentrations in the present study, although their observations were less frequent. The LAS concentration in the Tamagawa River is significantly higher than those in rivers in the United States, Canada, and Germany reported by Rapaport and Eckhoff (7). The higher concentration may be due to the input of larger amounts of untreated domestic wastes, which contain high concentrations of LAS, to the Tamagawa River. As shown in Figure 2, a pronounced seasonal trend is noted in the LAS concentration. LAS concentrations in winter months are about 10 times higher than those in summer months. In addition, LAS flux in summer months is ca. 5 times lower than that in winter months (Table I). This seasonal variation is probably due to the fact that bacteria in the river are more active in summer because of higher water temperatures and LAS are biodegraded more rapidly. The more rapid degradation of LAS in summer is consistent with results of laboratory incubation experiments (19),where optimum temperature for LAS biodegradation was about 25 OC, LAS degraded more slowly as water temperature decreased. The water temperature of the Tamagawa River fluctuated from 5 "C in winter to 30 OC in summer. Gerike et al. (6) reported similar seasonal variations in LAS concentrations and flux for German rivers. They attributed the seasonal variation in LAS concentration to that in microbial activity. This interpretation is consistent with ours. LAS compositionsshowed marked seasonal trends. LAS homologues with longer alkyl chains were less abundant in summer months than in winter months. LAS average chain length was 11.3 f 0.2 (n = 10) in summer months and 11.6 f 0.1 (n = 10) in winter months. In addition, external isomers were more depleted in summer months than in winter months. The ratio of 6-CI2 LAS + 5-CI2 LAS + 4'c12 LAS relative to 3-C12LAS + 2-C12LAS is used as an index of isomer distribution and referred as the I / E LAS ratio. The I / E LAS ratio is higher in summer months and lower in winter months, indicating that external isomers are more depleted in summer months (Figure 6). These pronounced seasonal variations in LAS composition in the river water support the more rapid biodegradation of LAS in summer than in winter. Because 2522 Environ. Scl. Technol., Vol. 26, No. 12, 1992
-
r-054
I
1
,o
ZLAS Flux = 50.1 x [Water F I O W ) ~ ' ' ~ _.
1
_
_
I
I
-
-
.-
_-_-
b
-
----7-------r --
1
10 IO2 Water Flow I m V s j
103
Flgure 7. Relationship between flux of total CLAS and water flow in the Tamagawa River at Chofu Dam. The solid line and dotted ilnes lndlcate the regression line and the 95% confidence intervals, respectively.
LAS with longer alkyl chains and externally substituted sulfophenyl groups are more susceptible to microbial degradation (38),more degraded LAS (in summer months) would be more depleted in longer homologues and external isomers than less degraded LAS (in winter months). (5) Annual LAS Flux to Tokyo Bay. Total CLAS flux during low flow at Chofu Dam is 187 kg/day or 67.9 ton/yr (Table I). LAS flux increased when the river rose. This increase can be accounted for by the increase of suspended LAS caused by resuspension of the sediments and dissolution of LAS from sediments and/or soils. The annual flux of LAS passing at Chofu Dam is estimated in a way similar to that of the LABs. As shown in Figure 7, a roughly linear relationship exists between log [flux of CLAS (kgjday)] and log [water flow (m3/s>](r = 0.54). K and n are 50.1 (10-251) and 0.45, respectively. The low regression coefficient is probably due to the seasonal fluctuation in LAS flux. The value of n (i.e,, 0.45) is lower than that for LABS (n = 1.08), indicating the dependence of flux on water flow is lower for LAS than for LABs. The daily flux of LAS calculated from the equation is integrated for 1yr, resulting in the annual flux of LAS. The annual flux of CLAS is estimated to be 71 ton/yr, with a range from 14 to 355 ton/yr. Almost all (96%) of this annual flux is explained by the transport at low flow (67.9 ton/yr). LAS carried by flush occupies only 4% of annual LAS flux, in contrast to the case of LABs, where 67% of the annual flux of LABS was transported by flush. The estimated LAS flux of the Tamagawa River is compared with the LAS accumulation rate in Tokyo Bay sediments. CLAS flux from the Tamagawa River is estimated a t 71 ton/yr (14-355 ton/yr). The amount of CLAS deposited in the total area of the bay is estimated at 0.4 ton/yr (IO). LAS flux from the Tamagawa River is much greater than the amount of LAS accumulated in whole area of Tokyo Bay, indicating that considerable amounts of LAS are degraded as they are transported from the river to the bay. The proportion of the population in the drainage of the Tamagawa River is 13% of that of the Tokyo Bay; the total supply of CLAS from all the rivers flowing into the bay is estimated at 550 ton/yr (71/0.13) with a range from 110 to 2700 ton/yr, based on estimated CLAS flux from the Tamagawa River to Tokyo Bay of 71 ton/yr. Therefore, only 0.07% (0.4-0.01 %) of the total supply from the rivers is accumulated in Tokyo Bay sediment. The remaining 99.9% of the LAS supplied from the rivers is degraded. Takada and Ogura (9)calculated that 80-100% of LAS
supplied to the Tamagawa Estuary is degraded within the estuary, based on an LAS-salinity relationship. Conclusion
(1)Annual suspended CLAB flux from the Tamagawa River to Tokyo Bay is estimated at 110 kg/yr, which comprises 6.4% of the LABs accumulated in Tokyo Bay sediment. This is consistent with the proportion of the population in the drainage area, considering the flux of dissolved LABS. On the other hand, annualLAS flux from the Tamagawa River to its estuary is estimated at 71 ton/yr. This is much greater than the amount of LAS accumulated in the bay sediment (0.4 ton/ yr), indicating that more than 99.9% of the LAS is degraded in the estuary and the bay. (2) LAB flux from the freshwater region to the Tamagawa Ektuary showed a small seasonal variation, while their isomeric composition (Le,, I/E LAB ratio) had a pronounced seasonal trend. On the other hand, LAS flux as well as LAS composition showed a big seasonal variation. LAS flux was by a factor of 10 higher in winter than in summer. This pronounced seasonal trend is caused by the variation in the microbial activity of LAS degradation, which depends on water temperature. The difference in magnitude of seasonal trends in the flux between LAS and LABs reflects the difference in their biodegradability. (3) Intermittent LAB transport to the coastal zone occurred associated with flush during/after rainfall. The suspended LAB transport by flush represents a predominant portion (67%) of their annual flux. In the case of LAS, continuous supply is relatively more important than intermittent supply (4% of the annual flux). This difference is caused by the difference in their hydrophobicity. Intermittent supply should be important for the riverine input of other hydrophobic pollutants (e.g., PAHs and PCBs) to the coastal zone. (4)Almost all LAS are supplied to the estuary as the dissolved form. This is reasonable from their hydrophilic nature. In contrast, 10430% of the LABS are transported as the dissolved form. This may be due to association of LABS with colloidal material and/or solubilization by surfactants (e.g., LAS). Transport associated with colloidal material may be significant for the other hydrophobic pollutants (e.g., PCBs). If a colloid-pollutant association escapes removal in estuaries, the pollutants may be widely transported to the open sea. Therefore, future effort should focus on the fates of dissolved hydrophobic pollutants in the coastal zone, especially in estuaries. Acknowledgments
We are grateful to Mr. Hiromasa Saito for his cooperation in collecting samples and to Ms. Susan McGroddy, Dr. Paul Sherblom, and Dr. Hiroshi Ogawa for their helpful comments on the manuscript. We also thank the Tokyo Metropolitan Bureau of Water Works for kindly providing facilities for collecting samples and data on water flow. Several graduates and undergraduates in our laboratories provided welcome assistance with the field work.
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Received for review May 21,1992. Revised manuscript received August 24, 1992. Accepted August 25, 1992. This work was supported by grants from the Ministry of Education in Japan (B-248-R14-3 and B-249-R14-3) and from the Tokyu Foundation for Better Environment (76). Envlron. Sci. Technol., Vol. 26, No. 12, 1992 2523
