View source for DA: Recommend restrictions to farmed salmon use?

Thic page contains the discussion in Science related to an article by Hites et al (2004).

=Structure of the assessment=

==Focus==
To study the recommendation about eating or not eating farmed salmon; and explore decision about actions on feed contaminants.

==Scope== 
* Both health risks and benefits related to consumption of farmed salmon are included.
* Monetary issues are excluded.
* Health effects: Total mortality, cardiovascular mortality, total cancer incidence and mortality, breast and liver cancer incidence
* Population: Adults in Western Europe (European Economic Area)
* Pollutants: Toxaphene, dieldrin, dioxin, PCB
* Nutrients: Omega-3 fatty acids
* Decision: see focus
* Time: Current situation, no dynamics, no discounting
* Methods used: Existing literature
* Environmental effects: not included

Describe the value judgements.

==Causal chain==
* '''Driving force:''' Fish is a good food and farmed salmon is easily available with a reasonable price.
* '''Pressures:''' Fish is healthy, but on the other hand it contains pollutants such as pesticide residues (Toxaphene, dieldrin) and persistent organic pollutants (dioxin, PCB).
* '''States:'''
** Farmed salmon consumed: Data comes from EPIC study looking at fish consumption in 10 European countries by gender. We take the minimum, the unweighed average and the maximum of these values (7.5, 15.3, 31 g/d) in the distribution to represent uncertainty in population average fatty fish intake. All fatty fish is assumed to be salmon.
** Pollutant concentrations in farmed salmon (in µg/kg in fresh weight): 
Dieldrin 3.299, 
Toxaphene 96.14, 
Dioxin 1.891e-003, 
PCB 36.25. 
Data according to Hites et al, 2004.
* '''Exposure:''' Pollutant exposures in general population (in µg/kg/d): 
Dieldrin 7.417e-004, 
Toxaphene 0.02094, 
Dioxin 4.209e-007, 
PCB 8.105e-003
Data according to Tuomisto et al, 2004 model
* '''Effects:''' 

** Dispute
*** Dose-response function has a threshold or may even be U-shaped.
*** Dose-response function is linear. In this assessment adopts this latter approach.


{|Border="1" cellspacing="0"
|+'''Pollutant effects (cancer mortality) cases/a'''
| ||BAU||More limits on feed pollutants
|-
|BAU||-205.5||-138.7
|-
|Recommend consumption restrictions||-149.3||-101.1
|-
|}

{|Border="1" cellspacing="0"
|+'''Net health benefit (cancer+cardiovascular) cases/a''')
| ||BAU||More limits on feed pollutants
|-
|BAU||31300||31680
|-
|Recommend consumption restrictions||23050||23430
|-
|}
Data according to Tuomisto et al, 2004

*'''Actions:'''

{|Border="1" cellspacing="0"
|+'''Expected farmed salmon intake after actions (g/d)''')
| ||BAU||More limits on feed pollutants
|-
|BAU||16.13||16.3
|-
|Recommend consumption restrictions||11.75||11.91
|-
|}
Data according to Tuomisto et al, 2004

==Value judgements==
* Values:
**Alternatives for farmed salmon are better, because they contain less pollutants: wild salmon, other fish, canola oil, flaxseed oil.
**Disgreement on the optimising strategy
*** Net health benefit (public health) should be the main prioirity.
*** Pollutant effect should be the main priority, and consumers themselves decide about the public health issues based on information provided.
* Conclusions:
** Pollutant risk is much smaller than the net health benefit of farmed salmon
** Some scientific and political uncertainties related to feed limits are important
** Scientific uncertainties related to recommendations are unimportant
* Questions:
** Should we change fish feed instead of giving fish consumption advisories?
** What has been done and what should be done to reduce pollutants in fish feed?
** Does omega 3 help other people than CHD patients?

==Synthesis==

=The Health Benefits of Eating Salmon=  
# THE RECENT REPORT BY R. A. HITES ET AL. about toxic contaminants in salmon (“Global assessment of organic contaminants in farmed salmon,” 9 Jan., p. 226) may have unintended negative consequences on human health.  
# Yes, the source of toxic contaminants in farmed fish should be investigated and reduced as much as reasonably possible, but the proven health benefits of omega-3 fatty acids should not be overlooked.  
#The GISSI prevention trial (1) showed that consumption of 700 mg daily of omega-3 fatty acids from fish reduced total mortality by 20% in Italians with coronary artery disease (CAD).  
#This corresponds to a number needed to treat (NNT) of 49 (95% confidence interval 30 to 175), indicating that one person with CAD avoids death when 49 people eat 21 g of omega-3 fatty acids monthly for 3.5 years.  
#A monthly diet of 21 g of omega-3 fatty acids is present in ~1190 g (42 ounces) of salmon.  
#On the basis of U.S. Environmental Protection Agency (EPA) estimates, Hites et al. suggest that consumption of 55 g monthly of the most contaminated salmon would increase theoretical cancer risk by 1 in 100,000.  
#If cancer risk were linear, 1190 g of salmon monthly would increase cancer risk by 22 cases per 100,000, corresponding to a number needed to harm (NNH) of 4500.  
#This suggests that one person would develop cancer for every 4500 people who eat 1190 g of the most contaminated salmon (21 g of omega-3 fatty acids) monthly.  
#Therefore, the ratio of the NNH for cancer to the NNT for total mortality in people with CAD is 4500/49 = 92.  
#This suggests that 92 Italians with CAD who eat 1190 g of salmon monthly would avoid death for every Italian that develops cancer.  
#This analysis suggests that eating even the most contaminated salmon has clear health benefits.  
#Clearly, salmon with fewer contaminants or other clean sources of omega-3 fatty acids would be better, but avoidance of salmon to avoid these contaminants without replacing the omega- 3 fatty acids from other sources would have adverse health implications.  
#The quality of the evidence in favor of the benefits of omega-3 fatty acids in people with CAD is high: The GISSI prevention trial was a randomized clinical trial.  
#The GISSI trial estimates were only for 3.5 years of treatment.  
#The benefit is likely greater for more prolonged treatment. 
#In contrast, the EPA guidelines are estimates based on nonhuman toxicity or observational studies: There is no clinical trial showing that these toxins, when given to humans, cause cancer.  
#Overall, this analysis suggests that ingestion of salmon should not be limited, especially in people with CAD.  

CHRISTOPHER M. REMBOLD  

University of Virginia, Box 801395, Charlottesville, VA 22908, USA.  

Reference 1. F.Valagussa et al., Lancet 354, 447 (1999).  

==Response==  

#REMBOLD RECOMMENDS THAT THE “INGESTION of salmon should not be limited, especially in people with [coronary artery disease].” 
#As we acknowledge in our Report, there are health benefits associated with consumption of omega-3 fatty acids from fish, and calculation of the overall riskbenefit of contaminants in fish that are high in heart-healthy fats is challenging.  
#To date, there has been no comprehensive assessment of the risk/benefit trade-offs associated with the consumption of such fish.  
#In fact, the most recent scientific statement from the American Heart Association, although recommending fish as a heart-healthy food, states that “the fish recommendations must be balanced with concerns about environmental pollutants, in particular PCB and methyl mercury…” (1).  
#In addition, omega-3 fatty acids do not protect against cancer (2).  
#To complicate matters, the contaminants we report in salmon are also associated with a variety of noncancer effects.  
#Of particular note are the anthropometric and neurobehavioral effects of PCBs in children exposed in utero and during early childhood (3).  
#A comprehensive risk/benefit analysis for contaminated, farmed Atlantic salmon must account for all health risks associated with exposure to contaminants in these fish.  
#Nevertheless, such an assessment, although helpful, is not essential to protect public health because there are many alternative sources of omega-3 fatty acids that have considerably lower contaminant concentrations, including wild Pacific salmon.  
#These sources include other seafood that is not contaminated and nonfish foods, including flaxseed, walnut and canola oils, nuts, and legumes.  
#One does not need to eat contaminated salmon to consume omega-3 fatty acids.  

RONALD A. HITES,1* JEFFERY A. FORAN,2 DAVID O. CARPENTER,3 M. COREEN HAMILTON,4 BARBARA A. KNUTH,5 STEVEN J. SCHWAGER6  

1School of Public and Environmental Affairs, Indiana University, Bloomington, IN 47405, USA. 2Midwest Center for Environmental Science and Public Policy, Milwaukee, WI 53202, USA. 3Institute for Health and the Environment, University at Albany, Rensselaer, NY 12144, USA. 4AXYS Analytical Services, Post Office Box 2219, 2045 Mills Road, Sidney, BC, Canada V8L 3S8. 5Department of Natural Resources, Cornell University, Ithaca, NY 14853, USA. 6Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, NY 14853, USA. E-mail: HitesR@Indiana.edu  

'''References'''  

1. P. M. Kris-Etherton,W. S. Harris, L. J. Appel, Circulation 106, 2747 (2002). 2. P. D. Terry, T. E. Rohan, A.Wolk, Am. J. Clin. Nutr. 77, 532 (2003). 3. S. I. Schantz, J. J.Widhom, D. C. Roce, Environ. Health Perspect. 111, 357 (2003).

=Risk-Benefit Analysis of Eating Farmed Salmon=

IN THEIR REPORT “GLOBAL ASSESSMENT OF
organic contaminants in farmed salmon,”
R. A. Hites and co-workers analyzed wild
and farmed salmon samples from North and
South America and Europe for organic pollutants
(9 Jan., p. 226). The authors conclude
that, because of chemical contaminants,
farmed salmon should not be eaten more
often than 0.25 to 1 times per month.
However, the model used does not take into
account any beneficial effects of eating fish.

We analyzed the risks and benefits of the
recommendation to reduce the intake of
farmed salmon to 1 meal (227 g) per month.
The authors estimated cancer risk of polychlorinated
biphenyls (PCBs), toxaphene,
and dieldrin using a U.S. Environmental
Protection Agency model, which maximizes
the estimated risk by assuming a linear correlation
between cancer and exposure and by
using upper confidence interval estimates (1).
We included cardiovascular benefits of
omega-3 fatty acids (2, 3), but no other positive
effects associated with fish. We calculated
the benefits as the best available estimates,
being careful not to exaggerate benefits, if
data were sparse.

We also performed a value-of-information
(VOI) analysis (4, 5) for the decision.
There is always uncertainty about the true
values of variables affecting the decision. It
often prevents the decision-maker from
knowing the optimal alternative. VOI is
defined as the expected benefit that occurs
when an uncertainty is resolved, and the
decision can be based on more solid evaluation.
In our analysis, political questions
(other than the decision under analysis) and
scientific uncertainties were both treated in
the same manner as uncertain variables.

The effects were estimated for the
European Economic Area countries (population
387 million). Excess cancer mortality due
to pollutants in farmed salmon was estimated
at 210 cases per year [90% confidence
interval (CI) 110 to 340], supporting restrictive
recommendations. The number of cancer
deaths that could be prevented by the restrictive
recommendation on farmed salmon use
was estimated at 40 deaths per year (90% CI
2 to 110). However, the recommendation
would worsen the net health effect (cancer and
cardiac deaths combined) by 5200 deaths per
year (90% CI 34 to 19,000). It is therefore
clear that if the main concern is the net health
benefit, the decision-maker will not recommend
restrictions. None of the scientific
uncertainties considered, e.g., levels of pollutants
in farmed versus wild salmon (4),
changed this conclusion. The cost of not
knowing (i.e., the VOI) whether pollutant
effect or net health effect should be considered
was estimated at 20 avoidable deaths per
year. As shown above, scientific uncertainties
have little relevance for the decision about
recommending reduction in the intake of
farmed salmon.

[[image:FarmedSalmonVOI.png]]

However, the importance of scientific
uncertainties depends on the decision under
analysis. This is clearly seen when considering
an alternative way to reduce the cancer
risk due to pollutants in farmed salmon. We
analyzed a decision to lower the amount of
pollutants in fish feed. This lowering was estimated
to save 360 deaths per year
(90% CI  3200 to +4100), mainly because of
possible increase in consumption of salmon.
In this case, several scientific and political
uncertainties influenced which decision alternative
appeared to be the optimal one (see
figure). The variable with the largest VOI was
how consumers would change their consumption
of salmon after being informed that
further regulations are needed for fish feed.

In conclusion, the question about
restricting consumption of farmed salmon
appears to be nonscientific, because the
outcome of the analysis was totally driven by
a political variable, whether to ignore the
health benefits of fish. The question about
fish feed regulation was partly scientific and
would benefit from further research.

JOUNI T. TUOMISTO,1 JOUKO TUOMISTO,1,2
MARKO TAINIO,1 MARJO NIITTYNEN,1
PIA VERKASALO,1 TERTTU VARTIAINEN,1,3
HANNU KIVIRANTA,1 JUHA PEKKANEN1

1Centre of Excellence of Environmental Health Risk
Analysis, Department of Environmental Health,
National Public Health Institute, Post Office Box 95,
FIN-70701 Kuopio, Finland. 2Department of Public
Health and General Practice, University of Kuopio
70210, Finland. 3Department of Environmental
Sciences, University of Kuopio, Kuopio 70210, Finland.

'''References and Notes'''

1. U.S. EPA, Guidance for Assessing Chemical
Contaminant Data for Use in Fish Advisory, vol. 2, Risk
Assessment and Fish Consumption Limits. (U.S. EPA,
Washington, DC, ed. 3, 2000).

2. J. N. Din, D. E. Newby, A. D. Flapan, Br. Med. J. 328, 30
(2004).

3. C. R. Harper, T. A. Jacobson, Arch. Int. Med. 161, 2185
(2001).

4. M. G. Morgan, M. Henrion, Uncertainty:A Guide to Dealing
with Uncertainty in Quantitative Risk and Policy Analysis
(Cambridge Univ. Press, Cambridge, 1990).

5. See supplementary online material at Science Online
at www.sciencemag.org/cgi/content/full/305/5683/
476/DC1.

6. This study was funded by the Academy of Finland,
grant 53307, the National Technology Agency of
Finland (Tekes), grant 40715/01, and European
Commission, contract QLK4-CT-1999-01446.

==Response==

TUOMISTO ET AL. PROVIDE AN INTERESTING
analysis of the risk/benefit trade-offs associated
with consuming farmed salmon with
elevated contaminant concentrations. We
agree with their point that any decision
regarding the consumption of a contaminated
food must balance risks and benefits.
As we state in our Report, the presence of
elevated levels of contaminants in farmed
salmon complicates the risk/benefit equation.
Without contaminants, farmed salmon
would indeed be an ideal source of protein,
rich in heart-healthy omega-3 fatty acids.

Cancer risk estimates allow comparison
of the health risks associated with
consumption of farmed Atlantic versus
wild Pacific salmon and demonstrate the
importance of considering alternative
sources of salmon that provide the benefits
of high omega-3 concentrations with
considerably lower contaminant concentrations.
Regardless of the methodological
issues, the risk/benefit equation is clearly
tipped in the direction of net benefit for
fish low in contaminants and high in hearthealthy
fats such as wild Pacific salmon.
Other foods can also provide these same
benefits, without commensurate contaminant-
associated risk.

Tuomisto et al. conclude that reducing
contaminants in fish feed is the most effective
way to reduce risk and preserve benefits
of consuming farmed Atlantic salmon.
We agree with this conclusion, although
further research is required to fully understand
the role of feed in contributing to
tissue concentrations of the chlorinated
organic contaminants in farmed Atlantic
salmon. We understand that some feed
producers have been taking steps to reconstitute
their feed, in part by looking to
substitutes for fish meal and oil (1). We
would expect a reduction in contaminants
in feed as a result, although the process
must be accompanied by a comprehensive
monitoring program to ensure that the
intended benefits are realized. Until then,
consumers need to be aware of the risks, as
well as benefits, of consuming contaminated
salmon so they can make informed
choices based on their own health
concerns.

RONALD A. HITES,1* JEFFERY A. FORAN,2 DAVID O.
CARPENTER,3 M. COREEN HAMILTON,4 BARBARA A.
KNUTH,5 STEVEN J. SCHWAGER6

1School of Public and Environmental Affairs,
Indiana University, Bloomington, IN 47405, USA.
2Midwest Center for Environmental Science and
Public Policy, Milwaukee,WI 53202, USA. 3Institute
for Health and the Environment, University at
Albany, Rensselaer, NY 12144, USA. 4AXYS
Analytical Services, Post Office Box 2219, 2045
Mills Road, Sidney, BC, Canada V8L 3S8.
5Department of Natural Resources, Cornell
University, Ithaca, NY 14853, USA. 6Department of
Biological Statistics and Computational Biology,
Cornell University, Ithaca, NY 14853, USA.
E-mail: HitesR@Indiana.edu

'''Reference'''

1. D. Rideout, Canadian Aquaculture Industry Alliance,
personal communication.

=Cancer Risk and Salmon Intake=

IN THEIR REPORT “GLOBAL ASSESSMENT OF
organic contaminants in farmed salmon,”
R. A. Hites et al. give firm recommendations
for safe monthly intake of farmed
Atlantic salmon on the basis of concentrations
of organic pollutants in raw fish (9
Jan., p. 226). In Norway, the advice not to
eat more than half a portion of farmed
salmon per month (approximately 110 g of
raw fish) received extensive attention
because the estimated per capita intake is
about 200 g of farmed salmon per month.
In the “Norwegian Women and Cancer
study,” there are data that may clarify the
implied cancer risk. In this study (1–3), the
consumption of fish was assessed by postal
questionnaires, with questions on species
(salmon and trout), seasonality, frequency,
and amount eaten. Because wild salmon is not
generally available in Norway, the consumption
information reported here corresponds
mostly to farmed fish. Follow-up was based
on linkage to the Cancer Registry of Norway,
registers of death, and emigration data for
64,674 women with complete information
(mean age = 51.1 years).

[[Image:CancerAndFarmedSalmon.png]]

As shown in the table, the relative risk
for cancer was not increased among
women having a higher self-reported
consumption than among those with less
than the recommended intake. We found no
indication of a dose response.

Dioxin concentrations in Norwegian
farmed Atlantic salmon, based on a larger
sample size, are about 20% lower than those
reported by Hites et al. (4). Our findings
suggest that the cancer risk assigned to PCBs,
dieldrin, and toxaphene is overestimated,
presumably reflecting the inherent uncertainty
in the EPA cancer slope factors employed (5).

Oily fish is an important source of essential
fatty acids and lipid soluble vitamins. The
positive health effects are well documented
for cardiovascular diseases (6). Unilateral
promotion of very limited health hazards
could affect the overall health of populations
by urging people to give up a healthy diet,
causing them to substitute fish with less
healthy and perhaps less safe foods.

EILIV LUND,1 DAGRUN ENGESET,1 ELIN ALSAKER,1
GUN SKEIE,1 ANETTE HJÅRTAKER,2 ANNE-KATRINE
LUNDEBYE,3 EVERT NIEBOR4

1Institute of Community Medicine, University of
Tromsø, 9037 Tromsø, Norway. 2Department of
Statistics, Institute of Basic Medical Science,
University of Oslo, Box 1122 Blindern, 0317 Oslo,
Norway. 3National Institute of Nutrition and
Seafood Research (NIFES), Box 176 Sentrum, 5804
Bergen, Norway. 4Department of Biochemistry,
McMaster University, 1200 Main Street West,
Hamilton, ON, Canada L8N 3Z5.

'''References'''

1. E. Lund et al., Cancer Causes Controls 14, 1001 (2003).

2. E. Riboli et al., Public Health Nutr. 5 (6B), 1113 (2002).

3. Supporting material available at www.ism.uit.no/kk/e

4. A.-K. Lundebye et al., Aquacul. Nutr., in press.

5. U.S. EPA, Guidance for Assessing Chemical
Contaminant Data for Use in Fish Advisories, vol. 2, Risk
Assessment and Fish Consumption Limits (U.S. EPA,
Washington, DC, ed. 3, 2000).

6. P. M. Kris-Etherton et al., Circulation 106, 2747
(2002).

==Response==

LUND ET AL.ADDRESS THE RISK/BENEFIT ISSUE
with a bit of epidemiological data. The risk
assessment used by EPA is to protect
against one extra case of cancer in 100,000
(not the more conservative and usual 1 ×
10 6). Lund et al. report on only 1517 cases
of cancer in a total population of about
61,000. This sample is much too small to
detect elevations at this level of risk. In
addition, the power of the study discussed
by Lund et al. to detect excess cancer risk
associated with consuming contaminated
fish is quite low. Indeed, using a cancer risk
of 1 in 100,000, as we did, gives <1 additional
case of cancer in the 64,000 people
they studied. Furthermore, the “higher
exposure group” in this study (individuals
consuming more than 110 g/month of fish,
or about one-half of a meal per month) is
likely still at the very low end of the exposure
range included in our study. The most
restrictive, risk-based advice for the most
contaminated fish was in this same range,
and the “safe consumption range” of
farmed Atlantic salmon from Norway
(consumption that reduces cancer risk to 1
× 10 5) is approximately one-half of a meal
per month.

Although omega-3 fatty acids do
protect against sudden cardiac death after a
heart attack, young people are not at risk of
heart attacks, but their risk of cancer at
older ages is increased by exposure to these
compounds. In addition, the noncancer
effects of exposures, such as reduced
cognitive function of children exposed
before birth, could overshadow a protective
effect against sudden cardiac death in
young people and were not factored into
the cancer-based risk analysis in our
Report.

RONALD A. HITES,1* JEFFERY A. FORAN,2 DAVID O.
CARPENTER,3 M. COREEN HAMILTON,4 BARBARA A.
KNUTH,5 STEVEN J. SCHWAGER6

1School of Public and Environmental Affairs,
Indiana University, Bloomington, IN 47405, USA.
2Midwest Center for Environmental Science and
Public Policy, Milwaukee, WI 53202, USA. 3Institute
for Health and the Environment, University at
Albany, Rensselaer, NY 12144, USA. 4AXYS
Analytical Services, Post Office Box 2219, 2045
Mills Road, Sidney, BC, Canada V8L 3S8.
5Department of Natural Resources, Cornell
University, Ithaca, NY 14853, USA. 6Department of
Biological Statistics and Computational Biology,
Cornell University, Ithaca, NY 14853, USA.
E-mail: HitesR@Indiana.edu

=Contaminant Levels in Farmed Salmon=

THE REPORT “GLOBAL ASSESSMENT OF
organic contaminants in farmed salmon”
by R. A. Hites et al. (9 Jan., p. 226) reaches
a conclusion that the contaminant levels in
farmed salmon are significantly different
than those in “wild” salmon by making
comparisons between different species of
salmon from different water sources. Yet
there have been many news stories (1) that
provide data indicating that
the levels in “wild” salmon
near areas such as Puget
Sound and the Columbia
River have contamination
levels comparable to the
highest contamination
levels in farmed salmon in
Scotland.

The authors state that “[u]ptake of
organic contaminants from water to fish is
a minor accumulation pathway.” However,
the reference that they cite (2) states that
the relative significance of water for both
uptake and elimination is a function of the
log Kow (octanol/water partition coefficients)
of the specific chemical. The range
of log Kow’s (3) for the chemicals in question
is similar to those of compounds for
which both feed and water can be a source
and contaminant-free water can depurate
(be removed from the organism) (4) on a
reasonable time scale (5).

Without data on the specific contaminants
in the feed and fish, it is not possible
to make an accurate transport model (6).
However, a rough model (7) indicates that
about 90% of the contamination in the
farmed salmon could be from the water,
not the feed. Thus, changing fish farm
locations or installing depuration systems
in a cleaner water area may be a preferable
solution to a contamination problem than
changing fish feed formulations; hence, it
is critical to know the real source of the
contaminants.

DALLAS E.WEAVER

Scientific Hatcheries, 5542 Engineer Drive,
Huntington Beach, CA 92649, USA. E-mail:
Deweaver@surfcity.net

References and Notes

1. For example, see R. McClure, L. Stiffler, “Sound’s
salmon carry high PCB levels,” Seattle Post-
Intelligencer, 15 Jan. 2004 (available at http://seattlepi.
nwsource.com/local/156714_warning15.html),
using data from Washington Department of Fish and
Wildlife PSAM program; see wdfw.wa.gov/fish/
psamp/findings.htm

2. R.W. Russell, F. A. P. C. Gobas, G. D. Haffner, Environ.
Toxicol. Chem. 18, 1250 (1999).

3. A. Sabljic, H. Giisten, J. Hermens, A. Opperhulred,
Environ. Sci. Technol. 27, 1394 (1993).

4. P. N. Fitzsimmons, J. D. Fernandez, A. D. Hoffman, B. C.
Butterworth, J. W. Nichols, Aquatic Toxicol. 55, 23
(2001).

5. F. Verweij, K. Booij, K. Satumalay, N. van der Molen, R.
van der Oost, Chemosphere 54, 1675 (2004).

6. M. C. Barber, Environ. Toxicol. Chem. 22, 1963 (2003).

7. Assuming mass-transport kinetics time constants on
the order of 40 days, food conversion ratios of 1:1
(dry feed/animal wet weight), standard feed tables
(feed rate as a function of size and temperature), and
normal life cycle for Atlantic Salmon.

==Response==

INDEED,THERE ARE ELEVATED CONCENTRATIONS
of contaminants in local populations of
wild Pacific salmon, such as those cited by
Weaver, and in Pacific salmon from the
Great Lakes (which are not sold
commercially). There are
likely other examples of local
contaminant hot spots in wild
Pacific salmon as well.
However, the wild Pacific
salmon from Alaska and
Canada that we collected
make up a substantial portion of wild fish
sold in commercial markets globally. Since
consumers purchase these wild salmon for
consumption, these samples were the most
appropriate for comparison with farmed
Atlantic salmon.

We state in our Report that the most
likely source of contaminants in farmed
Atlantic salmon is the feed. We disagree
with Weaver’s contention that the main
source is the water. Farmed Atlantic
salmon are fed over extended periods of
time a diet of fish feed with elevated
contaminant concentrations. Depuration
would only be pertinent if the contaminant
exposure occurred only at a limited number
of feedings. This is not the case.
Furthermore, the consistency of contaminant
concentrations between farms within
regions, which are likely to use feed
composed of fish from within their region,
suggests that accumulation from feed is the
likely pathway. In addition, it is unlikely
that contaminants from water contribute
significantly because these substances are
not very water soluble. However, further
studies of contaminant sources for farmed
species such as Atlantic salmon are needed.

RONALD A. HITES,1* JEFFERY A. FORAN,2 DAVID O.
CARPENTER,3 M. COREEN HAMILTON,4 BARBARA A.
KNUTH,5 STEVEN J. SCHWAGER6

1School of Public and Environmental Affairs,
Indiana University, Bloomington, IN 47405, USA.
2Midwest Center for Environmental Science and
Public Policy, Milwaukee, WI 53202, USA. 3Institute
for Health and the Environment, University at
Albany, Rensselaer, NY 12144, USA. 4AXYS
Analytical Services, Post Office Box 2219, 2045
Mills Road, Sidney, BC, Canada V8L 3S8.
5Department of Natural Resources, Cornell
University, Ithaca, NY 14853, USA. 6Department of
Biological Statistics and Computational Biology,
Cornell University, Ithaca, NY 14853, USA.
E-mail: HitesR@Indiana.edu


=Argumentation analysis of the discourse=

Hites et al. (original article):<br>
(S) Ingestion of salmon should be limited according to the type (wild/farmed) and the location of catch/raise<br>
&larr; Salmon contains organochlorine contaminants
:&larr; Organochlorine contaminants cause cancer
:&larr; Organochlorine contaminants cause other undesirable health effects
&larr; Farmed salmon contains more contaminants than wild salmon
:&larr; Feed given to farmed salmon contains more contaminants than wild salmon's feed
&larr; European salmon contains more contaminants than USA salmon
:&larr; European feed contains more contaminants than USA feed

(to be continued...)