Metal contamination of angler-caught fish from the Mersey Estuary

Metal contamination of angler-caught fish from the Mersey Estuary

Marine Environmenral ELSEVIER Research, Vol. 41, No. 3, pp. 281-297, 1996 Copyright 0 1996 Elsevier Science Limited Printed in Great Britain. All ri...

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Marine Environmenral

ELSEVIER

Research, Vol. 41, No. 3, pp. 281-297, 1996 Copyright 0 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 0141-1136/96/%15.00+0.00

0141-1136(95)00020-8

Metal Contamination of Angler-Caught Fish from the Mersey Estuary Sally E. Collings, Michael S. Johnson & Richard T. Leah Industrial

Ecology Research Centre, Department of Environmental & Evolutionary University of Liverpool, PO Box 147, Liverpool L69 3BX, UK

Biology,

(Received 28 May 1995; revised version received 28 August 1995; accepted 31 August 1995)

ABSTRACT A survey of angling in the Mersey Estuary was undertaken to determine geographical and seasonal patterns of angling, the dominant species and size range of [email protected], and the fate of the catch. Six core species of fish were sampled from five sites in the Mersey Estuary, Hoylake, on the north Wirral, and a reference site in the Solway Firth. Analysis of muscle tissue was undertaken for mercury, arsenic, lead, copper, zinc, chromium and cadmium. Mean mercury levels for the eel and flounder populations from most Mersey Estuary sites exceeded the limit values of 0.5 and 1.0 mg kg-’ for fishery products, as specified in EC Decision (9313511 EEC). Inner Mersey Estuary sites also showed mean concentrations of lead in eel and pounder in excess of the statutory limit of 2.0 mg kg-t. Arsenic levels were higher than the general UK food limit of 1.0 mg kg-‘, but the toxicological sign$cance of this is minimal. All other combinations of species-site-metals returned data consistent with expected ranges and which are of no concern to human health. Whilst the real practical risk to consumers of Mersey Estuary&h may be low, the concentrations of mercury in muscle reinforce the prudence of MAFF advice to abstain from the consumption of long-lived lipid(fat)-rich$sh, especially eels, from industrialised estuaries such as the Mersey.

INTRODUCTION

Extending 50 km into a densely populated area of NW England, the Mersey Estuary supports over 2 million people within 8 km of its shoreline and has long been used for the aqueous disposal of domestic sewage and industrial effluents. Consequent pollution of the Mersey Estuary dates at least to the Industrial Revolution 150 years ago, and is only now being addressed seriously with the advent of stricter legislation and more effective 281

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S. E. Callings et al

treatment at source. Together these constitute a targeted ‘clean-up’ campaign that has been demonstrated to have significantly reduced the total contaminant load in recent times (Head & Jones, 1991; NRA, 1995). Monitoring of fish for toxic substances is important from a regulatory viewpoint (Franklin & Jones, 1993) and as an indicator of both existing and historic water pollution, in estuaries and further offshore. This is reflected in the long-standing monitoring programmes in Liverpool Bay, which form part of an environmental programme investigating the impact of the dumping of sewage sludge at sea and the influence of the onshore chlor-alkali industry on fish caught in the region (Norton ef al.. 1984; Franklin, 1987). Previous studies of fish populations in the Irish Sea have revealed elevated levels of a number of trace elements, most notably mercury and arsenic (Leah et uf., 199 1, 1992, 1993). Moreover, duplicate diet studies (Haxton ef ul., 1979) and critical path analysis (Preston & Portmann, 198 1) have been undertaken for mercury, aimed at determining the health risk to human consumers of fish landed from Liverpool Bay. In contrast to the comprehensive monitoring of offshore fish populations, there is a paucity of data on the concentrations of trace element pollutants in fish caught from within the Mersey Estuary. This is at a time when, with the recent focus on environmental issues, attention has been drawn towards estuarine ecosystems, including the Mersey, where substantial improvements in water quality (Head & Jones, 1991) have resulted in improved angling prospects. The potential importance of contamination of fish within the Mersey Estuary is highlighted because of the direct connection between the estuarine food chain and human exposure to metals, through the consumption of fish caught by shoreline and boat anglers. During the last few years, guidance to the general public has been offered by the Ministry of Agriculture, Fisheries and Food cautioning against the consumption of fish from contaminated and industrialised estuaries. Such advisory notices have no statutory authority and the advice is often viewed as being very general. Though useful, it has stimulated inquiries about regional and even estuary-specific information, to serve a local need in risk assessment. The project reported here was commissioned by the UK National Rivers Authority in co-operation with the angling community utilising the Mersey Estuary. The objectives were to obtain quantitative information on the concentrations of trace metals in anglercaught fish from the Mersey Estuary and inner Liverpool Bay, and where possible to make comparisons with estuaries elsewhere in the UK and mainland Europe. It was intended that this database would contribute to an informed assessment of the health risk to human consumers of Mersey Estuary fish.

MATERIALS

AND

METHODS

A pilot study of the Mersey Estuary was undertaken in the winter of 1991-92 to determine geographical and seasonal patterns of angling, the dominant species and size range of landed and retained fish, and also the fate of the catch (Leah, 1992). This initial work was considered important because over 5000 licences for pleasure and competition angling have been issued through the Mersey Docks and Harbour Company since 1982. Some enthusiastic anglers (20&250) renew their permits annually, and at any one time 600-800 permits will be valid. Moreover, it is common to observe in excess of 100 shoreline anglers

Metal contaminationof angler-caught fish

Fig. 1.

283

Angling sites for shoreline and boat-caught fish in the Mersey Estuary, north Wirral coast and Solway Firth.

during a 24 h tidal cycle. Angling patterns within the estuary were found to be wide and varied, with more than 40 clubs organising shore-based and boat angling. Many clubs are affiliated to the North West Association of Sea Angling Clubs (NWASAC), which has national recognition and administers winter and summer competitive angling matches at different venues within the Mersey Estuary. However, not all anglers are competitive, and a significant number of fish are landed for sport or specifically for human consumption. The preliminary study showed that the shoreline of the Wirral Peninsula, which links Liverpool with the north Wales coast, is the most popular area for anglers, with sites varying according to season, tide times and the species targeted. Alexandra Dock is the principal angling site on the Liverpool shoreline. Sites further upstream, at Eastham and Otterspool, are also frequented on a seasonal basis (Fig. 1). Pilot questionnaires provided information on the relative importance of the species caught during different seasons of the year, as well as on the fate of the catch. The dominant species caught on a regular basis are popular sport and commercial fish of European Community coastal waters. These include dab (Limandu limanda L.) throughout the year, eel (Anguillu anguillu L.) in summer, and flounder (Plutichthys Jesus L.) mainly in the summer and autumn. The strongly migratory plaice (Pleuronectes plutessu L.) are landed for a few months only at the height of summer, and the migratory roundfish, cod (Gadus morhua L.) and whiting (Merlungius merlangus L.), are landed in winter. The latter three species are particularly favoured for human consumption. Approximately 45% of anglers on the Wirral shoreline retained all species of fish of a suitable size for domestic consumption, whilst 20% kept only cod and whiting as they were considered to be less contamined due to their migratory behaviour. A further 24% ate no fish at all, in most cases because of the perceived risk to health. The preliminary study was succeeded by the main period of sampling for analysis during 1992 and early 1993. Samples were donated from catches landed by shoreline and boat anglers. Sites ranged from Eastham and Otterspool on opposite shorelines in the

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inner Mersey Estuary, to Alexandra Dock in the mid-estuary on the Liverpool waterfront, and three further sites on the Wirral coast, all seawards of Alexandra Dock. These latter three were New Brighton, the Mersey Channel and Hoylake, between the Mersey and Dee Estuaries (Fig. 1). Samples were also acquired from boat catches from further offshore in Liverpool Bay. The Solway Firth, some 150 km north of the Mersey-Dee complex, was used as a reference site for the study. Age is an influential factor in the accumulation of pollutants by some fish species, so analysis was restricted to fish of a size suitable for human consumption, and in line with commercial size limits. Sample sizes for each species varied with season, but the pooled datasets (across-seasons, within-site) usually comprised 20-30 specimens larger than: 20 cm-dab, 25 cm-plaice, 27 cm-~-whiting, 25 cm- --flounder, 35 cm+od and 50 cmeel. These six core species were supplemented with samples from boat-anglers engaged in ‘wreck-fishing’ offshore in Liverpool Bay. These additional samples included skate (Raja batis), spotted ray (Raja montagui), dogfish (Scyliorhinus canicula), tope (Galeorhinus galeus), mackerel (Scomber xombrus), scad (Trachurus trachurus) and gurnard (Trig/a Eucerna). All samples were blast frozen before storage at - 18°C and later dissected, during which a muscle fillet was excised from the left dorsal surface. In view of the human exposure emphasis of the project, muscle was the principal tissue analysed. Other monitoring programmes serving wider objectives including surveillance of wildlife and natural food chains (e.g. Franklin & Jones, 1993) also routinely analyse liver tissue. In this study fish liver was analysed only as bulked tissue for selected species-site combinations, and then only as a basis for comparison with data published previously for Liverpool Bay (Franklin & Jones, 1994). Fish muscle was analysed for seven trace elements, namely mercury, cadmium, lead, arsenic, copper, zinc and chromium, all of which are included in the UK ‘Red List’ of the most dangerous substances entering the aquatic environment. Of these, mercury and cadmium are included in List 1 and the rest in List II of the European Community Directive 76/464/EEC. Analytical protocols were broadly in line with those described by Harper et al. (1989). Mercury was determined by cold vapour atomic absorption spectrometry using a modification of the stannous chloride reduction technique following digestion of a 2 g sub-sample in concentrated nitric acid (Evans et al., 1986; Leah et al., 1991). Other elements, except arsenic, were determined in the concentrated nitric acid digest by flame absorption spectrometry. with deuterium background correction for matrix interference where necessary. Total arsenic was determined by hydride generation -atomic absorption spectrometry using a modified nitric-perchloric-sulphuric acids wet oxidation technique (Leah et al., 1992). The International Reference Material (IRM), MAA- (International Atomic Energy Authority, Vienna) was included in every batch of samples as a quality control measure for recovery of mercury. Recoveries were consistently in the range 96104%. TORT-l (National Research Council, Canada) was used in each sample set as the reference material for lead, copper, zinc, cadmium and chromium, with a minimum 90% of the certified value as the recovery target. Since quantitative recovery of arsenic from biological tissue is not a simple, routine matter (Phillips, 1990), the analytical method adopted was monitored by analysis of more than one IRM within each batch of samples. The certified total arsenic values and percentage recoveries achieved were as follows: MAA 2 (IAEA, Vienna): 2.6 mg kg- ’ * 0.1 (SD), 92-105%; DORM 1 (National Research Council of Canada, Ottawa): 17.7 mg kg-’ f 2.1, 88-96%.

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285

The summary tables given subsequently show, at a minimum, the arithmetic mean values ( f standard deviation, SD) for trace elements in collections of fish made through 1992-93, and pooled as single datasets for each site-species combination. Quoted sample means are based on all samples within each dataset, in accordance with standard procedures adopted by MAFF (Franklin, pers. comm.). Samples that gave atomic absorption signals below the detection limit were recorded as being on the limit of detection for the purposes of data handling. The recording of some mean values as ‘ < ’ signifies a sample set that includes at least one value below the limit of detection. Data for mercury in fish muscle were subjected to Analysis of Variance (ANOVA) for between-site, within-species comparisons in respect of flounder and eel. These are species for which the sample sets were available for the inner Mersey Estuary and north Wirral coast, the angling sites most distant from one another within the Mersey catchment. ANOVAS were performed on logi, transformed data due to heterogeneity in the variances arising mainly from the differential spread of datapoints around the mean of the inner Mersey Estuary sites at Eastham and Otterspool, and both the north Wirral site at Hoylake and the Solway Firth.

RESULTS

AND DISCUSSION

Data for trace element concentrations in muscle tissue for each species-site combination covering the Mersey Estuary, north Wirral coast and Solway Firth are shown in Table 1 and Tables 5 and 6. Equivalent results for other species caught in Liverpool Bay are given in Table 4, and the concentrations of cadmium in bulked samples of fish liver are shown in Table 7. Mercury

Taking account of all sites, mean mercury concentrations in fish from the Mersey Estuary followed a consistent, species-based order of: eel > > flounder > dab > plaice > whiting > cod (Table 1). Mean values for all Mersey Estuary and Wirral coastline sites were usually higher than for the Solway reference site, especially in respect of dab, flounder and eel (p < 0.001). This pattern was also generally true for comparisons at the species level between the Mersey Estuary and other industrialised estuaries on the coastlines of Britain and mainland Europe (Table 2). Specifically, mercury levels in fish from the Mersey Estuary notably exceed data for the same species sampled during recent monitoring programmes in Liverpool Bay and the north-east Irish Sea (Franklin, 1991; Franklin & Jones, 1994). Mean values for mercury were generally higher at inner Mersey Estuary sites (e.g. Eastham, Otterspool) than elsewhere (e.g. Alexandra Dock Wall, Hoylake). This was particularly true for eels and flounder, where the contrast between the Mersey Estuary and north Wirral coastline was very significant (p < 0.001; Table 3). Mercury values for eel (0.51-2.56 mg kg -‘) and flounder (0.37-1.20 mg kg -I) were highest at the inner Mersey Estuary site of Eastham, close to the confluence with the Manchester Ship Canal. Moreover, the mean mercury values for eels were significantly higher than for all other Mersey Estuary species, based on an example within-site comparison for New Brighton fish (p
S. E. Callings et al.

286

TABLE 1 Mercury in Muscle Tissue of Fish from Sites in the Mersey Estuary (’ Species

Site

n

Length rcmj

Mean Hg &SD

Cod Cod Whiting Whiting Whiting Whiting Dab Dab Dab Dab Flounder Flounder Flounder Flounder Flounder Flounder Plaice Plaice Eel Eel Eel Eel Eel

Mersey Channel Solway Firth New Brighton Alexandra Dock Mersey Channel Solway Firth New Brighton Alexandra Dock Mersey Channel Solway Firth Eastham Otterspool New Brighton Alexandra Dock Hoylake Solway Firth New Brighton Solway Firth Eastham Otterspool New Brighton Hoylake Solway Firth

43 20 25 17 15 20 90 20 28 12 29 25 21 20 25 20 82 7 63 50 43 18 20

40.8 42.6 30.4 29.9 33.1 25. I 25.9 25.3 27.8 25.0 29.1 29.6 32.6 32.4 30.3 28.9 31.7 35.7 53.4 53.6 57.5 52.x 51.7

0.27 f 0.08 0.08 i 0.02 0.29 i 0.1 0.23 i 0.07 0.40 * 0.18 0.10*0.02 0.58 * 0.27 0.35iO.16 0.41 10.13 O.lO&O.O8 0.8OztO.19 0.63 IO.23 0.79 zt 0.32 0.47 * 0.19 0.27 f 0.08 0.1710.15 0.36*0.17 0.14io.07 1.35*0.50

0.13-0.36 0.03-O. 14 0.16-0.58 0.12-0.39 0.18-0.80 0.05-O. 15 0.05-I .59 0.1 l-O.63 0.20-0.72 0.02-0.25 0.37-I .20 0.30-1.18 0.31-1.81 0.23-l .O 0.14-0.44 0.06-0.67 0.12-0.87 0.06-0.26 0.51-2.56

I .2x * 0.49

0.3

“All data in mg kg-’ wet * SD (standard deviation)

0.24-0.29 0.07-0.09 0.25-0.34 0.19-0.26 0.31-0.40 0.09-O. 11 0.53-0.64 0.28-0.41 0.37-0.46 0.05-O. 14 0.73-0.87 0.54-0.72 0.67-0.91 0.40-0.56 0.24-0.3 1 0.10-0.23 0.33-0.40 0.09-0.20

Metal contamination of angler-caughtjish

287

TABLE 2

Mercury in Muscle Tissue of Marine Fish from European Waters Species

Dab Dab Dab Flounder Flounder Flounder Flounder Flounder Cod Cod Cod Whiting Whiting Whiting Plaice Plaice Plaice Multiple species Eel Eel Cod Whiting Plaice Flounder Dab Cod Whiting Plaice Flounder Dab

Location

Mean concn : mg kg-’ wet wt (range)

Tynemouth Dogger Bank Humber Estuary Thames Estuary Normandy Coast North Sea Inner Forth Thames Estuary Norwegian Coast Norwegian Coast Firth of Clyde

0.11 (0.04-0.25) 0.08 0.17 (0.05-0.33)

Shetland and Hebrides Tynemouth Firth of Clyde Thames Estuary Tynemouth Firth of Clyde Shetland and Hebrides Thames Estuary East Anglian rivers Mersey Estuary Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay

0.11 0.10 (0.04-0.22) 0.1-2.0 0.27 0.26 (0.16-0.41) 0.15 0.08 0.06 0.05-0.06 0.14 (0.05-0.43) 0.03-0.06 0.09 (0.07-O. 14) 0.03 (0.006-0.21) 0.04 0.03-0.05 0.18 (0.05-0.46) 0.32 (0.06-l .4) 0.90 (0.61-1.30) 0.17 (0.06-0.27) 0.32 (0.12-0.63) 0.13 (0.02-0.28) 0.16 (0.07-0.28) 0.24 (0.08-0.65) 0.13 0.31 0.13 0.31 0.22

Authors

Dixon & Jones, 1994 Franklin & Jones, 1993 Franklin & Jones, 1993 Franklin, 1992 Cossa et al., 1992 Franklin, 1987 Clark & Topping, 1989 Preston & Portmann, 198 1 Staveland et al., 1993 Staveland et al., 1993

Clark & Topping, 1989 Clark & Topping, 1989 Dixon & Jones, 1994 Clark & Topping, 1989 Franklin, 1992 Dixon & Jones, 1994 Clark & Topping, 1989 Clark & Topping, 1989 Preston & Portmann, 1981 Barak & Mason, 1990 Johnston et al., 1991 Franklin, Franklin, Franklin, Franklin, Franklin, Franklin Franklin Franklin Franklin Franklin

1991 199 1 199 1 1991 199 1 & Jones, & Jones, & Jones, & Jones, & Jones,

1994 1994 1994 1994 1994

Alexandra Dock) clearly breach the more recent limit values in EC Decision 93/351/EEC. These apply to most individual fish species (0.5 mg Hg kg-‘) and to a selected and narrower range, including sharks, eels, tuna and rays (1.0 mg Hg kg-‘). The limit values in EC Decision 93/351/EEC establish maxima for mercury in edible fishery products. Judged against the EC Decision, the mercury levels in cod, whiting, dab and plaice data are of low importance, though the migrant plaice population of the Mersey Estuary includes specimens with mercury values as low as 0.12 mg kg-’ and as high as 0.87 mg kg-‘. Mean values for Mersey Estuary dab also include a significant number of specimens with mercury levels above the relevant EC Decision threshold, with the site mean for New Brighton at 0.58 f 0.27 mg Hg kg-‘. Fish caught from boats in Liverpool Bay had mercury concentrations that varied according to species, the values of note being in the elasmobranchs, skate (0.27-3.14 mg kg-‘), dogfish (0.26-3.27 mg kg-‘) and tope (1.96286

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S. E. Callings et al.

Summary

of Analysis .~.

spPcif3

TABLE 3 of Variance for Mercury in Muscle of Fish” ~~~._.~ ~~~~~~

Sifrs

F-n&o

P

LSD at p < U.OOih

(a)

Mersey Estuary, North Wirral Coast and Solway Firth

66.3

< 0.001

0.23

(b) Flounder

Mersey Estuary, North Wirral Coast and Solway Firth

70.3

< 0.001

0.19

55.7

< 0.001

0.21

New Brighton

(c) Five’ species

(Mersey

Estuary)

UData transformed to log,,. hLeast Significant Difference between paired means (see Table 1) ‘Whiting, dab, flounder, plaice and eel (see Table I).

TABLE 4 Trace Metals in Muscle Tissue of Boat-Caught Species

Skate

Spotted Ray Dogfish Tope Mackerel Scad Gurnard

n

8 6 12 4 2s 11 I2

Length (tml 72.8 39.3 57.2 155.7 23.8 27.0 31.2

A.\

1.2t I.1 0.3+0.1 0.9+0.9 2.5 + 0.4 0.02 f 0.01 0.2 * 0. i 0 310.1

30.1 i9.9 IO.1 +2.5 21.3h9.5 9.8zt33.9 0.9 f- 0.4 I.1 l0.3 2.0 i I .3

Ph

1.4t 1x+

I.2 1.3

< 0.62 0.8+0.3 -C0.33 < 0.32 < 0.46

Fish from Liverpool Bay”

cu

Zil

Cr

Cd

< 0.23

4.8 * 0.4 5.3 * 0.7 10.7+ I.2 3.6 f 0.2 5.1 + I.1 3.950.4 4.0*oo.7

0.3*0.1 0.2*0.1 0.5 * 0.3 0.2 f 0. I co.17 CO.17 0.310.1

co.12 < 0.08
0.5ztO.l < 0.22 10.22 0.9 *cl.3 0.6ztO.1 c 0.23

“All data in mg kg -’ wet wt * SD.

mg kg-’ Table 4), all of which are subject to the upper threshold limit of EC Decision 93/ 351/EEC. Mean mercury concentrations in skate and tope from Liverpool Bay exceed the statutory limit of 1.0 mg kg ~‘. Overall, the results for mercury from this study are broadly consistent with previous reports for the Mersey Estuary (Johnston et al., 1991) and also published data from Leah et al. (1991, 1993). However, the data reported here are considerably higher than those from samples of the same species caught recently in Liverpool Bay and the wider Irish Sea, offshore the Mersey Estuary, as part of the Joint Monitoring Programme of the Oslo and Paris Commissions (Leah et al., 1993; Franklin & Jones, 1994). Arsenic

The toxicology of arsenic in seafood has been much debated since the discovery that it is usually present as refractory organic compounds (Lawrence ef al., 1986; Leah er al., 1992). The majority of arsenic in marine fish is in the form of arsenobetaine (Phillips, 1990), which is excreted unaltered by the metabolism of mammalian consumers, and is therefore of low toxicological significance (Kaise et al., 1985).

289

Metal contamination of angler-caughtjish TABLE 5 Arsenic in Muscle Tissue of Fish from Sites in the Mersey Estuary and Solway Firth” Species

Cod Cod

Whiting Whiting Whiting Whiting Plaice Plaice Dab Dab Dab Dab Flounder Flounder Flounder Flounder Flounder Flounder Eel Eel Eel Eel Eel

Site

n

Mean As f SD

Range

95% Confidence Limits

Mersey Channel Solway Firth New Brighton Alexandra Dock Mersey Channel Solway Firth New Brighton Solway Firth New Brighton Alexandra Dock

43 20 25 17 15 20 82

4.7* 1.9 4.3* 1.3 3.4* 1.7 3.0+ 1.6 2.9 f 0.9 4.1 f 1.6 10.7 f 5.9 10.2*9.5 7.7&2.4 7.2+ 1.9 5.1*2.2 7.0*3.3 6.2* 1.9 8.6 f 2.5 11.6*4 13.3*5.9 5.8h2.3 6.5 + 2.6 1.0*0.4 0.9*0.3 1.4ztO.6 1.1*0.5 1.1 zt0.6

1.9-9.0 1.4-6.9 1.4-8.3 1.8-6.4 1.2-5.1 1.8-7.6 1.6-29.2 2.7-29.4 1.9-13.6 3.1-9.5 0.8-10.7 3.0-12.6 3.2-10.7 4.5-13.5 4.4-19.1 5.9-26.2 3.2-12.9 2.5-13.7 0.3-1.9 0.4-1.7 0.1-2.6 0.5-2.8 0.4-2.7

2.9-7.0 3.7-4.6 3.2-4.5 2.3-3.7 2.5-3.4 3.4-4.8 9.4-12.0 4.0-25.9 7.2-8.2 6.3-8.0 4.3-6.0 5.2-8.9 5.4-6.9 7.6-9.5 10.0-13.2 10.4-15.7 4.9-6.7 5.4-7.7 0.9-l .o 0.8-1.0 1.2-1.5 0.9-l .4 0.9-l .4

Mersey Channel Solway Firth Eastham Otterspool New Brighton Alexandra Dock Hoylake Solway Firth Eastham Otterspool New Brighton Hoylake Solway Firth

90 20 28 12 29 25 27 20 25 20 63 50 43 18 20

nAll data in mg kg-’ wet wt f SD.

Controls governing the concentration of arsenic in human food in the UK originated as 1959 (Anonymous, 1959) when the speciation of arsenic was not considered. The regulation refers to total arsenic on the assumption that it would be mainly inorganic. The maximum permissible concentration of arsenic in food is currently 1.0 mg kg-‘, “except where arsenic in proportions exceeding one part per million is naturally present in that fish”. Previous studies have reported on the distribution and speciation of arsenic in plaice and whiting from Liverpool Bay and the Irish Sea (Leah et al., 1992). Site mean values for arsenic in Mersey Estuary fish are shown in Table 5, and broadly follow the order: flounder, plaice, dab > cod, whiting > eel. Consistent with previous reports (MAFF, 1982; Leah et al., 1992), flatfish showed higher mean values than roundfish, the total ranges of means (excluding eels) being 5.1-13.3 mg As kg-’ and 2.94.7 mg As kg-’ respectively, for the two classes. Amongst the Liverpool Bay fish, skate had by far the highest mean figure at 30.1 mg kg-’ (Table 4). The national Arsenic in Food Survey (MAFF, 1982) recognised that flatfish which live on or close to the sea bed, such as plaice, dab, flounder and skate, have a consistently higher level of arsenic than other species. Arsenic in Food Regulations,

S. E. Callings et al.

290

Lead, Copper,

Species Cod Cod Whiting Whiting Whiting Whiting Plaice Plaice Dab Dab Dab Dab Flounder Flounder Flounder Flounder Flounder Flounder Eel Eel Eel Eel

Eel

Zinc, Chromium

Site Mersey Channel Solway Firth New Brighton Alexandra Dock Mersey Channel Solway Firth New Brighton Solway Firth New Brighton Alexandra Dock Mersey Channel Solway Firth Eastham Otters.pool New Brighton Alexandra Dock Hoylake Solway Firth Eastham Otterspool New Brighton Hoylake Solway Firth

TABLE 6 and Cadmium in Muscle Tissue of Fish from Sites in the Mersey Estuary and Solway Firth” n

Ph

43 20 25 17 15 20 x2 7 90 20 3x I2 29 25 27 20 25 20 6.3 50 43 IX 20

1.10*0.51 co.31 < 0.66 < 0.42 < 0.94 <: 0.33 < 0.59 < 0.33 CO.41 c- 0.33 c 0.32 < 0.32 2.55 zt 0.82 c 0.61 c~0.74 < 0.40 c 0.34 < 0.32 2.24 f 0.95 < 0.84 < 0.84 ~0.61 < 0.49

CIA 0.27~tO.15 0.21*0.10 0.32 i 0.07 0.37 i 0.29 0.33io.14 0.27*0.09 CO.18 0.44*o.l0 CO.18 0.20 -i-0.07 0.63 * 0.29 CO.18 0.27iO.09 0.361tO.13 c 0.22 0.40 rt 0.09 0.30 f 0. I I 0.29ztO.12 0.76 + 0.33 1.06%0.58 0.92 * 0.69 0.83 i 0.34 0.85 * 0.30

Zn

Cr

Cd

4.1 kO.6 4.7 jI 0.8 4.21tO.4 4.1 hO.7 3.9io.4 4.4 f 0.5 5.5 IO.8 7.1 k2.2 5.3 It 0.7 5.6+ I.0 5.4* I.1 5.4* 1.2 7.81 I.5 6.51 I.8 7.912.0 6.9k2.7 12.0&4.0 9.4 * 3.9 25.7 f 6.6 25.7 zt 5.6 25.9i6.6 22.7 * 3.7 20.0 i 4.0

CO.18 < 0.22 < 0.29 co.19 co.17 0.22 * 0.08 < 0.2 ~0.16 co.19 co.17 ~0.18 ~0.16 < 0.25 < 0.27 ~0.18 co.19 < 0.26 ~0.16 < 0.25 < 0.43 < 0.32 < 0.26 < 0.25

< 0.09 < 0.08 < 0.09
“All data in mg kg ’ wet wt + SD.

In contrast to mercury there is no clear spatial pattern for arsenic in fish muscle. The Mersey Estuary sites were not only similar to one another and to the north Wirral coast site, they were no higher than the reference site at Solway Firth. Moreover, some species were notable in the Mersey Estuary especially for their low concentrations of arsenic, with the total range for eels across all sites being 0. I4 2.77 mg kg-‘, and the inner Mersey sites recording the lowest concentration ranges. This re-affirms earlier conclusions that the Mersey catchment is not the source of arsenic in the fish from deeper waters of Liverpool Bay (Leah et al., 1992). With over 98% of the arsenic burden of Mersey fish comprising non-toxic compounds, there is no cause for concern in respect of human consumption. Furthermore, the results compare favourably with those for Scottish (Falconer et al., 1983) and Norwegian (Staveland et al., 1993) waters distant from intensive industrial activity. Lead The Lead in Food Regulations 1979 (Great Britain Parliament, 1979) determine that lead in fish and shellfish serving as human food should not exceed 2.0 and 10.0 mg kgg’ wet weight, respectively. These thresholds compare with expected values for muscle tissue

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of fish from around the British coastline, including Liverpool Bay, of no higher than 0.005 mg kg-’ wet weight (Franklin & Jones, 1993, 1994). Concentrations of lead in muscle tissue of fish from the Mersey Estuary are given in Table 6. Most site means were very low, with the majority of Mersey Estuary samples and all those from the Solway Firth below the limits of analytical detection. However, population mean values for flounder (2.6 AO.8 mg kg-‘) and eel (2.2i 1.0 mg kg-‘) from Eastham, the inner estuary site, exceeded the statutory limit. The range of lead concentrations in Eastham flounder was 1.2-5.2 mg kg-‘, with eels recording 0.3-4.7 mg kg-‘. At all sites, samples of the eel population consistently returned more positive results than elsewhere, positive being above the analytical detection limit. To a lesser extent this was also true for plaice, for which the concentration range was < 0.29-1.4 mg kg-‘. The values for the Eastham site are considerably higher than might be expected from the experience of the Joint Monitoring Programme (Franklin & Jones, 1993) and are thought to be related to the proximity of the site to the exit of the Manchester Ship Canal into the Mersey Estuary. The historic significance of this source of lead contamination to the estuary is well documented (Bull et al., 1983). Copper Copper absorption by fish is regulated biologically and the concentrations in muscle tissue differ only marginally between species (Murray, 1981). Oil-rich species tend to show the highest copper values, probably related to their predominantly crustacean diet. Data for the Mersey Estuary and inner Liverpool Bay were found to be consistent with results of recent compliance monitoring in the latter area (Franklin & Jones, 1994), with mackerel 0.95 f 0.34 mg kg-’ and eel (1.06 f 0.58 mg kg-‘) having the highest mean values, and ranges of 0.62-l .88 mg kg-’ and 0.224.1 mg kg-‘, respectively (Table 4). Overall, the data for the Mersey Estuary compare favourably with those for other sectors of the British coastline monitored by MAFF, including the industrialised Thames and Humber Estuaries, and Morecambe Bay (Franklin & Jones, 1994). The range of means for flounder of commercial size taken from five sites spanning the Mersey Estuary and outer Dee Estuary (0.27-0.40 mg kg-‘) was marginally lower than for the Thames (0.56 mg kg-‘), the latter population having been sampled a decade ago (Rickard & Dulley, 1983). Mersey Estuary values for copper in flounder were also similar to more recent results for several sites off the Atlantic coast of France (0.16-0.33 mg kg-’ wet wt) (Cossa et al., 1992), and very similar to those for the Solway reference site (Table 6). The current UK recommendation for the maximum copper content of food is that it should not exceed 20 mg kg-’ wet wt, though higher levels in shellfish are permitted if the copper is of natural origin (MAFF, 1956). Considered alongside recent reports on the ‘expected’ levels of copper in fish, up to 0.6 mg kg-’ (wet wt) and in excess of 1.0 mg kg-’ in fat-and oil-rich species (Franklin & Jones, 1994), data for the Mersey Estuary have no legislative or human health risk implications. Zinc Portmann (1979) reported little spatial variation in the concentration range for zinc in muscle of fish from British coastal waters, with the majority of data between 4-6 mg kg-’ (wet wt). Some inter-specific variation was noted, with lipid-rich species giving higher

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concentrations, up to 17 mg kg- [. These mean values are broadly in line with those reported previously in Liverpool Bay (Franklin & Jones, 1994) and abo those from the present study of the same location (3.5-10.7 mg kg-‘), as well as the Mersey Estuary, eels and flounder excepted (3.9-7.1 mg kg-‘) (Table 6). The Mersey Estuary and Solway showed few differences, with the zinc ranges for cod, whiting, dab and plaice showing the typical two-fold concentration range across species (Portmann, 1979). Flounder and eel data did not conform to the pattern for other species. Zinc levels in flounder were elevated, and especially so away from the Mersey Estuary at Hoylake on the north Wirral coast and the Solway reference site. The full range of values for these populations of flounder was much broader than for other species, namely 7.4-23.2 mg kg-l and 4.7-18.0 mg kg-‘, respectively. Cossa et al. (1992) also reported a wide range of zinc values (3.6-18.0 mg kg-‘) for flounder from French coastal waters. Eels, a particularly lipid-rich species, also showed very high values across all sites, with means (including the reference site) of between 20.0 i 3.9 and 25.9 * 6.6 mg kg-’ (Table 6). The current UK recommendation for the zinc content of food advocates a maximum concentration of 50 mg kg-’ wet wt, with higher levels permissible in shellfish, and fish such as herring which are naturally rich in this trace element (MAFF, 1953). With ‘expected’ values of up to 6.0 mg kg--’ wet wt in muscle of most fish, up to 10 mg kg-’ in flounder and more in fatty species (Franklin & Jones, 1994), the zinc concentrations of fish from the Mersey Estuary are inconsequential in terms of human exposure. Chromium

Chromium is not usually an analytical target within routine surveillance of pollutants in fish, and there is little by way of contemporary information available for comparison purposes. Samples of roundfish and flatfish collected between 197s-73 during a major campaign embracing the North Sea, English Channel and Irish Sea, including Liverpool Bay, showed chromium levels consistently around or below the limit of detection of 0.2 mg kg-’ (Portmann, 1979). The present study showed mean chromium concentrations for fish from the Mersey Estuary and the Solway which are consistent with this earlier pattern. Populations of species collected offshore in inner Liverpool Bay, for example dogfish (0.5 kO.3 mg kg-’ ), did in some cases include individuals which gave positive results for chromium; but levels were generally very low (Table 4), and were consistently so from within the Mersey Estuary itself (Table 6). Cadmium

Some sixteen years ago it was reported that the contribution of fish and fishery products to cadmium in the food chains around the British coastline was so negligible that the protection of human health and fish stocks was not an issue (Portmann, 1979). Analytical constraints associated with assays of low levels of cadmium in fish muscle led to changes in protocols, so that only liver tissue has since been used in the routine assessment of cadmium. Analysis of muscle is now conditional upon there being high levels in the liver (e.g. Franklin & Jones, 1994). Efevated levels of cadmium were not found in muscle of fish from the Mersey Estuary or Solway Firth, which were very similar to one another at a variable detection limit of 0.08-0.10 mg kg-‘, or 0.12-0.16 mg kg-’ in the case of eels (Table 6).

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TABLE 7 Cadmium in Duplicate, flulked Samples of Fish Livers from Liverpuoi Bay and the Solway Firth” Species

Cod Cod Whiting Whiting Plaice Plaice Dab Dab Flounder Flounder Flounder Eel Eel Eel Eel Eel Skate Spotted Ray Dogfish Tape Mackerel Sead Gurnard

Site

Mersey Channel Solway Firth New Brighton Solway Firth New Brighton Solway Firth New Brighton Solway Firth Eastham New Brighton Solway Firth Eastham Otterspool New Brighton Hoylake Solway Firth Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay Liverpool Bay

n

Cd (mg kg -‘)

15+ 15+ 15-t 15+ 15+ 7 15-t 11 15+ 15+ 15+ 15+ Is+ is+ 13 15+ 8 6 12 4 15-t 10+ 10+

< 0.05 ( < 0.04, < 0.05) < 0.04 (< 0.04, < 0.05) < 0.04 (< 0.04,0.04) < 0.05 (< 0.05, < 0.05) < 0.05 (< 0.06, < 0.05) 0.87 (0.90, 0.83) < 0.04 ( < 0.04, < 0.04) 0.18 (0.20, 0.15) < 0.04 (< 0.04, < 0.04) 0.18 (0.21,0.16) 0.27 (0.25,0.30) < 0.04 (< 0.04, < 0.0s) < 0.05 (< 0.05, < 0.05) 0.09 (0.09,O.OS) < 0.05 ( < 0.05, < 0.04) 0.39 (0.42, 0.35) < 0.05 (< 0.05, < 0.06) < 0.05 (< 0.05, < 0.05) 0.30 (0.32, 0.28) 1.97 (1.90, 2.04) 0.26 (0.25, 0.27) 0.53 (0.55, 0.50) < 0.06 ( < 0.06, < 0.05)

“All data expressed in mg kg -’ wet wt as the mean of 2 replicates whose values are in parentheses.

For most species in the Mersey Estuary, the experience of low cadmium concentrations jn muscle applied equally to bulk liver tissue (Table 7). However, some species from inner Liverpool Bay, notably tope and scad, but also flatfish from further afield in the Solway Firth, showed significantly elevated levels of cadmium in liver, with the peak mean value

of 0.87 mg kg-’ occurring in plaice. Whether these elevated values are related to feeding strategy or to a contaminated diet reflecting local influences is unclear, however the latter seems possible as recent data for flounder from Morecambe Bay (0.28 mg kg-‘) and mussels from Whitehaven (2.3 mg kg-‘) are higher than for other sampling stations around the coastline (Franklin & Jones, 1994). Expected (wet wt) values for cadmium, based on previous sampling campaigns, are < 0.2 mg kg-’ in fish and < 0.3 mg kg-l in shellfish.

CONCLUSIONS The Mersey Estuary has long been the recipient of high inputs of mercury in industrial effluents (Preston & Portmann, 1981), and specifically from the chlor-alkali industry

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(Johnston et al., 1991). Only seven years ago water entering the Mersey Estuary from Eastham Lock carried a mercury loading of 2.5 kg day-’ (Langston, 1986). This is reflected in the differences in mercury in the muscle tissue burdens of fish from the inner Mersey Estuary and from the north Wirral coast, and also between populations that reside within the estuarine habitat for longer periods (e.g. dab, flounder) and those which are more strongly migratory (e.g. cod, whiting, plaice). Highest mercury burdens were found in sedentary species (e.g. eel). The inter-specific differences in mercury loadings appear to be related, at least in part, to known local migration patterns and behaviour. Thus mercury levels in Mersey Estuary flounder, a species that resides seasonally in the innermost estuary, and even in freshwater, are higher than or similar to flatfish that spend a great deal of their life within the estuary, moving only a short distance offshore (e.g. dab), and those that have distinct and short summer migrations to feed within the Mersey Estuary (e.g. plaice). In contrast to mercury, the data for arsenic suggest that the source of the elevated levels in fish muscle is not of Mersey Estuary origin, a conclusion drawn also from previous work on the fish populations of Liverpool Bay (Leah et al., 1992). Moreover, it is thought that the speciation of arsenic in fish muscle, being predominantly refractory arsenobetaine, is such that the anomalous values for not just the Mersey Estuary and Liverpool Bay, but also further north in the Solway Firth, are of little consequence as regards human health. The same outcome is the case for the Mersey Estuary as regards levels of copper, zinc, chromium and cadmium, for which there is no evidence of elevated concentrations in fish muscle. This is also, for the most part, true of lead levels in fish muscle, though values for the populations of flounder and eel at the inner Mersey Estuary site of Eastham exceeded the statutory limit due, it is thought, to the influence of contaminated waters fluxing from the Manchester Ship Canal. On the basis that there is no scope for complacency in the setting of standards that safeguard human health, the outcome of this study must be viewed in the context of cautionary News Releases issued by the Ministry of Agriculture, Fisheries and Food in 1988 and 1991. These were directed mainly at anglers, and at the risk to human health of consuming fish caught in estuaries affected by industrial activity. In 1993 the advice note to anglers, which has no statutory authority and is advisory only, was re-issued. The stimulus behind these publications was, primarily, data published on residual levels of pesticides in eels from the Mersey Estuary. There is reason to believe from the present study that the cautionary advice of MAFF is justified, particularly in respect of eels. The Mersey Estuary populations of this species have very high concentrations of mercury which probably reflect a combination of their longevity, habitat and feeding habits. Concentrations of mercury in flounder from the inner Mersey Estuary are also higher than might be considered prudent for human consumption, without recourse to consulting tolerable weekly intakes of mercury recommended by the World Health Organisation (FAO/WHO, 1974, Preston & Portmann, 1981). In conclusion, it would be prudent to abstain from significant consumption of eels caught in the Mersey Estuary. However, there is no reason to believe that this strongly cautionary approach to eels and mercury applies to all other combinations of species and trace elements. With the exception of specific combinations of sitee-elementtspecies, there is mostly evidence of low concentrations of trace metals in the muscle tissue of Mersey Estuary-caught fish.

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ACKNOWLEDGEMENTS The authors gratefully acknowledge financial support of the National Rivers Authority (NRA) in the undertaking of this project. They are also very grateful for the technical assistance of MS Diane Scrivens, and for the full and enthusiastic support of members of the North West Association of Sea Angling Clubs in providing samples, and even organising competitions in support of the project. The NRA is unable to give advice concerning the health risk of consuming fish caught in rivers and estuaries. The responsibility for advice on this matter resides with MAFF (Chemical Safety of Food Division) who issued the advice notes between 1988 and 1993.

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Report No. 76. Ministry of Agriculture, Fisheries and Food, Lowestoft, UK, 5Opp. Phillips, D. J. H. (1990). Arsenic in aquatic organisms: a review, emphasising chemical speciation. Aquatic Toxicol., 16(3), 151-86. Portmann, J. E. (1979). Chemical Monitoring of Residue levels infish and shellfish landed in England and Wales during 197t373. Aquatic Environment Monitoring Report No. 1. Ministry of Agriculture, Fisheries and Food, Lowestoft, UK, 75pp. Preston, A. & Portmann, J. E. (1981). Critical path analysis applied to the control of mercury inputs to United Kingdom coastal waters. Environ. Pollut., 2, 45144. Rickard, D. G. & Dulley, M. E. R. (1983). The levels of some heavy metals and chlorinated hydrocarbons in fish from the tidal Thames. Environ. Pollut. (Series B), 5,101-19. Staveland, G., Marthinsen, I., Norheim G. & Julshamn, K. (1993). Levels of environmental pollutants in flounder (Platichthys flesus L.) and cod (Gadus morhua L.) caught in the waterway of Glomma, Norway. II. Mercury and arsenic. Arch. Environ. Contam. Toxicol., 24, 187-93.