Mercury in 16 deep sea fish species from the Northeast Atlantic and food safety considerations Frantzen,
1 S. ,
Azad,
1 A.M. ,
Maage,
1,3 A.
1. NIFES, National Institute of Nutrition and Seafood research, Bergen. 2. IMR, Institute of Marine Research, Bergen 3. University of Bergen, Bergen
Introduction • Tusk is a deep sea fish species which previously has shown relatively high mercury concentrations in Norwegian waters • Also more knowledge is needed on mercury in other deep sea species caught in the same areas as tusk • During 2013-2016, 2773 fish of tusk, ling and 14 other species were sampled and analysed for Hg in fillet with a focus on seafood safety
Results and discussion Variation between species • Tusk (N = 1396) had the 4th highest mean Hg, with 19% > maximum level (ML) of the EU • Highest Hg in two cartilaginous fish species, blackmouth catshark (N=3) and ratfish (N=25), and bony fish blue ling (N=48) mainly caught in fjords • Ling (N = 822) had lower levels of Hg than tusk in almost all areas • Most other species had lower concentrations than tusk and ling Variation between areas • Hg levels in tusk, ling and haddock showed increasing trends from north (Barents Sea) to south (Skagerrak) • In the North Sea area, Hg levels generally increased from open ocean to enclosed fjord areas • Tusk from fjords on the west coast of southern Norway had relatively high Hg levels, even where no particular Hg source is known • For Sognefjorden, this has led to a dietary warning issued by the NFSA (Norwegian Food Safety Authority)
0.8
Tusk N = 1396
0.7 Barents Sea
EU maximum level
0.5
C 0.4
C
0.3 0.2
Norwegian Sea
AY
0.1 RW NO
Mean Hg mg/kg ww 1.5
Barents Sea
Norwegian Sea
North Sea
Skagerrak
NE Atlantic
0.75 0.15
Figure 1. Tusk sampling positions showing mean Hg levels 0.7
Common ling N = 822
0.6 Barents Sea
Hg (mg/kg ww)
0.5
Common ling (Molva molva) Ocean Coast Fjord
48
0.45 ± 0.36 (0.36)
0.12 - 2.0
29 %
1396 0.34 ± 0.33 (0.23)
0.005 - 2.7
19 %
18
0.19 ± 0.06 (0.18)
0.095 - 0.29
0%
822
0.18 ± 0.14 (0.15)
0.007 - 1.1
4.6 %
7
0.17 ± 0.08 (0.14)
0.038 - 0.28
0%
18
0.15 ± 0.07 (0.15)
0.031 - 0.27
0%
28
0.15 ± 0.12 (0.10)
0.058 - 0.49
0%
59
0.12 ± 0.04 (0.11)
0.069 - 0.25
0%
46
0.12 ± 0.11 (0.090)
0.024 - 0.67
0%*
0.12 ± 0.05 (0.12)
0.051 - 0.23
0%
0.11 ± 0.04 (0.12)
0.035 - 0.17
0%
0.070 ± 0.060 (0.052) 0.014 - 0.41
0%
0.063 ± 0.037 (0.056) 0.014 - 0.15
0%
0.030 ± 0.023 (0.020) 0.008 - 0.09
0%
b) 13 Bycatch species N = 327
C
Barents Sea
Barents Sea
0.3
ABE AB
AB
B
Mean Hg (mg/kg ww)
E
BE BCE
0.5 0.25 0.05
Skagerrak
Norwegian Sea
NE Atlantic
Mean Hg (mg/kg ww)
Northeast Atlantic
0.17
North Sea
Figure 3. Ling sampling position showing mean Hg levels Table 2. At different Hg levels, aamount of fish a 70 kg person can eat per week within tolerable weekly intake (TWI) of 1,4 µg/kg bw. Meals/wk Examples at TWI 0.47 Tusk, Hardangerfjorden, average 0.68 Tusk, Sognefjorden, average 0.91 EU's maximum level 1.3 Tusk average, ling from Hardangerfjorden 1.5 Tusk from the North Sea Tusk from Norwegian Sea south of 68°N, ling 2.3 average, hake average Tusk from open sea and coast north of 68°N Haddock average
Rose fish Beaked redfish
Figure 4. Ling. Geographical variation in Hg. Letters denote significant differences based on ANOVA on logHg.
0.28 0.056
Norwegian Sea
AY
North Sea
Whiting
RW
Norwegian Sea
Northern wolffish
NO
AY RW NO
Barents Sea
Mean Hg (mg/kg ww)
4.6 6.5
72 %
0.1
0.56
0.1 910 0.07 1300
0.33 - 0.83
a) Haddock N = 227
A
Northeast Atlantic
Hg Fish/wk at (mg/kg) TWI (g) 1.0 94 0.67 136 0.50 182 0.34 268 0.3 303 0.2 455
0.58 ± 0.14 (0.62)
EU maximum level
0.4
Norwegian Sea
25
Whiting 30 Merlangius merlangus Atlantic cod 6 Gadus morhua Haddock 227 Melanogrammus aeglefinus Spotted wolffish 27 Anarhichas minor Northern wolffish 12 Anarhichas denticulatus
% > ML (0.5 mg/kg) 0%*
D
0.2
North Sea
Species Blackmouth catshark Galeus melastomus Rat fish Chimaera monstrosa Blue ling Molva dipterygia Tusk Brosme brosme European hake Merluccius merluccius Common ling Molva molva Beaked redfish Sebastes mentella Rose fish Sebastes norvegicus Pollock Pollachius pollachius Greater forkbeard Physis blennoides Atlantic wolffish Anarhichas lupus
AY
Skagerrak
B
Figure 2. Tusk. Geographical variation in Hg. Letters denote significant differences based on ANOVA on logHg.
Northeast Atlantic North Sea
C
AC
A B
0.0
C
3
Hg (mg/kg vv) Mean ± SD (median) Min - Max 0.65 ± 0.30 (0.69) 0.33 - 0.93
N
RW
Boknafjord
D
0.6
Hg (mg/kg ww)
Hardangerfjord
D
Table 1. Concentrations of Hg in each of the 16 analysed fish species.
NO
Sognefjord
Tusk (Brosme brosme) Ocean Coast Fjord
Materials and methods • Sampling by fishermen 2013-2016 • 25 tusk, 25 ling and up to 6 + 6 “bycatch” species at each position • Fish were filleted and skinned • Fillets from each individual fish were homogenized, freeze-dried and analyzed separately • Analysis by ICP-MS after decomposition in microwave (Julshamn et al. 2007)
Skagerrak
Greater forkbeard Ratfifsh Pollack Hake Atlantic wolffish
Northeast Atlantic
0.085 0.017
Spotted wolffish Atlantic cod
North Sea Skagerrak
Blue ling Blackmouth catshark
Figure 5. Sampling positions with mean Hg for a) haddock and b) 13 «bycatch» species Food safety considerations for consumption of tusk • Tusk can accumulate high Hg levels compared to most other species • In some areas, levels of Hg in tusk are high enough to pose a risk for high consumers of locally caught tusk, and warnings have been issued against eating tusk from Sognefjorden and Hardangerfjorden • Consumption of commercially caught tusk is moderate to low and mainly in open sea where Hg levels are lower than in fjords Acknowledgements This project was funded by the Norwegian Food Safety Authority. Institute of Marine Research coordinated the sampling done by 23 different fishermen. All analyses were performed at NIFES. Thanks to all who contributed!
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