Dear All,
The salmon paper made it to the 6pm TV news here in Brisbane,
Australia last night. It was quite a long report showing the farms in the
Nthn Hemisphere and in Aust. Highlighting that the listed chemicals were way
less than all legal limits and that the EU farms had the worst problems and
then finishing off with pics of the PETA demostraters in Europe. And
interveiwing an Aust salmon farmer saying how wonderful and clean are our
salmon here.
Clare Winkel
-----Original Message-----
From: owner-seafood@ucdavis.edu [mailto:owner-seafood@ucdavis.edu]On Behalf
Of howgate
Sent: Saturday, 10 January 2004 7:09 AM
To: Santerre, Charles; seafood@ucdavis.edu
Subject: Re: Response to manuscript in Science - Farmed Salmon Safety
Oh dear! Another report, (Ronald A. Hites, R.A. et al., (2004), Global
assessment of organic contaminants in farmed salmon, Science, 303, 226-229),
finding that farmed salmon contain Highly Chlorinated Hydrocarbons (HCHs) in
the flesh. This is becoming an annual event. The topic was raised on the
Listserve last March following the EWG report (Easton, M.D.L., Luszniak, D.
& Von der Geest, D., (2002), Preliminary examination of contaminant loadings
in farmed salmon, wild salmon and commercial salmon feed. Chemosphere,
46,1053_1074). In early 2001 was the report by Jacobs et al (Investigation
of PCDDs, PCDFs and selected coplanar PCBs in Scottish farmed Atlantic
salmon (Salmo salar), Organohalogen Compounds, 47, 338_341). What does the
new study tell us that we don't already know? In fact very little, but in
more detail. Hites and co-workers measured HCHs in 700 or so samples of
farmed Atlantic salmon and wild Pacific salmon of several species. The
authors reported they did not sample wild Atlantic salmon because "... few
are available commercially..." , nor
farmed Pacific salmon " ... because they are not raised in any substantial
amounts ...". I note that the Jacobs et al study included wild Atlantic
salmon and the Easton et al study included farmed pacific salmon. The
authors therefore compared farmed Atlantic salmon with wild Pacific salmon.
Readers should decide for themselves whether this is an helpful or
meaningful comparison.
The results showed that for all HCHs measured mean concentrations in the
Atlantic salmon were significantly higher than in the Pacific salmon.
Comparisons of data on HCH concentrations in foods is a bit of a minefield
because of different ways of expressing concentrations. The Hites paper
shows summary data in the form of figures and expressed on a wet weight
basis except for what they list as 'dioxins' for which concentrations are
expressed at TEQs wet weight basis. PCBs and dioxins exist as many isomers
only a few of which are considered toxic and raw concentrations are weighted
by Toxic Equivalency factors (TEQ) for the individual isomers to give an
index expressing the relative toxicity of the totality of contaminants in
the sample. Some PCB isomers are considered to have similar toxic effects as
dioxins so the weighted PCB and dioxin concentration are usually added to
give an overall toxicity value. Hites and co-workers have done this and
their 'dioxin' values are combined TEQs for PCB and dioxin. Hites et al find
that Atlantic salmon sampled in Europe and Scandinavia have 'dioxin'
concentrations as TEQ wet weight basis of between 2 and 3 picog/g. Salmon
purchased in the USA and Canada, which are assumed to be predominately of
Chilean origin, are in the range 1-2 picog/g, and Pacific salmon are less
than 0.5 picog/g. The values for Atlantic salmon are comparable with those
found in other surveys of farmed salmon, though sometimes comparisons are
not direct because some surveys express concentrations on a lipid basis
rather than a wet weight basis and need to be corrected by the known or
assumed lipid content of the sample. Hence my conclusion expressed above
that the Hites et al paper has not told us anything we did not already know.
I consider it a major weakness of the Hites et al paper that the authors
do not make any comparisons of their data with those from other surveys. In
their bibliography they cite the Easton and the Jacobs studies I have
referred to above, but do not summarise the results and do not cite any
other reports. They do not report the results from food surveys in the UK
that show that concentrations of PCBs/dioxins in foods are decreasing quite
markedly over time; the estimated average dietary intake by adults in the UK
has fallen from 1.8 picog/kg body wt/day in 1997 to 0.9 picog/kg body
wieght/day in 2001. The authors should point out that concentrations of
PCBs/dioxins in the environment, including the aquatic environment, are
decreasing over time and risks to human health will reduce over time. The
authors have not summarised and compared data on PCBs/dioxins in species
other than salmonids some of which show concentrations higher that those
reported for farmed Atlantic salmon.
Hites et al acknowledge that "Individual contaminant concentrations in
farmed and wild salmon do not exceed U.S. Food and Drug Administration (FDA)
action or tolerance levels for PCBs and dieldrin", but do not comment on the
other HCHs. I have not attempted to find tolerable levels - if they exist -
for the other HCHs, but as the authors do not comment on risks for these
other contaminants I assume they are within limits. Though the authors cite
US FDA tolerance levels, the concentrations of combined PCBs and dioxins
expressed as TEQs are within the WHO recommendations which have been adopted
in many countries including the UK. Hites et al have determined the risks
from the US FDA model for fish advisories and have come up with the advice
shown in Figure 4 in their report - less than one meal/month of farmed
Atlantic salmon. They give no estimates of the confidence of these
estimates. Smith, G.C., et al. (2002, Intake estimation of polychlorinated
dibenzo_p_dioxins, dibenzofurans (PCDD/Fs) and polychlorinated biphenyls
(PCBs) in salmon: the inclusion of uncertainty. Food Additives and
Contaminants, 19, 770_778) have pointed to many uncertainties in estimating
the health risks of consumption of PCBs/dioxins.
Am I getting cynical and suspicious in my old age, or do I detect a
campaign behind this paper. The news about this study broke in the TV
teletext a little before 10.00 p.m local time (GMT). I checked the BBC web
page and found the news item which was clearly a press release. I was a bit
suspicious of this as I would not expect the BBC news editors to be pick up
a topic from Science on the day it was published. Though the item did not
acknowledge the source it included a link to Hites at the University of
Indiana and I asked for a copy of the copy. I was amazed to get it almost by
return; the actual times on the e-mail messages are 10.04 GMT for the
request and 10.08 GMT for the reply and attachment. The office in the
University must have been expecting responses to the press release. I note
that the authors of the paper acknowledge that "This research was initiated
and supported by the Environmental Division of the Pew Charitable Trusts.".
Note the 'initiated'. Environmental pressure groups have mounting a campaign
against salmon farming for some years now and it seems to me this study was
initiated as part of such a campaign rather that to objectively examine the
risk to human health of contaminants in fish.
Peter Howgate
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