Linear alkyl benzenes (LABs) in sediments of Port Phillip Bay (Australia)

Marine Environmental Research 23 (1987) 65-76

Linear Alkyl Benzenes (LABs) in Sediments of Port Phiilip Bay (Australia) A. P. Murray, C. F. Gibbs Marine Science Laboratories, Department of Conservation, Forests and Lands, PO Box 114, Queenscliff,3225, Australia

& E E. Kavanagh School of Science, Deakin University, Victoria, 3217, Australia (Received 10 October 1986; revised version received 15 June 1987: accepted 22 June 1987)

ABSTRACT Linear alkyl benzenes (LABs), which have been proposed as markers of the hydrocarbon component of domestic wastes, were measured in sediments from three areas of Port Phillip Bay (Australia). The concentrations found ( O - 1 9 # g g - 1 ) were generally lower than those reported for other coastal sediments from the USA and Japan. This is thought to reflect the small quanti O' of domestic wastes entering Port Phillip Bay. Compositional profiles showed that both physical and biological processes had acted to remove LABs ¢h~ring deposition. A t one site, unusual alkvl benzene compounds, but no conventional LABs. were detected. These compounds were probably synthesised terrestrially by the bacteria of a nearby sewage farm.

INTRODUCTION The term linear alkyl benzenes (LABs) has been used to describe a group of phenyl alkanes having a benzene ring attached at any position except the 1position of a straight alkyl chain of between 9 and 15 carbons (Eganhouse et al., 1983). LABs are produced synthetically as precursors of the alkyl 65 Marine Environ. Res. 0141-1136"87/$03"50 ~ Elsevier Applied Science Publishers ktd, England, 1987. Printed in Great Britain

66

.4. P. Murray, C. F. Gibbs, P. E. Kavanagh

benzenesulphonate {ABS) surfactants and they remain as minor constituents of these surfactants alter the sulphonation process. Thus, they appear in domestic ~vastes and some eventually find their way into the marine environment(Crisp e t a & 1979; Eganhouse & Kaplan, 1982: Ishiwatari et al., 1983). At one time, LABs were thought to be constituents of marine humic matter but they are now recognised as ubiquitous pollutants (Harvey et al., 1983; 1985). The presence of LABs in sediments is likely to have little ecological significance in itsetfl since LABs usually make up only a small part of the total sedimentary hydrocarbons (Crisp et al., 1979; Burns & Smith, 1978). However, they may be useful probes in the study of factors mediating the natural removal of hydrocarbons from marine sediments. Eganhouse et al. (1983) showed that certain LABs could be preserved for decades in marine sediments and that they could be used, under appropriate

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L.-I Bs in sediments o f Port Phillip Ba~. Australia

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conditions, as geochronological markers, They also recognised a welldefined pattern of compositional change in the LABs as they moved from wastewater to ocean particulates to marine sediments. These changes were similar in one respect to those produced by microbial oxidation of ABS surfactants. That is, external isomers (in which the phenyl group is attached near to the end of the alkyl chain) were degraded faster than the internal isomers. This microbial alteration of the LAB composition has recently been demonstrated in the laboratory by Bayona et al. (1986). Corio Bay (latitude approximately 38: 7'S, longitude approximately 144 ~ 25' E) is an arm of Port Phillip Bay (Fig. 1) in south-eastern Australia. LABs were first identified here during 1976 by Burns & Smith (1982), who determined the likely source to be a coastal oil refinery containing an LAB synthesis plant. Thus in Corio Bay, in contrast to other study areas, the major source of the LABs is well defined, as is their composition at that source. This encouraged us to study the environmental alteration of LABs using the known starting material to quantify changes in the LAB compositional profile. A subsidiary aim was to determine whether LABs were present in other Port Phillip Bay sediments. METHODS Sediment samples were collected in July 1984 as part of a general survey of hydrocarbons in the sediments of Port Phillip Bay. All the sampling sites (Fig. 1), except for site 7, represent a subset of those used in the earlier survey by Burns & Smith (1982). Sediment cores were collected in plexiglass tubes (5 cm diameter) by divers and transported on ice to the laboratory, where they were kept frozen (-20~C) until analysis. The sample from site 7 consisted of coarse sand and shell but all others were fine silty mud and were obviously anaerobic at the time of sampling. The cores were cut into 5-cm slices while still frozen and all material which had contacted the liner was scraped off and discarded. Between 20 and 80 g of wet sediment from the top 0-5 cm were placed in a Soxhlet apparatus, together with an internal standard, n-nonadecylbenzene (Alltech Associates, Ill., USA). The sample was then extracted first with methanol and then with dichloromethane (DCM) for 24h each. The methanol extract was diluted with water and hydrocarbons were partitioned into hexane. Combined hexane and dichloromethane extracts were concentrated to 2 ml and subjected to chromatography on columns of alumina (10 ml) and silica (10 ml) prepared in n-hexane. Three fractions were recovered following elution by: A - - 2 0 m l hexane (saturated hydrocarbons and 12% of LABs); B - - 2 0 m l 5% DCM/hexane followed by 20ml 15% DCM/hexane (88%

68

A. t}. Murray. C. E Gibbs, P. E. Kavanagh

LABs and other aromatics up to pyrene}; C - - 2 0 m l 50% DCM/hexane (containing the higher polycyclic aromatics). Fractions A and B were analysed separately by gas chromatography with a flame ionisation detector (GC/FID}. The remainder of these fractions was then combined and analysed by gas chromatography with mass selective detection {GC/MS). Samples from sites 2 and 3 were not analysed by GC/MS. Fraction C was analysed for polycyclic aromatic hydrocarbons and results for these compounds will be reported elsewhere. G C / F I D analyses employed a Hewlett-Packard 5794 instrument with splitless injection, a 50m x 0"31 mm fused-silica column bonded with 5% phenylmethyl silicone, helium carrier gas (50cms -t) and a temperature programme from 50 to 300°C at 5:C m i n - 1. GC/MS analyses were carried out by a contracting laboratory using a HP 5970A mass selective detector (MSD). A 25-m column was programmed at 5°Cmin-~ from 35 to 280~C and the MSD was operated in the selected ion monitoring (SIM) mode, monitoring ions at role 91 and 105. Results of G C / F I D and GC/MS analyses were interrelated by analysing a commercial mixture of LABs on both instruments and then calculating factors for the conversion of peak heights at m/e 91 to equivalent G C / F I D peak areas. The commercial LAB mixture, termed 'dobane', was supplied by Shell Chemicals (Aust. Ply Ltd). This mixture was also used to check the recovery of individual LABs through the analytical procedures. Two samples of 50 #g dobane and a blank were extracted and analysed in parallel with the sediments. TOC in sediments was measured by an adaptation of the method of Menzel & Vaccaro (1964) for waters. A subsample from each site was freezedried and ground to pass a 200-/~m sieve. Five 10-20 mg portions of each subsample were subjected to the wet digestion procedure and analysed using an Oceanography International organic carbon analyser. The relative standard deviation for this analysis was 19%. The presentation of results is designed to portray the effects of substituent position and alkyl chain length on the relative rates of loss of individual LABs. Hence, two types of plots were made, both of which make allowance for the relative abundance of the individual LABs in the dobane mixture (i.e. the presumed source material). The first type of plot was applied to the phenyltetradecanes (C-14 group). This was to show the effect of the position of phenyl substitution. The concentration of each phenyltetradecane isomer was divided by its relative abundance in dobane and the results were normalised to give a value of one for 7-phenyltetradecane. The values obtained were plotted against the position of the phenyl substituent. Hence the results show the loss of each of the phenyltetradecane isomers relative to 7-phenyltetradecane.

LABs in sediments of Port Phillip Bay, Australia

69

The second type of plot was made as follows: (a) the concentration of each compound was divided by its relative abundance in the dobane: (b) the results were norrnalised so that a value of one was obtained for the longest chain c o m p o u n d (7- and 8-phenylpentadecane, actually two compounds unresolved by GC); (c) the results for the components within each chain length group were averaged and this result was plotted against the chain length. Hence, these plots show the influence of chain length on the loss of LABs, relative to the C-15 isomers as a group. Mussels (Mytilus edulis) from 1 m depth at site 1 were analysed according to the procedures of Burns & Smith (1982). Gas chromatograph settings were identical, however, to those used for the sediment analyses.

RESULTS A N D DISCUSSION Recovery of the commercial LAB mixture through the analytical procedures averaged 93 + 4%. The procedures showed no significant discrimination in the recovery of individual LABs and no LABs were detected in the blank. The identities of individual LABs had been established in our laboratory previously using standards and GC/MS data (A. P. Murray & K. A. Burns, unpublished data). All concentrations were corrected for recovery of the internal standard, which varied from 63% to 105%. Gas chromatograms of the dobane LAB mixture and of the LABs and other aromatic hydrocarbons in sediments and mussels from site 1 are shown in Fig. 2. Overall LAB and TOC concentrations found in the sediment samples are shown in Table 1, together with the earlier data of Burns & Smith (1978) and data for other marine sediments from southern California and Japan. The five sites in Corio Bay, shown by Seedsman & Marsden (1980) to have sediments of similar physical characteristics ('silty clay'), also had similar organic carbon content ( 13-20 mg g- t). Site 6 in Hobsons Bay, of apparently similar sediment type, showed an organic carbon concentration approximately half that of the Corio Bay sites. At site 7, the much coarser sediment had a correspondingly low organic carbon content (2 mg g-L). The concentration of total LABs in Corio Bay sediments decreased sharply in the first few kilometres from the refinery. Except at site 1 (nearest the refinery), concentrations of LABs in Port Phillip Bay sediments were found to be lower than reported for sediments of Tokyo Bay and southern California (Table 1). This reflects the relatively small amount of domestic wastes entering Port Phillip Bay (Anon., 1973). The concentrations in Corio Bay sediments were also somewhat lower than those found during 1976 (Burns & Smith, 1978), although the ratio of LABs to total hydrocarbons

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TABLE I Concentration [dr', ~eight} of Total Linear Alkyl Benzenes (LAB) and Total Organic Carbon [TOCI in Port Phillip Bay and Other Coastal Sediments Location

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was about the same. This fact and discussions with staff of the refinery indicate that the reduction is due to improved effluent treatment. Differences between the composition of the sedimentary LABs and the presumed source material are shown graphically in Figs 3 and 4. An unmodified LAB mixture gives lines of approximately zero slope in both these plots, with point-to-point variation being a measure of the experimental error. Deviations from smooth curves in the sample plots also reflect experimental errors but, in addition, may be due to differences in the way bacteria degrade individual LABs. Rontani et al. (1985) have shown that the mechanism for bacterial oxidation of alkyl benzenes depends on whether the alkyl chains contain an even or odd number of carbon atoms. The plots in Fig. 3 all show the previously reported (Bayona et al., 1986) loss of external (e.g. 2-phenyl) relative to internal (e.g. 6-phenyl) isomers. This is most apparent for site 3, at which no 2-, 3- or 4-substituted LABs were detected. The loss of external isomers can be used as a rough guide to the extent o f microbial degradation of an LAB mixture. Eganhouse et al. (1983) found the LABs at their offshore site to be more depleted in external isomers than those at the inshore site. It was suggested that most degradation of LABs occurred in the water column over a period of days to weeks and, once

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LABs in sediments of Port Phillip Bay. Australia

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deposited in the sediments, the LABs did not degrade further over many }'ears. This explanation is consistent with our results, which show progressive loss of the external isomers with distance from the source, as far as site 3. The apparently less degraded suites of LABs at sites 4 and 5 may result from inputs from another source, probably urban run-off from the city of Geelong. A comparison of the LAB chromatograms with those of Eganhouse et al. (1983) indicated that the extent of degradation at site I was intermediate between that found at their inshore and offshore sites in southern Calitbrnia. This is interesting because it suggests that the LABs discharged to Corio Bay were degraded faster than those discharged, together with sewage effluent, to the southern Californian waters. The LABs in the Corio Bay samples appear more degraded than those subjected to 40 days' microbial attack in laboratory studies (Bayona et al., 1986). Thus microbial degradation of LABs before deposition in Corio Bay sediments may be very fast indeed. In Hobsons Bay, unlike Corio Bay, there is no obvious point source for the LABs. Thus the small amounts tbund at site 6 found their way to the bay via urban run-off, industrial waste discharge and in the small quantity of domestic waste entering the Yarra River. Figure 4 shows the loss of individual LABs as a function of alkyl chain length. All these plots show that shorter chain compounds were lost in preference to those with longer chains. This is not likely to be due to selective microbial action since Bayona et al. (1986) concluded that LABs subjected to microbial attack in vitro were depleted in the longer chains. A more likely explanation for the depletion of shorter chain LABs in the sediments is their higher water solubility. The solubility of alkyl benzenes decreases with increasing chain length (Sutton & Calder, 1975), and so washing of LAB mixtures adsorbed to settling particles and in the sediments would preferentially remove the shorter chain compounds. A similar argument was used by Hase & Hires (1977) to explain the distribution of alkyl PAH in the sediments of the Charles River basin, USA. If water solubility does determine the chain length distribution in sediments, the overlying water should b~eenriched in the shorter chain LABs. As yet no measurements of LABs in Port Phillip Bay water have been made. However, mussels taken from shipping piles near site 1 do contain a mixture of LABs enriched in the shorter chain compounds (Fig. 2). This implies a similar enrichment in the water. The chromatograms presented by Eganhouse & Kaplan (1982) show an enrichment of shorter chain LABs in the aqueous phase of their effluent samples as compared with the probable starting material. Finally, data presented by Kikuchi et al. (1986) lbr the ABS (i.e. the sulphonated LABs) clearly demonstrate an enrichment of shorter

74

,4. P. Murray, C. F. Gibbs, P. E. Kat'anagh

chain compounds in the water and the converse situation in sediments from the same site. The persistence of longer chain LABs in Corio Bay sediments has particular relevance to future studies of LABs in this area. Soon after the present samples were taken the refinery changed its method of producing LABs (O. Jansma. pers. comm.). LAB mixtures produced by the new process are very similar to those produced previously except that they contain almost no phenylpentadecanes. This means that future studies could use the abundance of these compounds relative to the other LABs as a measure of new inputs and the in situ degradation rate. An unusual suite of phenylalkanes was found in the sandy sediments at site 7. These compounds, containing from 11 to 14 carbons in the alkyl substituent, were revealed by GC/MS in a sample containing only 4/.tg gtotal hydrocarbons. They were not visible in GC/FID chromatograms. The GC/MS retention times of the unknown alkyl benzenes did not correspond to those of the conventional LABs. Furthermore, the rather simple GC pattern (five peaks only) did not suggest an association with the older detergent alkylate TABs (tetrapropylene alkyl benzenes; see Eganhouse et al., 1983). Unfortunately, we were not able to identity these unknown compounds by full GC/MS. However, we can suggest structures on the basis of their GC elution position relative to the LAB isomers. Each compound eluted between the 3- and 2-phenyl LAB isomers in each chain length group. If the compounds are monosubstituted (as is suggested by a strong GC/MS response at m/e 91 and 105), then the alkyl chains are probably branched. Phenylalkanes having branched alkyl chains of 11 to 14 carbon atoms have been found in certain members of the archaebacteria (Langworthy et al., 1982). Since the sewage treatment plant near to site 7 would harbour a large population of this class of bacteria, a microbial origin for the unknown phenylalkanes may be postulated. The absence of the more common LABs and other hydrocarbons in the sediments at site 7 may reflect either the efficiency of the sewage treatment plant or the transport of contaminant-laden small particles away from the area, or both. The latter explanation is consistent with the comparatively coarse nature of the sediment and low organic carbon content, which does not favour the adsorption and settling of trace organics.

CONCLUSIONS Concentrations of LABs in sediment samples from Port Phillip Bay were generally lower than those reported for marine sediments from other countries. In Corio Bay, LAB input from a point source overlayed a more

L.4 Bs in sediments of Port Phillip Bay. ,4ustralia

75

diffuse input, apparently from urban run-off. In other areas o f Port Phillip Bay LABs were present at low concentrations, and at one site near a sewage farm the sediments contained no detectable LABs, but did contain other alkyl benzenes of possible microbial origin. An examination of LAB composition in northern Corio Bay sediments revealed two processes acting to remove LABs during deposition. These were microbial oxidation and dissolution in water, the former being most effective for external isomers and the latter for the shorter chain compounds. An understanding of these processes assists future use of the LABs as markers of domestic/urban wastes and as surrogates in the study of hydrocarbon diagenesis in sediments.

ACKNOWLEDGEMENTS The authors are grateful for the expert help provided by the crew of R. V. Capitella and other staff of the operations section of the Marine Science Laboratories. We are grateful also to Mr O. Jansma of Shell Chemicals (Australia) for samples of dobane detergent atkylate. Mass spectrometric analyses were conducted by Dr R. E. Cox of the Australian Mineral Development Laboratories (AMDEL), Adelaide, South Australia.

REFERENCES Anon. (1973). Environmental study of Port Phillip Bay--Report on Phase One, 1968-1971. Fisheries and Wildlife Division and Melbourne and Metropolitan Board of Works, Melbourne, Victoria, Australia, 372 pp. Bayona, J. M., Albaiges, J., Solanas, A. M. & Grifoll, M. (1986). Selective aerobic degradation of linear alkyl benzenes by pure microbial cultures. Chemosphere, 15, 595-8. Burns, K. A. & Smith, J. L. (1978). Hydrocarbons in Port Phillip Bay sedirnents. Report No. 222 in the Ministry of Conservation Environmental Studies series, 14 pp. Department of Conservation, Forests and Lands, Melbourne, Australia. Burns, K. A. & Smith, J. L. (1982). Hydrocarbons in Victorian coastal ecosystems (Australia): Chronic petroleum inputs to Western Port and Port Phillip Bays. Arch. Environm. Contain. Toxicol., 11, 129~,0. Crisp, P. T., Brenner, S., Venkatesan, M. I., Ruth, E. & Kaplan, I. R. (1979). Organic chemical characterisation of sediment-trap particulates from San Nicolas, Santa Barbara, Santa Monica and San Pedro basins, California. Geochim. Cosmochim. Acta, 43, 1791-801. Eganhouse, R. P. & Kaplan, I. R. (1982). Extractable organic matter in municipal wastewaters. 2. Hydrocarbons: Molecular characterisation. Environ. Sci. Technol., 16, 541-51.

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.-t. P. Murray, C. F. Gibbs, P. E. Kavanagh

Eganhouse, R. R. Blumfield, D. L. & Kaplan, I. R. 11983). Long-chain alkylbenzenes as molecular tracers of domestic wastes in the marine environment. Ent'iron. Sci. Technol., 17, 523-30. Harvey, G. R., Boran, D. A.. Chesal, L. A. & Tokar, J. M. (1983). The structure of marine fulvic and humic acids. Mar. Chem., 12, 119-32. Harvey, G. R., Sinninghe-Damste, J. S. & De Leeuw, J. W. (1985). On the origin of alkylbenzenes in geochemical samples. Mar. Chem.. 16, 187-8. Hase, A. & Hites, R. A. (1977). On the origin of polycyclic aromatic hydrocarbons in the aqueous environment. In: Identification of organic pollutants in water (ed. by L. H. Keith), Ann Arbor Science Publishers Inc., Ann Arbor, Michigan. Ishiwatari, R., Takada, H., Yun, S.-J. & Matsumoto, E. (1983). Alkylbenzene pollution of Tokyo Bay sediments. Nature (London), 301,599-600. Kikuchi, M., Tokai, A. & Yoshida, T. (1986). Determination of trace levels of alkylbenzenesulfonates in the marine environment by high-performance liquid chromatography. Water Res., 20, 643-50. Langworthy, T. A., Tornabene, T. G. & Holzer, G. (1982). Lipids of archaebacteria. Zentrabl. Bakteriol. Mikrobiol. Hyg. Abt. I. Orig. C., 3~ 228-44. Menzel, D. W. & Vaccaro, R. F. t1964). The measurement of dissolved organic and particulate carbon in sea water. Limnol. Oceanogr., 9, 138-42. Rontani, J. F., Rambeloarisoa, E., Bertrand, J. C. & Giusti, G. (1985). Degradation of alkyl-substituted benzenes and their photooxidation products by a marine mixed bacterial population. Mar. Ent, iron. Res., 16, 301-14. Seedsman, R. W. & Marsden, M. A. H. (t980). Sediment distribution and movement within Corio Bay. Report to Ministry for Conservation, Victoria. Geology Dept, University of Melbourne, Victoria, Australia. Sutton, C. & Calder, J. A. (1975). Solubility of alkylbenzenes in distilled water and seawater at 25~C. J. Chem. Engineer. Data, 20, 320-2.