Di…di…dioxins

Dioxins are persistent organic pollutants (Photo: avlxyz – Flickr)

The title might be slightly over the top, as you might not die from poisoning with dioxins. But be aware that dioxins are a group of chemicals belonging to the “dirty dozen” of persistent organic pollutants or POPs for short. Persistent because once they have entered the body they are stored in fat tissue for a long time. Pollutants because they are all but indestructible once released into the environment and can easily spread across the world.

Commonly found at low levels in many foods, dioxins are highly toxic affecting a number of organs and systems. High accidental or intentional short-term exposure may result in skin damage, such as chloracne and patchy darkening of the skin, and altered liver function. This happened to Viktor Yushchenko, President of the Ukraine, whose face was disfigured by chloracne. Long-term exposure is according to the World Health Organization linked to impairment of the immune system, the developing nervous system, the endocrine system, reproductive functions and possibly cancer. But not all dioxins are equal.

What are dioxins?

Bare with me, here is first a little chemistry. Strictly speaking dioxin might refer to a single very toxic substance called TCDD (2,3,7,8- tetrachlorodibenzo para dioxin) and other polychlorinated dibenzo para dioxins (PCDDs). However, the name “dioxins” often includes also the family of structurally and chemically related polychlorinated dibenzofurans (PCDFs). And to confuse the situation even further, certain dioxin-like polychlorinated biphenyls (PCBs) with similar toxic properties might sometimes also be referred to as “dioxins” or dioxin-related compounds.

Of the 419 different dioxin-related compounds that have been identified, only about 30 are considered to have significant toxicity. The good thing is that they all act in a similar way, although to different degrees. Clever scientists thus grouped them together and talk about dioxin toxicity equivalents. It might be important though to discuss a little further about the different origins of dioxins on the one hand and dioxin-like PCBs on the other before lumping them together

origin of dioxins and related compounds

Dioxins (not including the PCBs) are unwanted byproducts of industrial processes, like smelting, chlorine bleaching of paper pulp and incomplete burning in waste incinerators. Natural processes, like volcanic eruptions and forest fires, contribute to dioxin formation.

Dioxins found in Sydney Harbour

Dioxins have also been linked to the manufacturing of some herbicides and pesticides. Remember Agent Orange, the herbicide mixture used during the Vietnam war to defoliate trees? It was contaminated with dioxins during the manufacturing process and caused considerable damage to the next Vietnamese generation. A link to certain types of cancers and also to diabetes is being further investigated.

A Union Carbide plant producing the same herbicide mixture was situated deep in Sydney Harbour. It closed many years ago but its legacy persists on the harbour floor. In 2006, the NSW Government was forced to close parts of Sydney Harbour for commercial fishing because testing found high levels of dioxins in some fish and seafood.

In contrast to dioxins, PCBs had widespread use in numerous industrial applications, due to their physical and chemical properties, such as non-flammability and low heat conductivity. They were produced in high volumes for over four decades until they were banned in the 1980s. The problem now is that long-term storage and improper disposal of PCB-based waste industrial oils may result in their release into the environment contaminating human and animal food supplies.

Dioxins in the food supply

Fish contributes to dioxin exposure

Dioxins in the environment will bio-accumulate in the food chain, that is the higher up in the chain the higher the levels found, with humans the ultimate end point. The European Food Safety Authority (EFSA) in a recent report identified fish, meat and dairy products as the highest contributors to European dietary exposure to the substances. Milk and dairy products were the major contributors for almost all infant and toddler groups, while it was fish and seafood products for the rest of the population. Very low levels are found in plants, water and air.

Comprehensive monitoring programmes conducted worldwide during the past two decades have shown that human exposure to dioxins and PCBs has decreased significantly over time. EFSA noted that over the recent ten-year period dietary exposure to dioxins and PCBs had been reduced by between 20 to 80% depending on dietary habits and European region.

However, accidents or deliberate fraud that still occur can negate the best of intentions.

Recent contamination incidents

Although levels of dioxins and PCBs seems to be falling in the general food supply, the real challenge is to keep contamination incidents from happening. Recent incidents have involved animal feed made from illegal waste industrial oil contaminating pork in Ireland and chicken and eggs in Belgium, the thickener guar gum from India contaminating a range of European processed food products, citrus pulp feed pellets from Brazil contaminating milk in Germany, bentonite clay used in feed production contaminating chickens, eggs and catfish in the USA.

Dioxins found in organic eggs

Equally, localised problem areas cannot be ignored. In a German testing program, high levels of dioxins were recently detected in sheep and deer liver not associated with any specific contamination source. Investigations summarised by EFSA indicated that these high levels were not due to poor husbandry practices or high localised contamination but were much more likely to be associated with the physiology and grazing patterns of the animals. Also in Germany, dioxins at three to six times permitted levels were discovered mid 2012 in eggs by routine tests on an organic farm. How the dioxin came into the eggs was unclear since tests showed no contamination of animal feed at the farm. A Dutch organic egg producer was affected by a similar problem in 2011. Fish from the Baltic Sea are consistently more contaminated with dioxins than fish from most other areas.

Many earlier incidents of food contamination have been reported in other parts of the world. Although all countries can be affected, most contamination cases have been reported in industrialised countries where adequate food contamination monitoring, greater awareness of the hazard and better regulatory controls are available for the detection of dioxin problems.

Continued vigilance is of utmost importance

Continued vigilance to protect food supply (Photo: nemone – Flickr)

Since food contributes to more than 90% of human exposure to dioxins, protecting the food supply is critical. Source-directed measures to reduce overall dioxin emissions were recommended by the Codex Alimentarius Commission to be implemented world-wide.

In the USA, federal agencies have taken a number of actions to reduce dioxin levels in food with quantifiable industrial emissions reduced by more than 75% from their levels in the 1980’s. In Europe, the European Commission produces regular progress reports to measure the effects of their regulatory controls of dioxins. The latest report claimed an overall reduction of industrial emissions of dioxins by about 80% over the past two decades. The Australian Government undertook a range of studies from 2001 to 2004 to measure emissions from sources such as bush fires, and dioxin levels in the environment, food and population claiming that levels were generally low. Health Canada continues to assess the concentrations of dioxin compounds in foods as well as any new research about their health effects.

It is not much we as individuals can do to reduce our exposure to dioxins. But we can pressure governments to continue their vigilance and not become complacent. Regular food monitoring should be in place to ensure that tolerance levels for dioxins are not exceeded. We should never forget that dioxins are among the most potent toxins requiring testing methods maybe more than 1000 times more sensitive than for most other contaminants.

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