Mark Thorson wrote:
> "Pete C." wrote:
>> Mark Thorson wrote:
>>> This study gives numbers comparing farmed vs. wild,
>>> and there's a huge difference, especially at the
>>> high end of the range.
>>>
>>> Environ Sci Technol. 2006 Sep 1;40(17):5347-54.
>>> PCBs, PCDD/Fs, and organochlorine pesticides in farmed
>>> Atlantic salmon from Maine, eastern Canada, and Norway,
>>> and wild salmon from Alaska.
>>> Shaw SD, Brenner D, Berger ML, Carpenter DO, Hong CS,
>>> Kannan K.
>>> Marine Environmental Research Institute, P.O. Box 1652,
>>> Blue Hill, Maine 04614, USA.
>>>
>>> Farmed Atlantic salmon (Salmo salar) from Maine and
>>> eastern Canada, wild Alaskan Chinook salmon (Oncorhynchus
>>> tshawytscha), and organically farmed Norwegian salmon
>>> samples were analyzed for the presence of polychlorinated
>>> biphenyls (PCBs), dioxin-like PCBs, polychlorinated
>>> dibenzo-p-dioxins (PCDDs), dibenzo-p-furans (PCDFs), and
>>> chlorinated pesticides. PCDD and PCDF congeners were not
>>> detected in > 80% of the samples analyzed. Total PCB
>>> concentrations (7.2-29.5 ng/g, wet weight, ww) in the
>>> farmed salmon were significantly higher than those in
>>> the wild Alaskan Chinook samples (3.9-8.1 ng/g, ww).
>>> Concentrations of PCBs, WHO PCB TEQs, and chlorinated
>>> pesticides varied significantly by region. PCB and WHO
>>> PCB TEQ concentrations in farmed salmon from eastern
>>> Canada were lower than those reported in samples
>>> collected two years earlier, possibly reflecting recent
>>> industry efforts to lower contaminant concentrations in
>>> feed. Organically farmed Norwegian salmon had the highest
>>> concentrations of PCBs (mean: 27 ng/g, ww) and WHO PCB
>>> TEQs (2.85 pg/g,ww); their TEQ values are in the higher
>>> range of those reported in farmed salmon from around the
>>> world. Removal of skin from salmon fillets resulted in
>>> highly variable reductions of lipids and contaminants,
>>> and in some skin-off samples, contaminant levels were
>>> higher, suggesting that skin removal does not protect
>>> the consumer from health risks associated with
>>> consumption of farmed salmon.
>> What I see from that data is that levels in both are quite variable, and
>> indeed some of the farmed samples had lower levels (7.2 ng/g) than some
>> of the wild samples (8.1 ng/g).
>>
>> Showing just the high and low of a group of samples is misleading since
>> you don't know what the distribution is. Those extremes may represent
>> only one sample, and make it very easy to distort the data to fit an
>> agenda. The only mean value given was for the organic farmed Norwegian
>> samples.
>>
>> It's entirely possible that most of the samples from both groups were in
>> the 7-8 ng/g range showing no difference between farmed and wild, or
>> most of the wild near 4 ng/g and most of the farmed near 29 ng/g showing
>> a huge difference.
>>
>> Again, it's incomplete data and subject to presentation in a manner that
>> may be misleading. Either way we're talking about extremely low levels.
>
> It's an abstract. The authors' conclusions are given
> in the abstract, but the detailed data is in the full
> paper, which is not online.
>
> But no competent scientist would make an assertion
> in an abstract that wasn't backed up by their data.
>
> Environ Sci Technol. 2005 Oct 1;39(19):7389-95.
> Polychlorinated biphenyls in salmon and salmon feed:
> global differences and bioaccumulation.
> Carlson DL, Hites RA.
> School of Public and Environmental Affairs, Indiana
> University, Bloomington, Indiana 47405, USA.
>
> Concentrations of 160 polychlorinated biphenyl (PCB)
> congeners or congener groups were determined in approximately
> 600 farmed Atlantic salmon from around the world and wild
> (ocean-caught) Pacific salmon from the Northeast Pacific.
> Concentrations and PCB congener profiles were analyzed
> to provide insight into the sources and uptake of PCBs in
> salmon as well as regional differences. Although total PCB
> concentrations in wild salmon appeared to be correlated to
> total lipid content, the increased proportion of total lipids
> in the farmed salmon could not account for the much greater
> PCB concentrations. We investigated the PCB congener patterns
> of hundreds of salmon samples using principal component analysis
> to further illuminate regional and species differences. Three
> major PCB patterns were observed, in most wild fish (except
> British Columbia and Oregon chinook), in farmed fish from the
> Atlantic, and in most farmed fish from the Pacific. The PCB
> congener profiles of farmed salmon often closely corresponded
> to a sample of commercial feed purchased in the same region,
> indicating that the feed is likely to be the major source of
> PCBs for farmed salmon. In such cases where PCB profiles in fish
> and feed were similar, a comparison of congener concentrations
> in fish and the feed showed that the majority of congeners, with
> some notable exceptions, were bioaccumulative to the same extent,
> irrespective of physical properties.

Here's the solution to all of this. Those who don't care may
continue to eat farm-raised fish, and those of us who do care will
not eat it.... Other than environmental ramifications,
cross-breeding, escapes, etc., that seems appropriate....

--
Jean B.