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Volatile halogenated compounds and chlorophenols in the Skagerrak
73
Journal of Sea Research 35 (1-3): 73-79 (1996)
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
KATARINA ABRAHAMSSON and ANJA EKDAHL Department of Analytical and Marine Chemistry, G~teborg University, S-412 96 GSteborg, Sweden
ABSTRACT A total of 680 seawater samples were collected and analysed for volatile halogenated organic compounds, and 280 seawater samples were analysed for chlorinated phenols in the Skagerrak. The sampiing was done along three transects along the Danish west coast on five occasions during the years 1991 to 1993. Pentachlorophenol (PCP) was the only chlorophenol detected on all occasions, which implies that it is transported as a dissolved species rather than particle bound. The results indicate that the origin of PCP in the Skagerrak is the Baltic and the coastal areas of Sweden and Norway. The biogenic volatile halocarbons constitute the largest fraction of the halocarbons in the area. The data support the findings that volatile chloroethenes are naturally produced. Therofore, the Skagerrak acts as a source for these compounds. The flux of the compounds investigated is directed from the sea to the atmosphere except for carbon tetrachloride.
Key words: Skagerrak, chlorinated phenolics, volatile halocarbons, distribution
1. INTRODUCTION The behaviour of pollutants in the environment is complex, since it simultaneously reflects the interplay between abiotic and biotic processes. The physico-chemical characteristics of a particular compound may be quite complicated in themselves. If that complexity is combined with the complexity of the mixing and transport pattern of a natural aquatic system, the results may be puzzling to an observer who tries to understand the fate of the compound in the environment. Usually, when we measure the distribution of a specific compound in a given system we only get information about what happens on one specific occasion. It is important that we seek information on the distribution of compounds in a given area on several occasions which reflect biological as well as physical cycles. Such distribution studies require a large number of samples to be analysed in a short period of time. This severely limits the choice of compounds suitable for such studies. From an environmental point of view, halogenated organic compounds are of great concern since they are known to be toxic and harmful to the environment (Buikema & McGinnis, 1979; Mattice et aL, 1981).
They can persist for extended periods of time in the ecosystem and accumulate in different trophic levels. They have also been used in large quantities throughout the Northern and Southern Hemispheres. Halogenated compounds found in the marine environment have two different origins: an anthropogenic one, and a biogenic one. The anthropogenic group is dominated by fluorinated and chlorinated compounds, whilst the biogenic group is traditionally believed to be dominated by brominated and iodinated compounds (Gribble, 1992). The anthropogenic sources of fluorine- and chlorine-substituted substances in the sea are land or river run-off, dry or wet deposition, and direct input from coastal industries through effluents (Voss et aL, 1981; Salkinoja-Salonen et aL, 1983; BrorstrSm-Lunden et aL, 1994). They are used as pesticides, solvents, anti-freezing agents etc., and they are also formed as by-products from chemical industries, or as combustion products. The biogenic sources are mainly through the formation of volatile halogenated compounds by marine algae (Gschwend et aL, 1985; Manley & Dastoor 1988; Coll6n et aL, 1994). Volatile halocarbons include a number of halogenated substances; some are known to have a purely anthropo-
74
K. ABRAHAMSSON & A. EKDAHL
genic origin, such as the chlorofluorohydrocarbons (CFC:s), carbon tetrachloride and methylchloroform. Their ability to catalyse the destruction of ozone both in the stratosphere and troposphere (Elliott & Rowland, 1987), has been in focus the last decades. While the anthropogenic contribution to the environment of these substances is relatively well known, the amounts released from biogenic sources, e.g. the marine organisms, are less well understood. The distribution of halogenated substances in the Skagerrak has been poorly investigated. The main area of investigation has been the southern, central and north-western parts of the North Sea (Newman & Agg, 1988; Salomons et al., 1988). Concentrations of different pesticides in the water column were reported by Holden (1987). The levels in most parts of the North Sea for 3'- HCH, (z-HCH, HCB, DDE, DDT and Dieldrin range from less than 0.02 to 1.7 ng-dm -3, with the highest values for the more hydrophilic ?HCH. These values were only slightly higher than those determined for the inflowing North Atlantic water. In certain coastal areas, however, the concentrations could be as high as 5 ng-dm -3 (ibid.). We studied the distribution of halogenated substances in the Skagerrak. To be able to distinguish different water masses, and to study the dominant means of distribution, we chose substances that are mainly transported conservatively in the water mass (volatile halocarbons), and compounds that tend to adhere to particles (chlorinated phenolics). 2. EXPERIMENTAL 2.1. CHEMICALS The chlorinated phenolics used were 2,4-dichlorophenol (AB reagents G6teborg), 2,6-dichlorophenol (Nova Kemi AB), 2,4,6-trichlorophenol (Merck), 3,4,5-trichlorophenol (EGA-Chemie), 2,3,4,6-tetrachlorophenol (ABC Div of Aldrich Chemical Company INC), 2,3,4,5-tetrachlorophenol (EGA-Chemie), pentachlorophenol (Fluka), 2,6-dibromophenol (Kodak). 3,4,5-trichlorocatechol, tetrachlorocatechol, 4,5,6-trichloroguaiacol and tetrachloroguaiacol were kindly provided by Professor Wachtmeister, University of Stockholm, Sweden. Standard stock solutions were prepared in acetone (Merck) and stored in a refrigerator. The volatile halogenated hydrocarbons investigated were chloroform (Merck), 1,1,1-trichloroethane (Fluka), 1-iodopropane (Fluka), 2-iodopropane (Fluka), trichloroethene (Mallinckrodt), dibromomethane (Merck), bromodichloromethane (Fluka), chloroiodomethane (Fluka), 2-iodobutane (Fluka), dibromochloromethane (Fluka), tetrachloroethene (Merck), 1-iodobutane (Fluka), bromoform (Merck), diiodomethane (Fluka) and bromotrichloromethane. Standard stock solutionsowere prepared in acetone (Merck) and stored at-18 C.
Norway
Sweden
North s e a
~ -
{Kattegat
Fig. 1. Map of the sampling transects. Transect 1: Hirtshals; 2: Hanstholm; 3: TyborSn. Samples were collected at seven stations along each transect. 2.2. ANALYTICAL PROCEDURES The chlorinated phenolics were determined as their acetylated derivatives according to Abrahamsson & Xie (1983) and the volatile halocarbons determined according to Abrahamsson & Klick (1990). The derivatization and liquid-liquid extraction procedures were made directly in the sampling bottles. The phenolic compounds were extracted by adding 1 cm 3 of hexane (Merck) containing 2,6-dibromophenol as internal standard (i.s.). The bottles were shaken for three min. The hexane phase (1 mm 3) was then used for gas chromatographic analysis. The detection limit for PCP was 0.1 ng-dm -3, and for the other chlorophenolics 1 ng-dm -3. The precision (relative standard deviation, n=5) was 1.0 to 8.9%. The volatile compounds were extracted by adding 1 cm 3 of distilled pentane, containing bromotrichloromethane as i.s., and shaken for five minutes. The extract was then injected onto the gas chromatographic column. The detection limits are in the range of 0.03-0.7 ng.dm -3, with a precision of 3 to 12%. The determinations of the chlorophenols, catechols and guaiacols were made with a Carlo Erba HRGC 5300 gas chromatograph equipped with a Ni 63 electron capture detector and on-column injector. The compounds were separated on a 30 m DB-1 fused silica column (J & W Scientific) with an internal diameter of 0.32 mm. The GC-conditions were hydrogen carrier gas flow rate of 2 cm3.min -1, and nitrogen make-up gas flow rate of 30 cm3"min -1, injector and detector temperature 275 ° , temperature program
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
75
TABLE 1 Mean concentrations of halogenated organic compounds in the Skagerrak. The values are calculated from five sampling occasions, except for PCP. The concentrations are given in ng.dm-3.
salinity CCI4 CHCI=CCI2 CCl2=CCl2 CH2Br2 CHBr3 CH2CII C4H91 CH212 PCP Tybor~n SCSW <32 0.92 1.9 0.4 0.2 3.7 0.15 1.7 nd 41 SNSW 3135 0.97_+0.20 3.8 _+0.74 0.52-+0.64 0.39_+0.046 1.3_+1.4 0.47-+0.47 nd 0.43-+1.1 nd Hanstholrn SCSW <32 0.85_+0.45 0.94_+0.47 0.52_+0.21 0.37_+0.13 3.1_+1.4 4.0 _+1.8 2.5 _+1.3 12.0_+5.9 19_+37 SNSW 3135 0.74_+0.51 2.4 _+1.6 0.55_+0.58 0.54_+0.64 2.5_+1.9 0.89_+1.8 0.38_+0.78 2.7+5.4 37_+44 Hirtshals SCSW <32 0.88_+0.38 2.3+_2.0 0.86_+0.33 0.42+0.31 3.7_+1.6 6.2 _+4.6 3.6 +~?..5 14.0_+7.2 31_+35 SNSW 3135 0.75_+0.72 2.7_+1.4 0.57_+0.65 0.59_+0.72 2.1_+1.6 0.47_+0.47 0.18_+0.40 2.5_+4.9 23+_25 The different salinity ranges symbolize different origin of water (North Sea Quality Status Report, 1993) SCSW Skagerrak coastal waters SNSW Southern North Sea waters CNSW Central North Sea waters AW Atlantic water 100°-230 ° at 15°-min -1 , 230°-260 ° at 30°'min q. The determination of the volatile halocarbons was made with a Carlo Erba 4160 gas chromatograph equipped with a Ni 63 electron capture detector (275°). The injector was an automatically driven liquid chromatography Valco valve with a 15-mm 3 loop. The compounds were separated on two fused silica columns connected with a capillary glass connector. The precolumn was a 30-m-long DB-1701 (J & W Scientific), with an internal diameter of 0.32 mm, and a film thickness of 0.1 #m. The separation column was a 30-m-long DB-5 (J & W Scientific) with an internal diameter of 0,32 mm, and a film thickness of 1 #m. Hydrogen carrier gas flow rate was 2 cm3.min -1, and nitrogen make-up gas flow rate 30 cm3.min q. The oven was held at 40 ° for two minutes, and then raised to 120 ° at a rate of 10°'min -1. The chromatographic peaks were integrated using a Jones Model JCL 6000 chromatography system.
each transect seven stations were sampled, and water was collected from different depths, giving a total of 30 water samples per transect. The determination of chlorinated phenolics was performed on the three first occasions, and volatile halogenated substances were determined on every occasion. The seawater samples were collected in brown glass bottles (100 cm 3) from Niskin water sample bottles. The chlorophenols, chlorocathecols and chloroguaiacols were determined shortly after they were available at the laboratory. The volatile hydrocarbons were determined on board the ship, within 24 hours after the samples had been collected. 3. RESULTS The distribution of halogenated compounds in the Skagerrak is dependent on the physical-chemical properties of the compounds, as well as the physical properties of the area of investigation.
2.3. SAMPLING AREA Water samples were collected along three transects (1: Hirtshals: N 57°30% E 9o56 ' to N 58°01 ', E 9°36'; 2: Hanstholm: N 57°10% E 8o34 ' to N 57°41% E 8°12'; and 3: Tybor6n: N 56°43% E 8o06 ' to N 56o43 ', E 6o38 ' see Fig. 1), along the Danish west coast on five occasions: September 1990, November 1990, April 1991, October 1992 and March 1993. On each occasion an effort was made to sample each transect twice. Along
3.1. VOLATILE HALOGENATED ORGANIC COMPOUNDS The biogenic compounds constitute the largest fraction of halocarbons in the water column (Table 1). The highest concentrations were found in the low salinity water from the Baltic (surface water), and in the in-flowing water from the North Atlantic. One might expect that the concentration levels of biogenic
76
K. ABRAHAMSSON & A. EKDAHL
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Fig. 2. The distribution of CH2Cll along transect 2 (Hanstholm) in September 1990. The iso-lines are given in ng.dm-3. volatile substances have a strong seasonal variation, since they are a result of biological activities. Table 2 gives the mean concentrations of three substances with a mainly biogenic origin, CH2CII, CHBr 3 and CH212, and one of a mainly anthropogenic origin, CCI 4. Seasonal variations could be seen for the iodinated substances, while this effect is not so pronounced for brominated compounds. Since they have quite long residence times in the water, the levels found cannot easily be explained by the presence or absence of phytoplankton or macroalgae. Surprisingly, the highest concentrations of diiodomethane were found in November, when levels of chlorophyll were low. However, as we have shown earlier (Abrahamsson & Ekdahl, 1993), there is no correlation between the amount of chlorophyll present and the concentration of halocarbons in the water mass, probably dependent on the relatively rapid degradation of chlorophyll. Moreover, the concentration of bromoform seems to decrease with time. Up to this point we do not have a good explanation for this finding. The compounds we measured do not give any information about the origin of different water masses. Not even the commonly used water mass tracer CCI4 gave any information on the complex mixing of different waters in the Skagerrak. However, it seems that
Sep90 Nov 90 Apr 91 Oct 92 March 93
CH2CII
CHBr3
CH212
n
0.65_+0.22 0.42+0.24 4.7_+4.0 0.16_+0.87 30 0.90_+0.31 0.87_+0.62 4.3_+3.9 15+~24 38 0.72+0.32 2.9+~2.9 4.4-+6.6 7.8-+8.3 38 2.5+~2..9 0.57-+0.51 2.2_+1.9 nd 30 0.92+0.22 0.19-+0.13 1.4+~2.2 1.5-+3.7 37
the distribution and the input of CCI4 is more homogeneous than that of the other ones. The distribution of halocarbons in the deep oceans usually shows elevated concentrations in the surface waters, which rapidly decrease with depth. Generally, this is valid for the deep water stations. In the shallow areas, where the water masses have different origins, no general pattern could be seen. However, on several occasions, the highest concentrations of biogenic halocarbons were found close to the sediment surface, which indicates a production of these compounds by benthic organisms (Fig. 2). Due to the complex mixing of different water masses no real relationship could be established between salinity and the presence of halocarbons. However, the levels of iodinated compounds, as well as brominated compounds, relate to each other. The net fluxes of the volatile halocarbons across the air-sea interface have been calculated according to Liss & Merlivat (1986): F=KxAC where F is the net flux in Gg.y-1, K is the transfer velocity in cm.h -1, and AC is the concentration difference between air and water. The average annual wind speed in the Skagerrak and in the North Sea was estimated to be 9.0 m-s"1, and the surface temperature was assumed to be 10°C. The surface area is 0.61 x 106 km 2. Table 3 shows the fluxes of four halocarbons across the sea surface. The surface water concentrations are average values for 173 samples taken at 5 m depth, and the air samples concentrations are average values for 15 samples. The net fluxes of CHBr3, CCI2=CCI 2 and CHCI=CCI 2 are from the water phase to the atmosphere, while for CCI4 the direction of the flux is the opposite. The origins of CCI2=CCI 2 and CHCI=CCI 2 are
TABLE 3 The flux of four volatile halocarbons between the water/air interface. F is the flux, H is the Henry Law constant, K is the transfer velocity. **From Gossett (1987), and * MacKay & Shiu (1981) CCI4 CHCI=CCI2 CCI2=CCI2 CHBr3
F (Gg'yq )
H (10°C)
K (cm.h-7)
-2 0.2 0.08 0.8
0.567* 0.163** 0.294** 0.026*
16 15 15 9.1
Cai r
(ppt)
1200 + 550 360 _+270 42 _+31 nd
Cwate r
(ng.dm -~)
1.3 _+1.1 2.8 _+2.7 0.63 +_0.39 3.4 +_1.5
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
TABLE 4 pKa, log Kow, and log D for phenolic compounds. Abbreviations: DCP dichlorophenol; TCP trichlorophenol; TeCP tetrachlorophenol; PCP pentachlorophenol; TCG trichloroguaicol; TeCG tetrachloroguaiacol; TCC trichlorocatechol, pKa and log Kow from Xie & Dyrssen (1984). compound pKa log Kow log D (pH 7) 2,4-DCP 8.09 3.21 3.18 2,6-DCP 6.79 2.84 2.42 2,4,6-TCP 6.21 3.75 2.89 3,4,5-TCP 7.81 4.36 4.3 2,3,4,5-TeCP 6.61 4.82 4.28 2,3,4,6-TeCP 5.62 4.42 3.02 PCP 4.9 5.04 2.94 4,5,6-TCG 7.2 3.21 3.53 TeCG 6.26 2.84 3.64 3,4,5-TCC 3.71 thought to be only man-made, but experiments with marine algae have shown that they also have a biological source (Abrahamsson et aL, 1995a). Therefore, the net fluxes are from seawater to the atmosphere. The flux of CHBr 3 is in the same order of magnitude as the investigation by Fogelqvist & Krysell (1991). The flow of biogenic halocarbons is predominantly carried out by water with a high salinity (North Atlantic). At Hirtshals, where the water with a salinity of 31
77
the amount of suspended particulate matter in the water. Chlorinated phenolics were measured on three occasions, September 1990, November 1990 and April 1991. It was only pentachlorophenol, PCP, that could be determined in the entire water column on all occasions. Since the acidity of PCP is relatively large, the theoretical distribution coefficient will decrease from 5.04 to 2.94, which implies that it is transported in the water phase as a dissolved species, rather than particle bound. This is in line with our earlier investigations of chlorinated phenolics (Xie et al., 1986; Abrahamsson & Ekdahl, 1993). The mean values given in Table 1 indicate that there are no significant differences in concentration between different water masses. The different water masses were given in the North Sea Quality Status Report (1993). The values of the relative standard deviation show that there are indeed large variations within different salinity ranges and between sampling occasions. The complicated mixing in the Skagerrak, with short residence times in the upper 100 m (20-100 days), is the likely explanation. The distribution of PCP along the transects varies not only between the different sampling occasions, but also 40-
2,3,4,6 - TeCP
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3.2. CHLORINATED PHENOLICS
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The levels of chlorinated compounds found in seawater are mainly dependent on their lipophilicity. Highly lipophilic substances will accumulate at phase boundaries, and therefore they should be found adsorbed to particles, or at the air-sea interface (Mackay et al., 1985). Chlorinated phenolic compounds comprise a variety of substances. They possess both hydrophilic and lipophilic properties. As can be seen from Table 4, the lipophilicity dominates at normal pH in seawater (8.2) for the guiacols and catechols. For the phenols the picture is somewhat different. For the stronger acids the ionic character will dominate at pH 8. The reasons for using chlorinated phenolics in distribution studies are twofold. First, the analysis is rapid, since it requires a small amount of sample (100 cm3), and the detection limits are fairly low (0.1 ng'dm -3 to 1 ng-dm-3). Secondly, this group of compounds gives information on the distribution pathways of compounds that are associated with particles, and compounds that are transported as dissolved species. However, no attempt was made to investigate
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were collected on three occasions.
78
K. ABRAHAMSSON & A. EKDAHL
between days (Abrahamsson & Ekdahl, 1993). In order to study the fraction of PCP associated with the organic layer of particles, water samples were filtered with 0.45 ~.m filters, and were compared with unfiltered samples. No significant difference could be observed. A comparison of the levels of pentachlorophenol measured in this investigation with other investigations of levels of chlorinated compounds, shows that our levels are 20 to 50 times higher. Holden (1987) reported values of less than 0.02 to 1.7 ng.dm -3 for DDE, DDT, Dieldrin, HCB, ~HCH and c~-HCH in the North Sea. The highest fluxes of PCP were found in waters with a salinity of 31
major sources for many organic pollutants. Considering the sedimentation of river-borne particles, a large fraction of the pollutants should be found in the estuarine sediments. For instance, Duinker et aL (1982) showed that the amount of organic pollutants in the rivers entering the German Bight was reduced compared to the amounts in the river waters, probably due to sorption to sedimenting particles. Hence, sediments in coastal areas act as sinks for these compounds. This is certainly true if the lipophilicity of the pollutants is significantly large, which is the case for compounds such as the non-ionic chlorinated pesticides. In our investigation the most lipophilic compounds, guiacols and catechols, could not be detected at all in the water column. Most likely these compounds are adsorbed to particles and then sedimented close to the outlets. The average flow of water across the different transects during the years of sampling was 0.4 Sv at Hirtshals, 0.6 Sv at Hanstholm, and approximately 0 Sv at TyborSn (Rydberg etaL, 1996). The flux of PCP in the Skagerrak was high in the water with a salinity of 31
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
1995a. Marine algae - a source of trichloroethylene and perchloroethytene.--Limnol. Oceanogr. 40" 13211326. ,1995b. Formation and distribution of halogenated volatile organics in sea water. In: A. Grimvall & E.W.B. De Leer. Naturally produced organohalogens. Kluwer, London: 317-326. Buikema, A.L. & M.J. McGinnis, 1979. Phenolics in aquatic ecosystems: a selected review of recent literature.--Mar. Environ. 2" 87-181. BrorstrSm-Lund6n, E., A. Lindskog & J. Mowrer, 1994. Concentrations and fluxes of organic compounds in the atmosphere of the Swedish west coast.--Atm. Environ. 28: 3605-3615. Collen, J., A. Ekdahl, K. Abrahamsson & M. Peders6n, 1994. The involvement of hydrogen peroxide in the production of volatile halogenated compounds by Meristiella gelidium (Rhodophyta).--Phytochemistry 36" 1197-1202. Duinker, J.C., M.T.J. Hillebrand, R.F. Nolting & S. Wellerhaus, 1982. The river Elbe: Processes affecting the behaviour of metals and organochlorines during estaurine mixing.--Neth. J. Sea Res. 15" 141-169. Elliott, S. & F.S. Rowland, 1987. Chlorofluorocarbons and stratospheric o z o n . ~ . Chem. Education. 64" 387-391. Fogelqvist, E. & M. Krysell, 1991. Naturally and anthropogenically produced bromoform in the Kattegatt, a semi-enclosed oceanic basin.--J. Atmos. Chem. 13" 315-319. Gossett, J.M., 1987. Measurements of Henry's law constants of C 1 and C2 chlorinated hydrocarbons.--Environ. Sci. Technol. 21: 202-208. Gribble, G.W., 1992. Naturally occurring organohalogen compounds - A survey.--J, nat. prod. 55" 1353-1395. Gschwend, P.M., J.K. MacFarlane & K.A. Newman, 1985. Volatile halogenated organic compounds released to sea water from temperate marine macro algae.--Science 227:1033-1036. Holden, A.V., 1987. Pesticides. In: P.J. Newman & A.R. Agg. Environmental Protection of the North Sea. Heinemann, Oxford, England: 67-84. Liss, P.S. & L. Merlivat, 1986. Air-sea exchange rates: introduction and synthesis. In: P. Buat-M~nard. The role of
79
air-sea exchange in geochemical cycling. D. Reidel Publishing Company, Dordrecht: 283-294. MacKay, D. & W.Y. Shiu, 1981. A critical review of Henry's law constants for chemicals of environmental interest.--J. Phys. Chem. Ref. Data 10" 1175-1199. MacKay, D., S. Paterson, B. Cheung & N.W. Brock, 1985. Evaluating the environmental behaviour of chemicals with a level III fugacity model.--Chemosphere 14" 335-374. Manley, S.L. & M.N. Dastoor, 1988. Methyl iodide production by kelp and associated microbes.--Mar. Biol. 98: 477-482. Mattice, J.S., S.C. Tsai, M.B. Burch & J.J. Beauchamp, 1981. Toxicity of trihalomethanes to common carp embryos.--Trans. Am. Fish Soc. 110" 261-269. Newman, P.J. & A.R. Agg, 1988. Environmental Protection of the North Sea. Heinemann, Oxford: 3-585. North Sea Task Force, 1993. North Sea Quality Status Report. Osto and Paris Commissions, London: 1-132. Rydberg, L., J. Haamer & O. Liungman, 1996. Fluxes of water and nutrients in and into the Skagerrak.--J. Sea Res. 35; 23-38. Salomons, W., B.L. Bayne, E.K. Duursma & U. F~rstner, 1988. Pollution of the North Sea. An assessment. Springer-Verlag, Berlin: 3-666. Salkinoja-Satonen, M.S., R. Hakulinen, R. Valo & J. Apajalahti, 1983. Biodegradation of recalcitrant organochlorine compounds in fixed film reactors.--Wat. Sci. Tech. 15: 309-319. Voss, R.H., J.T. Wearing & A. Wong, 1981. A novel gas chromatographic method for analyses of chlorinated phenolics in pulp mill effluents. In: L.H. Keith. Advances in the identification and analysis of organic pollutants in water. Ann Arbor Science Publishers Inc. Michigan: 1059-1095 Xie, T.-M. & D. Dyrssen, 1984. Simultaneous determination of partition coefficients and acidity constants of chlorinated phenols and guaiacols by gas chromatography.--Anal. Chim. Acta 160" 21-30. Xie, T.-M., K. Abrahamsson, E. Fogelqvist & B. Josefsson, 1986. Distribution of chlorophenolics in a marine environment.--Environ. Sci. Technol. 20" 457-463.
Journal of Sea Research 35 (1-3): 73-79 (1996)
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
KATARINA ABRAHAMSSON and ANJA EKDAHL Department of Analytical and Marine Chemistry, G~teborg University, S-412 96 GSteborg, Sweden
ABSTRACT A total of 680 seawater samples were collected and analysed for volatile halogenated organic compounds, and 280 seawater samples were analysed for chlorinated phenols in the Skagerrak. The sampiing was done along three transects along the Danish west coast on five occasions during the years 1991 to 1993. Pentachlorophenol (PCP) was the only chlorophenol detected on all occasions, which implies that it is transported as a dissolved species rather than particle bound. The results indicate that the origin of PCP in the Skagerrak is the Baltic and the coastal areas of Sweden and Norway. The biogenic volatile halocarbons constitute the largest fraction of the halocarbons in the area. The data support the findings that volatile chloroethenes are naturally produced. Therofore, the Skagerrak acts as a source for these compounds. The flux of the compounds investigated is directed from the sea to the atmosphere except for carbon tetrachloride.
Key words: Skagerrak, chlorinated phenolics, volatile halocarbons, distribution
1. INTRODUCTION The behaviour of pollutants in the environment is complex, since it simultaneously reflects the interplay between abiotic and biotic processes. The physico-chemical characteristics of a particular compound may be quite complicated in themselves. If that complexity is combined with the complexity of the mixing and transport pattern of a natural aquatic system, the results may be puzzling to an observer who tries to understand the fate of the compound in the environment. Usually, when we measure the distribution of a specific compound in a given system we only get information about what happens on one specific occasion. It is important that we seek information on the distribution of compounds in a given area on several occasions which reflect biological as well as physical cycles. Such distribution studies require a large number of samples to be analysed in a short period of time. This severely limits the choice of compounds suitable for such studies. From an environmental point of view, halogenated organic compounds are of great concern since they are known to be toxic and harmful to the environment (Buikema & McGinnis, 1979; Mattice et aL, 1981).
They can persist for extended periods of time in the ecosystem and accumulate in different trophic levels. They have also been used in large quantities throughout the Northern and Southern Hemispheres. Halogenated compounds found in the marine environment have two different origins: an anthropogenic one, and a biogenic one. The anthropogenic group is dominated by fluorinated and chlorinated compounds, whilst the biogenic group is traditionally believed to be dominated by brominated and iodinated compounds (Gribble, 1992). The anthropogenic sources of fluorine- and chlorine-substituted substances in the sea are land or river run-off, dry or wet deposition, and direct input from coastal industries through effluents (Voss et aL, 1981; Salkinoja-Salonen et aL, 1983; BrorstrSm-Lunden et aL, 1994). They are used as pesticides, solvents, anti-freezing agents etc., and they are also formed as by-products from chemical industries, or as combustion products. The biogenic sources are mainly through the formation of volatile halogenated compounds by marine algae (Gschwend et aL, 1985; Manley & Dastoor 1988; Coll6n et aL, 1994). Volatile halocarbons include a number of halogenated substances; some are known to have a purely anthropo-
74
K. ABRAHAMSSON & A. EKDAHL
genic origin, such as the chlorofluorohydrocarbons (CFC:s), carbon tetrachloride and methylchloroform. Their ability to catalyse the destruction of ozone both in the stratosphere and troposphere (Elliott & Rowland, 1987), has been in focus the last decades. While the anthropogenic contribution to the environment of these substances is relatively well known, the amounts released from biogenic sources, e.g. the marine organisms, are less well understood. The distribution of halogenated substances in the Skagerrak has been poorly investigated. The main area of investigation has been the southern, central and north-western parts of the North Sea (Newman & Agg, 1988; Salomons et al., 1988). Concentrations of different pesticides in the water column were reported by Holden (1987). The levels in most parts of the North Sea for 3'- HCH, (z-HCH, HCB, DDE, DDT and Dieldrin range from less than 0.02 to 1.7 ng-dm -3, with the highest values for the more hydrophilic ?HCH. These values were only slightly higher than those determined for the inflowing North Atlantic water. In certain coastal areas, however, the concentrations could be as high as 5 ng-dm -3 (ibid.). We studied the distribution of halogenated substances in the Skagerrak. To be able to distinguish different water masses, and to study the dominant means of distribution, we chose substances that are mainly transported conservatively in the water mass (volatile halocarbons), and compounds that tend to adhere to particles (chlorinated phenolics). 2. EXPERIMENTAL 2.1. CHEMICALS The chlorinated phenolics used were 2,4-dichlorophenol (AB reagents G6teborg), 2,6-dichlorophenol (Nova Kemi AB), 2,4,6-trichlorophenol (Merck), 3,4,5-trichlorophenol (EGA-Chemie), 2,3,4,6-tetrachlorophenol (ABC Div of Aldrich Chemical Company INC), 2,3,4,5-tetrachlorophenol (EGA-Chemie), pentachlorophenol (Fluka), 2,6-dibromophenol (Kodak). 3,4,5-trichlorocatechol, tetrachlorocatechol, 4,5,6-trichloroguaiacol and tetrachloroguaiacol were kindly provided by Professor Wachtmeister, University of Stockholm, Sweden. Standard stock solutions were prepared in acetone (Merck) and stored in a refrigerator. The volatile halogenated hydrocarbons investigated were chloroform (Merck), 1,1,1-trichloroethane (Fluka), 1-iodopropane (Fluka), 2-iodopropane (Fluka), trichloroethene (Mallinckrodt), dibromomethane (Merck), bromodichloromethane (Fluka), chloroiodomethane (Fluka), 2-iodobutane (Fluka), dibromochloromethane (Fluka), tetrachloroethene (Merck), 1-iodobutane (Fluka), bromoform (Merck), diiodomethane (Fluka) and bromotrichloromethane. Standard stock solutionsowere prepared in acetone (Merck) and stored at-18 C.
Norway
Sweden
North s e a
~ -
{Kattegat
Fig. 1. Map of the sampling transects. Transect 1: Hirtshals; 2: Hanstholm; 3: TyborSn. Samples were collected at seven stations along each transect. 2.2. ANALYTICAL PROCEDURES The chlorinated phenolics were determined as their acetylated derivatives according to Abrahamsson & Xie (1983) and the volatile halocarbons determined according to Abrahamsson & Klick (1990). The derivatization and liquid-liquid extraction procedures were made directly in the sampling bottles. The phenolic compounds were extracted by adding 1 cm 3 of hexane (Merck) containing 2,6-dibromophenol as internal standard (i.s.). The bottles were shaken for three min. The hexane phase (1 mm 3) was then used for gas chromatographic analysis. The detection limit for PCP was 0.1 ng-dm -3, and for the other chlorophenolics 1 ng-dm -3. The precision (relative standard deviation, n=5) was 1.0 to 8.9%. The volatile compounds were extracted by adding 1 cm 3 of distilled pentane, containing bromotrichloromethane as i.s., and shaken for five minutes. The extract was then injected onto the gas chromatographic column. The detection limits are in the range of 0.03-0.7 ng.dm -3, with a precision of 3 to 12%. The determinations of the chlorophenols, catechols and guaiacols were made with a Carlo Erba HRGC 5300 gas chromatograph equipped with a Ni 63 electron capture detector and on-column injector. The compounds were separated on a 30 m DB-1 fused silica column (J & W Scientific) with an internal diameter of 0.32 mm. The GC-conditions were hydrogen carrier gas flow rate of 2 cm3.min -1, and nitrogen make-up gas flow rate of 30 cm3"min -1, injector and detector temperature 275 ° , temperature program
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
75
TABLE 1 Mean concentrations of halogenated organic compounds in the Skagerrak. The values are calculated from five sampling occasions, except for PCP. The concentrations are given in ng.dm-3.
salinity CCI4 CHCI=CCI2 CCl2=CCl2 CH2Br2 CHBr3 CH2CII C4H91 CH212 PCP Tybor~n SCSW <32 0.92 1.9 0.4 0.2 3.7 0.15 1.7 nd 41 SNSW 31
each transect seven stations were sampled, and water was collected from different depths, giving a total of 30 water samples per transect. The determination of chlorinated phenolics was performed on the three first occasions, and volatile halogenated substances were determined on every occasion. The seawater samples were collected in brown glass bottles (100 cm 3) from Niskin water sample bottles. The chlorophenols, chlorocathecols and chloroguaiacols were determined shortly after they were available at the laboratory. The volatile hydrocarbons were determined on board the ship, within 24 hours after the samples had been collected. 3. RESULTS The distribution of halogenated compounds in the Skagerrak is dependent on the physical-chemical properties of the compounds, as well as the physical properties of the area of investigation.
2.3. SAMPLING AREA Water samples were collected along three transects (1: Hirtshals: N 57°30% E 9o56 ' to N 58°01 ', E 9°36'; 2: Hanstholm: N 57°10% E 8o34 ' to N 57°41% E 8°12'; and 3: Tybor6n: N 56°43% E 8o06 ' to N 56o43 ', E 6o38 ' see Fig. 1), along the Danish west coast on five occasions: September 1990, November 1990, April 1991, October 1992 and March 1993. On each occasion an effort was made to sample each transect twice. Along
3.1. VOLATILE HALOGENATED ORGANIC COMPOUNDS The biogenic compounds constitute the largest fraction of halocarbons in the water column (Table 1). The highest concentrations were found in the low salinity water from the Baltic (surface water), and in the in-flowing water from the North Atlantic. One might expect that the concentration levels of biogenic
76
K. ABRAHAMSSON & A. EKDAHL
9 i-
8 ~
7 I
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5 I
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TABLE 2 Mean surface water concentrations of four volatile halocarbons. The values are given in ng.dm-3. nd = not detected.
I
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/ De~lh
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200
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250 300
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Fig. 2. The distribution of CH2Cll along transect 2 (Hanstholm) in September 1990. The iso-lines are given in ng.dm-3. volatile substances have a strong seasonal variation, since they are a result of biological activities. Table 2 gives the mean concentrations of three substances with a mainly biogenic origin, CH2CII, CHBr 3 and CH212, and one of a mainly anthropogenic origin, CCI 4. Seasonal variations could be seen for the iodinated substances, while this effect is not so pronounced for brominated compounds. Since they have quite long residence times in the water, the levels found cannot easily be explained by the presence or absence of phytoplankton or macroalgae. Surprisingly, the highest concentrations of diiodomethane were found in November, when levels of chlorophyll were low. However, as we have shown earlier (Abrahamsson & Ekdahl, 1993), there is no correlation between the amount of chlorophyll present and the concentration of halocarbons in the water mass, probably dependent on the relatively rapid degradation of chlorophyll. Moreover, the concentration of bromoform seems to decrease with time. Up to this point we do not have a good explanation for this finding. The compounds we measured do not give any information about the origin of different water masses. Not even the commonly used water mass tracer CCI4 gave any information on the complex mixing of different waters in the Skagerrak. However, it seems that
Sep90 Nov 90 Apr 91 Oct 92 March 93
CH2CII
CHBr3
CH212
n
0.65_+0.22 0.42+0.24 4.7_+4.0 0.16_+0.87 30 0.90_+0.31 0.87_+0.62 4.3_+3.9 15+~24 38 0.72+0.32 2.9+~2.9 4.4-+6.6 7.8-+8.3 38 2.5+~2..9 0.57-+0.51 2.2_+1.9 nd 30 0.92+0.22 0.19-+0.13 1.4+~2.2 1.5-+3.7 37
the distribution and the input of CCI4 is more homogeneous than that of the other ones. The distribution of halocarbons in the deep oceans usually shows elevated concentrations in the surface waters, which rapidly decrease with depth. Generally, this is valid for the deep water stations. In the shallow areas, where the water masses have different origins, no general pattern could be seen. However, on several occasions, the highest concentrations of biogenic halocarbons were found close to the sediment surface, which indicates a production of these compounds by benthic organisms (Fig. 2). Due to the complex mixing of different water masses no real relationship could be established between salinity and the presence of halocarbons. However, the levels of iodinated compounds, as well as brominated compounds, relate to each other. The net fluxes of the volatile halocarbons across the air-sea interface have been calculated according to Liss & Merlivat (1986): F=KxAC where F is the net flux in Gg.y-1, K is the transfer velocity in cm.h -1, and AC is the concentration difference between air and water. The average annual wind speed in the Skagerrak and in the North Sea was estimated to be 9.0 m-s"1, and the surface temperature was assumed to be 10°C. The surface area is 0.61 x 106 km 2. Table 3 shows the fluxes of four halocarbons across the sea surface. The surface water concentrations are average values for 173 samples taken at 5 m depth, and the air samples concentrations are average values for 15 samples. The net fluxes of CHBr3, CCI2=CCI 2 and CHCI=CCI 2 are from the water phase to the atmosphere, while for CCI4 the direction of the flux is the opposite. The origins of CCI2=CCI 2 and CHCI=CCI 2 are
TABLE 3 The flux of four volatile halocarbons between the water/air interface. F is the flux, H is the Henry Law constant, K is the transfer velocity. **From Gossett (1987), and * MacKay & Shiu (1981) CCI4 CHCI=CCI2 CCI2=CCI2 CHBr3
F (Gg'yq )
H (10°C)
K (cm.h-7)
-2 0.2 0.08 0.8
0.567* 0.163** 0.294** 0.026*
16 15 15 9.1
Cai r
(ppt)
1200 + 550 360 _+270 42 _+31 nd
Cwate r
(ng.dm -~)
1.3 _+1.1 2.8 _+2.7 0.63 +_0.39 3.4 +_1.5
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
TABLE 4 pKa, log Kow, and log D for phenolic compounds. Abbreviations: DCP dichlorophenol; TCP trichlorophenol; TeCP tetrachlorophenol; PCP pentachlorophenol; TCG trichloroguaicol; TeCG tetrachloroguaiacol; TCC trichlorocatechol, pKa and log Kow from Xie & Dyrssen (1984). compound pKa log Kow log D (pH 7) 2,4-DCP 8.09 3.21 3.18 2,6-DCP 6.79 2.84 2.42 2,4,6-TCP 6.21 3.75 2.89 3,4,5-TCP 7.81 4.36 4.3 2,3,4,5-TeCP 6.61 4.82 4.28 2,3,4,6-TeCP 5.62 4.42 3.02 PCP 4.9 5.04 2.94 4,5,6-TCG 7.2 3.21 3.53 TeCG 6.26 2.84 3.64 3,4,5-TCC 3.71 thought to be only man-made, but experiments with marine algae have shown that they also have a biological source (Abrahamsson et aL, 1995a). Therefore, the net fluxes are from seawater to the atmosphere. The flux of CHBr 3 is in the same order of magnitude as the investigation by Fogelqvist & Krysell (1991). The flow of biogenic halocarbons is predominantly carried out by water with a high salinity (North Atlantic). At Hirtshals, where the water with a salinity of 31
77
the amount of suspended particulate matter in the water. Chlorinated phenolics were measured on three occasions, September 1990, November 1990 and April 1991. It was only pentachlorophenol, PCP, that could be determined in the entire water column on all occasions. Since the acidity of PCP is relatively large, the theoretical distribution coefficient will decrease from 5.04 to 2.94, which implies that it is transported in the water phase as a dissolved species, rather than particle bound. This is in line with our earlier investigations of chlorinated phenolics (Xie et al., 1986; Abrahamsson & Ekdahl, 1993). The mean values given in Table 1 indicate that there are no significant differences in concentration between different water masses. The different water masses were given in the North Sea Quality Status Report (1993). The values of the relative standard deviation show that there are indeed large variations within different salinity ranges and between sampling occasions. The complicated mixing in the Skagerrak, with short residence times in the upper 100 m (20-100 days), is the likely explanation. The distribution of PCP along the transects varies not only between the different sampling occasions, but also 40-
2,3,4,6 - TeCP
"4 []
cJ
30D o
3.2. CHLORINATED PHENOLICS
= o
The levels of chlorinated compounds found in seawater are mainly dependent on their lipophilicity. Highly lipophilic substances will accumulate at phase boundaries, and therefore they should be found adsorbed to particles, or at the air-sea interface (Mackay et al., 1985). Chlorinated phenolic compounds comprise a variety of substances. They possess both hydrophilic and lipophilic properties. As can be seen from Table 4, the lipophilicity dominates at normal pH in seawater (8.2) for the guiacols and catechols. For the phenols the picture is somewhat different. For the stronger acids the ionic character will dominate at pH 8. The reasons for using chlorinated phenolics in distribution studies are twofold. First, the analysis is rapid, since it requires a small amount of sample (100 cm3), and the detection limits are fairly low (0.1 ng'dm -3 to 1 ng-dm-3). Secondly, this group of compounds gives information on the distribution pathways of compounds that are associated with particles, and compounds that are transported as dissolved species. However, no attempt was made to investigate
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.
.
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Fig. 3. The relationship between the concentrations of 2,3,4,6-tetrachlerophenol and pentachlorophenol. The data
were collected on three occasions.
78
K. ABRAHAMSSON & A. EKDAHL
between days (Abrahamsson & Ekdahl, 1993). In order to study the fraction of PCP associated with the organic layer of particles, water samples were filtered with 0.45 ~.m filters, and were compared with unfiltered samples. No significant difference could be observed. A comparison of the levels of pentachlorophenol measured in this investigation with other investigations of levels of chlorinated compounds, shows that our levels are 20 to 50 times higher. Holden (1987) reported values of less than 0.02 to 1.7 ng.dm -3 for DDE, DDT, Dieldrin, HCB, ~HCH and c~-HCH in the North Sea. The highest fluxes of PCP were found in waters with a salinity of 31
major sources for many organic pollutants. Considering the sedimentation of river-borne particles, a large fraction of the pollutants should be found in the estuarine sediments. For instance, Duinker et aL (1982) showed that the amount of organic pollutants in the rivers entering the German Bight was reduced compared to the amounts in the river waters, probably due to sorption to sedimenting particles. Hence, sediments in coastal areas act as sinks for these compounds. This is certainly true if the lipophilicity of the pollutants is significantly large, which is the case for compounds such as the non-ionic chlorinated pesticides. In our investigation the most lipophilic compounds, guiacols and catechols, could not be detected at all in the water column. Most likely these compounds are adsorbed to particles and then sedimented close to the outlets. The average flow of water across the different transects during the years of sampling was 0.4 Sv at Hirtshals, 0.6 Sv at Hanstholm, and approximately 0 Sv at TyborSn (Rydberg etaL, 1996). The flux of PCP in the Skagerrak was high in the water with a salinity of 31
VOLATILE HALOGENATED COMPOUNDS AND CHLOROPHENOLS IN THE SKAGERRAK
1995a. Marine algae - a source of trichloroethylene and perchloroethytene.--Limnol. Oceanogr. 40" 13211326. ,1995b. Formation and distribution of halogenated volatile organics in sea water. In: A. Grimvall & E.W.B. De Leer. Naturally produced organohalogens. Kluwer, London: 317-326. Buikema, A.L. & M.J. McGinnis, 1979. Phenolics in aquatic ecosystems: a selected review of recent literature.--Mar. Environ. 2" 87-181. BrorstrSm-Lund6n, E., A. Lindskog & J. Mowrer, 1994. Concentrations and fluxes of organic compounds in the atmosphere of the Swedish west coast.--Atm. Environ. 28: 3605-3615. Collen, J., A. Ekdahl, K. Abrahamsson & M. Peders6n, 1994. The involvement of hydrogen peroxide in the production of volatile halogenated compounds by Meristiella gelidium (Rhodophyta).--Phytochemistry 36" 1197-1202. Duinker, J.C., M.T.J. Hillebrand, R.F. Nolting & S. Wellerhaus, 1982. The river Elbe: Processes affecting the behaviour of metals and organochlorines during estaurine mixing.--Neth. J. Sea Res. 15" 141-169. Elliott, S. & F.S. Rowland, 1987. Chlorofluorocarbons and stratospheric o z o n . ~ . Chem. Education. 64" 387-391. Fogelqvist, E. & M. Krysell, 1991. Naturally and anthropogenically produced bromoform in the Kattegatt, a semi-enclosed oceanic basin.--J. Atmos. Chem. 13" 315-319. Gossett, J.M., 1987. Measurements of Henry's law constants of C 1 and C2 chlorinated hydrocarbons.--Environ. Sci. Technol. 21: 202-208. Gribble, G.W., 1992. Naturally occurring organohalogen compounds - A survey.--J, nat. prod. 55" 1353-1395. Gschwend, P.M., J.K. MacFarlane & K.A. Newman, 1985. Volatile halogenated organic compounds released to sea water from temperate marine macro algae.--Science 227:1033-1036. Holden, A.V., 1987. Pesticides. In: P.J. Newman & A.R. Agg. Environmental Protection of the North Sea. Heinemann, Oxford, England: 67-84. Liss, P.S. & L. Merlivat, 1986. Air-sea exchange rates: introduction and synthesis. In: P. Buat-M~nard. The role of
79
air-sea exchange in geochemical cycling. D. Reidel Publishing Company, Dordrecht: 283-294. MacKay, D. & W.Y. Shiu, 1981. A critical review of Henry's law constants for chemicals of environmental interest.--J. Phys. Chem. Ref. Data 10" 1175-1199. MacKay, D., S. Paterson, B. Cheung & N.W. Brock, 1985. Evaluating the environmental behaviour of chemicals with a level III fugacity model.--Chemosphere 14" 335-374. Manley, S.L. & M.N. Dastoor, 1988. Methyl iodide production by kelp and associated microbes.--Mar. Biol. 98: 477-482. Mattice, J.S., S.C. Tsai, M.B. Burch & J.J. Beauchamp, 1981. Toxicity of trihalomethanes to common carp embryos.--Trans. Am. Fish Soc. 110" 261-269. Newman, P.J. & A.R. Agg, 1988. Environmental Protection of the North Sea. Heinemann, Oxford: 3-585. North Sea Task Force, 1993. North Sea Quality Status Report. Osto and Paris Commissions, London: 1-132. Rydberg, L., J. Haamer & O. Liungman, 1996. Fluxes of water and nutrients in and into the Skagerrak.--J. Sea Res. 35; 23-38. Salomons, W., B.L. Bayne, E.K. Duursma & U. F~rstner, 1988. Pollution of the North Sea. An assessment. Springer-Verlag, Berlin: 3-666. Salkinoja-Satonen, M.S., R. Hakulinen, R. Valo & J. Apajalahti, 1983. Biodegradation of recalcitrant organochlorine compounds in fixed film reactors.--Wat. Sci. Tech. 15: 309-319. Voss, R.H., J.T. Wearing & A. Wong, 1981. A novel gas chromatographic method for analyses of chlorinated phenolics in pulp mill effluents. In: L.H. Keith. Advances in the identification and analysis of organic pollutants in water. Ann Arbor Science Publishers Inc. Michigan: 1059-1095 Xie, T.-M. & D. Dyrssen, 1984. Simultaneous determination of partition coefficients and acidity constants of chlorinated phenols and guaiacols by gas chromatography.--Anal. Chim. Acta 160" 21-30. Xie, T.-M., K. Abrahamsson, E. Fogelqvist & B. Josefsson, 1986. Distribution of chlorophenolics in a marine environment.--Environ. Sci. Technol. 20" 457-463.