Environ. Sci. Technol. 1991, 25,547-550
COMMUNICATIONS Occurrence of Cationic Surfactants and Related Products in Urban Coastal Environments P. Fernindez, M. Valls, J. M. Bayona," and J. Albalg6s Environmental Chemistry Department, C. 1.D.-C.S. I.C., Jorge Girona Salgado, 18-26, 08034-Barcelona, Spain
Introduction The identification of specific molecular markers in urban wastewaters deserves special interest for assessing the pathways of transport, the regions of concentration, and, in fact, the environmental implications of wastewater discharges in coastal areas. Although over 50000 chemicals are used in technical applications ( I ) , only a small number have been evaluated as tracers of urban sewage pollution (2). Among them, surfactants and related products, probably the largest class of technical products of domestic use, are potential candidates for that purpose. Accordingly, previous studies have reported on the identification in municipal sludges and aquatic sediments of some refractory components derived from nonionic and anionic surfactants (3-5). Cationic surfactants are also widely used in consumer products as fabric softeners and antistatic agents, cosmetic formulations, and sanitizing and antiseptic components. Industrial applications as dispersing agents, corrosion inhibitors, and asphalt emulsifiers have also been reported (6). Although they are removed efficiently from sewage in wastewater treatment plants (>go%), trace amounts can be released into the aquatic environment. However, at present very little is known about their occurrence and fate in coastal waters. Very recently (7), we discovered a new group of conservative pollutants in urban sewage and coastal waters and sediments, the trialkylamines (TAMs), which were proposed as specific markers of cationic surfactants. The concurrence of these compounds in the aquatic compartments of coastal areas with tetraalkylammonium surfactants and with other hydrophobic components, namely, long-chain alkylnitriles (LANs), arising from their synthetic pathways, confirms the common origin of all of them and their value as molecular tracers of urban sewage pollution. Experimental Section Workup Procedure. Freeze-dried particulate matter, recovered from wastewaters and seawater on glass fiber filters (Whatman GF/C), was Soxhlet extracted with dichloromethane. Dissolved organic matter was recovered from filtrates by liquid-liquid extraction (dichloromethane). Sediments, collected with a box corer (top 2 cm), were freeze-dried and sequentially extracted with dichloromethane and methanol. Methanolic extracts were analyzed directly by FAB-MS and high-temperature GCMS, whereas dichloromethane extracts were fractionated by column chromatography using 8 g each of 5% waterdeactivated neutral alumina and silica (Merck, 70-230 mesh). A total of seven fractions (I-VII) was obtained by elution with 20 mL of increasing mixtures of dichloromethane in hexane ( O % , l o % , 20%, 5070, and loo%), of 10% methanol in dichloromethane and diethyl ether. 0013-936X/91/0925-0547$02.50/0
LANs and TAMs were eluted in fractions IV and VII, respectively. Fortified samples extracted and fractionated by the same procedure provided recoveries higher than 60-90% and relative standard deviations in the order of 5-10% for TAMs and LANs, respectively. I n s t r u m e n t a l Analysis. Fractions IV (dichloromethane-hexane, 1:1) and VI1 (diethyl ether) were analyzed with a Carlo-Erba Mega series GC instrument coupled to FID and NPD detectors using cold on-column injection. Detector temperatures were held at 380 and 320 "C, respectively. The oven temperature was programmed from 90 to 370 "C at 6 "C min-l. An OV-1 column (10 m x 0.25 mm i.d. and 0.15 pm of film thickness) was used with hydrogen as carrier gas (50 cm s-l). Methanolic extracts were directly injected into the GCFID, for the semiquantitative determination of DMDTAC as tertiary amines formed by thermal decomposition in the injector port (80% yield a t 400 "C) (8). HRGC-MS analyses were performed in a HewlettPackard 5988A instrument interfaced to a 9825A data system. Ion source and mass analyzer temperatures were set up to 200 and 120 "C, respectively. Electron impact mass spectra were obtained at 70 eV, scanning from 40 to 600 at 1.1 scans s-l. Positive ion chemical ionization mass spectra were also obtained for confirmation purposes, using 0.8 Torr methane or isobutane in the ion source. FAB-MS spectra were obtained in a VG updated MS9, equipped with a saddle field source and a VG11/250 data acquisition system. Sample matrices were prepared with thioglycerol saturated with sodium chloride being bombarded with a beam of -8 kV Xe atoms.
Results and Discussion Cationic surfactants may be bound to clay minerals, so that it is reasonable to assume that sediments, through precipitation of particulate material, may be a sink for these products in coastal areas. In fact, the qualitative analysis of sediments (Table I) collected in the vicinity of the Barcelona sewage outfall and its area of influence (Figure 1) showed clear evidence of dimethyldialkylammonium salts, when the methanol extracts were directly analyzed by FAB-MS. Although colorimetric and chromatographic methods exist for the determination of cationic surfactants in aquatic samples (9-13), the FAB-MS technique (24) provides rapid and conclusive information on the chemical identity of the species, namely, the number and length of the alkyl chains. These are indicated in the representative spectrum shown in Figure 2. Commercially, the synthesis of these quaternary ammonium salts involves the reaction of fatty acids with ammonia, in a combined liquid-phase-vapor-phase process, to form the corresponding fatty nitriles (I). These long-chain alkylnitriles
0 1991 American Chemical Society
Environ. Sci. Technol., Vol. 25, No. 3, 1991 547
Table I. Distribution of LANs, TAMS, and DMDTA Surfactants in a Coastal Environment (Figure 1 ) sampling sitea
LANs (RCN) R = C17d
R =
1 dissol 1 partic
0.5 f 0.3 2.3 f 0.6
CIS
780
1
2 dissol 2 partic 1
3 4
5 6
3 4
0.3 f 0.2 2.0 f 0.4 390
0.14 2.72
R = C1,
TAMS (CH3NRIR2) RI = Ci6; R1, R, = '218 Rz = CIS
DMDTA ((CHJ2NR1R2)+ RIB R1 = c16; RI, Rz = C1cd R2 = Clad Rz = Clad
~
Influent Urban Wastewater,* wg L-' 0.3 f 0.1 9f6 55 f 45 32 f 25 0.4 f 0.1 26 f 4 80 f 15 63 f 20 605
0.06 1.98
R1, Rz = C16
Primary Sewage Sludge, ng g-I dry wt 5230 18400 19100
0.02 2.35
820 32 13 8 0.1
410 26 5 9 -
630 43 18 7 0.2
35 270
28 122
63 213
-
-
-
-
-
++
++
+t
-
-
-
++ + +
Coastal Seawater, ng L-' 0.9 2.2 3.8 20.0
1.4 15.5
Sediments, ng g-' dry wt 4770 11100 580 2270 1700 5300 1040 4300 0.8 1.9
19100 2500 4600 4130 1.5
-
++ + + + -
Biota: ng g-' dry wt 34 153 49 132
260 147
-
-
+
"Numbers correspond to those indicated in Figure 1. bMean of three samples. 'Polychaetes sp. centrations in the p g / g and ng/g range, respectively.
d-,
+t
+ + + -
-
not determined;
++ and +, con-
100
17 H35CN
110
6
I1
0
W
W U > z
41'
2d
54
wa
Km
4
,BARCELONA .
0 100
I
Q
2'10'
Figure 1. Sampling sites. Station 2 was a transect parallel to the coast, as indicated.
(LANs) are converted by hydrogenation to primary or secondary amines, depending on the reaction conditions. Reductive alkylation of these amines with formaldehyde affords the trialkylamines (TAMS) (II), which are quaternized by exhaustive alkylation with methyl chloride to the final di- or trimethylalkylammonium salts (111) (15): RCOOH
+ NH3
--C
RCN (1)
Ht/NI
RCHzNHz + (RCH2)zNH
300 rnh
200
100
rP F4 34 ua
Km
4
*l
H3C,i,R1
"4
H3C'
'R2
I
(111)
lCHIO"z/N'
R = CI~HZ~-CI~HS R1 = CH3 or C14H20-C18H37 b = C14HZB-Cl8H37
RCHzN(CH3)z + (RCH2)zNCHs (11)
l
[RIRzN(CH~)ZI*CI(III)
Extensive purification of these products is not required to achieve the activity of the final product, so that most commercial cationic surfactants are associated with a mixture of their starting materials and reaction interme548
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Environ. Sci. Technol., Vol. 25, No. 3, 1991
268
0 100
200
300
400
500
600 rn/z
Figure 2. Mass spectra of octadecylnitrile ( I ) and methyldioctadecylamine (I I ) obtained by GC-EIMS of coastal sediment fractions I V and V I I , respectively, and of dimethyklialkylammonium surfactants (111) obtained by FAB-MS of the methanol sediment extract.
FRACTION
On the basis of these spectral data, the rest of the components were found to belong to homologous series with molecular ions ranging, respectively, between m / z 209-265 and 499-535, at intervals of 14 daltons. The positive-ion chemical-ionization mass spectra displayed, respectively, the (M I)+ and (M - 1)+ions as the base peaks, so that the concurrence of LANs (I) and TAMs(I1) in coastal sediments was conclusively established. It is worth mentioning that the profile exhibited by LANs is very close to that of natural fatty acids, including unsaturated species. On the other hand, we were also able to identify in fraction VI1 long-chain trialkylamines by using high-temperature GC-NPD (370 "C), as shown in Figure 3, thus supporting the idea that TAMs originate from impurities in the surfactant and not by in situ conversion from DMDTAC. The distribution of LANs and TAMs in surficial sediments off Barcelona (Table I) exhibits a concentration gradient consistent with the distance from the urban sources. However, it is apparent that there are relative differences among the samples in both sewage markers that may be attributed to their different fate in the aquatic environment. In fact, the ratio of LANs, TAMs, and DMDTAC in the commercial surfactant is roughly 1:1.6:3300, whereas in the sewage sludges and surface sediments is in the order of 1:20:50 (Table I), considering that the concentration of DMDTAC in these samples was found to be 100-200 pg/g. This mainly reflects the preferential decay of the surfactant throughout the sewage treatment process. Moreover, the ratio of TAMs to LANs is also substantially higher in all samples with respect to that in the surfactant. This increase most likely relates to (i) preferential chemical (hydrolysis) or biological degradiation of LANs or (ii) preferential dissolution of LANs or adsorption of TAMs. The data on the different water samples suggest degradation as the most probable mechanism, because the ratio is even higher in seawater. LANs seem to be also less persistent when the relative concentrations in sampling sites 1, 4, and 5 are compared. However, they may still be recognized in areas rather removed from the source (e.g., station 6). The preferential association of these components with the particulate phase, particularly in seawater (Table I), where presumably the physicochemical equilibrium conditions have been reached, suggests that adsorption and sedimentation constitute a significant transport pathway of these compounds in coastal environments, possibly preventing degradation. Differences in sorption partition coefficients (K,) may also contribute to the relative variability of concentrations. Although the ecotoxicity of these components in the marine environment is still unknown, their expected hydrophobicity may enhance the transfer and accumulation to marine, particularly benthic, biota. As shown in Table I, the levels in polychaetes collected in the area are quite high and should reflect a different behavior either physor biochemical, because these organisms icochemical Wow) are relatively more enriched in LANs. In any case, the widespread occurrence of LANs, TAMs, and DMDTAC surfactants in the different aquatic compartments has been demonstrated and provides a useful approach for assessing the distribution of urban sewage discharges in coastal areas. However, further research is required for a precise understanding of their fate in the marine environment.
+
30
tJrnin.1
240
T. ( " C )
m ?T
9 FRACTION
TLII
9b 260 3 h T. ('C) Figure 3. HRGC-NPD of fractions I V (alkylnitriles)and V I 1 (trialkylamines) of sediment extracts. Numbers on the peaks indicate the number of carbon atoms of the alkyl chains. 18' indicates an unsaturated species.
diates. In this respect, we found in dimethylditallowammonium chloride (DMDTAC), the most common cationic surfactant used in laundry detergents, concentrations of 300-320 Fg 8-l of CI4-Cl8 LANs (I) and of 450-500 yg g-' of TAMS (11). When we analyzed the different fractions of the above sediment extracts (Table I) by HRGC-NPD we found significant profiles in two of them, fractions IV and VI1 (Figure 3). The corresponding analysis by HRGC-MS suggested that alkylnitriles (I) and amines (11) could account for the major peaks in these chromatograms. Representative electron impact mass spectra are shown in Figure 2. Assignments were confirmed by synthesis of the indicated products (16, 17).
Acknowledgments
We are indebted to J. Rivera (CID-CSIC) for obtaining the FAB-MS spectra. Environ. Sci. Technol., Vol. 25, No. 3, 1991
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(13) De Ruiter, C.; Hefkens, J. C. H. F.; Brinkman, U. A. Th.; Frei, R. W.; Evers, M.; Matthijs, E.; Meijer, J. A. Int. J . Environ. Anal. Chem. 1987,31, 325-339. (14) Simms, J. R.; Keough, T.; Ward, S. R.; Moore, B. L.; Bandurraga, M. M. Anal. Chem. 1988,60, 2613-2620. (15) Jungerman, E. In Baileys industrial oil and fat products; Swern, D., Ed.; J. Wiley: New York, 1979; Vol. I, pp 587-686. (16) Smiley, R. A.; Arnold, C. J . Org. Chem. 1960,25, 257-258. (17) Ralston, A. W.; Eggenberger, D. N.; Du Brow, P. L. J . Am. Chem. SOC.1948, 70, 977-979.
Received for review July 31, 1989. Revised manuscript received November 16, 1989. Accepted December 1, 1989. Financial support was provided by the EEC through the EROS 2000 project.
