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Fluxes of Organic Contaminants from the River Catchment into, through and out of the Humber Estuary, UK
PII:
Marine Pollution Bulletin Vol. 37, Nos. 3±7, pp. 330±342, 1998 Ó 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/99 $ ± see front matter S0025-326X(99)00072-7
Fluxes of Organic Contaminants from the River Catchment into, through and out of the Humber Estuary, UK J. L. ZHOU *, T. W. FILEMANà, W. A. HOUSE§, J. L. A. LONG§, R. F. C. MANTOURAà, A. A. MEHARG , D. OSBORN and J. WRIGHT School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey LL59 5EY, UK àCentre for Coastal Marine Science, Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK §Centre for Ecology and Hydrology, Institute of Freshwater Ecology, River Laboratory, Wareham, Dorset BH20 6BB, UK Institute of Terrestrial Ecology, Monks Wood Research Station, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS, UK This paper summarises the work done on the distribution and reactivity of organic contaminants (simazine, atrazine, lindane, ¯uoranthene, pyrene, PCB 77, PCB 118) in the Humber Estuary and associated major rivers, as part of the LOIS programme. The preliminary ¯ux calculations show that the most important contributors of selected organic contaminants were the rivers Trent (45% of simazine, 20% of atrazine), Aire (30% of simazine and 33% of atrazine), Don (36 and 37% of ¯uoranthene and pyrene) and Ouse (18% of ¯uoranthene and pyrene). For lindane and PCBs, the Aire and Ouse were the key sources. The water ¯ow in all the rivers shows strong seasonal variations, as do the contaminant concentrations. As a result, the mean daily ¯uxes of these contaminants displayed a strong seasonality. Annual mean concentrations of simazine and atrazine decreased by more than 50% over the period 1994±1995 in most of the rivers, probably as a result of their restricted use in the UK. Mass balance calculations show that the Humber is a sink for atrazine, lindane, PCB 77 and PCB 118, although the degree of removal is generally much lower for atrazine and lindane than for PCB 77 and PCB 118. Mass balance results also show that the Humber can either be a source of ¯uoranthene and pyrene (in the suspended particulate phase), or a sink (in the dissolved phase), although overall the Humber acts as sink. The budget exercise represents an attempt to quantify the input and output of selected organic contaminants from catchment to ocean. However, due to limited data and assumptions involved in calculations, the estimates should be considered as an order of magnitude approximation. Further improvement both in resolution and accuracy is required. Ó 1999 Elsevier Science Ltd. All rights reserved
*Corresponding author. Tel: +01248-382858; fax: +01248-716367; e-mail: [email protected]
330
Keywords: LOIS; organic contaminants; PAHs; PCBs; herbicides; riverine inputs; mass balance.
Introduction It is well known that aquatic environments such as rivers, estuaries and coastal seas are under increasingly heavy anthropogenic pressure from organic contaminants such as herbicides, insecticides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and plasticisers (Donkin et al., 1991; Zhou et al., 1996; House et al., 1997; Tolosa et al., 1997). Some of these compounds may act as oestrogen mimics, with the ability to disrupt the normal functioning of sex hormones (Zhou and Rowland, 1997). To protect biota in the aquatic environment from further deterioration and damage by anthropogenic organics, environmental chemists have to study the route by which such contaminants are introduced, transported, transformed and stored. In other words, the cycling of anthropogenic organics through biological, geological and chemical processes are the keys to understanding how chemicals behave and interact with other compartments. As more and newer organic chemicals are produced and discharged, newer challenges for their detection and quanti®cation are presented. In addition, dierent compounds may have dierent sources, structures and, more importantly, physicochemical properties such as vapour pressure, water solubility and octanol/water partition coecients. There is therefore an urgent need to establish a framework by which biogeochemical budgeting of anthropogenic organics can be established. As part of the UK NERC's Land-Ocean Interaction Study (LOIS) programme, the River-AtmosphereCoast Study (RACS) aimed to estimate contemporary
Volume 37/Numbers 3±7/March±July 1998
¯uxes of materials into, through and out of the coastal zone to identify and quantify biogeochemical processes that govern such ¯uxes; to develop predictive models of these ¯uxes and transformation processes. There has been a LOIS core river monitoring programme for organic contaminants which concentrated on the major rivers ¯owing into the Humber Estuary (House et al., 1997), a river project examining sediment-associated contaminants (Long et al., 1998), and an estuarine and coastal zone project which focused on the Humber Estuary and its plume (Zhou et al., 1996). These three programmes have collaborated in sampling co-ordination, analytical method development and quality control. The purpose of this article is to integrate the results from these three programmes on the distribution and ¯uxes of micro-organic contaminants from catchment to ocean, so as to fully realise the objectives of LOIS.
Materials and Methods Study site The Humber river-estuarine system studied in this project is depicted in Fig. 1. The main survey sites at the tidal limits on the rivers Trent, Ouse, Don, Aire, Calder, Swale, Nidd, Ure and Derwent were sampled weekly from March 1994 till March 1995 for simazine and atrazine, and from September 1994 till January 1997 for lindane, PCB 77 and PCB 118. PAHs were not moni-
tored in the core programme of LOIS, the data reported here for ¯uoranthene and pyrene were abstracted from the riverine programme (Long et al., 1998). The estuarine programme carried out quarterly surveys in the Humber Estuary from October 1994 till March 1996 and two surveys in the plume in February and June 1995. Details of sampling sites can be found in Zhou et al. (1996, 1998). Organic contaminants An extensive list of compounds have been monitored by both the river and estuary programmes. However, for the purpose of this integration exercise, only seven compounds were chosen, i.e. atrazine, simazine, ¯uoranthene, pyrene, lindane, PCB 77 and PCB 118. Their properties are listed in Table 1. Data sources The data used in this study were drawn from three projects in the LOIS programme, to study contaminants in estuarine and coastal waters (Zhou et al., 1996) and in rivers (House et al., 1997; Meharg et al., 1998; Long et al., 1998). Full details on sampling, sample processing and analyses can be obtained from these four papers. The main dierence between river and estuarine sampling programmes is that in the river programme, ``whole-water'' samples were taken and analysed, i.e. no attempt was made to separate contaminants into dissolved and suspended particulate matter (SPM) phases.
Fig. 1 Geographic location of study area and sampling points in the LOIS rivers.
331
Marine Pollution Bulletin TABLE 1 Source and properties of selected organic contaminants at 20±25°C. Class
Sourcesa
Formula
MW
Vapour pressure (Pa)
Atrazinec
Triazine herbicides
A, Af, U
C8 H14 ClN5
215.68
4.00 ´ 10ÿ5
Simazinec
Triazine herbicides
A, Af, U
C7 H12 ClN5
201.67
8.50 ´ 110ÿ6
Lindanec
Organochlorine pesticides PAHs PAHs PCBs PCBs
I
C6 H6 Cl6
290.85
0.00374
F, I, Py, U F, I, Py, U I, U I, U
C6 H10 C6 H10 C12 H6 Cl4 C12 H5 Cl5
202.26 202.26 292.00 326.40
9.11 ´ 10ÿ5 1.91 ´ 10ÿ3 1.12 ´ 10ÿ3
Compound
Fluoranthene Pyrened PCB 77e PCB 118e
Log Kow
Log Koc
Half lifeb
30
2.75
2.00
5
2.18
2.11
7.3
3.7
3.0
0.245 0.132 0.093 0.034
5.33 5.17 5.62 6.74
4.58 4.85 4.85 4.90
2 yearsw 2 monthss 3 weeksw 8 monthss 2 yearsw 6 yearss
Water solubility (g/m3 )
a
A Agricultural; Af Antifouling; F Fossil fuels; I Industrial; Py Pyrolysis; U Urban. In half-life, w and s refer to water and sediment phases respectively. c From Mackay et al. (1997). d From Wild and Jones (1995). e From Mackay et al. (1992). b
In the estuarine programme, all the water samples had been ®ltered under pressure through GF/F ®lters.
Flux of Freshwater and Organic Contaminants to the Humber Estuary Various interpolation and extrapolation methods are available for calculating river loads of material (Walling and Webb, 1985; Webb et al., 1997). As there are only limited concentration data at weekly or even greater intervals for organic contaminants, the greatest problems lie with the reliability of the estimates of concentration (Walling and Webb, 1985). Because of the dependence on river ¯ow of many chemical species, the estimation of ¯ux based on discharge-weighted concentrations generally produced the best results. Even so, Webb et al. (1997) recently showed that standard ¯ux estimation procedures became increasingly unreliable for solutes with more complicated ¯ow-related behaviour and for those contaminants showing strong interactions with particulates. Considerable caution is therefore required in calculating and interpreting ¯uxes. This paper provides a preliminary ¯ux estimate of selected organic contaminants, which can be used as a basis for further improvement and re®ning. The ¯ux of freshwater and organic contaminants to the estuary is estimated using daily ¯ows and weekly contaminant records (quarterly for ¯uoranthene and pyrene) at the gauging stations closest to the tidal limits of the six rivers Trent, Ouse, Aire, Wharfe, Don and Derwent (Leeks et al., 1997), using the following equation: Flux
n X Ci Qi ; n i1
1
where Ci is the instantaneous contaminant concentration associated with individual samples, Qi is the in332
stantaneous water discharge at the time of sampling, n is the number of samples analysed. As only ``whole-water'' samples were determined, the ¯uxes obtained represented contaminants in both dissolved and SPM phases. For ¯uoranthene and pyrene, their levels in SPM had been measured using supercritical ¯uid extraction (Long et al., 1998), as a result, their ¯uxes in SPM phase were calculated using the following equation: Flux
n X Ci SQi ; n i1
2
where S is SPM concentration. The ¯uxes of ¯uoranthene and pyrene in the dissolved phase can then be calculated as the dierence between total ¯uxes (from Eq. (1)) and SPM-associated ¯uxes (from Eq. (2)) The distribution of atrazine between dissolved and SPM phases was estimated using the simple partition coecient, and generally none of the compound was present in the SPM phase. For lindane and PCBs, no attempt was made to dierentiate between the two phases, mainly because no concentration data were available for the dissolved or SPM phase, and their distribution behaviour is not as straightforward as atrazine. This approach does not include the contributions of minor or ungauged catchments, but the combined ¯ux of the six rivers accounts for at least 85% of the total freshwater ¯ux (Sanders et al., 1997). The ¯ow of freshwater to the Humber estuary over the study period is summarised in Fig. 2. The mean ¯ow over the period was 218 m3 sÿ1 , derived from the Trent system (37%) and the Ouse system (63%). This is similar to the longterm average ¯ow of the last ten years (NRA, 1993). The Ouse system ¯ow was dominated by the Aire and Ouse (jointly 60% of the Ouse system ¯ux). The mean ¯ow weighted contaminant concentrations at the head of each river (Fig. 3) show dependence on the type of contaminants. Generally, the highest levels (up to 510 ng lÿ1 )
Volume 37/Numbers 3±7/March±July 1998
Fig. 2 Annual mean river discharges to the Humber Estuary via its major tributaries over 1994±1996.
were found for atrazine, the lowest levels (<0.9 ng lÿ1 ) were found for PCB 77 and PCB 118; lying in between were the levels of lindane (3± 31 ng lÿ1 ), simazine (0±240 ng lÿ1 ), ¯uoranthene (14±240 ng lÿ1 ) and pyrene (12±214 ng lÿ1 ). There were also clear dierences between contaminant levels in dierent rivers. The Calder and Aire had the highest levels of all the contaminants, except for ¯uoranthene and pyrene when the Don surpassed the Aire. The Ouse had the lowest levels of all compounds except for ¯uoranthene and pyrene (when the Trent had the lowest) and PCB 77 (when the Trent and Don showed the lowest). The Trent and Don had intermediate levels of most contaminants. The mean daily ¯uxes of contaminants from the various rivers to the system over the study period are shown in Fig. 4. The total ¯uxes of simazine and atrazine between 1994 and 1995, ¯uoranthene and pyrene between 1995 and 1996, lindane, PCB 77 and PCB 118 between 1995 and 1997 were 1.327, 1.228, 0.457, 0.437, 0.242, 0.001 and 0.001 kg dÿ1 , respectively. The most signi®cant contributors to these ¯uxes were the Trent (45% of simazine and 20% of atrazine), the Aire (30% of simazine and 33% of atrazine), the Calder (20% of simazine, 41% of atrazine, 24% of ¯uoranthene and 22% of pyrene), the Don (36% and 37% of ¯uoranthene and pyrene, respectively) and the Ouse (18% of ¯uoranthene and pyrene). For lindane, PCB 77 and PCB 118, the main contributors were the Aire and Ouse. Some interannual variability in total mean water ¯ow is apparent (Fig. 2). The Trent, Ouse, Aire, Don and Wharfe all showed decreased water ¯ow from 1994 to 1996, except for 1995, when the Aire displayed an increased ¯ow. The Derwent showed similar mean water ¯ow throughout the period 1994±1996. Contaminant
concentrations at the tidal limits of major rivers also show strong annual variations (Fig. 3). Annual mean simazine and atrazine concentrations decreased by more than 50% in the Don, Trent, Aire and Calder. These reductions may relate closely to the restricted use of these two herbicides in the UK. For ¯uoranthene and pyrene, however, both increase and decrease have been observed; there was a more than 30% and 130% increase in the Don and Calder, respectively. There was a 18% and 10% reduction in ¯uoranthene, whilst a 43% and 31% reduction for pyrene in the Trent and Aire, respectively. Such changes may be related to the source of fossil fuel combustion and the prevailing weather conditions in in¯uencing the drift and deposition of combustion-derived particles. There is a considerable seasonal variation in the ¯ux of water to the estuary (Fig. 5). Within a single year there can be a factor of 40 between peak winter maximum and summer minimum ¯ows. Summer minimum ¯ows (40 m3 sÿ1 ) are approximately 20% of the annual mean ¯ow (200 m3 sÿ1 ). Concentrations of contaminants show pronounced seasonality at the tidal limit of most of the feed rivers. The seasonal variations of simazine and atrazine in major contributors of contaminants to the system, the Trent, Aire, Calder and Don, have been discussed (House et al., 1997). Generally simazine and atrazine show peaks in the spring and then later in the year during the early autumn when the ®rst major storm of the year produces an increase in discharge, although such a pattern is not found in the river Calder which shows peaks in concentration only at the time of application (House et al., 1997). The daily ¯ux of simazine and atrazine in the Trent (Fig. 6), is typical of the wide variations and cycles observed in other feed rivers. 333
Marine Pollution Bulletin
Fig. 3 Annual mean concentrations of organic contaminants at the tidal limits of major tributaries over 1994±1997.
Behaviour of Contaminants within the Tidal Rivers Flux calculations To examine whether a river is a source or sink of contaminants, ¯ux estimates are required. These are done following the procedure suggested by Lebo and Sharp (1992) that ¯uxes are estimated at three locations in a feed river. Instead of using integrated ¯uxes, mean daily ¯uxes calculated across the entire dataset are used, mainly because integrated ¯uxes are dicult to compare if the integration steps (sampling intervals) dier greatly between sites, or for dierent compounds at the same sites, as they do in this case. Generally, the data obtained for simazine, atrazine, lindane, PCB 77 and PCB 334
118 have the highest sampling resolutions, and the data sets for ¯uoranthene and pyrene at the tidal rivers have the lowest resolutions. As a result, the ¯ux estimation for atrazine, lindane and PCBs is more reliable than that for ¯uoranthene and pyrene. Removal or additions of contaminants are calculated as the dierence between computed mean daily ¯uxes and theoretical mean daily ¯uxes. The computed mean ¯ux is derived from the average of individual ¯uxes which are the product of ¯ow and in situ contaminant concentration at freshwater sites, whilst the theoretical mean daily ¯uxes are derived from inputs of water and contaminants at the tidal limits of the ®ve major rivers and assuming conservative behaviour of each. This approach is required because all points on the Ouse are
Volume 37/Numbers 3±7/March±July 1998
Fig. 4 Annual mean ¯uxes of organic contaminants at the tidal limits of major tributaries over 1994±1997.
below the con¯uence of at least two rivers. A simple parameterisation for increased ¯ow down river has been used to account for minor ungauged ¯ows. Flows at all ¯ux sites in the Ouse, Keadby, Flixborough Wharf and Trent Falls have been calculated by multiplying measured ¯ows at the tidal limits by 1.14. There are limitations to such estimates as all the compounds are assumed to behave conservatively in feed rivers. This may be true for compounds such as atrazine and simazine, but for lindane and the more hydrophobic PCBs and PAHs, this assumption is far from satisfactory. Secondly, the other sources of inputs (e.g. dry and wet deposition, sediment resuspension) are not considered here, yet H uhnerfuss et al. (1997) found that the mobility of PCBs in the German Bight was mainly associated with sediment transport and atmospheric inputs could be signi®cant for triazines. Tolosa et al.
(1997) even suggested that atmospheric deposition dominated the inputs of PCBs to the western Mediterranean. In addition, no data are available for assessing the impact of other mechanisms of removal such as degradation and isomerisation, which are important processes for lindane (H uhnerfuss et al., 1997), as is sedimentation for PCBs (Tolosa et al., 1997). Results and discussion Table 2 shows measured and theoretical ¯uxes and removal/addition percentages for dissolved contaminants at each site. Overall, the Trent is a major source of all contaminants studied, whilst the Ouse is a major sink of all compounds except for lindane. Speci®cally, the mean measured ¯uxes at Flixborough Wharf for atrazine (0.328 kg dÿ1 ), ¯uoranthene (0.057 kg dÿ1 ), pyrene (0.057 kg dÿ1 ), lindane (0.0740 kg dÿ1 ), PCB 77 335
Marine Pollution Bulletin
Fig. 5 Daily mean ¯ow (m3 sÿ1 ) at the Trent Falls, derived from the sum of ¯ows at the tidal limits of the major tributaries.
Fig. 6 Seasonal variation of simazine and atrazine daily ¯uxes in the Trent.
336
Estuary
Boothferry Bridge
Ouse
Trent falls
Whitgift Church
Swine¯eet
Theoretical ¯ux Measured ¯ux Rem/addn Keadby Theoretical ¯ux Measured ¯ux Rem/addn Flixborough Wharf Theoretical ¯ux Measured ¯ux Rem/addn
Theoretical ¯ux Measured ¯ux Rem/addn
Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical Measured ¯ux Rem/addn
Cromwell
¯ux ¯ux ¯ux ¯ux ¯ux
Trent
Measured Measured Measured Measured Measured
Cromwell Spotbrough Methley Bridge Beal Skelton
Input
TABLE 2
0.269 0.042 0.633 0.373 0.009
1994
0.933 0.408 ÿ56
0.670 0.104 ÿ84 0.740 0.115 ÿ84 0.740 0.178 ÿ76
0.169 0.226 +34 0.193 0.391 +102 0.193 0.358 +85
0.169 0.061 0.289 0.502 0.086
1995
0.834 0.404 ÿ51
0.497 0.104 ÿ79 0.551 0.143 ÿ74 0.551 0.186 ÿ66
0.248 0.227 ÿ8 0.283 0.348 +23 0.283 0.328 +16
0.248 0.047 0.547 0.408 0.028
1994±1995
Atrazine (kg dÿ1 )
0.099 0.032 ÿ67
0.038 0.038 ÿ1 0.064 0.033 ÿ48 0.064 0.042 ÿ33
0.031 0.020 ÿ35 0.035 0.058 +66 0.035 0.054 +53
0.031 0.022 0.051 0.020 0.014
1995
0.409 0.054 ÿ87
0.389 0.045 ÿ88 0.389 0.045 ÿ88
0.232
0.020 0.049 +150 0.020 0.062 +210
0.017
0.017 0.138 0.154 0.060 0.143
1996
0.251 0.038 ÿ85
0.135 0.038 ÿ72 0.226 0.036 ÿ84 0.226 0.043 ÿ81
0.022 0.020 ÿ8 0.025 0.055 +120 0.025 0.057 +128
0.022 0.080 0.102 0.040 0.078
1995±1996
Fluoranthene (kg dÿ1 )
Theoretical and measured mean ¯uxes of dissolved contaminants at sampling sites in tidal rivers.a
0.088 0.061 ÿ31
0.041 0.044 +7 0.062 0.036 ÿ42 0.062 0.041 ÿ35
0.042 0.023 ÿ45 0.048 0.047 ÿ2 0.048 0.045 ÿ6
0.042 0.019 0.040 0.024 0.012
1995
0.426 0.082 ÿ81
0.387 0.060 ÿ84 0.387 0.045 ÿ88
0.229
0.039 0.062 +59 0.039 0.080 +106
0.034
0.034 0.139 0.136 0.072 0.129
1996
0.267 0.066 ÿ75
0.135 0.044 ÿ67 0.225 0.042 ÿ81 0.225 0.042 ÿ81
0.037 0.023 ÿ37 0.042 0.052 +25 0.042 0.057 +36
0.037 0.079 0.068 0.048 0.070
1995±1996
Pyrene (kg dÿ1 )
Volume 37/Numbers 3±7/March±July 1998
337
338
Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Theoretical ¯ux Measured ¯ux Rem/addn Keadby Theoretical ¯ux Measured ¯ux Rem/addn Flixborough Wharf Theoretical ¯ux Measured ¯ux Rem/addn Boothferry Bridge Theoretical ¯ux Measured ¯ux Rem/addn Swine¯eet Theoretical ¯ux Measured ¯ux Rem/addn Whitgift Church Theoretical ¯ux Measured ¯ux Rem/addn Trent falls Theoretical ¯ux Measured ¯ux Rem/addn
Cromwell Spotbrough Methley Bridge Beal Skelton Cromwell
0.0179 0.0040 0.0010 0.0398 0.0627 0.0179 0.0540 +200 0.0204 0.1040 +410 0.0204 0.0812 +297 0.1169 0.0290 ÿ75 0.1214 0.0390 ÿ68 0.1214 0.1960 +61 0.1418 0.1030 ÿ27 0.1215 0.0750 ÿ38 0.1215 0.0450 ÿ63 0.1465 0.0410 ÿ72
0.0250 0.0620 +148 0.0250 0.0372 +49 0.1158
0.0219 0.0050 0.1990 0.0797 0.0199 0.0219
1996
0.0030
0.0219 0.0030
1997 0.0199 0.0040 0.1090 0.0598 0.0438 0.0199 0.0540 +170 0.0227 0.0970 +322 0.0227 0.0740 +221 0.1181 0.0290 ÿ76 0.1227 0.0460 ÿ63 0.1227 0.1710 +38 0.1454 0.0930 ÿ36
1995±1997 0.0004 0 0 0.0007 0.0024 0.0004 0.0005 +25 0.0004 0.0010 +150 0.0004 0.0005 +25 0.0035 0.0064 +83 0.0035 0.0014 ÿ60 0.0035 0.0002 ÿ94 0.0039 0 ÿ100
1995
0.0007 0 ÿ100 0.0007 0 ÿ100 0.0007 0 ÿ100
0 0 0 0 0 0 0.0007
0
0 0 0 0.0006
1996
0.0022
0.0022
0.0022
0 0.0022
0
0
0
0.0019
0 0
1997 0.0002 0 0 0.0007 0.0014 0.0002 0.0004 +100 0.0002 0.0008 +300 0.0002 0.0003 +50 0.0024 0.0053 +121 0.0024 0.0012 ÿ50 0.0024 0.0002 ÿ92 0.0026 0 ÿ100
1995±1997
PCB77 (kg dÿ1 )
0 0 0.0001 0.0001 0.0023 0 0.0005 +100 0 0.0028 +100 0 0.0010 +100 0.0027 0.0070 +159 0.0027 0.0020 ÿ26 0.0027 0.0002 ÿ92 0.0027 0 ÿ100
1995
0.0001 0 ÿ100 0.0001 0 ÿ100 0.00001 0 ÿ100
0 0 0 0 0 0 0.0001
0 0 0.0021 0.0001 0 0
1996
0.0013
0.0011
0.0011
0.00011
0.0002
0.0002
0.0002
0.0010
0.0002 0
1997
0 0 0.0011 0.0002 0.0013 0 0.0050 +100 0 0.0023 +100 0 0.0008 +100 0.0017 0.0070 +312 0.0017 0.0013 ÿ24 0.0017 0.0002 ÿ88 0.0017 0 ÿ100
1995±1997
PCB118 (kg dÿ1 )
a Estimates of removal (rem,ÿve) and addition (addn,+ve) are given as percentages of theoretical ¯uxes. For lindane, PCB 77 and PCB 118, their ¯uxes were derived from ``whole-water'' samples, as a result, such ¯uxes are the combined ones associated with both dissolved and SPM phases.
Estuary
Ouse
Trent
Input
1995
Lindane (kg dÿ1 )
TABLE 2 (CONTINUED)
Marine Pollution Bulletin
Volume 37/Numbers 3±7/March±July 1998
(0.0003 kg dÿ1 ) and PCB 118 (0.0008 kg dÿ1 ) are 116%, 228%, 136%, 321%, 150% and 200% of their predicted mean ¯ux at Flixborough Wharf and 132%, 259%, 154%, 372%, 150% and 100% of their theoretical mean ¯uxes at Cromwell Lock. The tidal Trent therefore serves as an important source of these contaminants (Table 2). The ¯uxes of atrazine (0.186 kg dÿ1 ), ¯uoranthene (0.043 kg dÿ1 ), pyrene (0.042 kg dÿ1 ), PCB 77 (0.0002 kg dÿ1 ) and PCB 118 (0.0002 kg dÿ1 ) at Whitgift Church are 34%, 19%, 19%, 8% and 12%, respectively of the predicted values at this site, suggesting the Ouse is a sink for the above compounds. However, the ¯ux of lindane at Whitgift Church (0.1710 kg dÿ1 ) is 138% of the predicted value at this site, suggesting the Ouse is a net source for lindane. The ¯uxes of PCB 77 and PCB 118 at Flixborough Wharf are 50% and 100% greater than river input values, indicating the Trent is a key source of these PCBs. On the other hand, between 88% and 92% of PCB ¯uxes are removed at Whitgift Church, suggesting that the Ouse acts as a major sink. The ¯uxes of these six contaminants at the Trent Falls are signi®cantly lower than those predicted, suggesting again the Trent Falls as a major sink for these contaminants, especially for PCB 77 and PCB 118. The results for contaminants on SPM are shown in Table 3. It is clear that both the Trent and Ouse have signi®cantly higher ¯uxes of contaminants than those predicted assuming conservative behaviour, hence these rivers are sources for the contaminants. The ¯uxes at the Trent Falls are more than 8 times higher than those
expected, suggesting it to be a major source from which these two PAHs originate. The other contaminants (atrazine, lindane, PCB 77 and PCB 118) are not listed in Table 3 as their levels are below the limit of detection by GC/MS (1 ng gÿ1 dry weight).
Behaviour of Contaminant within the Estuary Dissolved contaminants The salinity plots of dissolved atrazine and lindane concentration from April 1995 estuarine survey show that atrazine behaves conservatively, whilst lindane behaves non-conservatively (Zhou et al., 1996). To expand the data sets obtained from seasonal surveys, all the dissolved contaminant concentrations are combined and plotted against salinity (Fig. 7). The results show that atrazine displays the best linear relationship with salinity (r2 0.62), while lindane has a poor correlation with salinity (r2 0.17). For ¯uoranthene and pyrene, their concentration shows no relationship with salinity, suggesting that they behave non-conservatively. It has also been shown by Zhou et al. (1998) that the partition of ¯uoranthene and pyrene between Humber sediment particles and water shows no strong correlation with particulate organic carbon content. They suggest that ¯uoranthene and pyrene associated with particles are actually present in the form of soot and soot-like particles which are not actively involved in particle/water equilibrations. As a result, early ¯ux calculations indicating that the Trent Falls is a major sink for these
TABLE 3 Theoretical and measured mean ¯uxes of contaminants on SPM at sampling sites in tidal rivers. Fluoranthene (kg dÿ1 )
Input
Trent
Cromwell Spotbrough Methley Bridge Beal Skelton Cromwell Keadby Flixborough Wharf
Ouse
Boothferry Bridge Swine¯eet Whitgift Church
Estuary
Trent falls
Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn
Pyrene (kg dÿ1 )
1995
1996
1995±1996
1995
1996
1995±1996
0.0101 0.0118 0.0067 0.0262 0.0025 0.0101 0.0115 +14 0.0115 0.5320 +4526 0.0115 0.5420 +4613 0.0327
0.0053 0.1600 0.0082 0.0084 0.0029 0.0053 0.0299 +464 0.0060 0.9860 +16333 0.0060 0.7790 +12883 0.0129
0.0069 0.0860 0.0075 0.0173 0.0027 0.0069 0.0207 +200 0.0079 0.7590 +9508 0.0079 0.6600 +8254 0.0228
0.0090 0.0112 0.0068 0.0285 0.0022 0.0090 0.0090 0 0.0103 0.4370 +4143 0.0103 0.5800 +5531 0.0350
0.0058 0.1520 0.0082 0.0094 0.0029 0.0058 0.0298 +414 0.0066 0.8520 +12809 0.0066 0.6910 +10369 0.0140
0.0069 0.0814 0.0075 0.0190 0.0025 0.0069 0.0194 +181 0.0079 0.6440 +8052 0.0079 0.6360 +7951 0.0245
0.0462 0.8540 +1748 0.0462 0.8430 +1725 0.0577 1.1540 +1900
0.1953 0.6000 +207 0.1953 2.8610 +1365 0.2013 1.9820 +885
0.1208 0.7690 +536 0.1208 1.8520 +1430 0.1287 1.4300 +1011
0.0478 0.7120 +1390 0.0478 0.6900 +1344 0.0581 0.9420 +1521
0.1873 0.6040 +222 0.1873 2.6160 +1297 0.1939 1.7780 +816
0.1173 0.6760 +476 0.1173 1.6530 +1309 0.1252 1.2210 +875
339
Marine Pollution Bulletin
Fig. 7 Salinity pro®les of dissolved organic contaminants in the Humber Estuary over 1995±1996.
contaminants are not surprising. PCB 77 and PCB 118 are present at very low levels, approaching the detection limits, and their estuarine pro®les show no correlation with salinity either.
Flux of Contaminants to the Coastal Zone To make estimations of the net removal or additions of organic contaminants within the Humber Estuary, the in¯ow ¯ux of such contaminants from feed rivers and the out¯ow ¯ux passing through Spurn Head into the Plume were calculated (Table 4). The in¯ow ¯ux is obtained from Tables 2 and 3 whilst the out¯ow ¯ux is derived by averaging calculated ¯uxes at Spurn Head from various estuarine surveys, including both dissolved 340
and particulate phases. The results show that the Humber system is a large sink of dissolved and particulate PCB 77 and PCB 118 (100% of total loading). For the more soluble compounds atrazine and lindane, they are removed to a lesser extent, 28% and 13%, respectively. Atrazine is less hydrophobic than lindane, it is expected to behave more conservatively, and hence to be removed less by the system. However, as the results do not support this prediction, further investigation is required. For ¯uoranthene and pyrene, both removal and addition were observed; between 50% and 52% of dissolved species were removed whilst 81% and 49% more SPM-related species were introduced. The mass balance encompassing the two phases suggests that the Humber system is a sink for all the six compounds, this
Volume 37/Numbers 3±7/March±July 1998 TABLE 4 Summary of river inputs and export of selected organic contaminants between 1994 and 1997. River inputs (kg dÿ1 )
Output to coastal zone (kg dÿ1 )
Removal/addition (%)
Dissolved
SPM
Total
Dissolved
SPM
Total
Dissolved
SPM
Total
0.834 0.251 0.267
0 0.129 0.125
0.834 0.380 0.392 0.1454 0.0026 0.0017
0.603 0.126 0.128 0.126 0 0
0 0.234 0.186 0 0 0
0.603 0.360 0.314 0.126 0 0
ÿ28 ÿ50 ÿ52
0 +81 +49
ÿ28 ÿ5 ÿ20 ÿ13 ÿ100 ÿ100
Atrazine Fluoranthene Pyrene Lindane PCB 77 PCB 118
is particularly the case for the two PCBs. The ¯uxes of the six contaminants to the Humber coastal zone over the period 1994±1996 were therefore as follows: atrazine (0.603 kg dÿ1 ), ¯uoranthene (0.360 kg dÿ1 ), pyrene (0.314 kg dÿ1 ), lindane (0.126 kg dÿ1 ), PCB 77 (0 kg dÿ1 ) and PCB118 (0 kg dÿ1 ).
Conclusions A thorough mass balance calculation of selected organic contaminants in the Humber river-estuary continuum was carried out to investigate their source, reactivity and fates. The results show that the Humber system is a sink for all the organic contaminants studied, regardless of their origin, solubility, hydrophobicity or degradation potential. The Humber estuary removes between 13% and 100% of atrazine, lindane, PCB 77 and PCB 118, although the degree of removal is substantially more signi®cant for the more hydrophobic compounds PCB 77 and PCB 118. Atrazine and lindane are removed by 28% and 13%, respectively. The higher percentage of atrazine removal is slightly surprising, as it is more soluble and less hydrophobic than lindane, as a result, atrazine is expected to be more completely transported out of the system. Such discrepancies may be due to additional inputs of lindane in the estuary, or other important sinks for atrazine yet to be recognised. Further work is needed to explain such results. For the PAHs, the trend is more complex. Whilst about 50% of dissolved ¯uoranthene and pyrene were removed from the system, 81% and 49% of more SPM-associated ¯uoranthene and pyrene had been added to the system. The total balance shows that 5% and 20% of rivertransported ¯uoranthene and pyrene have been removed from the estuary. For several reasons the results should be regarded as an order of magnitude estimation of organic contaminant budget in the Humber. First of all, the sampling intervals for contaminant concentrations are weekly or even quarterly (for PAHs); as a result, the accuracy of these estimates is variable, and particularly poor for ¯uoranthene and pyrene. Secondly, in the LOIS core programme for rivers, only ``whole-water'' samples were analysed; hence, the distribution of contaminants between dissolved and particulate phases is unknown, al-
though results have shown that signi®cant concentrations of micro-organic contaminants may be transported in association with suspended particulate phase (Long et al., 1998) and the levels of ¯uoranthene and pyrene have been determined in SPM samples. Estimation based on partition theory has been carried out to derive atrazine concentrations in the dissolved and particulate phases. Consequently, the mass balance calculation in these two phases may be less accurate, although the total budget should still be valid. Thirdly, assumptions such as the conservative behaviour of contaminants have been introduced in calculating removal or addition in feed rivers; these may pose problems for the highly hydrophobic compounds such as PCBs and PAHs. Finally, other sources of inputs (atmospheric deposition, sediment resuspension, sewage) and sinks (degradation, sedimentation) were not considered during the current calculations. The mass balance results reported here should therefore be regarded for guidance only and may be used as a basis for further research. We gratefully acknowledge the funding of the work by the UK Natural Environment Research Council, which forms part of the LOIS RACS programme. This is LOIS Publication Number 630. With thanks to Drs P. Donkin and J. W. Readman (Plymouth Marine Laboratory), Prof S. Rowland (University of Plymouth), and Drs J. E. Rae and A. Parker (University of Reading) for their contributions and co-operation. We also thank S. Evans and D. Orr for sampling and laboratory assistance. Donkin, P., Widdows, J., Evans, S. V. and Brinsley, M. D. (1991) QSAR for the sublethal response of marine mussels (Mytilus edulis). Science of the Total Environment 109/110, 461±476. House, W. A., Leach, D., Long, J. L. A., Cranwell, P., Smith, C., Bharwaj, L., Meharg, A., Ryland, G., Orr, D. O. and Wright, J. (1997) Micro-organic compounds in the Humber rivers. Science of the Total Environment 194/195, 357±371. H uhnerfuss, H., Bester, K., Landgra, O., Pohlmann, T. and Selke, K. (1997) Annual balances of hexachlorocyclohexanes, polychlorinated bipheyls and triazines in the German Bight. Marine Pollution Bulletin 34, 419±426. Lebo, M. E. and Sharp, J. H. (1992) Modelling phosphorus cycling in a well-mixed coastal plain estuary. Estuarine Coastal Shelf Science 35, 235±252. Leeks, G. J. L., Neal, C., Jarvie, H. P., Casey, H. and Leach, D. V. (1997) The LOIS river monitoring network: strategy and implementation. Science of the Total Environment 194/195, 101±109. Long, J. L. A., House, W. A., Parker, A. and Rae, J. E. (1998) Microorganic compounds associated with sediments in the Humber rivers. Science of the Total Environment 210/211, 229±253. Mackay, D., Shiu, W. -Y. and Ma, K. -C. (1992) Illustrative Handbook of Physical-chemical Properties and Environmental
341
Marine Pollution Bulletin Fate for Organic Chemicals, Vol. 1, Monoaromatic Hydrocarbons, Chlorobenzenes, and PCBs. Lewis Publishers, Boca Raton, p. 704. Mackay, D., Shiu, W. -Y. and Ma, K. -C. (1997) Illustrative Handbook of Physical-chemical Properties and Environmental Fate for Organic Chemicals, Vol. 5, Pesticide Chemicals, p. 812. Lewis Publishers, Boca Raton. Meharg, A. A., Wright, J. and Osborn, D. (1998) The frequency of environmental quality standard (EQS) exceedance for chlorinated organic pollutants in rivers of the Humber catchment. Science of the Total Environment 210/211, 219±228. NRA (1993) The quality of the Humber Estuary 1980-1990: Report of the National Rivers Authority, p. 108. National Rivers Authority, Bristol, UK. Sanders, R. J., Jickells, T., Malcolm, S., Brown, J., Kirkwood, D., Reeve, A, Taylor, J., Horrobin, T. and Ashcroft, C. (1997) Nutrient ¯uxes through the Humber estuary. Journal of Sea Research 37, 3± 23. Tolosa, I., Readman, J. W., Fowler, S. W., Villeneuve, J. P., Dachs, J., Bayona, J. M. and Albaiges, J. (1997) PCBs in the western Mediterranean. Temporary trends and mass balance assessment. Deep Sea Research II 44, 907±928. Walling, D. E. and Webb, B. W. (1985) Estimating the discharge of contaminants to coastal waters by rivers: some cautionary comments. Marine Pollution Bulletin 16, 488±492.
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Webb, B. W., Philips, J. M., Walling, D. E., Littlewood, I. G., Watts, C. D. and Leeks, G. J. L. (1997) Load estimation methodologies for British rivers and their relevance to the LOIS RACS (R) programme. Science of the Total Environment 194/195, 379±389. Wild, S. R. and Jones, K. C. (1995) Polynuclear aromatic hydrocarbons in the United Kingdom Environment: a preliminary source inventory and budget. Environment Pollution 88, 91±108. Zhou, J. L., Fileman, T. W., Evans, S., Donkin, P., Mantoura, R. F. C. and Rowland, S. J. (1996) Seasonal distribution of dissolved pesticides and polynuclear aromatic hydrocarbons in the Humber estuary and Humber coastal zone. Marine Pollution Bulletin 32, 599±608. Zhou, J. L., Fileman, T. W., Evans, S., Donkin, P., Llewellyn, C., Readman, J. W., Mantoura, R. F. C. and Rowland, S. J. (1998) Fluoranthene and pyrene in the suspended particulate matter and surface sediments of the Humber estuary, UK. Marine Pollution Bulletin 36, 587±597. Zhou, J. L. and Rowland, S. J. (1997) Evaluation of the interactions between hydrophobic organic pollutants and suspended particles in estuarine waters. Water Research 31, 1708±1718.
Marine Pollution Bulletin Vol. 37, Nos. 3±7, pp. 330±342, 1998 Ó 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0025-326X/99 $ ± see front matter S0025-326X(99)00072-7
Fluxes of Organic Contaminants from the River Catchment into, through and out of the Humber Estuary, UK J. L. ZHOU *, T. W. FILEMANà, W. A. HOUSE§, J. L. A. LONG§, R. F. C. MANTOURAà, A. A. MEHARG , D. OSBORN and J. WRIGHT School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey LL59 5EY, UK àCentre for Coastal Marine Science, Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK §Centre for Ecology and Hydrology, Institute of Freshwater Ecology, River Laboratory, Wareham, Dorset BH20 6BB, UK Institute of Terrestrial Ecology, Monks Wood Research Station, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS, UK This paper summarises the work done on the distribution and reactivity of organic contaminants (simazine, atrazine, lindane, ¯uoranthene, pyrene, PCB 77, PCB 118) in the Humber Estuary and associated major rivers, as part of the LOIS programme. The preliminary ¯ux calculations show that the most important contributors of selected organic contaminants were the rivers Trent (45% of simazine, 20% of atrazine), Aire (30% of simazine and 33% of atrazine), Don (36 and 37% of ¯uoranthene and pyrene) and Ouse (18% of ¯uoranthene and pyrene). For lindane and PCBs, the Aire and Ouse were the key sources. The water ¯ow in all the rivers shows strong seasonal variations, as do the contaminant concentrations. As a result, the mean daily ¯uxes of these contaminants displayed a strong seasonality. Annual mean concentrations of simazine and atrazine decreased by more than 50% over the period 1994±1995 in most of the rivers, probably as a result of their restricted use in the UK. Mass balance calculations show that the Humber is a sink for atrazine, lindane, PCB 77 and PCB 118, although the degree of removal is generally much lower for atrazine and lindane than for PCB 77 and PCB 118. Mass balance results also show that the Humber can either be a source of ¯uoranthene and pyrene (in the suspended particulate phase), or a sink (in the dissolved phase), although overall the Humber acts as sink. The budget exercise represents an attempt to quantify the input and output of selected organic contaminants from catchment to ocean. However, due to limited data and assumptions involved in calculations, the estimates should be considered as an order of magnitude approximation. Further improvement both in resolution and accuracy is required. Ó 1999 Elsevier Science Ltd. All rights reserved
*Corresponding author. Tel: +01248-382858; fax: +01248-716367; e-mail: [email protected]
330
Keywords: LOIS; organic contaminants; PAHs; PCBs; herbicides; riverine inputs; mass balance.
Introduction It is well known that aquatic environments such as rivers, estuaries and coastal seas are under increasingly heavy anthropogenic pressure from organic contaminants such as herbicides, insecticides, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and plasticisers (Donkin et al., 1991; Zhou et al., 1996; House et al., 1997; Tolosa et al., 1997). Some of these compounds may act as oestrogen mimics, with the ability to disrupt the normal functioning of sex hormones (Zhou and Rowland, 1997). To protect biota in the aquatic environment from further deterioration and damage by anthropogenic organics, environmental chemists have to study the route by which such contaminants are introduced, transported, transformed and stored. In other words, the cycling of anthropogenic organics through biological, geological and chemical processes are the keys to understanding how chemicals behave and interact with other compartments. As more and newer organic chemicals are produced and discharged, newer challenges for their detection and quanti®cation are presented. In addition, dierent compounds may have dierent sources, structures and, more importantly, physicochemical properties such as vapour pressure, water solubility and octanol/water partition coecients. There is therefore an urgent need to establish a framework by which biogeochemical budgeting of anthropogenic organics can be established. As part of the UK NERC's Land-Ocean Interaction Study (LOIS) programme, the River-AtmosphereCoast Study (RACS) aimed to estimate contemporary
Volume 37/Numbers 3±7/March±July 1998
¯uxes of materials into, through and out of the coastal zone to identify and quantify biogeochemical processes that govern such ¯uxes; to develop predictive models of these ¯uxes and transformation processes. There has been a LOIS core river monitoring programme for organic contaminants which concentrated on the major rivers ¯owing into the Humber Estuary (House et al., 1997), a river project examining sediment-associated contaminants (Long et al., 1998), and an estuarine and coastal zone project which focused on the Humber Estuary and its plume (Zhou et al., 1996). These three programmes have collaborated in sampling co-ordination, analytical method development and quality control. The purpose of this article is to integrate the results from these three programmes on the distribution and ¯uxes of micro-organic contaminants from catchment to ocean, so as to fully realise the objectives of LOIS.
Materials and Methods Study site The Humber river-estuarine system studied in this project is depicted in Fig. 1. The main survey sites at the tidal limits on the rivers Trent, Ouse, Don, Aire, Calder, Swale, Nidd, Ure and Derwent were sampled weekly from March 1994 till March 1995 for simazine and atrazine, and from September 1994 till January 1997 for lindane, PCB 77 and PCB 118. PAHs were not moni-
tored in the core programme of LOIS, the data reported here for ¯uoranthene and pyrene were abstracted from the riverine programme (Long et al., 1998). The estuarine programme carried out quarterly surveys in the Humber Estuary from October 1994 till March 1996 and two surveys in the plume in February and June 1995. Details of sampling sites can be found in Zhou et al. (1996, 1998). Organic contaminants An extensive list of compounds have been monitored by both the river and estuary programmes. However, for the purpose of this integration exercise, only seven compounds were chosen, i.e. atrazine, simazine, ¯uoranthene, pyrene, lindane, PCB 77 and PCB 118. Their properties are listed in Table 1. Data sources The data used in this study were drawn from three projects in the LOIS programme, to study contaminants in estuarine and coastal waters (Zhou et al., 1996) and in rivers (House et al., 1997; Meharg et al., 1998; Long et al., 1998). Full details on sampling, sample processing and analyses can be obtained from these four papers. The main dierence between river and estuarine sampling programmes is that in the river programme, ``whole-water'' samples were taken and analysed, i.e. no attempt was made to separate contaminants into dissolved and suspended particulate matter (SPM) phases.
Fig. 1 Geographic location of study area and sampling points in the LOIS rivers.
331
Marine Pollution Bulletin TABLE 1 Source and properties of selected organic contaminants at 20±25°C. Class
Sourcesa
Formula
MW
Vapour pressure (Pa)
Atrazinec
Triazine herbicides
A, Af, U
C8 H14 ClN5
215.68
4.00 ´ 10ÿ5
Simazinec
Triazine herbicides
A, Af, U
C7 H12 ClN5
201.67
8.50 ´ 110ÿ6
Lindanec
Organochlorine pesticides PAHs PAHs PCBs PCBs
I
C6 H6 Cl6
290.85
0.00374
F, I, Py, U F, I, Py, U I, U I, U
C6 H10 C6 H10 C12 H6 Cl4 C12 H5 Cl5
202.26 202.26 292.00 326.40
9.11 ´ 10ÿ5 1.91 ´ 10ÿ3 1.12 ´ 10ÿ3
Compound
Fluoranthene Pyrened PCB 77e PCB 118e
Log Kow
Log Koc
Half lifeb
30
2.75
2.00
5
2.18
2.11
7.3
3.7
3.0
0.245 0.132 0.093 0.034
5.33 5.17 5.62 6.74
4.58 4.85 4.85 4.90
2 yearsw 2 monthss 3 weeksw 8 monthss 2 yearsw 6 yearss
Water solubility (g/m3 )
a
A Agricultural; Af Antifouling; F Fossil fuels; I Industrial; Py Pyrolysis; U Urban. In half-life, w and s refer to water and sediment phases respectively. c From Mackay et al. (1997). d From Wild and Jones (1995). e From Mackay et al. (1992). b
In the estuarine programme, all the water samples had been ®ltered under pressure through GF/F ®lters.
Flux of Freshwater and Organic Contaminants to the Humber Estuary Various interpolation and extrapolation methods are available for calculating river loads of material (Walling and Webb, 1985; Webb et al., 1997). As there are only limited concentration data at weekly or even greater intervals for organic contaminants, the greatest problems lie with the reliability of the estimates of concentration (Walling and Webb, 1985). Because of the dependence on river ¯ow of many chemical species, the estimation of ¯ux based on discharge-weighted concentrations generally produced the best results. Even so, Webb et al. (1997) recently showed that standard ¯ux estimation procedures became increasingly unreliable for solutes with more complicated ¯ow-related behaviour and for those contaminants showing strong interactions with particulates. Considerable caution is therefore required in calculating and interpreting ¯uxes. This paper provides a preliminary ¯ux estimate of selected organic contaminants, which can be used as a basis for further improvement and re®ning. The ¯ux of freshwater and organic contaminants to the estuary is estimated using daily ¯ows and weekly contaminant records (quarterly for ¯uoranthene and pyrene) at the gauging stations closest to the tidal limits of the six rivers Trent, Ouse, Aire, Wharfe, Don and Derwent (Leeks et al., 1997), using the following equation: Flux
n X Ci Qi ; n i1
1
where Ci is the instantaneous contaminant concentration associated with individual samples, Qi is the in332
stantaneous water discharge at the time of sampling, n is the number of samples analysed. As only ``whole-water'' samples were determined, the ¯uxes obtained represented contaminants in both dissolved and SPM phases. For ¯uoranthene and pyrene, their levels in SPM had been measured using supercritical ¯uid extraction (Long et al., 1998), as a result, their ¯uxes in SPM phase were calculated using the following equation: Flux
n X Ci SQi ; n i1
2
where S is SPM concentration. The ¯uxes of ¯uoranthene and pyrene in the dissolved phase can then be calculated as the dierence between total ¯uxes (from Eq. (1)) and SPM-associated ¯uxes (from Eq. (2)) The distribution of atrazine between dissolved and SPM phases was estimated using the simple partition coecient, and generally none of the compound was present in the SPM phase. For lindane and PCBs, no attempt was made to dierentiate between the two phases, mainly because no concentration data were available for the dissolved or SPM phase, and their distribution behaviour is not as straightforward as atrazine. This approach does not include the contributions of minor or ungauged catchments, but the combined ¯ux of the six rivers accounts for at least 85% of the total freshwater ¯ux (Sanders et al., 1997). The ¯ow of freshwater to the Humber estuary over the study period is summarised in Fig. 2. The mean ¯ow over the period was 218 m3 sÿ1 , derived from the Trent system (37%) and the Ouse system (63%). This is similar to the longterm average ¯ow of the last ten years (NRA, 1993). The Ouse system ¯ow was dominated by the Aire and Ouse (jointly 60% of the Ouse system ¯ux). The mean ¯ow weighted contaminant concentrations at the head of each river (Fig. 3) show dependence on the type of contaminants. Generally, the highest levels (up to 510 ng lÿ1 )
Volume 37/Numbers 3±7/March±July 1998
Fig. 2 Annual mean river discharges to the Humber Estuary via its major tributaries over 1994±1996.
were found for atrazine, the lowest levels (<0.9 ng lÿ1 ) were found for PCB 77 and PCB 118; lying in between were the levels of lindane (3± 31 ng lÿ1 ), simazine (0±240 ng lÿ1 ), ¯uoranthene (14±240 ng lÿ1 ) and pyrene (12±214 ng lÿ1 ). There were also clear dierences between contaminant levels in dierent rivers. The Calder and Aire had the highest levels of all the contaminants, except for ¯uoranthene and pyrene when the Don surpassed the Aire. The Ouse had the lowest levels of all compounds except for ¯uoranthene and pyrene (when the Trent had the lowest) and PCB 77 (when the Trent and Don showed the lowest). The Trent and Don had intermediate levels of most contaminants. The mean daily ¯uxes of contaminants from the various rivers to the system over the study period are shown in Fig. 4. The total ¯uxes of simazine and atrazine between 1994 and 1995, ¯uoranthene and pyrene between 1995 and 1996, lindane, PCB 77 and PCB 118 between 1995 and 1997 were 1.327, 1.228, 0.457, 0.437, 0.242, 0.001 and 0.001 kg dÿ1 , respectively. The most signi®cant contributors to these ¯uxes were the Trent (45% of simazine and 20% of atrazine), the Aire (30% of simazine and 33% of atrazine), the Calder (20% of simazine, 41% of atrazine, 24% of ¯uoranthene and 22% of pyrene), the Don (36% and 37% of ¯uoranthene and pyrene, respectively) and the Ouse (18% of ¯uoranthene and pyrene). For lindane, PCB 77 and PCB 118, the main contributors were the Aire and Ouse. Some interannual variability in total mean water ¯ow is apparent (Fig. 2). The Trent, Ouse, Aire, Don and Wharfe all showed decreased water ¯ow from 1994 to 1996, except for 1995, when the Aire displayed an increased ¯ow. The Derwent showed similar mean water ¯ow throughout the period 1994±1996. Contaminant
concentrations at the tidal limits of major rivers also show strong annual variations (Fig. 3). Annual mean simazine and atrazine concentrations decreased by more than 50% in the Don, Trent, Aire and Calder. These reductions may relate closely to the restricted use of these two herbicides in the UK. For ¯uoranthene and pyrene, however, both increase and decrease have been observed; there was a more than 30% and 130% increase in the Don and Calder, respectively. There was a 18% and 10% reduction in ¯uoranthene, whilst a 43% and 31% reduction for pyrene in the Trent and Aire, respectively. Such changes may be related to the source of fossil fuel combustion and the prevailing weather conditions in in¯uencing the drift and deposition of combustion-derived particles. There is a considerable seasonal variation in the ¯ux of water to the estuary (Fig. 5). Within a single year there can be a factor of 40 between peak winter maximum and summer minimum ¯ows. Summer minimum ¯ows (40 m3 sÿ1 ) are approximately 20% of the annual mean ¯ow (200 m3 sÿ1 ). Concentrations of contaminants show pronounced seasonality at the tidal limit of most of the feed rivers. The seasonal variations of simazine and atrazine in major contributors of contaminants to the system, the Trent, Aire, Calder and Don, have been discussed (House et al., 1997). Generally simazine and atrazine show peaks in the spring and then later in the year during the early autumn when the ®rst major storm of the year produces an increase in discharge, although such a pattern is not found in the river Calder which shows peaks in concentration only at the time of application (House et al., 1997). The daily ¯ux of simazine and atrazine in the Trent (Fig. 6), is typical of the wide variations and cycles observed in other feed rivers. 333
Marine Pollution Bulletin
Fig. 3 Annual mean concentrations of organic contaminants at the tidal limits of major tributaries over 1994±1997.
Behaviour of Contaminants within the Tidal Rivers Flux calculations To examine whether a river is a source or sink of contaminants, ¯ux estimates are required. These are done following the procedure suggested by Lebo and Sharp (1992) that ¯uxes are estimated at three locations in a feed river. Instead of using integrated ¯uxes, mean daily ¯uxes calculated across the entire dataset are used, mainly because integrated ¯uxes are dicult to compare if the integration steps (sampling intervals) dier greatly between sites, or for dierent compounds at the same sites, as they do in this case. Generally, the data obtained for simazine, atrazine, lindane, PCB 77 and PCB 334
118 have the highest sampling resolutions, and the data sets for ¯uoranthene and pyrene at the tidal rivers have the lowest resolutions. As a result, the ¯ux estimation for atrazine, lindane and PCBs is more reliable than that for ¯uoranthene and pyrene. Removal or additions of contaminants are calculated as the dierence between computed mean daily ¯uxes and theoretical mean daily ¯uxes. The computed mean ¯ux is derived from the average of individual ¯uxes which are the product of ¯ow and in situ contaminant concentration at freshwater sites, whilst the theoretical mean daily ¯uxes are derived from inputs of water and contaminants at the tidal limits of the ®ve major rivers and assuming conservative behaviour of each. This approach is required because all points on the Ouse are
Volume 37/Numbers 3±7/March±July 1998
Fig. 4 Annual mean ¯uxes of organic contaminants at the tidal limits of major tributaries over 1994±1997.
below the con¯uence of at least two rivers. A simple parameterisation for increased ¯ow down river has been used to account for minor ungauged ¯ows. Flows at all ¯ux sites in the Ouse, Keadby, Flixborough Wharf and Trent Falls have been calculated by multiplying measured ¯ows at the tidal limits by 1.14. There are limitations to such estimates as all the compounds are assumed to behave conservatively in feed rivers. This may be true for compounds such as atrazine and simazine, but for lindane and the more hydrophobic PCBs and PAHs, this assumption is far from satisfactory. Secondly, the other sources of inputs (e.g. dry and wet deposition, sediment resuspension) are not considered here, yet H uhnerfuss et al. (1997) found that the mobility of PCBs in the German Bight was mainly associated with sediment transport and atmospheric inputs could be signi®cant for triazines. Tolosa et al.
(1997) even suggested that atmospheric deposition dominated the inputs of PCBs to the western Mediterranean. In addition, no data are available for assessing the impact of other mechanisms of removal such as degradation and isomerisation, which are important processes for lindane (H uhnerfuss et al., 1997), as is sedimentation for PCBs (Tolosa et al., 1997). Results and discussion Table 2 shows measured and theoretical ¯uxes and removal/addition percentages for dissolved contaminants at each site. Overall, the Trent is a major source of all contaminants studied, whilst the Ouse is a major sink of all compounds except for lindane. Speci®cally, the mean measured ¯uxes at Flixborough Wharf for atrazine (0.328 kg dÿ1 ), ¯uoranthene (0.057 kg dÿ1 ), pyrene (0.057 kg dÿ1 ), lindane (0.0740 kg dÿ1 ), PCB 77 335
Marine Pollution Bulletin
Fig. 5 Daily mean ¯ow (m3 sÿ1 ) at the Trent Falls, derived from the sum of ¯ows at the tidal limits of the major tributaries.
Fig. 6 Seasonal variation of simazine and atrazine daily ¯uxes in the Trent.
336
Estuary
Boothferry Bridge
Ouse
Trent falls
Whitgift Church
Swine¯eet
Theoretical ¯ux Measured ¯ux Rem/addn Keadby Theoretical ¯ux Measured ¯ux Rem/addn Flixborough Wharf Theoretical ¯ux Measured ¯ux Rem/addn
Theoretical ¯ux Measured ¯ux Rem/addn
Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical Measured ¯ux Rem/addn
Cromwell
¯ux ¯ux ¯ux ¯ux ¯ux
Trent
Measured Measured Measured Measured Measured
Cromwell Spotbrough Methley Bridge Beal Skelton
Input
TABLE 2
0.269 0.042 0.633 0.373 0.009
1994
0.933 0.408 ÿ56
0.670 0.104 ÿ84 0.740 0.115 ÿ84 0.740 0.178 ÿ76
0.169 0.226 +34 0.193 0.391 +102 0.193 0.358 +85
0.169 0.061 0.289 0.502 0.086
1995
0.834 0.404 ÿ51
0.497 0.104 ÿ79 0.551 0.143 ÿ74 0.551 0.186 ÿ66
0.248 0.227 ÿ8 0.283 0.348 +23 0.283 0.328 +16
0.248 0.047 0.547 0.408 0.028
1994±1995
Atrazine (kg dÿ1 )
0.099 0.032 ÿ67
0.038 0.038 ÿ1 0.064 0.033 ÿ48 0.064 0.042 ÿ33
0.031 0.020 ÿ35 0.035 0.058 +66 0.035 0.054 +53
0.031 0.022 0.051 0.020 0.014
1995
0.409 0.054 ÿ87
0.389 0.045 ÿ88 0.389 0.045 ÿ88
0.232
0.020 0.049 +150 0.020 0.062 +210
0.017
0.017 0.138 0.154 0.060 0.143
1996
0.251 0.038 ÿ85
0.135 0.038 ÿ72 0.226 0.036 ÿ84 0.226 0.043 ÿ81
0.022 0.020 ÿ8 0.025 0.055 +120 0.025 0.057 +128
0.022 0.080 0.102 0.040 0.078
1995±1996
Fluoranthene (kg dÿ1 )
Theoretical and measured mean ¯uxes of dissolved contaminants at sampling sites in tidal rivers.a
0.088 0.061 ÿ31
0.041 0.044 +7 0.062 0.036 ÿ42 0.062 0.041 ÿ35
0.042 0.023 ÿ45 0.048 0.047 ÿ2 0.048 0.045 ÿ6
0.042 0.019 0.040 0.024 0.012
1995
0.426 0.082 ÿ81
0.387 0.060 ÿ84 0.387 0.045 ÿ88
0.229
0.039 0.062 +59 0.039 0.080 +106
0.034
0.034 0.139 0.136 0.072 0.129
1996
0.267 0.066 ÿ75
0.135 0.044 ÿ67 0.225 0.042 ÿ81 0.225 0.042 ÿ81
0.037 0.023 ÿ37 0.042 0.052 +25 0.042 0.057 +36
0.037 0.079 0.068 0.048 0.070
1995±1996
Pyrene (kg dÿ1 )
Volume 37/Numbers 3±7/March±July 1998
337
338
Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Theoretical ¯ux Measured ¯ux Rem/addn Keadby Theoretical ¯ux Measured ¯ux Rem/addn Flixborough Wharf Theoretical ¯ux Measured ¯ux Rem/addn Boothferry Bridge Theoretical ¯ux Measured ¯ux Rem/addn Swine¯eet Theoretical ¯ux Measured ¯ux Rem/addn Whitgift Church Theoretical ¯ux Measured ¯ux Rem/addn Trent falls Theoretical ¯ux Measured ¯ux Rem/addn
Cromwell Spotbrough Methley Bridge Beal Skelton Cromwell
0.0179 0.0040 0.0010 0.0398 0.0627 0.0179 0.0540 +200 0.0204 0.1040 +410 0.0204 0.0812 +297 0.1169 0.0290 ÿ75 0.1214 0.0390 ÿ68 0.1214 0.1960 +61 0.1418 0.1030 ÿ27 0.1215 0.0750 ÿ38 0.1215 0.0450 ÿ63 0.1465 0.0410 ÿ72
0.0250 0.0620 +148 0.0250 0.0372 +49 0.1158
0.0219 0.0050 0.1990 0.0797 0.0199 0.0219
1996
0.0030
0.0219 0.0030
1997 0.0199 0.0040 0.1090 0.0598 0.0438 0.0199 0.0540 +170 0.0227 0.0970 +322 0.0227 0.0740 +221 0.1181 0.0290 ÿ76 0.1227 0.0460 ÿ63 0.1227 0.1710 +38 0.1454 0.0930 ÿ36
1995±1997 0.0004 0 0 0.0007 0.0024 0.0004 0.0005 +25 0.0004 0.0010 +150 0.0004 0.0005 +25 0.0035 0.0064 +83 0.0035 0.0014 ÿ60 0.0035 0.0002 ÿ94 0.0039 0 ÿ100
1995
0.0007 0 ÿ100 0.0007 0 ÿ100 0.0007 0 ÿ100
0 0 0 0 0 0 0.0007
0
0 0 0 0.0006
1996
0.0022
0.0022
0.0022
0 0.0022
0
0
0
0.0019
0 0
1997 0.0002 0 0 0.0007 0.0014 0.0002 0.0004 +100 0.0002 0.0008 +300 0.0002 0.0003 +50 0.0024 0.0053 +121 0.0024 0.0012 ÿ50 0.0024 0.0002 ÿ92 0.0026 0 ÿ100
1995±1997
PCB77 (kg dÿ1 )
0 0 0.0001 0.0001 0.0023 0 0.0005 +100 0 0.0028 +100 0 0.0010 +100 0.0027 0.0070 +159 0.0027 0.0020 ÿ26 0.0027 0.0002 ÿ92 0.0027 0 ÿ100
1995
0.0001 0 ÿ100 0.0001 0 ÿ100 0.00001 0 ÿ100
0 0 0 0 0 0 0.0001
0 0 0.0021 0.0001 0 0
1996
0.0013
0.0011
0.0011
0.00011
0.0002
0.0002
0.0002
0.0010
0.0002 0
1997
0 0 0.0011 0.0002 0.0013 0 0.0050 +100 0 0.0023 +100 0 0.0008 +100 0.0017 0.0070 +312 0.0017 0.0013 ÿ24 0.0017 0.0002 ÿ88 0.0017 0 ÿ100
1995±1997
PCB118 (kg dÿ1 )
a Estimates of removal (rem,ÿve) and addition (addn,+ve) are given as percentages of theoretical ¯uxes. For lindane, PCB 77 and PCB 118, their ¯uxes were derived from ``whole-water'' samples, as a result, such ¯uxes are the combined ones associated with both dissolved and SPM phases.
Estuary
Ouse
Trent
Input
1995
Lindane (kg dÿ1 )
TABLE 2 (CONTINUED)
Marine Pollution Bulletin
Volume 37/Numbers 3±7/March±July 1998
(0.0003 kg dÿ1 ) and PCB 118 (0.0008 kg dÿ1 ) are 116%, 228%, 136%, 321%, 150% and 200% of their predicted mean ¯ux at Flixborough Wharf and 132%, 259%, 154%, 372%, 150% and 100% of their theoretical mean ¯uxes at Cromwell Lock. The tidal Trent therefore serves as an important source of these contaminants (Table 2). The ¯uxes of atrazine (0.186 kg dÿ1 ), ¯uoranthene (0.043 kg dÿ1 ), pyrene (0.042 kg dÿ1 ), PCB 77 (0.0002 kg dÿ1 ) and PCB 118 (0.0002 kg dÿ1 ) at Whitgift Church are 34%, 19%, 19%, 8% and 12%, respectively of the predicted values at this site, suggesting the Ouse is a sink for the above compounds. However, the ¯ux of lindane at Whitgift Church (0.1710 kg dÿ1 ) is 138% of the predicted value at this site, suggesting the Ouse is a net source for lindane. The ¯uxes of PCB 77 and PCB 118 at Flixborough Wharf are 50% and 100% greater than river input values, indicating the Trent is a key source of these PCBs. On the other hand, between 88% and 92% of PCB ¯uxes are removed at Whitgift Church, suggesting that the Ouse acts as a major sink. The ¯uxes of these six contaminants at the Trent Falls are signi®cantly lower than those predicted, suggesting again the Trent Falls as a major sink for these contaminants, especially for PCB 77 and PCB 118. The results for contaminants on SPM are shown in Table 3. It is clear that both the Trent and Ouse have signi®cantly higher ¯uxes of contaminants than those predicted assuming conservative behaviour, hence these rivers are sources for the contaminants. The ¯uxes at the Trent Falls are more than 8 times higher than those
expected, suggesting it to be a major source from which these two PAHs originate. The other contaminants (atrazine, lindane, PCB 77 and PCB 118) are not listed in Table 3 as their levels are below the limit of detection by GC/MS (1 ng gÿ1 dry weight).
Behaviour of Contaminant within the Estuary Dissolved contaminants The salinity plots of dissolved atrazine and lindane concentration from April 1995 estuarine survey show that atrazine behaves conservatively, whilst lindane behaves non-conservatively (Zhou et al., 1996). To expand the data sets obtained from seasonal surveys, all the dissolved contaminant concentrations are combined and plotted against salinity (Fig. 7). The results show that atrazine displays the best linear relationship with salinity (r2 0.62), while lindane has a poor correlation with salinity (r2 0.17). For ¯uoranthene and pyrene, their concentration shows no relationship with salinity, suggesting that they behave non-conservatively. It has also been shown by Zhou et al. (1998) that the partition of ¯uoranthene and pyrene between Humber sediment particles and water shows no strong correlation with particulate organic carbon content. They suggest that ¯uoranthene and pyrene associated with particles are actually present in the form of soot and soot-like particles which are not actively involved in particle/water equilibrations. As a result, early ¯ux calculations indicating that the Trent Falls is a major sink for these
TABLE 3 Theoretical and measured mean ¯uxes of contaminants on SPM at sampling sites in tidal rivers. Fluoranthene (kg dÿ1 )
Input
Trent
Cromwell Spotbrough Methley Bridge Beal Skelton Cromwell Keadby Flixborough Wharf
Ouse
Boothferry Bridge Swine¯eet Whitgift Church
Estuary
Trent falls
Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Measured ¯ux Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn Theoretical ¯ux Measured ¯ux Rem/addn
Pyrene (kg dÿ1 )
1995
1996
1995±1996
1995
1996
1995±1996
0.0101 0.0118 0.0067 0.0262 0.0025 0.0101 0.0115 +14 0.0115 0.5320 +4526 0.0115 0.5420 +4613 0.0327
0.0053 0.1600 0.0082 0.0084 0.0029 0.0053 0.0299 +464 0.0060 0.9860 +16333 0.0060 0.7790 +12883 0.0129
0.0069 0.0860 0.0075 0.0173 0.0027 0.0069 0.0207 +200 0.0079 0.7590 +9508 0.0079 0.6600 +8254 0.0228
0.0090 0.0112 0.0068 0.0285 0.0022 0.0090 0.0090 0 0.0103 0.4370 +4143 0.0103 0.5800 +5531 0.0350
0.0058 0.1520 0.0082 0.0094 0.0029 0.0058 0.0298 +414 0.0066 0.8520 +12809 0.0066 0.6910 +10369 0.0140
0.0069 0.0814 0.0075 0.0190 0.0025 0.0069 0.0194 +181 0.0079 0.6440 +8052 0.0079 0.6360 +7951 0.0245
0.0462 0.8540 +1748 0.0462 0.8430 +1725 0.0577 1.1540 +1900
0.1953 0.6000 +207 0.1953 2.8610 +1365 0.2013 1.9820 +885
0.1208 0.7690 +536 0.1208 1.8520 +1430 0.1287 1.4300 +1011
0.0478 0.7120 +1390 0.0478 0.6900 +1344 0.0581 0.9420 +1521
0.1873 0.6040 +222 0.1873 2.6160 +1297 0.1939 1.7780 +816
0.1173 0.6760 +476 0.1173 1.6530 +1309 0.1252 1.2210 +875
339
Marine Pollution Bulletin
Fig. 7 Salinity pro®les of dissolved organic contaminants in the Humber Estuary over 1995±1996.
contaminants are not surprising. PCB 77 and PCB 118 are present at very low levels, approaching the detection limits, and their estuarine pro®les show no correlation with salinity either.
Flux of Contaminants to the Coastal Zone To make estimations of the net removal or additions of organic contaminants within the Humber Estuary, the in¯ow ¯ux of such contaminants from feed rivers and the out¯ow ¯ux passing through Spurn Head into the Plume were calculated (Table 4). The in¯ow ¯ux is obtained from Tables 2 and 3 whilst the out¯ow ¯ux is derived by averaging calculated ¯uxes at Spurn Head from various estuarine surveys, including both dissolved 340
and particulate phases. The results show that the Humber system is a large sink of dissolved and particulate PCB 77 and PCB 118 (100% of total loading). For the more soluble compounds atrazine and lindane, they are removed to a lesser extent, 28% and 13%, respectively. Atrazine is less hydrophobic than lindane, it is expected to behave more conservatively, and hence to be removed less by the system. However, as the results do not support this prediction, further investigation is required. For ¯uoranthene and pyrene, both removal and addition were observed; between 50% and 52% of dissolved species were removed whilst 81% and 49% more SPM-related species were introduced. The mass balance encompassing the two phases suggests that the Humber system is a sink for all the six compounds, this
Volume 37/Numbers 3±7/March±July 1998 TABLE 4 Summary of river inputs and export of selected organic contaminants between 1994 and 1997. River inputs (kg dÿ1 )
Output to coastal zone (kg dÿ1 )
Removal/addition (%)
Dissolved
SPM
Total
Dissolved
SPM
Total
Dissolved
SPM
Total
0.834 0.251 0.267
0 0.129 0.125
0.834 0.380 0.392 0.1454 0.0026 0.0017
0.603 0.126 0.128 0.126 0 0
0 0.234 0.186 0 0 0
0.603 0.360 0.314 0.126 0 0
ÿ28 ÿ50 ÿ52
0 +81 +49
ÿ28 ÿ5 ÿ20 ÿ13 ÿ100 ÿ100
Atrazine Fluoranthene Pyrene Lindane PCB 77 PCB 118
is particularly the case for the two PCBs. The ¯uxes of the six contaminants to the Humber coastal zone over the period 1994±1996 were therefore as follows: atrazine (0.603 kg dÿ1 ), ¯uoranthene (0.360 kg dÿ1 ), pyrene (0.314 kg dÿ1 ), lindane (0.126 kg dÿ1 ), PCB 77 (0 kg dÿ1 ) and PCB118 (0 kg dÿ1 ).
Conclusions A thorough mass balance calculation of selected organic contaminants in the Humber river-estuary continuum was carried out to investigate their source, reactivity and fates. The results show that the Humber system is a sink for all the organic contaminants studied, regardless of their origin, solubility, hydrophobicity or degradation potential. The Humber estuary removes between 13% and 100% of atrazine, lindane, PCB 77 and PCB 118, although the degree of removal is substantially more signi®cant for the more hydrophobic compounds PCB 77 and PCB 118. Atrazine and lindane are removed by 28% and 13%, respectively. The higher percentage of atrazine removal is slightly surprising, as it is more soluble and less hydrophobic than lindane, as a result, atrazine is expected to be more completely transported out of the system. Such discrepancies may be due to additional inputs of lindane in the estuary, or other important sinks for atrazine yet to be recognised. Further work is needed to explain such results. For the PAHs, the trend is more complex. Whilst about 50% of dissolved ¯uoranthene and pyrene were removed from the system, 81% and 49% of more SPM-associated ¯uoranthene and pyrene had been added to the system. The total balance shows that 5% and 20% of rivertransported ¯uoranthene and pyrene have been removed from the estuary. For several reasons the results should be regarded as an order of magnitude estimation of organic contaminant budget in the Humber. First of all, the sampling intervals for contaminant concentrations are weekly or even quarterly (for PAHs); as a result, the accuracy of these estimates is variable, and particularly poor for ¯uoranthene and pyrene. Secondly, in the LOIS core programme for rivers, only ``whole-water'' samples were analysed; hence, the distribution of contaminants between dissolved and particulate phases is unknown, al-
though results have shown that signi®cant concentrations of micro-organic contaminants may be transported in association with suspended particulate phase (Long et al., 1998) and the levels of ¯uoranthene and pyrene have been determined in SPM samples. Estimation based on partition theory has been carried out to derive atrazine concentrations in the dissolved and particulate phases. Consequently, the mass balance calculation in these two phases may be less accurate, although the total budget should still be valid. Thirdly, assumptions such as the conservative behaviour of contaminants have been introduced in calculating removal or addition in feed rivers; these may pose problems for the highly hydrophobic compounds such as PCBs and PAHs. Finally, other sources of inputs (atmospheric deposition, sediment resuspension, sewage) and sinks (degradation, sedimentation) were not considered during the current calculations. The mass balance results reported here should therefore be regarded for guidance only and may be used as a basis for further research. We gratefully acknowledge the funding of the work by the UK Natural Environment Research Council, which forms part of the LOIS RACS programme. This is LOIS Publication Number 630. With thanks to Drs P. Donkin and J. W. Readman (Plymouth Marine Laboratory), Prof S. Rowland (University of Plymouth), and Drs J. E. Rae and A. Parker (University of Reading) for their contributions and co-operation. We also thank S. Evans and D. Orr for sampling and laboratory assistance. Donkin, P., Widdows, J., Evans, S. V. and Brinsley, M. D. (1991) QSAR for the sublethal response of marine mussels (Mytilus edulis). Science of the Total Environment 109/110, 461±476. House, W. A., Leach, D., Long, J. L. A., Cranwell, P., Smith, C., Bharwaj, L., Meharg, A., Ryland, G., Orr, D. O. and Wright, J. (1997) Micro-organic compounds in the Humber rivers. Science of the Total Environment 194/195, 357±371. H uhnerfuss, H., Bester, K., Landgra, O., Pohlmann, T. and Selke, K. (1997) Annual balances of hexachlorocyclohexanes, polychlorinated bipheyls and triazines in the German Bight. Marine Pollution Bulletin 34, 419±426. Lebo, M. E. and Sharp, J. H. (1992) Modelling phosphorus cycling in a well-mixed coastal plain estuary. Estuarine Coastal Shelf Science 35, 235±252. Leeks, G. J. L., Neal, C., Jarvie, H. P., Casey, H. and Leach, D. V. (1997) The LOIS river monitoring network: strategy and implementation. Science of the Total Environment 194/195, 101±109. Long, J. L. A., House, W. A., Parker, A. and Rae, J. E. (1998) Microorganic compounds associated with sediments in the Humber rivers. Science of the Total Environment 210/211, 229±253. Mackay, D., Shiu, W. -Y. and Ma, K. -C. (1992) Illustrative Handbook of Physical-chemical Properties and Environmental
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