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PCB - Polychlorinated biphenyls
For several years now, PCB pollution of French rivers and lakes and its impact on the population has been a topical issue. Since 2003, AFSSA and its experts have been working on this difficult topic and have issued over twenty Opinions in order to assess the precise health risks associated with consuming PCB-contaminated fish, to provide the State with scientific and technical support in managing the risk associated with these contaminants and to help define European regulations on NDL-PCBs.
What are PCBs?
PCBs, or polychlorinated biphenyls, are chlorinated aromatic compounds also known as pyralenes in France. The family of PCBs comprises 209 substances also known as congeners.
There are two types of PCBs, each of which have a distinct mechanism of action:
- “Dioxin-Like” PCBs or DL-PCBs are able to bind to the same cell receptor as dioxins (Ah receptor). Because their mechanism of action on cells is similar to that of dioxins, their toxicity (like that of dioxins) is expressed as a toxic equivalency factor of the toxicity of TCDD (2,3,7,8-Tetra-Chloro-Dibenzo para-Dioxin), more commonly known as the Seveso dioxin.
- “Non Dioxin-Like” PCBs or NDL-PCBs have a different mechanism of action to dioxins.
NDL-PCBs are found in higher quantities in river fish than DL-PCBs.
Of the PCBs, seven congeners are found especially in contaminated products, generally accounting for 50% of the amount of PCB. Their levels are therefore used to quantify the contamination of a product by PCBs: and they are called PCB indicators (PCBis).
Where are PCBs found?
These compounds used to be used in industry, as a mixture, for their insulating properties (electrical transformers) and their chemical and physical stability (inks, paints). But their production and use were gradually reduced through the 1970s before finally being banned in 1987. Chemically stable and of low biodegradability, these molecules are classified as persistent organic pollutants. They gradually build up in the environment, particularly in reservoirs such as marine or river sediments.
Presenting a marked affinity for fats (lipophilia), PCBs gradually accumulate in the food chain, becoming particularly concentrated in the fatty tissues of animals. As a result, the foods with the highest PCB levels are foods of animal origin with high fat content, such as oily fish in contact with contaminated sediment and milk, dairy products and eggs. Food is therefore the main contamination route for the general population (over 90% of total exposure).
What effects do PCBs have on health?
In the human body, these substances tend to accumulate in the fatty tissue.
They are eliminated slowly (over several years) through stools. They are also found in mother's milk and blood lipids, where they are measured. PCB toxicity is mainly linked to the accumulation in the body over time (body burden). This means that occasional exposure to these molecules through a highly contaminated food will have little effect on health.
High PCB exposure (accidental discharges, work-related exposure) may trigger skin reactions (chloracne, pigmentation of the nails and skin), eye reactions (hypersecretion) and liver problems (transitory changes in hepatic enzyme activity).
For lower, chronic exposure levels, the most alarming manifestations associated with PCBs are neuro-behavioural effects, which have been observed in young children who were heavily exposed to PCBs during pregnancy and breastfeeding.
Other effects have been reported in adults: metabolic disturbances, thyroid conditions.
Based on the entire corpus of available international literature on the subject, AFSSA has issued recommended critical levels for PCBs below which the probability of effects on health is considered insignificant (Opinion of 5 March 2010 regarding the health impact for the French population of critical levels of PCBs). The details of this Opinion's contents are provided in the “Critical blood concentration levels for PCBs” section.
Tolerable daily intakes, levels that a person may consume daily throughout his/her lifetime without the risk of adverse effects, have been established by the WHO (2001) and EFSA (European Food Safety Authority) (2002) for DL-PCBs (and dioxins), and then by the WHO and AFSSA (2003) for NDL-PCBs. These figures were obtained on the basis of toxicological studies conducted in animals by applying safety margins with account taken of susceptibility differences between species and individuals.
As for any toxin, PCB-risk assessments involve comparing population exposure to the tolerable daily intake.
What regulations exist for PCBs in food?
The risk represented by a compound is managed by establishing maximum levels in foodstuffs. If these are exceeded, the food is considered to be unfit for consumption and its sale is banned.
Before 2006, the maximum total PCB limit was 2mg/kg of fish. Since 26 June 2006, this maximum limit has been replaced by a more restrictive maximum DL-PCB level, set by the European Union. EC regulation 1881/2006 sets maximum levels for all dioxins and dioxin-like PCBs in the following foods: beef, mutton, poultry and pork flesh and liver; fish flesh and fishery products; eel flesh; milk and dairy products; eggs and egg-derivative-based products; beef, mutton, poultry and pork fats and mixed animal fats; vegetable oils and fats; marine animal oils.
No regulatory level has been set for NDL-PCBs to date, but discussions are under way in Europe to set regulatory maximum levels. AFSSA is taking an active part in these discussions. In this context, AFSSA issued an Opinion in October 2007 on the setting of maximum NDL-PCB levels in a variety of foods (1).
(1) Opinion of 23 October 2007 on the establishment of relevant maximum levels for non dioxin-like polychlobiphenyls (NDL-PCB) in some foodstuffs.
April 2010
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