Environ. Sci. Technol. 1992, 26, 2409-2493
BTEX from Gasoline-Oxygenate Compounds; API Publication 4531;American Petroleum Institute: Washington, DC, 1991. (17) Brookman, G. T.;Flanagan, M.; Kebe, J. 0. Laboratory studies on solubilities of petroleum hydrocarbons in groundwater. TRC Environmental Consultants project 2663-N31-00,prepared for Environmental Affaris Department, American Petroleum Institute, Washington, DC, 1985. (18) Morris, K.R.;Abramowitz, R.; Pinal, R.; Davis, P.; Yalkowsky, S. H. Chemosphere 1988,17,285-298. (19) Banerjee, S.;Yalkowski, S. H. Anal. Chem. 1988, 60, 2153-2155. (20) Barker, J. F.; Patrick, G. C.; Major, D. Ground Water Monit. Rev. 1987,7(4),64-71.
(21) Verscheuren, K. Handbook of Environmental Data on Organic Chemicals, 2nd ed.; Van Nostrand Reinhold Co.: New York, 1983. (22) Barker, J. F.; Hubbard, C. E.; Lemon, L. A.; Vooro, K. A. In Hydrocarbon Contaminated Soils and Groundwater; Calabrese, E. J., Kostecki, P. T., Eds.; Lewis Publishers: Chelsea, MI, 1977;Chapter 7,pp 103-113.
Received for review January 15,1992. Revised manuscript received August 11,1992. Accepted August 14,1992.Funding for this study was provided by the American Petroleum Institute (API) and by the Ontario University Research Incentive Fund (URIF). A NATO Collaborative Research Grant facilitated this research.
Hydroxylamine Hydrochloride-Acetic Acid-Soluble and -Insoluble Fractions of Pelagic Sediment: Readsorption Revisited David Z.
and Greg A. Wandied
US. Geological Survey, M/S 902, Menlo Park, California 94025, and US. Geological Survey, M/S 990, 12202 Sunrlse Valley Drive, Reston, Virginia 22092
The extraction of the rare earth elements (REE) from deep-ocean pelagic sediment, using hydroxylamine hydrochloride-acetic acid, leads to the separation of approximately 70% of the bulk REE content into the soluble fraction and 30% into the insoluble fraction. The REE pattern of the soluble fraction, i.e., the content of REE normalized to average shale on an element-by-element basis and plotted against atomic number, resembles the pattern for seawater, whereas the pattern, as well as the absolute concentrations,in the insoluble fraction resembles the North American shale composite. These results preclude significant readsorption of the REE by the insoluble phases during the leaching procedure. Introduction Pelagic sediment is a complex mixture of detrital debris and seawater-derived material (1). The detrital fraction consists of terrigenous material (introduced to the oceans via riverine and aeolian transport) and marine volcanic debris. The seawater-derived fraction is present predominantly as iron and manganese oxyhydrides (the hydrogenous fraction) and CaC03,opal, and organic detritus (the biogenic fraction). The distribution and abundance of the detrital and seawater fractions, their composition and rates of accumulation, and their alteration products vary within the oceans over a wide range (2-6). Despite this complexity, geochemists have attempted to identify the composition of these fractions, in order to examine the past record of such phenomena as aeolian transport of terrigenous material, biological productivity in the photic zone, hydrothermal activity along midocean ridges, and sediment diagenesis as it might relate to metallogenesis. Efforts to partition the major and minor elements of sediment among these various fractions have adopted one of two quite different approaches. One has been to model the bulk composition, assuming end-member compositions for the different fractions (7,8).The second has been to isolate the various fractions by leaching sediments using one of a number of sequential procedures, which have been 'U.S. Geological Survey, Menlo Park,CA. t U.S. Geological Survey, Reston, VA.
developed by geochemists interested in freshwater as well as marine environments (S21). Modeling has dealt largely with the major oxide composition of the sediment, whereas leaching experiments have tended to focus on its minor element composition. Both procedures have limitations, but studies utilizing various leaching procedures have come under exceptionally sharp attack (22,23).Belzile et al. (16) and Tessier and Campbell (20,21) have addressed, in some detail, many of the problems identified with the leaching techniques (17-24). In this paper we examine the effects of sediment drying prior to leaching and possible readsorption of dissolved elements during the leaching experiment. We consider the following: (1)the leaching of the rare earth element(s) (REZ) from a natural (pelagic) sediment by the acid-reducing solution of hydroxylamine hydrochlorideacetic acid (HHAA), (2) their leaching by HC1, and (3) the extent of readsorption of REE by the insoluble residue by leaching the insoluble residue using HC1. Chester and Hughes (IO) developed the widely used HHAA technique, specifically for the strongly oxidized sediment of the deep ocean. The aim of their work was to isolate the seawater-derivedfraction of heavy metals in the sediment from the detrital fraction. The detrital fraction was assumed to be composed of lithogenic material. Chester and Hughes further showed that it was relatively nonreactive in their procedure (IO),and this has been substantiated by subsequent research (15). The seawater-derived fraction was considered to be present largely as oxides of Fe and Mn. HHAA also dissolves CaC03, but they selected a sample that contained little CaC03, as have we. Also, work by Palmer has shown that this component likely contributes negligibly to the heavy metal inventory of the sediment, even at relatively high CaC03 contents, and this finding can be extended to include the REE (25). The results of our research on the leaching of the REE, thus, further evaluate the earlier leaching experiments of Chester and Hughes (IO)and address recently advanced criticisms of this technique. Compared with a single heavy metal, the REE present a major advantage for examining the problems associated with leaching experiments that attempt to ascertain the partitioning of elements in sed-
Not subject to U S . Copyright. Published 1992 by the American Chemical Soclety
Envlron. Sci. Technol., Vol. 26, No. 12, 1992
2489
Table I. Treatment of Sample Aliquants (in Duplicate) Prior to Analysis of the Insoluble Residue by INAA" (1)Untreated sediment analyzed in this experiment and in 1984 (15,28,36).Analysis gives bulk REE content of the sediment, dried at 25 and 60 OC, respectively. (2)Sediment (wet) leached with 50 mL of HHAA [lM hydroxylamine hydrochloride and 25% (v/v) acetic acid] for 4 h at room temperature, continuously shaken. Procedure is that recommended by Chester and Hughes (IO). The fraction of REE in the residue is referred to as the HHAA-insoluble fraction in the text and figures. The HHAA-soluble fraction is obtained by reducing the REE values in the residue by the percent loss of weight on leaching (12%) and subtracting from the untreated-sample values (3)Sediment dried at 25 (this study) and 60 "C (15) and then treated according to the procedure in (2) (4)Sediment sample (wet) first treated with 50 mL of HHAA. The leachate was decanted and the residue washed and then treated for 1 h with 0.2 M HCI (22).The difference in content with the HHAA-insoluble fraction gives an estimate of the upper limit for REE readsorption during a single HHAA leaching (5) Sediment (wet) leached for 1 h with 0.2 M HCl (22).The HC1-soluble fraction is obtained as described above (2) (6)Sediment (wet) leached for 2 h with 0.2 M HCl "All experiments were carried out at room temperature and shaken continuously. Three-gram samples (wet weight) were used in the initial step of all six treatments.
iments and sedimentary rocks. This is particularly true when several of the group of REE are analyzed rather than merely an individual of the group. The REE exhibit a slight decrease in ionic radius with increasing atomic number and, within the sedimentary environment, they have a valence of 3+. Ce is the only exception, being oxidized to the relatively insoluble 4+ valence state in seawater (26). As a result of this similarity, the REE are only slightly fractionated during weathering, aeolian and riverine transport, and sedimentation. Their relative concentrations in any one component of the sediment thus reflect the source of that component, in much the same way that stable isotope ratios of, for example, strontium and neodymium are interpreted (27). Technique The sample analyzed in this study was taken from box core DJ 18 (10-14 cm), collected by the R/V Oceanographer (cruise RP-1-OC78) at DOMES site A (09'25.6' N, 151'31.2' W) in the North East Pacific Basin. The sediment is a siliceous clay (28) of Quaternary age (29),composed of approximately 20-25% biogenic silica (opal), 75% detrital material, 0.4% organic carbon, and 0.5% Mn and Fe (present as hydrous oxides). Subcores of the box core were stored in D-tubes at 4 ' C to maintain moisture content and reduce bacterial activity. Aliquants of the sample were weighed wet, leached without drying, and then dried prior to analysis. Five aliquants were weighed wet and then dried a t 25 'C to a constant weight, to measure moisture content. The weight loss was 66.5 f 1%for all five analyses. This value has been used to convert the wet weight of samples to a dry weight basis. Two aliquants were dried before leaching to evaluate the effect of drying. The leaching experiments were carried out on 10 aliquants of the sample using HHAA, HC1, and the two in sequence (Table I). All leaching experiments were carried out in duplicate. The REE of the insoluble residues were measured by neutron activation analysis (INAA) as discussed by Baedecker and McKown (30).Thus, the amount of the REE actually leached was determined by difference between the treated aliquants and the untreated sample. The precision for INAA is better than 10% for most of the analyses. Previous analyses of the same sample, made in 1985 (28), show agreement within 10% of most of the currently reported values (columns 1and 3 of Table 11) despite the sample in the previous experiment having been dried prior to leaching. T b is the exception. Duplicate analyses in this study agree within 5%. One advantage of this procedure to evaluate readsorption is that natural sediment is used in the experiment rather than a synthetic mixture of standard minerals and organic compounds. A synthetic mixture may or may not react during the chemical leaching as its sedimentary 2490
Environ. Scl. Technoi., Vol. 26, No. 12, 1992
Table 11. REE Concentrations (ppm) in Insoluble Residues of Sample Aliquants Treated with HHAA and HCl and in Untreated Sediment" untreated elem sample (1) (2) La Ce Nd Sm Eu Tb Yb Lu LoLd
65 (66)* 85 (84)
70 (71) 20 (20) 4.5 (4.4) 3.2 (2.8) 9.8 (9.4) 1.4 (1.4)
25 43 21 4.5 0.96
insoluble residue HHAA HCl dried (3) HC1 (4) 1 h (5) 2 h (6)
24 (Wb 44 (50) 19 (21) 4.3 (4.3) 0.88
23
37
32
40
88c
80
16
36
30
3.6
8.9
6.9
0.76
1.9
1.5
0.54
1.3
1.0
2.1
4.0
3.3
0.28
0.57
0.48
13
12
14
(0.82)
0.68 2.5 0.34 12
0.69 (0.57) 2.3 (2.3) 0.33 (0.35) 13
"Numbers in heading refer to Table I. bAnalyses in parentheses were carried out in 1985 (28), on samples dried at 60 OC prior to leaching. This value is higher than Ce in the bulk sediment (column l), owing to the loss of 12% by weight of sediment on leaching. The value should be reduced by this amount to give the concentration of insoluble Ce in the bulk sediment. dLoL loss on leaching, in weight percent of dry sample, approximately 10% of which is present as sea salt. This estimate is based on a decrease of Na, on washing in distilled water, from 3.68 to 0.63%.
counterparts (21). In addition, no elemental tracers are added to the experiment. The major disadvantage is that we do not actually measure readsorption, but can merely place an upper limit on its possible effect. Other studies also have had to infer readsorption, the single exception being the study by Tipping et al. (19). The advantage of INAA over several of the other techniques used to measure the REE is that INAA measures the total inventory of REE in the sample. Other techniques, for which the sample must be dissolved with a mixture of HF and other acids, run the risk of introducing severe inaccuracies associated with the dissolution step prior to analysis for REE (31, 32). One source of these inaccuracies is the incomplete dissolution of highly insoluble trace minerals such as rutile and zircon, which can contain high concentrations of REE and relative concentrations far different from that of the bulk sample (33). Results and Discussion The "AA solution leaches between 55% (Ce) and 82% (Eu and Tb) of the REE in sample DJ 18 (10-14). Chester
.. .. .
and Hughes (10)found that similar amounts of the heavy metals Mn and Ni and minor amounts of Fe, albeit relative to their bulk contents, were leached by this solution. These results are similar to those of Bowser et al. (11),Calvert et al. (12),Boust et al. (141,Piper (I5),Lyle et al. (131, Health and Dymond (34),Fischer et al. (35),and others who used this, or another somewhat different, technique. The l-h HC1 technique leaches significantly less of all REE than the HHAA procedure (less than 60% of all REE and less than 10% of the Ce). The 2-h HC1 leach removes an additional 510%. This result is similar to that reported by Heath and Dymond (34),who found that a second HC1 treatment leached significant amounts of Fe from pelagic, Bauer Basin sediment. This behavior of Fe, i.e., the possible incomplete dissolution of the seawaterderived component, may account for the seemingly low Ce recovery of 10% by the HC1 leach. Elderfield et al. (27) have shown that the seawater-derived Ce in pelagic sediment is largely associated with a hydrous iron oxide phase, whereas the other REE are associated predominantly with a phosphatic phase (15,27). Treatment with HC1, following the initial leach with HHAA, removes only an additional approximately 4% of all REE. These low yields for the HC1 extraction, following the treatment with HHAA, indicate negligible REE readsorption during the HHAA treatment, based on the behavior of a radioactive Eu tracer in a 0.2 M HC1 solution (22).
The aliquants dried prior to leaching with HHAA and those analyzed in an earlier study of the DJ samples (28) gave the same results as those treated without drying. The agreement was not totally unexpected as the sediment accumulated on the sea floor under strongly oxidizing conditions was stored wet under oxidizing conditions, was dried under oxidizing conditions, and was leached under oxidizing conditions. The results of the leaching experiments reported here and, specifically, the estimate of readsorption are in sharp contrast to those of Sholkovitz (22),who has questioned the validity of the interpretation of REE partitioning in pelagic sediment based on HHAA extractions (14,25).He observed that up to 70% of a radioactive-labeled Eu tracer was (reladsorbed during the leaching of a nearshore sediment with HHAA,and by implication, 70% of the entire REE group was (reladsorbed. None of the Eu was (re)adsorbed in an HCl solution of 0.2 M and stronger concentration. Clearly, 70% of the Eu and the other REE cannot be readsorbed during the initial HHAA leaching of pelagic sediment if up to 82% is solubilized, as shown in Table 11. Previously published studies of pelagic sediment have reported similar high efficiencies (14,15,28, 361,a finding that critics of this technique have failed to acknowledge (22). The apparent difference between these results and those of Sholkovitz is possibly due to the following factors: 1. Sholkovitz analyzed sediment collected from Buzzards Bay, MA. Although this sediment may be "typical coastal sediment" (22),it is not representative of pelagic sediment, the type of sediment for which Chester and Hughes (IO)specifically designed their HHAA technique. Important differences between the two types of sediment are likely to be a higher concentration of organic matter, as well as a much larger labile component of organic matter, in the bay sediment and a higher concentration of metal oxides in the pelagic sediment. It is, perhaps, unreasonable to expect that any single leaching technique, applied indiscriminately to two such different sediments, should yield other than ambiguous results.
...
. .
.
,
. . . .. . .
.
.
.
. ..
. ..
.
.
1
f\ f 01
La Ce
Nd
Sm Eu Tb Rare Earth Element
Yb Lu
F W e 1. REE pattern of the soluble fractions in sample DJ 18 (10-14). Values have been normaked to shale on an e l e m e n t - b y e basis. See Table I for a descrlptlon of the leaching procedure. The REE contents of the two soluble fractions were adjusted to their concentration in the bulk sedlment by reduclng their concentrations In the Insoluble residues by bss of weight of sediment on leeching (Table 11). The relathre depletion of Ce In both soluble fractions Is referred to In the text as a negathre anomaly. I t Is calculated using the following equation: [Ce](anomaly) = log [3[Ce0]/(2[La'] [Nd'])], where the asterisked values are shale-normallred. The Ce anomaly for the HHAA-sdrble fractbn is, thus, 0.31. The readsorptkn maximum m e represents the REE fraction leached by HCI, following the HHAA leaching, column 2 minus column 4 In Table 11.
+
2. Chester and Hughes recommended the use of 1 g of sediment (dry weight) in 50 mL of a solution 1 M hydroxylamine hydrochloride in 25% acetic acid (v/v), shaken for 4 h, at room temperature. On the other hand, Sholkovitz did not use these conditions but rather two alternative schemes: 0.02 M hydroxylamiie hydrochloride in 25% acetic acid (v/v), shaken for 1 h at room temperature and 0.04 M hydroxylamine hydrochloride in 25% acetic acid (v/v), shaken for 6 h, at 96 "C. Although the near-complete leaching of Fe and Mn is achieved at the higher temperature and lower concentration (IO),"at high temperatures the clay mineral lattices appear to be attacked" (ref 10, p 256). But more to the point, these procedures simply do not reproduce the conditions recommended by Chester and Hughes and used by subsequent workers. 3. Eu may not have been the best REE choice for estimating the behavior of the entire group. It can occur in both the 2+ and 3+ valence states. Evidence supports its occurrence as 3+ in the marine pelagic environment and during its extraction from pelagic sediments by HHAA (its shale-normalized content in marine pelagic and detrital phases is similar to that of its neighboring REE; Figures 1 and 2 and references cited above and in the figure captions). This is possibly not the case for Eu in coastal sediments and Buzzards Bay sediment specifically. Elderfield and Sholkovitz (37)have shown that the 1.75 M HC1-soluble fraction of this sediment (their labile fraction) clearly has a negative Eu anomaly. Although this does not offer any direct evidence that Eu will behave anomalously in the HHAA-reducing leaching experiment, it d m suggest that Eu may not be representative of the other REE in leaching experiments of this and other coastal sediments. The REE pattern of the fraction solubilized by 1 M "-25% AA also suggests that HHAA is a highly selective leaching solution for the REE in pelagic sediment. The pattern has a negative Ce anomaly and slight enrichment of the heavy REE (Figure 1); this pattern is similar to the pattern for seawater (Figure 2) and is unique to seawater and several sediment phases that unequivocally have a marine origin (15,25-28,36-38). The fact that this soluble Environ. Sci. Technoi., Vol. 26, No. 12, 1992 2491
other REE in the HC1-insoluble residue show even larger variation with the NASC (Figure 2).
10
t
msedlm
0 1
La Ce
Nd
Sm Eu
Tb Rare Earth Element
Yb Lu
Flgure 2. REE patterns for Pacific Ocean near-surface -water (26), NASC (33), bulk sedlrnent of sample DJ 18 (10-14), and the HHAAand HCi-insoluble fractions of the DJ sample, all normallzed to shale (75). The slightly higher Ce content in the HCI-lnsoluble fraction than in the bulk sediment reflects a greater loss of weight for the bulk sediment of about 12% than the loss of Ce of about 10%. The open circles, which are plotted along the curve for the NASC, represent the content of REE in the HHAA-lnsolubleresidue, calculated on a biogenic silica-free basis.
fraction constitutes approximately 70% of the bulk REE inventory in the sediment and exhibits a seawater-type REE pattern strongly suggesta that it has a seawater origin and is not merely some operationally defined fraction of the sediment. These data do not establish the host phase for the soluble fraction of REE, but rather its source. As noted earlier, Elderfield et al. (27) and Piper (15) have shown that a major host is a phosphatic phase. The composition of the HHAA-insoluble residue of sample DJ 18 (10-14) supports this interpretation of the leaching experiment. In contrast to the soluble fraction, the insoluble residue has roughly a flat, shale-normalized pattern (Figure 2) and an absolute REE concentration similar to that of the North America shale composite (NASC) plus marine biogenic silica. The insoluble residue is composed of approximately 75% detrital material, whose dominant source is likely the North American continent ( 2 , 6 , 39), and 25% biogenic opal (28);it has an La concentration of 25 ppm (Table 11,column 2). If we assume the La content of biogenic silica is 5.8 ppm, ita content in isolated plates of the diatom Ethmodiscus rex (27),and adjust for the amount of biogenic silica in the insoluble residue and its contribution of La, the La content in the detrital fraction alone is 31 ppm. The La content of the NASC is 31.1 ppm (33). The other REE values of the insoluble residue, similarly adjusted, also plot on or close to the NASC curve (Figure 2). This agreement is far better than we might have expected, given the heterogeneity of the NASC (33) and the uncertainty that any set of average values is representative of such a complex source. One major uncertainty in the calculation itself is the amount of biogenic silica present. If we consider a minimum Si02:A1203ratio for the detrital fraction of 2.2:l (40) and a maximum value of 3.3:l (41) in order to estimate the content of biogenic silica, the La content in the detrital fraction will range from 29 to 34 ppm. Also, if the biogenic silica fraction has a negligible REE content, similar to biogenic CaC03 (25),then the detrital fraction will have a La content of 33 ppm. Still, all values are close to the NASC value of 31.1 ppm. These same calculations,based on the La content of the HC1-insoluble fraction, give an La content in the detrital debris of 44-52 and 49 ppm. These values are approximately 50% higher than the La content of the NASC. The 2492 Envlron. Sci. Technol., Vol. 26, No. 12, 1992
Summary and Conclusions The HHAA-soluble fraction of the pelagic sediment sample contains approximately 70% of the total 3+ REE inventory, slightly less in the case of Ce. The REE pattern of this fraction resembles the pattern for seawater. It has a negative Ce anomaly of -0.31 and a slight enrichment of the heavy REE over the light REE. By contrast, the REE pattern of the insoluble residue, as well as the absolute concentration of REE, is virtually identical to the NASC. These results, which parallel the leaching results AA, of heavy metals, strongly suggest that 1 M "-25% as recommended by Chester and Hughes ( I O ) , selectively leaches the seawater-derived fraction of REE from oxic pelagic sediments, as well as the marine fraction of heavy metals ( I Q I 5 ) . The recovery of only a minor fraction of REE upon leaching the sediment residue with HC1, furthermore, precludes significant readsorption. Leaching the sediment with HC1 alone removes less of the total REE inventory than did HHAA. Although the pattern of the soluble fraction also resembles the pattern for seawater, the high REE content of the HC1-insoluble residue indicates that a significant portion of the seawater-derived REE in the sediment is not solubilized, Ce more so than the 3+ REE. For example, the Ce content of the insoluble residue is 88 ppm (Table 11), which adjusts to a content of about 115 ppm on a biogenic silica-free basis. This is 70% higher than the Ce content of the NASC (33). The low yield of Ce achieved by leaching with HC1 might result from the incomplete dissolution of a seawater-derived iron phase, with which Ce possibly coprecipitated. Although HHAA separates the marine fraction of REE from the detrital fraction, it is unlikely that it or any other single leaching technique will give unambiguous results when applied to different types of sediment (e.g., oxidizing versus reducing). Moreover, a single technique is likely inadequate to address such different questions as the partition of elements among their host phases (detrital, biogenic, and authigenic), as opposed to studies investigating the supply of elements to the sea floor by source phases (terrigenous,volcanic, biogenic, and hydrogenous). The success of a leaching procedure to address the questions being asked can probably only be evaluated by analyzing each step of the procedure using the actual sediment being investigated. The REE, as well as stable isotopes of several elements, represent particularly attractive elements for evaluating many of the techniques currently used by geochemists. Literature Cited (1) Goldberg, E.D.In Marine Geology; Sherpard, F.A., Ed.; Harper and Row: New York, 1963; pp 436-466. (2) Griffin, J. J.;Goldberg, E.D.In The Sea, 1st ed.; Hill, M. N., Ed.; John Wiley: New York, 1963;Vol. 3,Chapter 26. (3) Skornyakova, I. S.Int. Geol. Rev. 1965,7, 2161-2174. (4) Piper, D. L.;Williamson, M.E.Mar. Geol. 1977,23,285-303. ( 5 ) Bostrom, K.;Lysen, H.; Moore, C. Chem. Geol. 1978,23, 11-20. (6) Windom, H. L. Geol. SOC.Am. Bull. 1969,80,761-782. (7) Dymond, J. In Nazca Plate: Crustal Formation and Andean Conuergence;Kulm, L. D.,Dymond, J., Dmch, E.J., Huasong, D.M.,Eds.; Mem.-Geol. SOC.Am. 1981,No.154, 133-173. (8) b i n e n , M.;Pisias, N. Geochim. Cosmochim. Acta 1984,48, 47-62. (9) Goldberg, E.D.;Arrhenius, G. Geochim. Cosochim. Acta 1958,13,153-212.
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Chester, R.; Hughes, M. J. Chem. Geol. 1967,2,249-262. Bowser, C. J.; Mills, B. A.; Callender, E. In Marine Geology and Oceanography of the Pacific Manganese Nodule Province; Bischoff, J., Piper, D. Z., Eds.; Plenum: New York, 1979;Vol. 9, pp 587-619. (12) Calvert, S. E.; Price, N. B.; Heath, G. R.; Moore, T. C. J. Mar. Res. 1978,36, 161-183. (13) Lyle, M.; Heath, G. R.; Robbins, J. Geochim. Cosmochim. Acta 1984,48,1705-1715. (14) Boust, D.; Carpenter, M. S. N.; Joron, J. L. Chem. Geol. 1988,68,69-87. (15) Piper, D. Z.Geochim. Cosmochim.Acta 1988,52,2127-2145. (16) Belzile, N.: Lecomte, P.; Tessier, A. Environ. Sei. Technol. i989,23,ioi5-1020. (17) Tessier, A.; Campbell, P. G. C.; Bisson, M. Anal. Chern. 1979,51,844-851. (18) Rendall, P. S.;Battery, G. E.; Cameron, A. J. Environ. Sei. Technol. 1980,14,314-318. (19) Tipping, E.; Hetherington, N. B.; Hilton, J.; Thompson, D. W.; Bowles, E.; Hamilton-Taylor, J. Anal. Chem. 1985,57, 1944-1946. (20) Tessier, A.; Campbell, P. G. C. Anal. Chem. 1988, 60, 1475-1476. (21) Tmier, A.;Campbell, P. G. C. Water Res. 1991,25,115-117. (22) Sholkovitz, E. R. Chem. Geol. 1989,77, 47-51. (23) Nirel, P. M. V.; Morel, F. M. M. Water Res. 1990, 24, 1055-1056. (24) Nirel, P. M. V.; Thomas, A. J.; Martin, J. M. In Speciation of Fission and Activation Products in the Environment; Bulman, R. A., Cooper, J. R., Eds.; Elaevier: London, 1986; pp 19-26. (25) Palmer, M. A.Earth Planet. Sei. Lett. 1985,73,285-298. (26) DeBaar, H. J. W.; Bacon, M. P.; Brewer, P. G.; Bruland, K. W. Geochim. Cosmochim. Acta 1985,49, 1943-1959.
(27) Elderfield, H.; Hawkesworth, C. J.; Greaves, M. J.; Calvert, S. E. Geochim. Cosmochim. Acta 1981,45,513-528. (28) Piper, D. Z.;Rude, P. D. Open-File Rep.-U.S. Geol. Surv. 1985,NO.85-353. (29) Piper, D. Z.;Blueford, J. R. Deep-sea Res. 1982, 29, 927-952. (30) Baedecker, P. A.;McKnown, D. M. U.S. Geol. Surv. Bull. 1986,No. 1770. (31) Sholkovitz, E. R. Am. J . Sci. 1988,288,236-281. (32) Sholkovitz, E. R. Chem. Geol. 1990,88, 333-347. (33) Gromet, L. P.; Dymet, R. F.; Haskin, L. A,; Korotev, R. L. Geochim. Cosochim. Acta 1984,48,2469-2482. (34) Heath, G. R.; Dymond, J. Geol. SOC.Am. Bull. 1977,88, 723-733. (35) Fischer, K.; Dymond, J.; Lyle, M.; Soutar, A.; Rau, S. Geochim. Cosmochim. Acta 1986,50,1535-1543. (36) Piper, D.Z.;Rude, P. D.; Monteith, S. Mar. Geol. 1987,74, 41-55. (37) Elderfield, H.; Sholkovitz, E. R. Earth Planet. Sei. Lett. 1987,82,280-288. (38) Goldberg, E. D.; Koide, M.; Schmitt, R.; Smith, R. J. Geophys. Res. 1963,68,4209-4217. (39) Hurley, P. M.; Hart, S. R.; Pinson, W. H.; Fairbairn, H. W. Geol. Soc. Am. Bull. 1959, 70, 1622 (abstract). (40) Eggimann, D. W.;Manheim, F. T.; Betzer, P. R. J. Sediment. Petrol. 1979,50,215-226. (41) Bischoff, J. L.; Heath, G. R.; Leinen, M. In Marine Geology and Oceanography of the Pacific Manganese Nodule Province; Bishoff, J. L., Piper, D. Z., Eds.; Plenum Press: New York, 1979;pp 397-436.
Received for review March 9,1992. Revised manuscript received July 6, 1992. Accepted August 31, 1992.
Determination of Alkyl Sulfate Surfactants in Natural Waters Nicholas J. Fendlnger,' Willlam M. Begley, D. C. McAvoy, and W. S. Eckhoff The Procter and Gamble Company, The Ivorydale Technical Center, 5299 Spring Grove Avenue, Cincinnati, Ohio 45217
rn An analytical technique was developed to monitor alkyl sulfate (AS) surfactants in natural water samples and determine AS removal during wastewater treatment. The method utilizes a reverse-phase extraction column followed by strong anionic and cationic exchange column cleanup steps. AS are then derivatized with N,O-bis(trimethy1sily1)trifluoroacetimide with 1% trichloromethylsilaneand analyzed by GC/FID as trimethylsilyl ethers. Total AS concentrations in wastewater varied as a function of time and were correlated with expected consumer use patterns of AS-containing products. Flow-weighted average total AS concentrations in influent wastewater were at least 2.4 times lower than expected based on mass balance predictions and were probably due to AS loss during wastewater conveyance. Removal of AS at two trickling filter treatment plants exceeded 90%. AS was not detected in the receiving streams monitored.
Introduction Alkyl sulfates (AS) are anionic surfactants that are currently used in shampoos, bath preparations, cosmetics, medicines, toothpaste, rug shampoos, hard surface cleaners, and light- and heavy-duty laundry applications (I). AS used in consumer products have alkyl chain lengths that range from C12to CIS (Figure 1)and may contain some methyl or ethyl branching. Total AS use in the United States is -1.4 X 105 metric tons/year with 9.1 X 104metric 0013-936X/92/0926-2493$03.00/0
tonslyear used in consumer products (2). Despite their widespread use, AS are usually measured in environmental samples by nonspecific analytical techniques such as methylene blue active substance (MBAS). This type of analysis measures AS along with other anionic surfactanta that contain sulfate or sulfonate functionalities (e.g., linear alkylbenzenesulfonate). The nonspecific methods are also subject to interferences from nonsurfactant organic sulfonates, sulfates, carboxylates,phenols, cationic surfactants, and amines as well as inorganic thiocyanates,cyanates, nitrates, and chlorides (3). Because AS are expected to be a small and variable fraction of the MB active material in natural waters, no correlation between levels of MBAS and AS is anticipated. Other approaches used to measure AS in product formulations and in water samples include gas chromatography (GC), liquid chromatography (LC), and LC/mass spectrometry (MS). GC techniques involve conversion of AS into a volatile moiety by reaction with a strong acid (HI, HBr) to form an alkyl halide (4, 5). Although this method has been shown suitable for environmental samples (51, the technique does not resolve AS from alkylethoxy sulfate. Because AS do not contain a chromophoric group, LC techniques that have been developed incorporate postcolumn extraction and derivatizationsteps to gain adequate sensitivity (6,7).Even though LC methods with postcolumn extraction and derivatization steps can be potentially used for environmental applications, the
0 1992 American Chemical Soc:lety
Environ. Scl. Technol., Vol. 26, No. 12, 1992 2493
