PCBs, or polychlorinated biphenyls, are persistent chemical pollutants in the environment found widely around the world. Where do these substances come from? What effects can they have on health? And how are they regulated in food? Read on …
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Updated on 24/08/2016
PCBs, identity sheet
PCBs, or Polychlorinated biphenyls
What are PCBs?
PCBs or polychlorinated biphenylsare chlorinated aromatic compounds also known as pyralenes in France. These compounds were previously used in industry, as mixtures, for their insulating properties (in electrical transformers) and their chemical and physical stability (in inks, paints). The class of PCBs comprises 209 substances, also known as congeners. There are two types of PCBs, each of which has 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-tetrachlorodibenzo-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: they are called PCB indicators (PCBis).
Where are PCBs found?
These compounds were formerly used in industry, but their production and use were gradually reduced through the 1970s before finally being banned in 1987. Chemically stable and of low biodegradability, these compounds are classified as persistent organic pollutants. They gradually build up in the environment, particularly in reservoirs such as marine or river sediments.
PCBs have a marked affinity for fats (lipophilia), and 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 also butter. Food is therefore the main contamination route for the general population (over 90% of total exposure).
The regulations implemented to reduce contamination in the environment and foodstuffs have resulted in a considerable drop in exposure of the French population over the last 20 years.
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 compounds through a highly contaminated food will have little effect on health.
In chronic exposure, however, 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 and thyroid conditions.
Based on the entire corpus of available international literature on the subject, the Agency has issued critical blood concentration levels for PCBs below which the probability of effects on health is considered insignificant (Opinion of 5 March 2010). In addition 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 to take account of susceptibility differences between species and individuals.
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 (temporary changes in hepatic enzyme activity).
What regulations are there for PCBs in food?
The risk represented by a chemical 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 in France was 2mg/kg of fish. In December 2006, EC Regulation 1881/2006 set maximum levels for all dioxins and dioxin-like PCBs in several foods(beef, lamb, poultry and pork flesh and liver; fish flesh and fishery products; eel flesh; milk and dairy products; eggs and egg products; fat from beef, lamb, poultry and pork, and mixed animal fats; vegetable oils and fats; marine animal oils).
In December 2011, Regulation (EU) 1259/2011, which came into force on 1 January 2012, revised the previous Regulation by lowering the maximum levels for dioxin-like PCBs in foods and also by introducing maximum levels for NDL-PCBs in the same foods, as well as in other categories of foods such as wild freshwater fish, fish liver and foodstuffs for consumption by infants and young children