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Sources and fate of organic contaminants in the Mersey estuary volatile organohalogen compounds
Marine PollutionBulletin 0025-326X/92 S5.00+0.00 © 1992 Pergamon Press pie
Marine Pollution Bulletin, Volume 24, No. 2, pp. 82-91, 1992. Printed in Great Britain.
Sources and Fate of Organic Contaminants in the Mersey Estuary Volatile Organohalogen Compounds H. R. ROGERS, B. CRATHORNE and C. D. WATTS WRc Medmenham Laboratory, Henley Road, P.O. Box 16, Marlow, Bucks, UK
A study of the concentrations and distribution of a range of volatile organohalogen compounds (VOCIs) in the Mersey estuary and its freshwater inputs was conducted between 1987 and 1990. The relative importance of the main freshwater inputs as sources of VOCIs to the estuary have been estimated, and the Manchester Ship canal (MSC) and River Weaver have been identified as important sources. Estimated maximum VOCI inputs from the MSC and River Weaver were 43 kg day -~ chloroform; 32 kg day-~ carbon tetrachloride; 147 kg day-! trichioroethene; 125 kg day -1 tetrachloroethene; and 12 kg day-1 bromoform. The spatial distribution of contaminants in the estuary has been investigated and the data have been interpreted by using mixing curves and a simple flux model. The concentrations of the VOCls declined seawards and it is estimated that a large proportion (80-95%) of VOC! inputs are lost from surface waters after entering the estuary, mainly by volatilisation.
The Mersey estuary, widely regarded as being one of the most polluted in Europe, receives contaminated freshwater inputs and discharges of crude sewage, trade effluents, and partially treated sewage from many points throughout its tidally mixed zone. A major pollution alleviation scheme was initiated in 1981 (Dixon, 1985) to improve the aesthetic, biological, and chemical condition of the estuary and although there has been considerable research into trace metals in the estuary (Campbell et al., 1988; Taylor, 1986) there is a lack of detailed information on organic contaminants. Some water quality studies have been carried out on specific contaminants such as alkyl lead compounds (Towner & Riley, 1984) and phthalate esters (Preston & A1Omran, 1986) but in general the range and concentration of organic contaminants, and their fate in the estuary has not received detailed study. A study of the sources and fates of organic contaminants in the Mersey estuary was undertaken between 1987 and 1990, the aim of which was to provide information on the inputs and fate of organic contaminants in the 82
Mersey estuary, and to improve understanding of the processes affecting their fate in the estuarine environment. A range of VOCls were amongst the compounds selected for study because major manufacturing plants involved with their production are situated in the upper Mersey estuary around Runcorn, and also because the industrialized zone around the River Mersey and its catchment is a possible area of usage of the chemicals. Chloroform and carbon tetrachloride are included on the priority hazardous substance listing produced following the Third International Conference on the Protection of the North Sea 1990. Consequently, a knowledge of concentrations in freshwater inputs and estuarine waters is relevant to future monitoring programmes. In this study the estuarine distributions of a range of volatile organohalogen compounds (VOCls) were determined by conducting longitudinal surveys, and the major freshwater sources of these contaminants to the estuary were identified. Further papers in this series will present data on toluene, chlorophenols, organochlorine pesticides, and other contaminants analysed using GC-MS techniques. S a m p l i n g strategy
The spatial distributions of a range of volatile organohalogens were determined in the tidal estuary by performing longitudinal mid-channel sampling surveys at or within an hour of slack high water. During some surveys additional bank-side, and mid-channel samples were collected. Samples were also taken from the main freshwater inputs to the estuary (Fig. 1). The major freshwater inputs into the estuary are at HoMey Weir (at the tidal limit), and the Weaver sluices which discharge water from the River Weaver and the Manchester Ship canal. Sampling at HoMey weir provided information about the influx of organic contaminants originating from the non-tidal River Mersey which receives inputs from much of the Manchester conurbation. Samples from the River Weaver upstream of the Manchester Ship canal confluence provided data on organic contaminants in the other major freshwater source. Industrial discharges into the Manchester Ship canal
Volume 24/Number 2/February 1992
1. 2. 3. 4. •. 6. 7. 8. 9. 10. 11. 12. 13.
/ /
~Sl Ik~e from Tklal Limit {kin) S5.1 42.4 42.4 39.2
Cmsby C h ~ Sellcombe. tt~4 Nenows Seacombe Landing Stage "l"mnmere CHI Terminal Eesthem Lock Stan~w Point Mamch~ter Sh~ ~n41 I ~ v m Gowy W e r * m t W ~ t ~ C~m~ WidheS West 81ink Runcom Old LOck FiddlerJ Ferry Howley w e f
3~.4 IS.4 8.6
0.0
/f
!
/
/
' (
LIVERPOOL
/
I
RUNCORN ELLESMERE PORT
// FRODSHAM
kN
R. R. Gowy
Fig. 1 Location of freshwater input and estuarine sampling stations in the Mersey estuary.
(MSC) and the 'levelling tide' phenomenon have been shown to be responsible for the periodic influx of contaminants such as organo-lead compounds into the estuary (Towner & Riley, 1984). The 'levelling tide' effect is due to the need to adjust and maintain the canal water at a statutory level in response to variable tidal heights, by opening and closing Eastham Lock and the Weaver sluices. Monitoring of the concentrations of alkyl lead compounds in the Mersey estuary has been undertaken since 1979, when high mortalities of migrating birds were attributed to a discharge of these compounds in the MSC (Wilson et al., 1986). Bearing this effect in mind, samples were taken from the canal during periods of contaminant accumulation (i.e. interlevelling periods) when Eastham Lock (i.e. the seaward end of the canal) is effectively closed to the estuary, and data therefore probably correspond to maximal or 'worst case' levels of VOCls. Under high spring or 'levelling' tide conditions the estuarine water level exceeds the statutory water level for the MSC (8.9 m above chart datum at Liverpool) and the lock gates at Eastham are opened to avoid lock damage due to the reversed water pressure. Consequently the MSC is effectively flushed with influent seawater between Eastham Lock and the River Weaver confluence thereby introducing a pulse of contaminated water into the estuary via the Weaver sluices. In order to observe the effects of periodic inputs the estuarine sampling surveys were phased behind the MSC sampling by 3 or 4 days to give information on the dispersion of the influx of contaminants and its rate of decay. It was not feasible to take sufficient samples to study all aspects of contaminant distribution in the estuary so the following assumptions were made in order to facilitate sampling: 1. Although Bowden & Gilligan
(1971) classified the Mersey estuary as 'partially mixed', we have assumed the estuary to be 'well mixed', with little vertical stratification. 2. Lateral variations were not addressed in detail, although some bank versus mid-channel samples were collected to assess such variability.
Sampling procedure All water samples from the freshwater inputs and the estuary were taken sub-surface at a nominal depth of 0.5 m. Estuarine samples were collected from a rigid hulled z-boat, a jet boat, or from the shore at, or around, high slack water. Water samples were collected in 40 ml glass vials sealed with an open top screw cap with a PTFE lined septum. The vials were rinsed and then filled to overflowing without any headspace or bubbles, from bulk samples (500 ml) collected from the side of the boat. Freshwater input samples were collected using a sprung PTFE-capped 2.5 1. Winchester in a weighted bottle cage that enabled samples to be collected at otherwise inaccessible sites, and 40 ml sub-samples were immediately decanted from the 2.5 1. bulk sample. Samples were stored in a cool box whilst in transit to the laboratory and were extracted and analysed within 24 h of collection.
Analysis The analytical procedure was developed from a method used for the determination of VOCls in sewage sludge and water (HMSO, 1985). Pentane (10 or 16 ml) containing 1,2-dibromopropane as an internal standard was injected into the inverted vial through the 40 ml vial septum displacing an equivalent volume of the 83
Marine Pollution Bulletin
sample through a second second syringe needle. The sample was then extracted by shaking for 10 min. Because the total sample was extracted no differentiation was made between particulate and dissolved phases. Pentane sub-samples (2 ml) were syringed from the vial and 2 ~1 aliquots analysed by gas chromatography-electron capture detection using a 30 m DB624 fused silica column (Jones Chromatography) with automated on-column injection. Determinands were quantified by an internal standard method. Analytical intercomparison exercises were carried out with ICI and NRA laboratories but the results are not reported in this paper.
Results Sample replication During the survey on 28 June 1989, triplicate subsamples from the bulk samples were analysed to determine the significance of volatilization losses during sampling (Table 1). The coefficients of variation for these analyses were all less than 15% with a mean value of 3%, indicating that the decanting of sub-samples from a bulk sample did not cause significantly different volatilization losses between successive samples. Since the sub-samples were not true replicates the data in fact represent both the errors involved with taking replicate field samples, and components of analytical precision.
Sampling variability Three bulk 2.5 1. estuarine water samples were collected at Widnes West Bank (16 November 1989) at approximately 2 m intervals in order to provide some information on the importance of small-scale sampling variability in VOC1 concentrations (Table 2). It was initially intended that the samples would be taken midchannel in the estuary but severe gales caused abandonment of the boat survey, and shore samples were collected instead. The three bulk samples were each analysed in triplicate to enable better intercomparison. Although the samples showed significant differences in suspended solids concentration, the concentration data for VOCls in the bankside samples showed good agreement. The data suggest that there is no significant smallscale variability in the bankside surface water concentrations of VOCls.
Freshwater inputs Initial consultation with North West Water (NWW) identified the Manchester Ship canal (MSC) as a freshwater input that receives many effluent discharges. A major manufacturer of chlorinated solvents, particularly C 1 and C2 halogenated compounds, discharges effluent believed to contain carbon tetrachloride into the River Weaver upstream of the canal at Northwich, and a lesser discharge enters the canal at Runcorn (a third discharge enters the estuary just upstream of the Runcorn-Widnes suspension bridge). Consequently, a suite of volatile organohalogen compounds including carbon tetrachloride were determined in water samples from two sites on the canal at Eastham Lock (site no. 5, Fig. 1), at Ellesmere Port (site no. 7, Fig. 1) and also on 84
the River Weaver at the Weston canal weir (site no. 9, Fig. 1). The data in Table 3 for the freshwater surveys carried out between 1987 and 1989 show that relatively low concentrations of VOCls were present in samples from the River Mersey at Howley Weir, the River Gowy, and Ditton Brook, and this suggests that these inputs are not important sources of haloforms or halogenated C1 and C2 compounds to the estuary. In contrast, significantly higher concentrations of all the determinands were detected in samples from the River Weaver, and at the two sites on the Manchester Ship canal. Particularly high concentrations of chloroform, carbon tetrachloride, and trichloroethene were found in the MSC and the River Weaver during the surveys (2.2-70 ~tg 1-1 CHC13; 0.3-110 ~tg 1-1 CC14; 3.3-970 ~tg 1-j TCE) whilst the bromo-compounds were generally present at lower levels. The bromocompounds, bromoform, bromodichloromethane and dibromochloromethane, were not present at significant concentrations in the low salinity freshwater samples from Howley Weir, the River Gowy or Ditton Brook (generally <0.2 ~xg 1-1). However, it is interesting to note that the highest concentrations of bromoform were found in the MSC and the River Weaver (i.e. mean conc. CHBr 3 8.8 ~tg 1-~; mean salinity 8.7%o; mean chlorinity 4.8%o). This is in agreement with other studies which noted that brominated haloforms were dominant in brackish waters with chlorinities >3%o (Helz & Hsu, 1978; Sugam & Helz, 1981). Although bromoform and other VOCls may originate from industrial effluent discharged into the River Weaver and the MSC, it is possible that in situ generation is also occurring due to haloform type reactions with hypochlorite waste from a local chlor-alkali plant. Similar concentrations (N90 ~tg 1-1) of 'total' haloforms have been found in coastal waters in the immediate vicinity of Kuwaiti desalination plant/power plant sea outfalls that discharge chlorinated seawater (Ali & Riley, 1986).
Estimates of VOCI inputs The mean concentrations and loads of VOCls in the freshwater inputs to the estuary are shown in Table 3. The River Mersey at Howley Weir and the Manchester Ship canal provide the main freshwater influx contributing an estimated 1620 M1 day -1, and 1310 M1 day -1, respectively. It is clear from the mean load data that the Manchester Ship canal is the most important source of volatile organohalogen compounds to the estuary. Mean fluxes of 43 kg day -1 chloroform, 32 kg day -1 carbon tetrachloride, 147 kg day -1 trichloroethene, and 125 kg day -1 tetrachloroethene have been estimated using mean temporal concentration data from five sampling surveys between November 1987 and November 1989, and mean values for determinands at the three sites within the canal/River Weaver system. These data should be regarded as a maximum estimate of inputs because sampling was usually timed to immediately precede a levelling tide event when contaminant accumulation in the canal should be at its highest. Also, the median concentrations of some compounds were considerably lower than the mean
V o l u m e 2 4 / N u m b e r 2 / F e b r u a r y 1992
TABLE 1 'Total' c o n c e n t r a t i o n s (~tg I-~) of volatile o r g a n o h a l o g e n c o m p o u n d s (VOCIs) in successive d e c a n t e d s u b - s a m p l e s of freshwater inputs to the M e r s e y estuary, 28 June 1989. Site
CHCI~
CHCI2Br
CHCIBr 2
CHBr 3
1,1,1 - T C E
CC14
TCE
C2C14
Sal.
Weaver/WestonCanal
a b c x cv
20.1 21.2 21.2 20.8 2.9
a b c x cv
0.5 0.5 0.5 0.5 0
a b c x cv
0.5 0.5 0.5 0.5 0
a b c x cv
1.4 1.4 1.4 1.4 0
a b c x cv
7.3 7.7 7.7 7.6 3.9
a b c x cv
13.9 15.1 15.2 14.7 4.8
a b c x cv
3.3 3.3 3.3 3.3 0
a b c x cv
7.7 8.5 8.6 8.3 6.0
13.3
MSCEasthamJetty
a b c x cv
50.5 49.1 59.3 52.9 10
a b c x cv
1.0 1.0 1.0 1.0 0
a b c x cv
2.6 2.7 2.8 2.7 3.7
a b c x cv
8.6 8.8 9.2 8.8 3.4
a b c x cv
6.9 7.1 6.7 6.9 2.9
a b c x cv
4.5 4.6 4.5 4.5 2.2
a b c x cv
81.8 86.0 65.5 77.8 14
a b c x cv
13.4 14.0 14.2 13.9 2.9
10.0
MSCEPdock
a b c x cv
37.1 37.8 35.8 36.9 2.7
a b c x cv
0.9 0.9 (I.9 0.9 0
a b c x cv
1.9 1.9 1.9 1.9 0
a b c x cv
7.0 6.8 6.7 6.8 2.9
a 11.7 b 0.8 c 0.7 x 0.7 cv 14.3
a b c x cv
8.2 8.4 8.1 8.2 2.4
a b c x cv
4.5 4.6 4.4 4.5 2.2
a b c x cv
3.3 3.3 3.3 3.3 l)
10.4
Sal. = salinity; a, b, and c were triplicate sub-samples; x ~ m e a n c o n c e n t r a t i o n (gg I-~); cv = coefficient of variation; E P ~ E l l e s m e r e Port. N o m e n c l a t u r e : C H C l 3 = c h l o r o f o r m ; C H C l 2 B r = b r o m o d i c h l o r o m e t h a n e ; C H C l B r 2 = d i b r o m o c h l o r o m e t h a n e ; C H B r 3 ~ b r o m o f o r m ; 1,1,1-TCE= 1,1,1 -trichloroethane; T C E = trichloroethene; CCI 4 ~ c a r b o n tetrachloride.
TABLE 2 Small-scale s a m p l i n g variability data for volatile o r g a n o h a l o g e n c o m p o u n d s in b a n k s i d e M e r s e y estuary samples collected at W i d n e s West Bank, 16 N o v e m b e r 1989 (gg l-I). CHC13
EDC
CC14
CHBr~
1,1,1-TCE
TCE
CHC12Br
C2CI 4
CHCIBr 2
Sal.
SS
a 0.8 a 0.8 a 0.8
a <3 a <3 a <3
a 2.4 a 2.5 a 2.4
a 0.7 a 0.8 a 0.8
a <0.2 a <0.2 a <0.2
a 0.4 a 1).3 a 0.3
a 0.1 a 0.1 a 0.1
a 0.9 a 0.8 a 0.7
a 0.2 a 0.2 a 0.3
12.71
159
b 0.9 b 0.9 b 1.0
b <3 b <3 b <3
b 2.7 b 2.7 b 2.7
b 0.5 b 0.7 b 0.7
b <0.2 b <0.2 b <0.2
b 0.3 b 0.4 b 0.4
b 0.1 b 0.1 b 0.1
b 0.8 b 0.9 b 0.9
b 0.3 b 0.3 b 0.3
12.85
132
c 0.9 c 0.9
c c
c 2.6 c 2.9
c 0.7 c 0.6
c c
c 11.4 c 0.4
c 0.1 c 0.1
c 1.0 c 0.4
c 0.3 c 0.2
12.80
97
<3 <3
<0.0 <0.2
a, b, and c were s u b - s a m p l e s from three 2.51. bulk samples collected at a b o u t 2 m intervals along the shore wall. Nomenclature: C H C 1 3 = c h l o r o f o r m ; E D C = l , 2 - d i c h l o r o e t h a n e ; CHCl2Br=bromodichloromethane; CHClBr2=dibromochloromethane; CHBr3=bromoform; 1 , 1 , 1 - T C E = 1,1,1-trichloroethane; T C E = t r i c h l o r o e t h e n e ; CCl4~carbon tetrachloride; C 2 C L = t e t r a c h l o r o e t h y l e n e ; Sal. = salinity %0; SS = s u s p e n d e d solids (mg I L).
TABLE 3 E s t i m a t e d loads of volatile o r g a n o h a l o g e n c o m p o u n d s in m a i n freshwater inputs to the M e r s e y estuary and m e a n concentrations* of volatile o r g a n o h a l o g e n c o m p o u n d s (~g 1-1).
F r e s h w a t e r input H o M e y Weir M e a n conc. M e d i a n conc. M e a n load (kg day -~) M a n c h e s t e r Ship Canal+ M e a n cone. M e d i a n conc. M e a n load (kg day -~)
CHCI 3
1,1,l-C2H3C1 ~
0.6 0.7 1.0
0.4 0.4 (1.7
32.5 13.1 43
2.7 2.5 3.5
CCI 4
CHBr~
C2C14
<0.1 < 0.1 < 0.2
1.1 1.2 1.8
0.6 0.6 1.0
<0.25 //.25 0.4
<0.1 < 0.1 < l).2
<0.1 < 0.1 < 0.2
1620
24.2 16.7 32
112 10.8 147
95.3 6.9 125
8.8 6.9 11.5
4.5 2.6 5.9
1.3 1.0 1.7
1310
0.4 0.4 0.02
0.2 0.2 0.0 I
57
< 0.1 0.1 < 0.004
< 0.1 0.1 < 0.004
40
Ditton B r o o k M e a n conc. M e d i a n conc. M e a n load (kg day -~)
0.5 0.4 0.03
0.7 0.7 0.04
0.9 0.1 0.05
0.6 0.6 0.03
0.4 0.4 0.02
< 0.3 0.3 < 0.01
River G o w y M e a n conc. M e d i a n conc. Mean load (kg day ~)
1.8 0.7 0.07
8.3 1.5 0.3
0.9 0.3 0.04
2.8 0.2 0.11
0.2 0.1 0.01
0.4 0.3 0.01
CHCIBr,
CHC12Br
M o d a l flow + MI day -~
C~HCI~
*Calculated from data for samples collected o n 2 N o v e m b e r 1987, 13 April 1988, 22 June 1988, 17 N o v e m b e r 1988, and 9 N o v e m b e r 1989. t M e a n values calculated from s u m m e d c o n c e n t r a t i o n data for the River Weaver, M a n c h e s t e r Ship canal at E a s t h a m Lock and E l l e s m e r e Port. ~:Head (1990), pets. comm.
85
Marine Pollution Bulletin
values indicating that there was quite a wide range of concentrations between surveys. The relatively high concentrations of VOCls found in the Manchester Ship canal and River Weaver mainly originate from industrial effluent inputs. Although the River Mersey at Howley Weir supplies the largest freshwater input to the estuary (1620 M1 day -~) our data indicate that it contributes relatively small amounts of VOCIs when compared to the Manchester Ship canal/River Weaver system. Trichloroethene and tetrachloroethene were the predominant VOCIs in the River Mersey inflow with mean loadings of 1.8 kg day -1 and 1.0 kg day -L, respectively. These compounds are widely used as metal degreasing solvents (Fischer et al., 1982) and probably originate from diffuse upstream sources. Ditton Brook showed much lower levels o f the VOCls, with mean loadings of less than 0.05 kg day -1 for all determinands, and the River Gowy showed a similar pattern with the exception of 1,1,1-trichloroethane (0.3 kg day-l), and trichloroethene (0.11 kg day-l). These two tributaries therefore appear to be only minor sources of VOCls to the estuary.
Estuarine waters
Generally the most important process affecting the distribution of contaminants in estuaries is the degree of mixing of freshwater and seawater. Diffusive mixing in estuaries results from the density difference between fresh and saline waters, and this is combined with the advective mixing due to tidal motion. Interpretation of the data for the VOCls have been made using concentration versus salinity plots to establish whether the data are consistent with conservative behaviour. The estuarine mixing curves for four longitudinal surveys of the VOCIs in the estuary are shown in Figs 2-9. Several observations can be made regarding the survey data for the VOCls: 1. The freshwater samples from the MSC~and River Weaver generally contained the highest concentrations of VOCIs (<0.1-970 ~tg 1-1) and these are the major sources of these contaminants to the estuary. Mersey estuarine waters showed generally lower concentrations (<0.1-35.8 ~tg l-l). The negative correlation between total concentrations of all the VOCls with salinity confirms that the freshwater end-member is the source
c h l o r o f o r m conc. ug.l.-1
6
[]
+ + + .
2
+ 1
18.4.88
19.7.89
-• O. +
i
i
I
I
i
I
5
10
15
20
25
30
35
salinity o/no CCI4
+
[]
+
0
5.11.87
24.11.88
+
0
•
Fig. 2 Total concentration of chloroform vs. salinity.
c o n e . ug.I.-1
50 + 40 + + 30
+ +
•
5.11.87
+
18.4.88
-~
24.11.88
[]
19.7.89
20 "1111
10
m+
o I
t
5
10
15
20
salinity o/oo
86
25
30
35 Fig. 3 Total concentration of carbon tetrachloride vs. salinity.
Volume 24/Number 2/February 1992
of the contaminants. Tetrachloroethylene showed pronounced positive deviations in its salinity plots between 20-30%0 (Fig. 6) indicating inputs mid-estuary. 2. Estimated freshwater input loadings (Table 3) indicate that the main source of the three bromocompounds is the MSC and this is further confirmed by the estuarine distributions (Figs 7-9) for 5 November 1987, 18 April 1988, 24 November 1988, and 19 July 1989 surveys which show pronounced mid-salinity concentration maxima for bromoform, dibromochloromethane, and bromodichloromethane. Concentrations of the bromo-compounds declined to <0.2 ~tg 1-~ at salinities greater than 25%0. 3. The 5 November 1987, 18 April 1988 and 24 November 1988 surveys were carried out about 3-4 days after a levelling tide, and the maximum concentrations observed in the inner estuary which are observed at and around high slack water (salinities of 7.5-15%o) reflect the effect of tidal flushing of the Manchester Ship canal into the inner estuary. 4. The lower concentrations of VOCIs at salinities between 20-30%0 show the effect of dilution of inputs
3
from the estuary with relatively clean influent seawater. 5. It is likely that sewage effluent and crude sewage outfalls contribute to the total input of VOCls to the estuary. However, the importance of these possible sources has not been determined in this study. 6. Concentrations of VOCls found in the outer estuary in the Crosby Channel were generally <0.1 ixg 1-1 for all determinands. Our data is of the same order as average concentrations of 1,1,1-TCE (0.25 ~tg l-l), TCE (0.3 ~tg 1-1), CCI 4 (0.25 Ixg 1-1), and tetrachloroethene (0.12 ~tg 1-1) previously detected in Liverpool Bay and coastal waters around the Mersey estuary (Pearson & McConnell, 1975). The range of concentrations of carbon tetrachloride and 1,1,1-TCE found in the estuary are comparable to those found during a study of VOCls in the River Brazos, USA (McDonald et al., 1988) which also receives discharges of chemical industry effluent containing VOCls. The concentrations of VOCls in the Mersey estuary are about three orders of magnitude higher than reported open ocean water concentrations (Fogelqvist, 1985) reflecting the influence of inputs from freshwater sources.
1,1,1,-TCE conc ug.I.-1
2.5
2
4-
1.5
• 4-
44-
-~
[]
5.11.87 18.4.88 24.11.88 19.7.89
i
4-
0.5
~
0 0
5
[ |,1-1
I
I
I
I
I
10
15
20
25
30
35 Fig. 4 Total concentration of 1,1,1-TCE vs. salinity.
salinity o/oo T C E c o n c ug.I,-1
• 4I
I
[]
4-
5.11.87 18.4.88 24.11.88 19.7.89
4-
4-
++
•
+.
I
I
I
I
I
10
15
20
25
30
salinity o/oo
35
Fig. 5 Total concentration of TCE vs. salinity.
87
Marine Pollution Bulletin
Estuarine flux calculations Extensive monitoring of estuarine VOC1 concentrations was not possible but the data from four surveys have been used to provide estimates of the flux of VOCls passing through the estuary. Officer (1979) described a simple means of calculating the downstream flux of dissolved c o m p o n e n t s using data for the freshwater flow, the salinity gradient and the longitudinal distribution of concentrations of the component. The flux calculations have the following limitations and assumptions: i. Steady state conditions are assumed. 2. Lateral variations are ignored. 3. The estuary is regarded as one-dimensional (concentration data varying with longitudinal position). 4. T h e estimated fluxes depend on concentration data from only two surveys. Officer (1979) showed that the flux of a constituent in an estuary could be calculated in terms of the freshwater flow, the longitudinal distribution of the constituent and the salinity profile, assuming that under
2.5
tetrachloroethylene
cone
steady state conditions the net flux of salt through any section of an estuary is zero. The net seaward flux of a dissolved c o m p o n e n t (Fx) through a downstream section of the estuary, x, is given by: Adc Zx = Rc - K x - dx
where R = river flow K X = longitudinal dispersion coefficient A = cross sectional area of estuary normal to flow c = concentration of c o m p o n e n t at section s = salinity at section d c = concentration gradient of c o m p o n e n t dx For steady state, one dimensional conditions, RS-Kx
Ads dx - 0
dx dc F× = Rc - R s - - ' - ds dx
+
1.5
+ 18.4.88 I -~ 24.11.88 [] 19.7.89
+ + +
44-4-
4++
4-
[]
[]
[][]
+
[]
0
4+~ ~3+
I
I
I
I
I
I
5
10
15
20
25
30
salinity bromoform
conc
35
o/oo
Fig. 6 Total concentration of tetrachloroethylene vs. salinity.
ug.l.-1
1.6
1.4 1.2 1 0.8
+
+
0.6
+
[]
+
0.4
4-
+
+
5.11.87 18.4.88 24.11.88 19.7.89
i
+ +
4-
0.2
[] ~-~3crn -tl3~
0 10 88
(3)
ug.l.-1
2
0
(2)
and rearranging in terms of c and s (salinity),
Fx = R c - s
0.5
(1)
I
I
I
I
15
20
25
30
salinity
o/oo
35
Fig. 7 Total concentration of bromoform vs. salinity.
(4)
Volume 2 4 / N u m b e r 2/February 1992
Equation 4 has been used to provide estimates of VOCls fluxes in the estuarine segments between Fiddler's Ferry and Runcorn Old Lock in the upper estuary, and between Tranmere Oil Terminal and the Narrows (i.e. the deep straight channel connecting Liverpool Bay with the inner estuary) at Seacombe in the outer estuary (see Fig. 10). The freshwater flow at Fiddler's Ferry was assumed to be the input over Howley Weir (1620 MI day-l), whilst at Tranmere the additional flow from the MSC/River Weaver was included (total flow 2930 M1 day-I). For the purposes of these calculations the River Mersey at Howley Weir and the RSC/River Weaver input are assumed to be the only significant freshwater flows and any losses of components down the estuary are assumed to be via volatilization to the atmosphere. Any loss of VOCls via sediment sorption has been assumed to be negligible when compared to volatilization because these compounds have low octanol water partition coefficients (chloroform log Kow=2.0; tetrachloroethene log Kow = 2.9; Oliver, 1989). It should be noted that freshwater flow data for the MSC and River Weaver are
difficult to estimate because of the complexity of these inputs and the data are thus only approximate. The following mass balance equation was used: Flux V = Flux A - Flux B + Flux C Flux Flux Flux Flux
A B C V
(5)
= = = =
Flux at Fiddler's Ferry/Runcorn section. Flux at Tranmere/Seacombe section. MSC input (see Table 3). Loss of VOCI between Runcorn and Seacombe. The flux estimates shown in Table 4 indicate that with the exception of carbon tetrachloride relatively small amounts of volatile organohalogen compounds are entering the estuary via the narrow upper estuary at Runcorn. An estimated 40-50 kg carbon tetrachloride enters the estuary per day across the Fiddler's Ferry/ Runcorn Old Lock section, and this high figure appears to contradict the low estimates for CC14 inputs across the Howley Weir calculated from freshwater flow and input concentration data (<0.2 kg day-t). However, there is an industrial effluent discharge upstream of the Runcorn bridge, that is known to contain C C l 4 , and this
bromodichloromethane oono ug.I.-1
0.6
0.5
0.4
4-
0.3
+t3- +~+
0.2
++
÷
0.1
•
0
0
r7 E t ~ E ~ ' , ,,-u~,~ iv-q ~L-w
•
5.11.87
-t-
18.4.88
~
24.11.88
[]
19.7.89
~
I
I
I
I
I
I
5
10
15
20
25
30
35 Fig. 8 Total concentration of bromodichloromethane vs. salinity.
aalinity o / o o dibromochloromethane conc ug.l.-1
1.4
1.2 1 •
5.11.87
÷
18.4.88
0.8 24.11.88
0.6 []
0
• +~¢ -H- • q--
0.4
+
19.7.89
•
0.2
+ 0 0
~/l[7~l
I
IIII--J I
I
I
I
I
I
I
5
10
15
20
25
30
aalinity o / o o
35 Fig. 9 Total concentration of dibromochloromethane vs. salinity.
89
Marine Pollution Bulletin
probably accounts for the elevated flux at Runcorn. At the seaward section in the Narrows the fluxes of all the VOCls have mean values that are less than 10 kg day-~ and the estimated losses (Flux V), which are assumed to be mainly due to volatilization (Wakeham et al., 1983) are comparable to the inputs from the MSC/River Weaver. The negative value of Flux V for 1,1,1-TCE on 18 April 1988 could be due to: 1. An additional input of 1,1,1-TCE from a source other than the Manchester Ship canal in the outer estuary, and/or, 2. An underestimate of the MSC input, Flux C.
lives for trichloroethylene and tetrachloroethylene of 2.5 and 6 years (Pearson & McConnell, 1975). The bioaccumulation of VOCIs by marine biota, and sorption by sedimentary material are probably minor loss routes because of the low octanol-water partition coefficients for these contaminants, and bacterial degradation has been found to be important only under anaerobic conditions (Vargas & Ahlert, 1987). The rate of transfer of carbon tetrachloride through the air-water interface has been estimated using a simplified mass transfer relationship (Ambrose et al,, 1988): dCw Kv . . . .
Loss processes
dt
The abiotic degradation of VOCls in water by hydrolysis can be regarded as a slow loss process (chloroform hydrolysis t l / 2 = 1 0 0 0 years, Xie et al., 1986; 1,1,1-trichloroethane hydrolysis tl/2=1.7 years, Gerkens & Franklin, 1989) but photodegradation is a more important removal process for volatile organohalogenated compounds generally, with estimated half-
D
Cw
(6)
where Cw = dissolved concentration in water, (gg l-l), 4.4 ~tg 1-j (mean of estuarine concentrations 18 April 1988). D = depth, mean high water springs 9.3 m, mean low water springs 0.9 m. Kv =rate constant, 2.55 m day -1 (Dilling, 1977). 1. Seacombe. Narrows. 2. Tranmere 3. Runcorn Old Lock 4. Fiddler's Ferry 5. Weaver sluices
tJ~rixx~ ..3 Rune,ore
)-
~
Ble~ellDPoll
Fig. 1O Estuarine sections for VOCI flux estimations. TABLE 4 Estimated fluxes for VOCIs in the Mersey estuary (kg day-t).
Compound CCI 4 CHC13 C2HCI 3 CHBr3 1,1,1-TCE CHCIzBr CHCIBr 2 Flux Flux Flux Flux
90
A= B= V= C=
Flux A 5 November 18 April 1987 1988 42 3 6 0.6 2 0.5 0.6
52 1 1 0.6 1 0.02 0.5
Flux B 5 November 18 April 1987 1988 10 7 15 1 4 0.3 |.5
9 0,6 0,6 0,6 17 0,3 0,6
Flux between Fiddler's Ferry and Runcorn. Flux between Tranmere and the Narrows at Seacombe. Loss of constituent between Runcorn and Seacombe (assumed to be by volatilization). Estimated Manchester Ship canal input (Table 3).
Flux V 5 November 18 April 1987 1988 64 39 138 12 2 2.2 5.1
75 43 147 12 --12 1.7 5.9
Flux C
32 43 147 12 4 2 6
Volume 24/Number 2/February 1992
Using equation 6 and the parameter values above, a (NRA, North West Division) for their co-operation and for providing survey vessels, Dr. P. C. Head (NWW plc) for providing flow inforrate loss of about 1 ~g 1-I day -1 is obtained for E e l 4 mation, and Dr. R. Otter (DOE) for useful discussions. when D=9.3 m (MHWS) and about 12.5 ~tg 1-/ day-1 when D=0.9 m (MLWS). These predicted rates of loss Ali, M. Y. & Riley, J. P. (1986). The distribution of halomethanes in the coastal waters of Kuwait. Mar. Pollut. Bull. 17,409-414. suggests that CC14 concentrations decline rapidly with Ambrose, R. B., Wool, T. A., Connolly, J. P. & Schanz, R. W. (1988). half-lives within the range of 4-48 h. However, the WASP4, a hydrodynamic and water quality model--model theory, user's manual and programmer's guide. EPA/600/3-87/039. liquid-gas transfer rates may not be a true estimate of K. F. & Gilligan, R. M. (1971). Characteristic features of real estuarine exchange rates as no account has been Bowden, estuarine circulation as represented in the Mersey estuary. LimnoL taken for enhanced volatilization due to turbulence or Oceanogr. 16,490. wind stress. Although predictive equations have limi- Campbell, J. A., Whitelaw, K., Riley, J. P., Head, P. C. & Jones, P. D. (1988). Contrasting behaviour of dissolved and particulate nickel tations when applied to real systems because of the and zinc in a polluted estuary. Sci. Tot. Env. 71,141-155. difficulty in including the impact of factors such as Dilling, W. L. (1977). Interphase transfer processes. II. Evaporation rates of chloro-methanes, -ethanes, -ethylenes, -propanes, and weather conditions, wind stress, surface area to depth propylenes from dilute aqueous solutions. Comparisons with ratio, stratification, and tidal mixing, we can conclude theoretical predictions. Env. Sci. Tech. 11,405-409. that a large proportion of the VOCls discharged into Dixon, A. (1985). The Mersey estuary pollution alleviation scheme. J. Inst. War. Eng. Sci. 39,401 413. the estuary are lost by evaporation to the atmosphere.
Conclusions The Manchester Ship canal (MSC) and the River Weaver have been shown to be important sources of volatile organohalogen compounds to the Mersey estuary. Although the River Mersey supplies the largest freshwater input to the estuary our data indicate that it contributes relatively small amounts of VOCIs compared to the MSC/River Weaver system. Volatilization to the atmosphere is expected to be a major process controlling the fate of VOCls in the freshwater inputs and in the estuary, but dilution of freshwater inputs during tidal mixing also appears to be an important factor influencing VOC! distributions in the estuary. There was a negative correlation between total concentrations of VOCls with salinity, confirming that the freshwater end-member was the primary source of the contaminants. Two main sources of carbon tetrachloride to the estuary were identified; the Manchester Ship canal/River Weaver and another input upstream of the Runcorn bridge in the upper estuary. Estimates of the fluxes of the VOCls at the seaward section in the Mersey Narrows have mean values that are less than 10 kg day -1 and simple mass balance calculations show that significant losses of VOCls (between 80-90% of inputs), are occurring within the estuary, mainly via volatilization. The data produced from this study should serve as a useful basis for future monitoring of the estuary, especially as a series of pollution alleviation measures are currently being ~ntroduced.
This work was carried out under contract to the Department of the Environment who have given their permission to publish. The authors would like to thank the analysis group at WRc Medmenham for carrying out the VOCI analyses, Dr. P. D. Jones and Mr. A. Wither
Fischer, M., Friesel, P., Koch, G., Milde, G. & Rosskamp, E. (1982). Evaluation of water pollution caused by chlorinated ethylenes. Contract No. U71/515. EC Report No. XI/400/83. Fogelqvist, E. (1985). Carbon tetrachloride, tetrachloroethylene, l,l,1trichloroethylene and bromoformin Arctic seawater. J. Geophys. Res. 90, 9181-9193. Gerkens, R, R. & Franklin, J, A. (1989). The rate of degradation of l,l,l-trichloroethane in water by hydrolysis and dechlorination. Chemosphere 19, 1929-1937. Helz, G. R. & Hsu, R. Y. (1978). Volatile chloro- and bromocarbons in coastal waters. Limnol. Oceanogr. 23,858-869. HMSO (1985). Methods for the Examination of Waters and Associated Materials. Chlorobenzenes in water, organochlorine pesticides and PCBs in turbid waters, halogenated solvents and related compounds in sewage sludge and waters, 1985. McDonald, T. J., Kennicutt, M. C., Brooks, J. M. & Graham-Road, T. S. (1988). Volatile organic compounds at a coastal Gulf of Mexico site. Chemosphere 17, 123-136. Officer, C. B. (1979). Discussion of the behaviour of non-conservative dissolved constituents in estuaries. Est. Coast. Mar. Sci. 9, 91-94. Oliver, B. G. (1989). Analysis of volatile halogenated and purgeable organics. In Analysis of Trace Organics in the Aquatic Environment (B. K. Afghan & A. S. Y. Chau, eds), pp. 00-00. CRC Press, Florida. Pearson, C. R. & McConnell, G. (1975). Chlorinated C1 and C2 hydrocarbons in the marine environment. Proc. Royal Soc, Lond., B 189, 305-332. Preston, M. R. & AI-Omran, L. A. (1986). Dissolved and particulate phthalate esters in the River Mersey Estuary. Mar Pollut. Bull. 17, 548-553. Sugam, R. & Helz, G. R. (1981). Chlorine speciation in seawater; a metastable equilibrium model for CI and Br species. Chemosphere 10,41-57. Taylor, D. (1986). Changes in the distribution patterns of trace metals in sediments of the Mersey estuary in the last decade (1974-83). Sci. Tot. Env. 49,257-295. Towner, J. V. & Riley, J. P. (1984). The distribution of alkyl lead species in the Mersey. Mar Pollut. Bull. 15,153-158. Vargas, C. & Ahlert, R. C. (1987). Anaerobic degradation of chlorinated solvents. J. Wat. Poll. Con. Fed. 59,964-968. Wakeham, S. G., Davis, A. C. & Karas, J. L. (1983). Mesocosm experiments to determine the fate and persistence of volatile organic compounds in coastal seawater. Env, Sci. Tech. 17, 611-617. Wilson, K. W., Head, P. C. & Jones, P. D. (1986). Mersey estuary (UK) bird mortalities--causes, consequences and correctives. Wat. Sci. Tech. 18, 171-180. Xie, T. M., Abrahamsson, K., Fogelquist, E. & Josefsson, B. (1986). Distribution of chl0rophenolics in a marine environment, Env. Sci. Tech. 20,457-463.
91
Marine Pollution Bulletin, Volume 24, No. 2, pp. 82-91, 1992. Printed in Great Britain.
Sources and Fate of Organic Contaminants in the Mersey Estuary Volatile Organohalogen Compounds H. R. ROGERS, B. CRATHORNE and C. D. WATTS WRc Medmenham Laboratory, Henley Road, P.O. Box 16, Marlow, Bucks, UK
A study of the concentrations and distribution of a range of volatile organohalogen compounds (VOCIs) in the Mersey estuary and its freshwater inputs was conducted between 1987 and 1990. The relative importance of the main freshwater inputs as sources of VOCIs to the estuary have been estimated, and the Manchester Ship canal (MSC) and River Weaver have been identified as important sources. Estimated maximum VOCI inputs from the MSC and River Weaver were 43 kg day -~ chloroform; 32 kg day-~ carbon tetrachloride; 147 kg day-! trichioroethene; 125 kg day -1 tetrachloroethene; and 12 kg day-1 bromoform. The spatial distribution of contaminants in the estuary has been investigated and the data have been interpreted by using mixing curves and a simple flux model. The concentrations of the VOCls declined seawards and it is estimated that a large proportion (80-95%) of VOC! inputs are lost from surface waters after entering the estuary, mainly by volatilisation.
The Mersey estuary, widely regarded as being one of the most polluted in Europe, receives contaminated freshwater inputs and discharges of crude sewage, trade effluents, and partially treated sewage from many points throughout its tidally mixed zone. A major pollution alleviation scheme was initiated in 1981 (Dixon, 1985) to improve the aesthetic, biological, and chemical condition of the estuary and although there has been considerable research into trace metals in the estuary (Campbell et al., 1988; Taylor, 1986) there is a lack of detailed information on organic contaminants. Some water quality studies have been carried out on specific contaminants such as alkyl lead compounds (Towner & Riley, 1984) and phthalate esters (Preston & A1Omran, 1986) but in general the range and concentration of organic contaminants, and their fate in the estuary has not received detailed study. A study of the sources and fates of organic contaminants in the Mersey estuary was undertaken between 1987 and 1990, the aim of which was to provide information on the inputs and fate of organic contaminants in the 82
Mersey estuary, and to improve understanding of the processes affecting their fate in the estuarine environment. A range of VOCls were amongst the compounds selected for study because major manufacturing plants involved with their production are situated in the upper Mersey estuary around Runcorn, and also because the industrialized zone around the River Mersey and its catchment is a possible area of usage of the chemicals. Chloroform and carbon tetrachloride are included on the priority hazardous substance listing produced following the Third International Conference on the Protection of the North Sea 1990. Consequently, a knowledge of concentrations in freshwater inputs and estuarine waters is relevant to future monitoring programmes. In this study the estuarine distributions of a range of volatile organohalogen compounds (VOCls) were determined by conducting longitudinal surveys, and the major freshwater sources of these contaminants to the estuary were identified. Further papers in this series will present data on toluene, chlorophenols, organochlorine pesticides, and other contaminants analysed using GC-MS techniques. S a m p l i n g strategy
The spatial distributions of a range of volatile organohalogens were determined in the tidal estuary by performing longitudinal mid-channel sampling surveys at or within an hour of slack high water. During some surveys additional bank-side, and mid-channel samples were collected. Samples were also taken from the main freshwater inputs to the estuary (Fig. 1). The major freshwater inputs into the estuary are at HoMey Weir (at the tidal limit), and the Weaver sluices which discharge water from the River Weaver and the Manchester Ship canal. Sampling at HoMey weir provided information about the influx of organic contaminants originating from the non-tidal River Mersey which receives inputs from much of the Manchester conurbation. Samples from the River Weaver upstream of the Manchester Ship canal confluence provided data on organic contaminants in the other major freshwater source. Industrial discharges into the Manchester Ship canal
Volume 24/Number 2/February 1992
1. 2. 3. 4. •. 6. 7. 8. 9. 10. 11. 12. 13.
/ /
~Sl Ik~e from Tklal Limit {kin) S5.1 42.4 42.4 39.2
Cmsby C h ~ Sellcombe. tt~4 Nenows Seacombe Landing Stage "l"mnmere CHI Terminal Eesthem Lock Stan~w Point Mamch~ter Sh~ ~n41 I ~ v m Gowy W e r * m t W ~ t ~ C~m~ WidheS West 81ink Runcom Old LOck FiddlerJ Ferry Howley w e f
3~.4 IS.4 8.6
0.0
/f
!
/
/
' (
LIVERPOOL
/
I
RUNCORN ELLESMERE PORT
// FRODSHAM
kN
R. R. Gowy
Fig. 1 Location of freshwater input and estuarine sampling stations in the Mersey estuary.
(MSC) and the 'levelling tide' phenomenon have been shown to be responsible for the periodic influx of contaminants such as organo-lead compounds into the estuary (Towner & Riley, 1984). The 'levelling tide' effect is due to the need to adjust and maintain the canal water at a statutory level in response to variable tidal heights, by opening and closing Eastham Lock and the Weaver sluices. Monitoring of the concentrations of alkyl lead compounds in the Mersey estuary has been undertaken since 1979, when high mortalities of migrating birds were attributed to a discharge of these compounds in the MSC (Wilson et al., 1986). Bearing this effect in mind, samples were taken from the canal during periods of contaminant accumulation (i.e. interlevelling periods) when Eastham Lock (i.e. the seaward end of the canal) is effectively closed to the estuary, and data therefore probably correspond to maximal or 'worst case' levels of VOCls. Under high spring or 'levelling' tide conditions the estuarine water level exceeds the statutory water level for the MSC (8.9 m above chart datum at Liverpool) and the lock gates at Eastham are opened to avoid lock damage due to the reversed water pressure. Consequently the MSC is effectively flushed with influent seawater between Eastham Lock and the River Weaver confluence thereby introducing a pulse of contaminated water into the estuary via the Weaver sluices. In order to observe the effects of periodic inputs the estuarine sampling surveys were phased behind the MSC sampling by 3 or 4 days to give information on the dispersion of the influx of contaminants and its rate of decay. It was not feasible to take sufficient samples to study all aspects of contaminant distribution in the estuary so the following assumptions were made in order to facilitate sampling: 1. Although Bowden & Gilligan
(1971) classified the Mersey estuary as 'partially mixed', we have assumed the estuary to be 'well mixed', with little vertical stratification. 2. Lateral variations were not addressed in detail, although some bank versus mid-channel samples were collected to assess such variability.
Sampling procedure All water samples from the freshwater inputs and the estuary were taken sub-surface at a nominal depth of 0.5 m. Estuarine samples were collected from a rigid hulled z-boat, a jet boat, or from the shore at, or around, high slack water. Water samples were collected in 40 ml glass vials sealed with an open top screw cap with a PTFE lined septum. The vials were rinsed and then filled to overflowing without any headspace or bubbles, from bulk samples (500 ml) collected from the side of the boat. Freshwater input samples were collected using a sprung PTFE-capped 2.5 1. Winchester in a weighted bottle cage that enabled samples to be collected at otherwise inaccessible sites, and 40 ml sub-samples were immediately decanted from the 2.5 1. bulk sample. Samples were stored in a cool box whilst in transit to the laboratory and were extracted and analysed within 24 h of collection.
Analysis The analytical procedure was developed from a method used for the determination of VOCls in sewage sludge and water (HMSO, 1985). Pentane (10 or 16 ml) containing 1,2-dibromopropane as an internal standard was injected into the inverted vial through the 40 ml vial septum displacing an equivalent volume of the 83
Marine Pollution Bulletin
sample through a second second syringe needle. The sample was then extracted by shaking for 10 min. Because the total sample was extracted no differentiation was made between particulate and dissolved phases. Pentane sub-samples (2 ml) were syringed from the vial and 2 ~1 aliquots analysed by gas chromatography-electron capture detection using a 30 m DB624 fused silica column (Jones Chromatography) with automated on-column injection. Determinands were quantified by an internal standard method. Analytical intercomparison exercises were carried out with ICI and NRA laboratories but the results are not reported in this paper.
Results Sample replication During the survey on 28 June 1989, triplicate subsamples from the bulk samples were analysed to determine the significance of volatilization losses during sampling (Table 1). The coefficients of variation for these analyses were all less than 15% with a mean value of 3%, indicating that the decanting of sub-samples from a bulk sample did not cause significantly different volatilization losses between successive samples. Since the sub-samples were not true replicates the data in fact represent both the errors involved with taking replicate field samples, and components of analytical precision.
Sampling variability Three bulk 2.5 1. estuarine water samples were collected at Widnes West Bank (16 November 1989) at approximately 2 m intervals in order to provide some information on the importance of small-scale sampling variability in VOC1 concentrations (Table 2). It was initially intended that the samples would be taken midchannel in the estuary but severe gales caused abandonment of the boat survey, and shore samples were collected instead. The three bulk samples were each analysed in triplicate to enable better intercomparison. Although the samples showed significant differences in suspended solids concentration, the concentration data for VOCls in the bankside samples showed good agreement. The data suggest that there is no significant smallscale variability in the bankside surface water concentrations of VOCls.
Freshwater inputs Initial consultation with North West Water (NWW) identified the Manchester Ship canal (MSC) as a freshwater input that receives many effluent discharges. A major manufacturer of chlorinated solvents, particularly C 1 and C2 halogenated compounds, discharges effluent believed to contain carbon tetrachloride into the River Weaver upstream of the canal at Northwich, and a lesser discharge enters the canal at Runcorn (a third discharge enters the estuary just upstream of the Runcorn-Widnes suspension bridge). Consequently, a suite of volatile organohalogen compounds including carbon tetrachloride were determined in water samples from two sites on the canal at Eastham Lock (site no. 5, Fig. 1), at Ellesmere Port (site no. 7, Fig. 1) and also on 84
the River Weaver at the Weston canal weir (site no. 9, Fig. 1). The data in Table 3 for the freshwater surveys carried out between 1987 and 1989 show that relatively low concentrations of VOCls were present in samples from the River Mersey at Howley Weir, the River Gowy, and Ditton Brook, and this suggests that these inputs are not important sources of haloforms or halogenated C1 and C2 compounds to the estuary. In contrast, significantly higher concentrations of all the determinands were detected in samples from the River Weaver, and at the two sites on the Manchester Ship canal. Particularly high concentrations of chloroform, carbon tetrachloride, and trichloroethene were found in the MSC and the River Weaver during the surveys (2.2-70 ~tg 1-1 CHC13; 0.3-110 ~tg 1-1 CC14; 3.3-970 ~tg 1-j TCE) whilst the bromo-compounds were generally present at lower levels. The bromocompounds, bromoform, bromodichloromethane and dibromochloromethane, were not present at significant concentrations in the low salinity freshwater samples from Howley Weir, the River Gowy or Ditton Brook (generally <0.2 ~xg 1-1). However, it is interesting to note that the highest concentrations of bromoform were found in the MSC and the River Weaver (i.e. mean conc. CHBr 3 8.8 ~tg 1-~; mean salinity 8.7%o; mean chlorinity 4.8%o). This is in agreement with other studies which noted that brominated haloforms were dominant in brackish waters with chlorinities >3%o (Helz & Hsu, 1978; Sugam & Helz, 1981). Although bromoform and other VOCls may originate from industrial effluent discharged into the River Weaver and the MSC, it is possible that in situ generation is also occurring due to haloform type reactions with hypochlorite waste from a local chlor-alkali plant. Similar concentrations (N90 ~tg 1-1) of 'total' haloforms have been found in coastal waters in the immediate vicinity of Kuwaiti desalination plant/power plant sea outfalls that discharge chlorinated seawater (Ali & Riley, 1986).
Estimates of VOCI inputs The mean concentrations and loads of VOCls in the freshwater inputs to the estuary are shown in Table 3. The River Mersey at Howley Weir and the Manchester Ship canal provide the main freshwater influx contributing an estimated 1620 M1 day -1, and 1310 M1 day -1, respectively. It is clear from the mean load data that the Manchester Ship canal is the most important source of volatile organohalogen compounds to the estuary. Mean fluxes of 43 kg day -1 chloroform, 32 kg day -1 carbon tetrachloride, 147 kg day -1 trichloroethene, and 125 kg day -1 tetrachloroethene have been estimated using mean temporal concentration data from five sampling surveys between November 1987 and November 1989, and mean values for determinands at the three sites within the canal/River Weaver system. These data should be regarded as a maximum estimate of inputs because sampling was usually timed to immediately precede a levelling tide event when contaminant accumulation in the canal should be at its highest. Also, the median concentrations of some compounds were considerably lower than the mean
V o l u m e 2 4 / N u m b e r 2 / F e b r u a r y 1992
TABLE 1 'Total' c o n c e n t r a t i o n s (~tg I-~) of volatile o r g a n o h a l o g e n c o m p o u n d s (VOCIs) in successive d e c a n t e d s u b - s a m p l e s of freshwater inputs to the M e r s e y estuary, 28 June 1989. Site
CHCI~
CHCI2Br
CHCIBr 2
CHBr 3
1,1,1 - T C E
CC14
TCE
C2C14
Sal.
Weaver/WestonCanal
a b c x cv
20.1 21.2 21.2 20.8 2.9
a b c x cv
0.5 0.5 0.5 0.5 0
a b c x cv
0.5 0.5 0.5 0.5 0
a b c x cv
1.4 1.4 1.4 1.4 0
a b c x cv
7.3 7.7 7.7 7.6 3.9
a b c x cv
13.9 15.1 15.2 14.7 4.8
a b c x cv
3.3 3.3 3.3 3.3 0
a b c x cv
7.7 8.5 8.6 8.3 6.0
13.3
MSCEasthamJetty
a b c x cv
50.5 49.1 59.3 52.9 10
a b c x cv
1.0 1.0 1.0 1.0 0
a b c x cv
2.6 2.7 2.8 2.7 3.7
a b c x cv
8.6 8.8 9.2 8.8 3.4
a b c x cv
6.9 7.1 6.7 6.9 2.9
a b c x cv
4.5 4.6 4.5 4.5 2.2
a b c x cv
81.8 86.0 65.5 77.8 14
a b c x cv
13.4 14.0 14.2 13.9 2.9
10.0
MSCEPdock
a b c x cv
37.1 37.8 35.8 36.9 2.7
a b c x cv
0.9 0.9 (I.9 0.9 0
a b c x cv
1.9 1.9 1.9 1.9 0
a b c x cv
7.0 6.8 6.7 6.8 2.9
a 11.7 b 0.8 c 0.7 x 0.7 cv 14.3
a b c x cv
8.2 8.4 8.1 8.2 2.4
a b c x cv
4.5 4.6 4.4 4.5 2.2
a b c x cv
3.3 3.3 3.3 3.3 l)
10.4
Sal. = salinity; a, b, and c were triplicate sub-samples; x ~ m e a n c o n c e n t r a t i o n (gg I-~); cv = coefficient of variation; E P ~ E l l e s m e r e Port. N o m e n c l a t u r e : C H C l 3 = c h l o r o f o r m ; C H C l 2 B r = b r o m o d i c h l o r o m e t h a n e ; C H C l B r 2 = d i b r o m o c h l o r o m e t h a n e ; C H B r 3 ~ b r o m o f o r m ; 1,1,1-TCE= 1,1,1 -trichloroethane; T C E = trichloroethene; CCI 4 ~ c a r b o n tetrachloride.
TABLE 2 Small-scale s a m p l i n g variability data for volatile o r g a n o h a l o g e n c o m p o u n d s in b a n k s i d e M e r s e y estuary samples collected at W i d n e s West Bank, 16 N o v e m b e r 1989 (gg l-I). CHC13
EDC
CC14
CHBr~
1,1,1-TCE
TCE
CHC12Br
C2CI 4
CHCIBr 2
Sal.
SS
a 0.8 a 0.8 a 0.8
a <3 a <3 a <3
a 2.4 a 2.5 a 2.4
a 0.7 a 0.8 a 0.8
a <0.2 a <0.2 a <0.2
a 0.4 a 1).3 a 0.3
a 0.1 a 0.1 a 0.1
a 0.9 a 0.8 a 0.7
a 0.2 a 0.2 a 0.3
12.71
159
b 0.9 b 0.9 b 1.0
b <3 b <3 b <3
b 2.7 b 2.7 b 2.7
b 0.5 b 0.7 b 0.7
b <0.2 b <0.2 b <0.2
b 0.3 b 0.4 b 0.4
b 0.1 b 0.1 b 0.1
b 0.8 b 0.9 b 0.9
b 0.3 b 0.3 b 0.3
12.85
132
c 0.9 c 0.9
c c
c 2.6 c 2.9
c 0.7 c 0.6
c c
c 11.4 c 0.4
c 0.1 c 0.1
c 1.0 c 0.4
c 0.3 c 0.2
12.80
97
<3 <3
<0.0 <0.2
a, b, and c were s u b - s a m p l e s from three 2.51. bulk samples collected at a b o u t 2 m intervals along the shore wall. Nomenclature: C H C 1 3 = c h l o r o f o r m ; E D C = l , 2 - d i c h l o r o e t h a n e ; CHCl2Br=bromodichloromethane; CHClBr2=dibromochloromethane; CHBr3=bromoform; 1 , 1 , 1 - T C E = 1,1,1-trichloroethane; T C E = t r i c h l o r o e t h e n e ; CCl4~carbon tetrachloride; C 2 C L = t e t r a c h l o r o e t h y l e n e ; Sal. = salinity %0; SS = s u s p e n d e d solids (mg I L).
TABLE 3 E s t i m a t e d loads of volatile o r g a n o h a l o g e n c o m p o u n d s in m a i n freshwater inputs to the M e r s e y estuary and m e a n concentrations* of volatile o r g a n o h a l o g e n c o m p o u n d s (~g 1-1).
F r e s h w a t e r input H o M e y Weir M e a n conc. M e d i a n conc. M e a n load (kg day -~) M a n c h e s t e r Ship Canal+ M e a n cone. M e d i a n conc. M e a n load (kg day -~)
CHCI 3
1,1,l-C2H3C1 ~
0.6 0.7 1.0
0.4 0.4 (1.7
32.5 13.1 43
2.7 2.5 3.5
CCI 4
CHBr~
C2C14
<0.1 < 0.1 < 0.2
1.1 1.2 1.8
0.6 0.6 1.0
<0.25 //.25 0.4
<0.1 < 0.1 < l).2
<0.1 < 0.1 < 0.2
1620
24.2 16.7 32
112 10.8 147
95.3 6.9 125
8.8 6.9 11.5
4.5 2.6 5.9
1.3 1.0 1.7
1310
0.4 0.4 0.02
0.2 0.2 0.0 I
57
< 0.1 0.1 < 0.004
< 0.1 0.1 < 0.004
40
Ditton B r o o k M e a n conc. M e d i a n conc. M e a n load (kg day -~)
0.5 0.4 0.03
0.7 0.7 0.04
0.9 0.1 0.05
0.6 0.6 0.03
0.4 0.4 0.02
< 0.3 0.3 < 0.01
River G o w y M e a n conc. M e d i a n conc. Mean load (kg day ~)
1.8 0.7 0.07
8.3 1.5 0.3
0.9 0.3 0.04
2.8 0.2 0.11
0.2 0.1 0.01
0.4 0.3 0.01
CHCIBr,
CHC12Br
M o d a l flow + MI day -~
C~HCI~
*Calculated from data for samples collected o n 2 N o v e m b e r 1987, 13 April 1988, 22 June 1988, 17 N o v e m b e r 1988, and 9 N o v e m b e r 1989. t M e a n values calculated from s u m m e d c o n c e n t r a t i o n data for the River Weaver, M a n c h e s t e r Ship canal at E a s t h a m Lock and E l l e s m e r e Port. ~:Head (1990), pets. comm.
85
Marine Pollution Bulletin
values indicating that there was quite a wide range of concentrations between surveys. The relatively high concentrations of VOCls found in the Manchester Ship canal and River Weaver mainly originate from industrial effluent inputs. Although the River Mersey at Howley Weir supplies the largest freshwater input to the estuary (1620 M1 day -~) our data indicate that it contributes relatively small amounts of VOCIs when compared to the Manchester Ship canal/River Weaver system. Trichloroethene and tetrachloroethene were the predominant VOCIs in the River Mersey inflow with mean loadings of 1.8 kg day -1 and 1.0 kg day -L, respectively. These compounds are widely used as metal degreasing solvents (Fischer et al., 1982) and probably originate from diffuse upstream sources. Ditton Brook showed much lower levels o f the VOCls, with mean loadings of less than 0.05 kg day -1 for all determinands, and the River Gowy showed a similar pattern with the exception of 1,1,1-trichloroethane (0.3 kg day-l), and trichloroethene (0.11 kg day-l). These two tributaries therefore appear to be only minor sources of VOCls to the estuary.
Estuarine waters
Generally the most important process affecting the distribution of contaminants in estuaries is the degree of mixing of freshwater and seawater. Diffusive mixing in estuaries results from the density difference between fresh and saline waters, and this is combined with the advective mixing due to tidal motion. Interpretation of the data for the VOCls have been made using concentration versus salinity plots to establish whether the data are consistent with conservative behaviour. The estuarine mixing curves for four longitudinal surveys of the VOCIs in the estuary are shown in Figs 2-9. Several observations can be made regarding the survey data for the VOCls: 1. The freshwater samples from the MSC~and River Weaver generally contained the highest concentrations of VOCIs (<0.1-970 ~tg 1-1) and these are the major sources of these contaminants to the estuary. Mersey estuarine waters showed generally lower concentrations (<0.1-35.8 ~tg l-l). The negative correlation between total concentrations of all the VOCls with salinity confirms that the freshwater end-member is the source
c h l o r o f o r m conc. ug.l.-1
6
[]
+ + + .
2
+ 1
18.4.88
19.7.89
-• O. +
i
i
I
I
i
I
5
10
15
20
25
30
35
salinity o/no CCI4
+
[]
+
0
5.11.87
24.11.88
+
0
•
Fig. 2 Total concentration of chloroform vs. salinity.
c o n e . ug.I.-1
50 + 40 + + 30
+ +
•
5.11.87
+
18.4.88
-~
24.11.88
[]
19.7.89
20 "1111
10
m+
o I
t
5
10
15
20
salinity o/oo
86
25
30
35 Fig. 3 Total concentration of carbon tetrachloride vs. salinity.
Volume 24/Number 2/February 1992
of the contaminants. Tetrachloroethylene showed pronounced positive deviations in its salinity plots between 20-30%0 (Fig. 6) indicating inputs mid-estuary. 2. Estimated freshwater input loadings (Table 3) indicate that the main source of the three bromocompounds is the MSC and this is further confirmed by the estuarine distributions (Figs 7-9) for 5 November 1987, 18 April 1988, 24 November 1988, and 19 July 1989 surveys which show pronounced mid-salinity concentration maxima for bromoform, dibromochloromethane, and bromodichloromethane. Concentrations of the bromo-compounds declined to <0.2 ~tg 1-~ at salinities greater than 25%0. 3. The 5 November 1987, 18 April 1988 and 24 November 1988 surveys were carried out about 3-4 days after a levelling tide, and the maximum concentrations observed in the inner estuary which are observed at and around high slack water (salinities of 7.5-15%o) reflect the effect of tidal flushing of the Manchester Ship canal into the inner estuary. 4. The lower concentrations of VOCIs at salinities between 20-30%0 show the effect of dilution of inputs
3
from the estuary with relatively clean influent seawater. 5. It is likely that sewage effluent and crude sewage outfalls contribute to the total input of VOCls to the estuary. However, the importance of these possible sources has not been determined in this study. 6. Concentrations of VOCls found in the outer estuary in the Crosby Channel were generally <0.1 ixg 1-1 for all determinands. Our data is of the same order as average concentrations of 1,1,1-TCE (0.25 ~tg l-l), TCE (0.3 ~tg 1-1), CCI 4 (0.25 Ixg 1-1), and tetrachloroethene (0.12 ~tg 1-1) previously detected in Liverpool Bay and coastal waters around the Mersey estuary (Pearson & McConnell, 1975). The range of concentrations of carbon tetrachloride and 1,1,1-TCE found in the estuary are comparable to those found during a study of VOCls in the River Brazos, USA (McDonald et al., 1988) which also receives discharges of chemical industry effluent containing VOCls. The concentrations of VOCls in the Mersey estuary are about three orders of magnitude higher than reported open ocean water concentrations (Fogelqvist, 1985) reflecting the influence of inputs from freshwater sources.
1,1,1,-TCE conc ug.I.-1
2.5
2
4-
1.5
• 4-
44-
-~
[]
5.11.87 18.4.88 24.11.88 19.7.89
i
4-
0.5
~
0 0
5
[ |,1-1
I
I
I
I
I
10
15
20
25
30
35 Fig. 4 Total concentration of 1,1,1-TCE vs. salinity.
salinity o/oo T C E c o n c ug.I,-1
• 4I
I
[]
4-
5.11.87 18.4.88 24.11.88 19.7.89
4-
4-
++
•
+.
I
I
I
I
I
10
15
20
25
30
salinity o/oo
35
Fig. 5 Total concentration of TCE vs. salinity.
87
Marine Pollution Bulletin
Estuarine flux calculations Extensive monitoring of estuarine VOC1 concentrations was not possible but the data from four surveys have been used to provide estimates of the flux of VOCls passing through the estuary. Officer (1979) described a simple means of calculating the downstream flux of dissolved c o m p o n e n t s using data for the freshwater flow, the salinity gradient and the longitudinal distribution of concentrations of the component. The flux calculations have the following limitations and assumptions: i. Steady state conditions are assumed. 2. Lateral variations are ignored. 3. The estuary is regarded as one-dimensional (concentration data varying with longitudinal position). 4. T h e estimated fluxes depend on concentration data from only two surveys. Officer (1979) showed that the flux of a constituent in an estuary could be calculated in terms of the freshwater flow, the longitudinal distribution of the constituent and the salinity profile, assuming that under
2.5
tetrachloroethylene
cone
steady state conditions the net flux of salt through any section of an estuary is zero. The net seaward flux of a dissolved c o m p o n e n t (Fx) through a downstream section of the estuary, x, is given by: Adc Zx = Rc - K x - dx
where R = river flow K X = longitudinal dispersion coefficient A = cross sectional area of estuary normal to flow c = concentration of c o m p o n e n t at section s = salinity at section d c = concentration gradient of c o m p o n e n t dx For steady state, one dimensional conditions, RS-Kx
Ads dx - 0
dx dc F× = Rc - R s - - ' - ds dx
+
1.5
+ 18.4.88 I -~ 24.11.88 [] 19.7.89
+ + +
44-4-
4++
4-
[]
[]
[][]
+
[]
0
4+~ ~3+
I
I
I
I
I
I
5
10
15
20
25
30
salinity bromoform
conc
35
o/oo
Fig. 6 Total concentration of tetrachloroethylene vs. salinity.
ug.l.-1
1.6
1.4 1.2 1 0.8
+
+
0.6
+
[]
+
0.4
4-
+
+
5.11.87 18.4.88 24.11.88 19.7.89
i
+ +
4-
0.2
[] ~-~3crn -tl3~
0 10 88
(3)
ug.l.-1
2
0
(2)
and rearranging in terms of c and s (salinity),
Fx = R c - s
0.5
(1)
I
I
I
I
15
20
25
30
salinity
o/oo
35
Fig. 7 Total concentration of bromoform vs. salinity.
(4)
Volume 2 4 / N u m b e r 2/February 1992
Equation 4 has been used to provide estimates of VOCls fluxes in the estuarine segments between Fiddler's Ferry and Runcorn Old Lock in the upper estuary, and between Tranmere Oil Terminal and the Narrows (i.e. the deep straight channel connecting Liverpool Bay with the inner estuary) at Seacombe in the outer estuary (see Fig. 10). The freshwater flow at Fiddler's Ferry was assumed to be the input over Howley Weir (1620 MI day-l), whilst at Tranmere the additional flow from the MSC/River Weaver was included (total flow 2930 M1 day-I). For the purposes of these calculations the River Mersey at Howley Weir and the RSC/River Weaver input are assumed to be the only significant freshwater flows and any losses of components down the estuary are assumed to be via volatilization to the atmosphere. Any loss of VOCls via sediment sorption has been assumed to be negligible when compared to volatilization because these compounds have low octanol water partition coefficients (chloroform log Kow=2.0; tetrachloroethene log Kow = 2.9; Oliver, 1989). It should be noted that freshwater flow data for the MSC and River Weaver are
difficult to estimate because of the complexity of these inputs and the data are thus only approximate. The following mass balance equation was used: Flux V = Flux A - Flux B + Flux C Flux Flux Flux Flux
A B C V
(5)
= = = =
Flux at Fiddler's Ferry/Runcorn section. Flux at Tranmere/Seacombe section. MSC input (see Table 3). Loss of VOCI between Runcorn and Seacombe. The flux estimates shown in Table 4 indicate that with the exception of carbon tetrachloride relatively small amounts of volatile organohalogen compounds are entering the estuary via the narrow upper estuary at Runcorn. An estimated 40-50 kg carbon tetrachloride enters the estuary per day across the Fiddler's Ferry/ Runcorn Old Lock section, and this high figure appears to contradict the low estimates for CC14 inputs across the Howley Weir calculated from freshwater flow and input concentration data (<0.2 kg day-t). However, there is an industrial effluent discharge upstream of the Runcorn bridge, that is known to contain C C l 4 , and this
bromodichloromethane oono ug.I.-1
0.6
0.5
0.4
4-
0.3
+t3- +~+
0.2
++
÷
0.1
•
0
0
r7 E t ~ E ~ ' , ,,-u~,~ iv-q ~L-w
•
5.11.87
-t-
18.4.88
~
24.11.88
[]
19.7.89
~
I
I
I
I
I
I
5
10
15
20
25
30
35 Fig. 8 Total concentration of bromodichloromethane vs. salinity.
aalinity o / o o dibromochloromethane conc ug.l.-1
1.4
1.2 1 •
5.11.87
÷
18.4.88
0.8 24.11.88
0.6 []
0
• +~¢ -H- • q--
0.4
+
19.7.89
•
0.2
+ 0 0
~/l[7~l
I
IIII--J I
I
I
I
I
I
I
5
10
15
20
25
30
aalinity o / o o
35 Fig. 9 Total concentration of dibromochloromethane vs. salinity.
89
Marine Pollution Bulletin
probably accounts for the elevated flux at Runcorn. At the seaward section in the Narrows the fluxes of all the VOCls have mean values that are less than 10 kg day-~ and the estimated losses (Flux V), which are assumed to be mainly due to volatilization (Wakeham et al., 1983) are comparable to the inputs from the MSC/River Weaver. The negative value of Flux V for 1,1,1-TCE on 18 April 1988 could be due to: 1. An additional input of 1,1,1-TCE from a source other than the Manchester Ship canal in the outer estuary, and/or, 2. An underestimate of the MSC input, Flux C.
lives for trichloroethylene and tetrachloroethylene of 2.5 and 6 years (Pearson & McConnell, 1975). The bioaccumulation of VOCIs by marine biota, and sorption by sedimentary material are probably minor loss routes because of the low octanol-water partition coefficients for these contaminants, and bacterial degradation has been found to be important only under anaerobic conditions (Vargas & Ahlert, 1987). The rate of transfer of carbon tetrachloride through the air-water interface has been estimated using a simplified mass transfer relationship (Ambrose et al,, 1988): dCw Kv . . . .
Loss processes
dt
The abiotic degradation of VOCls in water by hydrolysis can be regarded as a slow loss process (chloroform hydrolysis t l / 2 = 1 0 0 0 years, Xie et al., 1986; 1,1,1-trichloroethane hydrolysis tl/2=1.7 years, Gerkens & Franklin, 1989) but photodegradation is a more important removal process for volatile organohalogenated compounds generally, with estimated half-
D
Cw
(6)
where Cw = dissolved concentration in water, (gg l-l), 4.4 ~tg 1-j (mean of estuarine concentrations 18 April 1988). D = depth, mean high water springs 9.3 m, mean low water springs 0.9 m. Kv =rate constant, 2.55 m day -1 (Dilling, 1977). 1. Seacombe. Narrows. 2. Tranmere 3. Runcorn Old Lock 4. Fiddler's Ferry 5. Weaver sluices
tJ~rixx~ ..3 Rune,ore
)-
~
Ble~ellDPoll
Fig. 1O Estuarine sections for VOCI flux estimations. TABLE 4 Estimated fluxes for VOCIs in the Mersey estuary (kg day-t).
Compound CCI 4 CHC13 C2HCI 3 CHBr3 1,1,1-TCE CHCIzBr CHCIBr 2 Flux Flux Flux Flux
90
A= B= V= C=
Flux A 5 November 18 April 1987 1988 42 3 6 0.6 2 0.5 0.6
52 1 1 0.6 1 0.02 0.5
Flux B 5 November 18 April 1987 1988 10 7 15 1 4 0.3 |.5
9 0,6 0,6 0,6 17 0,3 0,6
Flux between Fiddler's Ferry and Runcorn. Flux between Tranmere and the Narrows at Seacombe. Loss of constituent between Runcorn and Seacombe (assumed to be by volatilization). Estimated Manchester Ship canal input (Table 3).
Flux V 5 November 18 April 1987 1988 64 39 138 12 2 2.2 5.1
75 43 147 12 --12 1.7 5.9
Flux C
32 43 147 12 4 2 6
Volume 24/Number 2/February 1992
Using equation 6 and the parameter values above, a (NRA, North West Division) for their co-operation and for providing survey vessels, Dr. P. C. Head (NWW plc) for providing flow inforrate loss of about 1 ~g 1-I day -1 is obtained for E e l 4 mation, and Dr. R. Otter (DOE) for useful discussions. when D=9.3 m (MHWS) and about 12.5 ~tg 1-/ day-1 when D=0.9 m (MLWS). These predicted rates of loss Ali, M. Y. & Riley, J. P. (1986). The distribution of halomethanes in the coastal waters of Kuwait. Mar. Pollut. Bull. 17,409-414. suggests that CC14 concentrations decline rapidly with Ambrose, R. B., Wool, T. A., Connolly, J. P. & Schanz, R. W. (1988). half-lives within the range of 4-48 h. However, the WASP4, a hydrodynamic and water quality model--model theory, user's manual and programmer's guide. EPA/600/3-87/039. liquid-gas transfer rates may not be a true estimate of K. F. & Gilligan, R. M. (1971). Characteristic features of real estuarine exchange rates as no account has been Bowden, estuarine circulation as represented in the Mersey estuary. LimnoL taken for enhanced volatilization due to turbulence or Oceanogr. 16,490. wind stress. Although predictive equations have limi- Campbell, J. A., Whitelaw, K., Riley, J. P., Head, P. C. & Jones, P. D. (1988). Contrasting behaviour of dissolved and particulate nickel tations when applied to real systems because of the and zinc in a polluted estuary. Sci. Tot. Env. 71,141-155. difficulty in including the impact of factors such as Dilling, W. L. (1977). Interphase transfer processes. II. Evaporation rates of chloro-methanes, -ethanes, -ethylenes, -propanes, and weather conditions, wind stress, surface area to depth propylenes from dilute aqueous solutions. Comparisons with ratio, stratification, and tidal mixing, we can conclude theoretical predictions. Env. Sci. Tech. 11,405-409. that a large proportion of the VOCls discharged into Dixon, A. (1985). The Mersey estuary pollution alleviation scheme. J. Inst. War. Eng. Sci. 39,401 413. the estuary are lost by evaporation to the atmosphere.
Conclusions The Manchester Ship canal (MSC) and the River Weaver have been shown to be important sources of volatile organohalogen compounds to the Mersey estuary. Although the River Mersey supplies the largest freshwater input to the estuary our data indicate that it contributes relatively small amounts of VOCIs compared to the MSC/River Weaver system. Volatilization to the atmosphere is expected to be a major process controlling the fate of VOCls in the freshwater inputs and in the estuary, but dilution of freshwater inputs during tidal mixing also appears to be an important factor influencing VOC! distributions in the estuary. There was a negative correlation between total concentrations of VOCls with salinity, confirming that the freshwater end-member was the primary source of the contaminants. Two main sources of carbon tetrachloride to the estuary were identified; the Manchester Ship canal/River Weaver and another input upstream of the Runcorn bridge in the upper estuary. Estimates of the fluxes of the VOCls at the seaward section in the Mersey Narrows have mean values that are less than 10 kg day -1 and simple mass balance calculations show that significant losses of VOCls (between 80-90% of inputs), are occurring within the estuary, mainly via volatilization. The data produced from this study should serve as a useful basis for future monitoring of the estuary, especially as a series of pollution alleviation measures are currently being ~ntroduced.
This work was carried out under contract to the Department of the Environment who have given their permission to publish. The authors would like to thank the analysis group at WRc Medmenham for carrying out the VOCI analyses, Dr. P. D. Jones and Mr. A. Wither
Fischer, M., Friesel, P., Koch, G., Milde, G. & Rosskamp, E. (1982). Evaluation of water pollution caused by chlorinated ethylenes. Contract No. U71/515. EC Report No. XI/400/83. Fogelqvist, E. (1985). Carbon tetrachloride, tetrachloroethylene, l,l,1trichloroethylene and bromoformin Arctic seawater. J. Geophys. Res. 90, 9181-9193. Gerkens, R, R. & Franklin, J, A. (1989). The rate of degradation of l,l,l-trichloroethane in water by hydrolysis and dechlorination. Chemosphere 19, 1929-1937. Helz, G. R. & Hsu, R. Y. (1978). Volatile chloro- and bromocarbons in coastal waters. Limnol. Oceanogr. 23,858-869. HMSO (1985). Methods for the Examination of Waters and Associated Materials. Chlorobenzenes in water, organochlorine pesticides and PCBs in turbid waters, halogenated solvents and related compounds in sewage sludge and waters, 1985. McDonald, T. J., Kennicutt, M. C., Brooks, J. M. & Graham-Road, T. S. (1988). Volatile organic compounds at a coastal Gulf of Mexico site. Chemosphere 17, 123-136. Officer, C. B. (1979). Discussion of the behaviour of non-conservative dissolved constituents in estuaries. Est. Coast. Mar. Sci. 9, 91-94. Oliver, B. G. (1989). Analysis of volatile halogenated and purgeable organics. In Analysis of Trace Organics in the Aquatic Environment (B. K. Afghan & A. S. Y. Chau, eds), pp. 00-00. CRC Press, Florida. Pearson, C. R. & McConnell, G. (1975). Chlorinated C1 and C2 hydrocarbons in the marine environment. Proc. Royal Soc, Lond., B 189, 305-332. Preston, M. R. & AI-Omran, L. A. (1986). Dissolved and particulate phthalate esters in the River Mersey Estuary. Mar Pollut. Bull. 17, 548-553. Sugam, R. & Helz, G. R. (1981). Chlorine speciation in seawater; a metastable equilibrium model for CI and Br species. Chemosphere 10,41-57. Taylor, D. (1986). Changes in the distribution patterns of trace metals in sediments of the Mersey estuary in the last decade (1974-83). Sci. Tot. Env. 49,257-295. Towner, J. V. & Riley, J. P. (1984). The distribution of alkyl lead species in the Mersey. Mar Pollut. Bull. 15,153-158. Vargas, C. & Ahlert, R. C. (1987). Anaerobic degradation of chlorinated solvents. J. Wat. Poll. Con. Fed. 59,964-968. Wakeham, S. G., Davis, A. C. & Karas, J. L. (1983). Mesocosm experiments to determine the fate and persistence of volatile organic compounds in coastal seawater. Env, Sci. Tech. 17, 611-617. Wilson, K. W., Head, P. C. & Jones, P. D. (1986). Mersey estuary (UK) bird mortalities--causes, consequences and correctives. Wat. Sci. Tech. 18, 171-180. Xie, T. M., Abrahamsson, K., Fogelquist, E. & Josefsson, B. (1986). Distribution of chl0rophenolics in a marine environment, Env. Sci. Tech. 20,457-463.
91