Lanna Harder posted a message on 24 January about mercury in stated species
of fish, and asking for more information.
If the statement she includes in quotes is an exact quotation of the
official position then all packages of these species will always have to
carry the warning label, but so should all packages of fish as all fish
contain mercury. The issue should be what constitutes an excessive mercury
content, that is, one is harmful to the consumer. I believe the current
action level in the USA for mercury content of fish is 1 ppm, but I am not
sure if that applies to specific species or to all species of fish. It is
not clear to me why the State Attorney is asking grocery chains to go
further than regulations require, but it is not up to me to comment on that;
I would like to address the question of more information and databases.
I am not aware of a comprehensive, readily available, compilation of data on
mercury contents of fish, though there is much information in various
reports and in papers in journals. The best, clearly written, and quite
comprehensive, review of aspects of mercury in fish and implications for
human health that I have come across is: Johnston, J.N. & Savage, G.P.,
1991, Mercury consumption and toxicity with reference to fish and fishmeal,
Nutrition Abstracts and Reviews (Series A), 61, 74-116. A publication
dealing with human health aspects is: World Health Organization, 1990,
Environmental Health Criteria, No. 101: Methylmercury, ISBN 92 4 157101 2,
WHO, Geneva, Switzerland. Pollution-related matters are reviewed in :
GESAMP, 1986, IMO/FAO/UNESCO/WMO/IAEA/UN/UNEP Joint Group of Experts on the
Scientific Aspects of Marine Pollution. Review of potentially harmful
substances - Arsenic, mercury and selenium, Reports and Studies GESAMP 28,
International Maritime Organization, London. You should be able to consult,
borrow or copy these publications through a University library. There is a
report by the National Academy of Sciences, Toxicological Effects of
Methylmercury (2000), which can be read on the NAS web site, but this covers
more aspects than just mercury in fish.
The Johnston & Savage review includes a table of mercury contents, or rather
ranges of mercury contents, of many species of fish culled from published
literature. Values, in ppm, for tunas are:
yellowfin, 0.06-1.32
skipjack, 0.27-0.52
swordfish, 0.03-4.4.
For 'canned tunas of various species', the values are 0.04-1.00.
You might like to note 3 species not listed by the State Attorney, but which
are recorded in the table to have high mercury contents:
marlin, Makoira ampla, 0.35-14.0
snapper, Chrysophrys auratus, .010-1.5
red snapper, Lutjanus campechanus, 0.28-1.46.
The values are as total mercury. The form of mercury in fish of most concern
to toxicologists is methylmercury, but in fish with high contents of mercury
more than 90% of the mercury is in the organic form so values just listed
reflect the toxic hazard to humans. What is striking about these data is the
wide range in mercury contents. The general mercury content in the oceans is
<0.05ppm, but much higher contents are found in localized areas. These are,
for example, waters receiving pollution from chemical processes, (the
Minimata episode), from geochemical processes - run-off from rivers draining
mercury-ore bearing rocks, areas of geothermal vents, and areas of volcanic
activity. The natural process are much more important for injecting mercury
into the marine environment than pollution. Mercury, in its organic form,
accumulates up the food chain so high concentrations are found in highly
predatory species in areas of high mercury content in the water. It also
accumulates over the lifetime of the fish so older, and hence, within a
species, higher concentrations are found in larger fish. Given these sources
of natural variation, it is not surprising to find variation in measured
mercury contents between and within species. It is possible that some of the
data in the Johnston & Savage review come from material deliberately sampled
from areas of known or expected high mercury content as an objective of the
investigation, and might not reflect values in fish generally presented for
sale.
There must be a large database of mercury contents in tunas in the records
of tuna canning companies. In many countries the limit for mercury content
of canned food is set at the lower limit of 0.5ppm and quite strictly
enforced by surveillance. For example, Yess, N.J. 1993, U.S. Food and Drug
Administration survey of methyl mercury in canned tuna, Journal of AOAC
International. 76, 36-38, reports the results of analyzing 220 samples of
canned tuna. The mean methylmercury content was 0.17ppm and a range
<0.1-0.75ppm. The paper refers to 2 previous surveys by the FDA with similar
results. Again, these values might not, in fact are unlikely to be,
representative of values of mercury in raw tuna offered in grocery chains.
The canners deliberately select smaller sizes of fish to lower the
probability of getting high mercury contents, and possible select from
fishing areas known not to result in fish with high mercury contents.
Methylmercury accumulates in the oil component of the flesh and in those
processes involving a precooking step - loss of oily cook liquor - and
removal of dark meat - high in oil - the mercury content of the canned meat
could be lower than in the raw material. I haven't seen any reports on a
comparison of mercury contents in fish before or after canning to confirm
this expectation, but I suppose there are some out there.
I wrote above I was not aware of a readily available database on mercury
contents of fish, but a report to the Codex Alimentarius Commission's
Committee on Fish and Fishery Products meeting in 1994 provides extensive
data. The reference is: Definition of predatory species of fish to which the
higher levels of methyl mercury applies, CX/FFP 94/15. It is included in the
papers attached to the report of the 21st session of the Committee and I
have searched the Codex web site, but the report, though listed , is not
available for view either in HTLM or PDF format, (many are). Interested
readers might be able to get a copy thorough their country representative
bodies on Codex committees. The background to the title is that regulatory
agencies in some countries impose 2 limits on mercury content in fish, one,
typically 0.5ppm, for non-predatory species, another, 1ppm, for predatory
species. The report presents data on mercury contents of fish as a help
towards harmonising lists of what could be 'predatory' species. The data in
the report is culled from the GEMS database of WHO. This is data on
contaminants in food supplied by governments and might not necessarily have
appeared elsewhere. The data are summarised for a fish species as median and
the 90th percentile values. Almost all the values are based of sample sizes
in at least the tens and some in the thousands. I will list some pertinent
values as the trivial name of the fish (zoological names are not given),
country of sampling, sample size in brackets, median and 90th percentile:
albacore tuna Spain (3 129) 0.49 0.95
bigeye tuna Spain (3 727) 0.81 1.60
bluefin tuna Spain (16 032) 0.6 1.18
yellowfin tuna Spain (15 431) 0.48 0.92
skipjack tuna Spain (2 740)1.10 2.00
tuna fish USA (29) 0.13 0.49
marlin New Zealand (34) 1.20 1.40
swordfish Spain (7853) 1.53 3.03
swordfish USA (45) 1.00 1.50
swordfish USA (65) 1.00 1.65
swordfish USA (33) 1.20 1.80
swordfish USA (11) 1.10 1.40
porbeagle Spain (7049) 2.12 4.20
shark USA (28) 1.40 2.45
Leanna, I do not know what you can conclude from all this for the purpose of
labelling. If the data above are representative of what is for sale in the
USA, of the tunas, it seems to me that it might not be necessary to label
yellowfin tuna as being harmful, bigeye and bluefin possibly to be on the
safe side, skipjack definitely. Swordfish and shark definitely, and marlin
too if it comes your way.
A footnote for you to ponder over. The state whose population has the
highest per caput consumption of fish is the Maldive Islands at
165kg/person/year, live weight, about 100kg edible portion weight,
contributing 96% of the consumption of animal protein. Almost all of this is
tuna and mostly of the small-sized species - skipjack, bigeye, little -
though not necessarily small-sized specimens of the species. Consumption of
100kg/year edible portion is equivalent almost to 2 main course portion/day.
Compare that with the usual advisories in the USA about consumption of tuna.
I am not aware of any surveys of the health of the citizens of the Maldive
islands, nor of any values for typical mercury contents of the tunas they
consume, but it could be worth an investigation. I could not find anything
pertinent on the PubMed web site.
Peter Howgate
----- Original Message -----
From: "Leanna Harder" <rsmoker@northcoast.com>
To: "Seafood @ UC Davis" <seafood@ucdavis.edu>
Sent: Friday, January 24, 2003 8:07 PM
Subject: methyl-mercury
> Good Morning Listers.
> Recently there was an article in the San Francisco Chronicle (Sat. Jan.
> 18, 2003)
> where (I'm quoting) "State Attorney General Bill Lockyer is suing five
> grocery chains that operate in California, seeking to make them post
> warning labels on packages of swordfish, shark and fresh tuna that
> contain mercury."
> It goes on and names stores and the Prop. 65 a1986 voter-approved
> initiative that requires businesses to notify customers if they are
> being exposed to toxic chemicals.
> I'm not sure if its ok to talk about this on listserve. We are a small
> business supplying some stores in northern California with frozen
> albacore loins smoked albacore, frozen ahi and smoked ahi named in this
> article. Some of the stores have pulled these products from their
> market for now until there is further information.
> 1.Does anyone know where I can find anyfurther info on this topic and,
> 2.Can anyone tell me if there is a data base or where I can find out how
>
> much mercury is in my products- do I need to have testing done?
> Thank you in advanced
> Leanna Harder
>
>
>
>
>
>
>
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