Lachs auf dem Tisch: Was ist drin in dem Fisch? DOK: LACHS FÜR JEDERMANN Der hohe Umweltpreis der Fischfarmen Film Jeremy Bristow Prod.: BBC/NHU Deutsche Bearbeitung: Andreas Schriber Redaktion: Otto C. Honegger / Beat Wieser
Lachs ist nicht gleich Lachs. Ein Grotssteil der feinen Party-Häppchen und preiswerten Frühstücks-Schnäppchen kommt aus Lachs-Farmen. Das heisst: Intesivhaltung, Massenfütterung und bisweilen auch Antibiotikas - wie bei der Schweinemast. Der Film, gedreht in Grossbritannien, Kanada und Norwegen, zeigt die Folgen: Die wildlebenden Lachse leiden unter der Wasserverschmutzung der Zuchten, zudem stecken sie sich immer wieder mit Krankheiten der Zuchtlachse an. Noch gibt es ihn, den wild lebenden Lachs, aber er ist in Gefahr.
98 Prozent des atlantischen Lachses lebt eingezwängt in Zuchtfarmen. Die Edelfische als Massenware in Intensivhaltung sind ein trauriger Anblick. Allein in Schottland sind in den letzten drei jahrzehnten 300 Lachsfarmen entstanden. An Schottlands Westküste ist der Wildlachs ein seltener Fisch geworden.
Fischer und Wissenschafter sind überzeugt, der Rückgang der Wildlachse sei eine Folge der zunehmenden Parasiten. Und daran seien die Fischfarmen schuld. Doch der Vertreter einer Zuchtlachs-Firma entgegnet, das seien nur Vermutungen: "Die Beweise fehlen." Für gute Resultate manipulieren Fischfarmer an allen Ecken und Enden: Fütterung, Wassertemperatur, Lichtzufuhr und Zuchtauswahl. Die gestressten Tiere sind anfälliger auf Krankheiten und Missbildungen. Aber auch Grösse und Gewicht können manipuliert werden - gentechnisch. Doch damit nicht genug: Etwa 15 Millionen Tonnen Meerfisch werden jährlich in der Fischfarmindustrie verfüttert. Viele dieser verfütterten Fische sind angereichert mit schlecht abbaubaren organischen Giften, wie etwa fiftigen Rückständen aus Industrieabfällen und Pflanzenschutzmitteln. So landen manche Giftstoffe unverhofft in Form von Zuchtlachs auf unserem Teller. Allerdings: In der Schweiz verkaufter Lachs wird regelmässig von kantonalen Lebensmittel-Labors kontrolliert. Und bisher sind den Schweizer Behörden keine Zuchtlachse mit zu hohen Umweltgift-Anteilen ins Netz gegangen.
Erwähnenswert ist, das die giftigen Innereinen der Lachse "rezikliert" werden, sie werden wieder verfüttert!
Die Empfehlung den Verzehr bei einer Portion Lachs pro Woche zu belassen, sollte ernstgenommen werden.
Besonders gefährdet durch die schwer abbaubaren Gifte sind Kinder.
PCB contaminierte Fische sind nachweislich verantworlich für Lernschwierigkeiten. Verusacht nicht wieder gut zu machende Hemmungen in der Entwicklungsphase des Kindes.
Dioxins in farmed salmon: is there a health risk?
At the very start of the year 2001 UK news media reported on the presence of "dioxins" in farmed salmon from several UK farms that would be much higher than the
levels found in wild salmon. These observations were obtained from studies by two scientists, Miriam Jacobs, a PhD-student from Surrey University and Michael
Easton, from the David Suzuki Foudation in Canada. In the news reports it was also said that the consumption of one portion of farmed salmon would exceed the upper
limit of the WHO-recommended tolerably daily intake (TDI) for dioxins, e.g. 4 pg/kg body weight per day for total dioxin toxicity. Taken at face value these reports
certainly seem quite alarming to the consumers as well as to the feed producers and aquaculture industry involved in producing farmed salmon. However, the dioxin
analysis and risk assessment issues are very complex and requires a careful evaluation of the facts and the interpretations to allow for a scientifically justified and
understandable message to the general public. First a number of aspects of the complicated nature of dioxin analysis and risk assessment are given, secondly these
aspects are considered in the light of the press releases on "dioxins in farmed salmon".
1) Some aspects of the complex issues involved in dioxin's risk analysis
What are dioxins?
The term "dioxin" refers to the chemical that was formed in large quantities during an explosion in a herbicide factory in Seveso Italy (1976) causing large scale skin
problems (chloracne). Nowadays, the term "dioxins" refers to a complex group of chemicals, comprising more than 400 compounds, that are persistent, bioaccumulate
in the food chain and are toxic. "Dioxins" can be devided in three main classes of compounds, i.e. polychlorodibenzo-p-dioxins (PCDDs), -dibenzofurans (PCDFs) and
-dioxin-like biphenyls (PCBs). With respect to the "dioxin" contamination found in salmon, and as a matter of fact in all fish species the later group, e.g. the PCBs are
the predominating ones.
PCBs have been produced and used in a wide variety of industrial applications from the 1930s until mid 1980s. Most of the PCBs used in the past have entered the
environment, mainly the aquatic environment. Their resistance to biological breakdown and their tendency to dissolve in lipids have resulted in food chain accumulation
of these compounds, which are nowadays found in in all compartments of the environment and in biota, mainly in aquatic species, such as fish. Among the 209
members of the PCB family, there are 13 congeners showing a dioxin-like toxicity, they are refered to as "dioxin-like PCBs", or sometimes co-planar PCBs (because
planarity is a prerequisite for dioxin toxicity).
PCDDs ansd PCDFs
PCDDs and PCDFs have never been intentionally produced ,or used. They are by-products of e.g., production of organochlorine herbicides, wood preservatives and of
the burning of wastes, both domestic and industrial. There are in total 210 compounds in this family, 17 of which are considered toxic. Although their sources are
different from the PCBs, they have also entered the environment, including the aqueous environment, but to a much lower extent than the PCBs. However, PCDDs and
PCDFs share common environmental fate properties with PCBs, therefore they are also found in lipids, and are accumulated in the food chain.
How are "dioxins" measured?
The "golden standard" for measuring PCDDs, PCDFs and dioxin-like PCBs is the so-called high resolution mass spectrometry (HR-MS) method. The development of
this method has taken over 20 years before one was able to detect and measure the very tiny amounts of these compounds in food and environmental samples. These
levels are generally in the order of picograms per gram of product, i.e. a picogram is 0,000.000.000.001 gram. Therefore extremely sensitive methods of detection,
such as HR-MS are required.
Another complication is, that one has to discriminate, detect and quantify all 17 PCDD and PCDFs, as well as the 13 dioxin-like PCBs, which requires complex and
tedious work-up procedures. The analysis turn around time is long (about 3 weeks) and the costs of dioxin analysis are therefore very high, i.e. about 1000 pounds per
How to quantify dioxin toxicity?
The most complicated part is the quantitation of the dioxin toxicity. The main reason for this is that each individual member of the "dioxins" has a different toxic
potency, e.g. the dose that causes a toxic response is very different for the individual compounds and may range from 1 to 100.000 fold difference. This means that one
can not simply convert, or predict the dioxin toxicity of complex mixtures as found in e.g. food items on the basis of measured concentrations of the chemicals (as is
done by the HR-MS method).
An international group of dioxin experts, under the coordination of WHO has developed a method to calculate the total toxic risk of mixtures of dioxins and dioxin-like
compounds, which is represented by the expression TEQ (total dioxin like toxic equivalence). In order to be able to do this, one had to come up with numbers,
representing the relative toxicity of an individual dioxin, or dioxin-like compound, the socalled toxic equivalency factors (TEFs). The way the translation, or conversion
from chemical data to toxicity data is performed, is as follows:
for each dioxin, or dioxin-like compound its concentration is multiplied by the relative toxicity (TEF factor) and these outcomes are added up to obtain the toxic
equivalence (TEQ) for all dioxins and dioxin-like compounds measured in a sample, e.g. fish.
x TEF1 =
x TEF2 =
x TEF3 =
x TEFn =
Total dioxin toxicity of mixture:
This TEF-method by itself is a reasonably good method to translate a complicated chemical data set into a single number, the sumTEQ, or TEQ.
However, the matter is more complicated than this; first different sets of TEF-values are proposed and used by different scientists and regulators in the past and
presence, and probably different again in the near future; secondly, there are different practises of analysis of dioxins: some only measure the 17 PCDDs and PCDFs
(resulting in I-TEQs, e.g. the list of TEF values for PCDDs and PCDFs only proposed by a NATO expert group and adopted by many European countries in the
beginning 1990s), others include only 3 ,7 or 13 dioxin-like PCBs (which results in WHO-TEQs, with estimates of missing compounds by relative ranges of
occurrence) ; thirdly, the TEF concept assumes additivity of the compounds, but both synergistic and antagonistic interactions between PCDD/Fs and PCBs in particular
have been reported. Thus, it remains difficult to compare different results from different laboratories.
Improved technology for monitoring dioxin-contamination in e.g. food, feed
Recently, new, biologically-based methods (CALUX) have been developed, which directly measure the total dioxin toxic equivalence (TEQ), using cells that light-up
when exposed to dioxins or dioxin-like PCBs. With this method there is no confusion on the TEQ outcome, everyone using this method will always measure all dioxins
and dioxin-like PCBs, there is no TEF number picking game needed. Other advantages of these CALUX methods are that they are more sensitive, much faster and
much cheaper than the chemical methods (HR-MS). These methods will be highly useful for frequent monitoring of dioxin contamination levels in fish feed, fish and
other products and thus will allow for a better quality control of feed and food in the near future.
Where are "dioxins" found?
Dioxins and dioxin-like PCBs are found in every corner of our globe, in each environmental compartment and in our food, feed, and even in human body fluids, like
mother's milk. This is mainly due to man-made activities in the past century, although there still exist sources of new input in the environment, e.g. countries from
former Soviet Union and illegal dumping.
In the aquatic environment the levels of dioxin-like PCBs are higher than of dioxins (PCDDs and PCDFs). In addition, there are higher levels of PCBs in fish from
freshwater areas, where river sediments still contain fairly high levels of these compounds, somewhat lower levels in fish residing mainly in estuaries and lowest levels
in fish from the open seas, oceans. In general there is a slow, down-ward trend in PCB levels in fish and in sediments e.g. PCB levels have dropped by almost 75% at
most locations since the beginning of the 1980s.
Fatty fish usually contain more PCBs per fresh weight than lean fish. This may be different when expressing the results per gram of lipid. Within the fish body, the
PCBs are mainly found in the lipid rich tissues, such as liver. Fish oil therefore, contains most of the PCBs found in fish products. However large differences can be
expected in levels of PCBs in fish oil, dependent on the catchment's site, type of fish and pre-treatment of the fish oil.
At what level are "dioxins" dangerous?
This is a delicate issue and a complicated one. Firstly, to get rid of a frequently noted misconception among the general public, " the mere presence of a toxic compound
in e.g. a food item, is usually conceived as harmful". This is not true, this is totally dependent on whether the dose (level) is high enough to reach a level in the body that
may cause harm".
A second complication in the perception of risk by exposure to dioxins is, that the "highly toxic nature of dioxins is interpreted as causing acute and detrimental toxic
effects early after exposure (e.g. like potassium cyanide causing immediate death). Dioxin's toxicity however, is mainly characterised by its chronic long-term effects
e.g. enhancement of cancer development and effects on reproduction and behavioural development. These toxicities are of a chronic type, that is they are only visible
after extended periods of time following exposure, or after long lasting exposure to low levels of the compounds.
The later aspect "long lasting exposure to low levels of dioxins" is the most problematic aspect of dioxin toxicity and risk assessment. Since dioxins are very resistant to
biodegradation, they accumulate in the human body (in human the half life of dioxins is between 6-10 years, which means that for each quantity of dioxins ingested, it
takes 6-10 years to eliminate half of the ingested amount).
Tolerable daily intake
One of the most crucial aspects in risk assessment of dioxins, as was recognised during the "WHO re-evaluation of the dioxin tolerable daily intake (TDI) in 1998" is the
body burden of dioxins when women are in their child-bearing age. It was first observed in some studies in the Netherlands, Germany, and the USA that children born
to mothers with a relatively high body burden of "dioxins" performed somewhat poorer on a number of cognitive and locomotor function tests. It should be noted
however, that all children performed within the normal clinical range on the tests issued. A negative relationship between "dioxin" body burdens and behavioural test
scores was only visible in a population-based comparison.
These findings were interpreted by the WHO experts as "at background exposure (meaning normal diet, normal environmental contamination levels) women at the upper
bound of "dioxin" body burdens showed the first subtle signs of effects in children. The daily intake of "dioxins" that resulted, after accumulation over time, in the
upper bound body burdens of dioxins was around 10-40 pg TEQ/kg body weight per day in women giving birth to their first child (around the age of 30) Using a safety
factor of 10 (for extrapolation of lowest effect to no effect dose in human) a tolerably daily intake range of 1- 4 pg TEQ/kg BW/day was obtained. This value was
supported by toxicological information in experimental animals.
The WHO expert group advised a TDI range instead of one value, because a) the different end point considered pointed out a range of levels for lowest and for no
observed effects levels, b) the background intake of "dioxins" by the general population in many of the Western industrialized societies is already in the range of 1-2 pg
TEQ kg body weight/per day. Adopting the most stringent TDI of 1, or even below 1 pg TEQ/kg BW/day at once would possibly have to result in banning a high
proportion of food items from our present day's food basket. The advice was focussed on adopting the upper bound TDI of 4 pg TEQ/kg BW/day as soon as possible
and use the 1 pg TEQ/kg BW/day as target value to stimulate industry and governmental regulators to install and use measures to reduce the levels of dioxins in our
The present day's TDI values as reported in the food and drug act of most countries in Europe is still 10 pg TEQ/kg body weight/day. It is anticipated that the TDI values
for "dioxins" as advised by the WHO will soon be implemented, although it is not sure which TDI (the upper, or the lower bound) will be adopted .
Finally it is stressed that the TDI value is a limit value for a life time dioxin intake, that is: the TDI limit protects individual from a life time dioxin exposure of e.g 4 pg
TEQ/kg BW/day. For food items that are consumed less frequently it is more appropriate to use a weekly (TWI), or even a monthly (TMI) intake as a basis for a limit
value for exposure.
2) How to interpret the "dioxins in Salmon" reports ?
The "dioxins in salmon" press releases are based on two bodies of information: one report by Miriam Jacobs, University of Surrey, which is actually a, non-peer
reviewed extended abstract presented at the "dioxin conference 2000 in Monterey, CA, USA in august 2000 and published in the meeting report series: Organohalogen
Compounds, vol 47 (2000); the other information is from Michael Easton, of the David Suzuki Foundation, Canada, which is actually a non-published personal
communication. In both cases the number of samples analysed is very low and thus would only allow a "snap-shot' type of information on the state of contamination of
the various salmon, at different locations and of the fish feed.
In Miriam Jacobs report the salmon samples (10 farmed and 2 wild) were analysed for the 17 PCDD/F compounds and 7 dioxin-like PCB compounds by a laboratory of
the US-EPA. The analyses were performed well with good quality assurance and quality control measures taken.
The total TEQ of dioxin like activity determined by HR-MS and converted using the most recent set of WHO-TEF-values indicated that farmed salmon contained
between 14 and 35 pg TEQ/g lipid of "dioxins", while the two wild salmon species contained 22 and 23 pg TEQ/g lipid of "dioxins". The main contribution to the total
TEQ in salmon is from the dioxin-like PCBs. Although these levels of "dioxins" are quite high in comparison to other food items (chicken, beef, milk) they are within
the range of dioxin-like PCB levels found in oily fish species in the North Sea and in fresh water fish species.
The data of Dr. Jacobs contrast with the personal communication on findings by Dr Easton, that wild salmon contains 10 fold less "dioxins" in comparison to farmed
salmon. One reason for the discrepancy may be the contamination level at the catchment's site of the wild salmon, which may differ considerably between different
locations. Further monitoring studies should be performed to resolve this issue.
How much salmon can be consumed safely?
Salmon obviously has a number of health benefits, e.g, due to the presence of omega-fatty acids. The down side is the presence of contaminants, like the "dioxins". At
present no legislation for e.g. product limit values exist in the EU for "dioxins" in fish. However it is anticipated that legislation will emerge during 2001. The WHO
have advised guidelines for tolerable daily intakes of "dioxins". Up till now the tolerable daily intake for "dioxins", not including the dioxin-like PCBs!, is 10 pg/kg BW
per day in the food and drugs act of most European countries. In 1998, the WHO has re-evaluated the TDI for "dioxins", also to include the dioxin-like PCBs. There
1998 recommendation is a tolerably daily intake is between 1 and 4 pg TEQ/kg body weight per day. The upper level being the maximum limit value, while the lower
level of 1 is the ultimate goal for the near future.
It is therefore reasonable, to consider the upper bound TDI of 4 pg TEQ/kg BW per day advised by the WHO, but not yet implemented in the food and drug act as the
maximum tolerable daily intake. This recommended TDI is more stringent than the TDI in the food and drug act of today and, it also takes into account the dioxin-like
PCBs, which was is not the case in the present days TDI of 10 pg/kg BW per day for PCDDs and PCDFs only (which would be equal to almost 30 pg TEQ/kg BW per
day if dioxin-like PCBs were included).
Using the newly recommended WHO upper bound TDI a maximum daily intake that is still safe is 4 pg TEQ/kg BW per day. On average the daily intake of "dioxins"
through food by the general population in Northern European countries is nowadays around 2 pg TEQ/kg BW/day. The maximal additional intake that still would not
exceed the 4 pg TEQ/kg BW per day level is therefore 2 pg TEQ/kg BW per day. Since salmon is not a daily consumption food item it is better to use the weekly intake,
which amounts to 14 pg TEQ/kg BW per week. For a 70 kg person this would mean 70 x 14 =980 pg TEQ per week maximum. The most contaminated salmon in Dr
Jacobs study contained 3,5 pg TEQ per gram wet weight (35 pg TEQ/g lipid, with an average lipid content of 10%). This would mean that a weekly consumption of
around 280 gram of salmon (280 x 3,5 = 980 pg TEQ/week) would still not exceed the weekly maximum additional intake and therefore would be still safe to eat from a
dioxin contamination point of view, when considering the more stringent upper bound WHO recommended TDI of 4 pg TEQ/kg BW (or a TWI of 28 pg TEQ/kg BW).
What about the risk for children?
It is clear that young children are more vulnerable to the adverse action of dioxins and dioxin-like PCBs. During a Dutch study on possible impacts of dioxin exposure
from mother's milk it became clear that the most sensitive time window for possible adverse effects is the prenatal stage of life. The foetus can be exposed to small
quantities of dioxins and dioxin-like PCBs via the placenta. The body burden of women at child bearing age is therefore the key factor in determining exposure levels to
foetuses and its possible impacts on cognitive and motor development. Pregnant mothers with the highest body burdens of dioxins and dioxin-like PCBs (e.g. above 35
pg TEQ/g lipid in mothers milk) gave birth to children that showed a somewhat poorer performance using different behavioural test paradigms. It was therefore
recommended that the daily intake of dioxins and dioxin-like PCBs (which was (and still is) 10 pg/kg BW/day for PCDDs and PCDFs only according to the food and
drug act) should be further reduced to limit the possibilities of unwanted effects on child development. These data, among others have led to the more stringent WHO
TDI values of 1-4 pg TEQ/kg BW per day.
In the Netherlands, young children hardly have oily fish in their diet. Therefore it is not very likely that young children will be at risk from consumption of oily fish,
e.g. salmon. Also, consumption by pregnant women of salmon at an average consumption level (less than 1 oily fish meal per week) does contribute only little to the
total body burden that they have already accumulated over their life time. Nevertheless, every effort should be made to reduce the levels of dioxin and dioxin-like
contaminants in fish and other food items, to ensure a better and more health food in the near future.
In the near future the lower bound TDI will need to be reached. Therefore the levels of dioxins and in particular the dioxin-like PCBs in food items need to be reduced
further. The general environmental trend of PCB contamination in fish is declining at a slow but steady rate. It has already dropped by 75% since the 1980s and it will
probably continue to come down in the near future. Any effort to speed up the environmental decline (e.g. by assuring no new input into the environment and clean up
of highly contaminated river sediments and dredged materials) should be taken. However, it is realised that very little additional measures can be taken, due to the large
scale environmental contamination of PCBs that already exist globally.
From the fish farming point of view there are much better opportunities to speed up further reduction of contaminant levels in farmed fish. More stringent control
measures and monitoring efforts, using novel fast and low cost screening methods (eg. CALUX), to select the fish oil and fish meal with the lowest contamination level
of dioxins as well as fish oil clean-up treatment procedures (e.g. char coal treatment) could reduce contamination levels well below the environmental levels as observed
in wild fish. This opportunity would certainly create added value in terms of a better food quality and a much improved consumer acceptance of farmed fish.
Professor of Environmental Toxicology
Institute for Environmental Studies
Vrije Universiteit Amsterdam
Last updated: 20-Mar-01