In the spring of 1999 high concentrations of dioxins and PCB were found in Belgian poultry. The contamination was traced back to animal feed that had been contaminated during the processing by oil containing dioxins and PCBs. This incident clearly shows that in a global food market consumers in most countries may be exposed to unwanted contaminants in the food. In Sweden the concentrations of PCBs, dioxins, and DDE (one DDT metabolite) have, due to governmental regulations, decreased in the environment since the 1980's. This was seen in mother's milk, a good indicator of concentrations of persistent organic pollutants (POPs) in the environment and food chain. Incidents such as the one in Belgium may reverse the recent downward trend of POPs in food and give unacceptably high exposures to certain POPs to humans through the food chain. The result may be unwanted health effects, such as damage to the motor and neurologic development of the infant, impairment of the immune system, and increased risk for certain cancer types for adults such as non-Hodgkin lymphoma. We have previously reported on increased concentrations of PCBs, chlordanes (previously used as insecticides) and the brominated flame retardant 2,2',4,4'-tetrabrominated diphenyl ether (TBDE) in patients with non-Hodgkin lymphoma compared with persons without cancer. The findings indicate that these types of pollutants may be a part in the etiology of non-Hodgkin lymphoma, a malignant disease with increasing incidence in the Western world. The concentration of POPs will also be too high in mother's milk with concomitantly unacceptable exposure to the breast fed infant.
The incident in Belgium is unfortunately not unique. In the fall of 1999, it was reported that sewage sludge had been mixed into French animal feed. The EU commission is currently investigating this. Sewage sludge contains many POPs and other chemical substances that are not acceptable in animal feed. These contaminants may ultimately end up in food for humans. Examples of such contaminants are PCBs, dioxins, brominated flame retardants, polyacrylamide/acrylamide, traces of antibiotic drugs, cadmium, silver, platinum, wolfram, and uranium. The list can be made much longer and contains most of the more persistent chemicals, both identified and unidentified, used in an industrialized society.
For a number of years we have investigated cancer risks of certain POPs, studies supported mainly by the Swedish Cancer and Allergy Foundation. Food is the main exposure route - 90-95% - to the Swedish population. As one part of our studies, we checked the amounts of certain POPs in 8 types of Swedish food based on usual consumption. The concentrations (as ng/g fat) of PCBs (the sum of 9 congeners), hexachlorobenzene (HCB, previously used as a pesticide and also produced during combustion of materials containing chlorine), DDE, and brominated flame retardant (TBDE) were measured (see Table). Since these POPs are fat-soluble the concentrations of fat in the various foods are also given. We calculated the POP exposure through consumption of 100 g of each of these 8 food types.
The results of this study showed that the concentrations are similar in meat and dairy products. Ecologically produced cheese did not differ from other cheese in this respect. Ecological food is generally eaten in order to avoid pesticides currently used rather than to minimize exposure to this group of POPs. The concentrations in margarine were low since margarine is a vegetable product. Notably high concentrations were found in herring, though somewhat lower in Baltic (small) herring. Although being a pilot study (only one sample was analyzed for each food type), the results clearly show that consumption of fatty fish from the Baltic sea may still give an unacceptably high exposure to certain POPs. This single sample showed that the consumption of 100 g of herring gives a PCB exposure of 86.4 ng/g adipose tissue to a human being with a bodyweight of 50 kg. In fact, we can assume the exposure is higher, since we did not analyze the concentration of all PCB congeners known to be food contaminants. This exposure may be compared with the repeated daily PCB intake of 140-900 ng/g adipose tissue causing health effects on the fetus and baby according to US estimates. The safety margin is thus virtually non-existent. The results showed that fatty Baltic fish may give 40-100 times higher exposure to PCBs than meat. Of course, more analyses are necessary for a comprehensive risk calculation.
Brominated flame retardants have, since the 1970's, increasingly been used in, for example, electronic and electrical equipment, cables, synthetic textiles (e.g., babies' nightclothes), plastics, paints, and in mining and other drilling operations. Studies in Sweden show increasing concentrations in mother's milk with the concentrations doubling every 5 years. Brominated flame-retardants are chemically rather similar to PCBs and may have similar health effects. Our results show that the tetra brominated diphenyl ether TBDE is distributed throughout the ecosystem. The concentrations are relatively low in the terrestrial food chain (meat and dairy products) but high in the aquatic (fatty fish). Rigorous efforts are needed to avoid a disaster with potentially serious health risks to animals and humans. We note that it can be assumed that, in addition to the few POPs for which we analyzed, there are numerous other both identified and yet unidentified types with potential negative health effects.
The poisoning of food in Belgium caused increased concentrations of dioxins and PCB in animal feed. The concentrations largely exceeded acceptable daily intakes. If contaminated sewage sludge is added to animal feed or used on farmland, the current relatively low concentrations of certain POPs in meat and dairy products will increase. In the long run restrictions for consumption of these base types of food would have to be introduced, as has been the case in Sweden for fatty fish from the Baltic Sea.
For these reasons, sewage sludge must not be used on fields used for production of food or on land with grazing animals either now or in the future. A grazing cow consumes roughly 2-kg soil per day. Another route for the transfer of pollutants in sewage sludge to food is via grass, hay, and feed grain. Though there is limited uptake of POPs by the roots of the plants, these toxic chemicals evaporate and can stick to the wax-like surface of plants. However, root vegetables may have an uptake through the wax-like outer layer of the roots themselves.
Notably, the concentration of brominated flame retardants found in sewage sludge from one Swedish sewage treatment plant has increased 10 times over the last 10-year period. As a consequence of this finding, the Swedish farmer's organization (LRF) recently proclaimed a moratorium on the spreading of sewage sludge on farm lands.
In the Table we give results on a lipid basis and also exposure by consumption of 100 g of each type of food:
Fat concen- PCB DDE HCB TBDE
tration (ng/g) (ng/g) (ng/g) (ng/g)
Minced pork 12,1% 3,67 2,08 0,59 0,09
-100 g 44,4 ng 25,2 ng 7,1 ng 1,1 ng
Minced meat 8,3% 4,62 4,84 <0,60 <0,07
-100 g 38,3 ng 40,2 ng 5,0 ng 0,6 ng
Butter 71,1% 2,99 2,16 1,96 0,04
-100 g 212,6 ng 153,6 ng 139,4 ng 2,8 ng
Margarine 66,3% 0,05 0,02 0,02 0,01
-100 g 3,3 ng 1,3 ng 1,3 ng 0,7 ng
Cheese 31,8% 3,36 4,65 1,63 <0,27
-100 g 273,5 ng 147,9 ng 51,8 ng 8,6 ng
Cheese, eco-
logical 29,5% 3,23 2,49 1,65 <0,40
-100 g 348,1 ng 73,5 ng 48,7 ng 11,8 ng
Herring 1,55% 2786,5 326,80 27,88 72,48
-100 g 4319,1 ng 506,5 ng 43,2 ng 112,3 ng
Baltic herring 2,03% 815,52 1189,8 28,00 58,05
-100 g 1655,5 ng 2415,3 ng 56,8 ng 117,8 ng
(An article in Dagens Nyheter October 11, 1999 was based on this information)
Lennart Hardell, MD, PhD
Associate Professor
Department of Oncology
÷rebro Medical Center
SE-701 85 ÷rebro
Swden
Phone + 46 19 15 15 46
Fax + 46 19 10 17 68
E-mail: lennart.hardell@orebroll.se