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Dioxins and You

By Dr. Jaime Abella Sison, Agriculture Monthly (Vol. 15, 03.2011).  Posted 03.28.2011.

Here is a summary of frequently asked questions about dioxins, prepared using information from the European Commission, World Health Organization, Food and Agriculture Organization and the U.S. Centers for Disease Control and Prevention.


What are dioxins?

Dioxins belong to a group of dangerous chemicals known as persistent organic pollutants. Dioxins are of concern because of their highly toxic potential. Experiments have shown they affect a number of organs and systems. Once dioxins have entered the body, they endure a long time because of their chemical stability and their ability to be absorbed by fat tissue where they are then stored in the body. Their half-life in the body is estimated to be 7 to 11 years. In the environment, dioxins tend to accumulate in the food chains. The higher in the animal food chain one goes, the higher the concentration of dioxins.

"Dioxin" is a general term for a large group of fat-soluble organo-chlorine compounds, the polychlorinated-dibenzodioxins and dibenzofurans, about 30 of which are significantly toxic. This group includes TCDD (2, 3, 7, 8-tetrachloro-dibenzo-para-dioxin), which is the most toxic, and the dioxin-like polychlorinated byphenyls (PCBs).

Dioxins are measured in parts per trillion (ppt); a part per trillion is roughly equivalent to a drop of ink in an Olympic-size swimming pool. In the United States, industrial sources of dioxins released into the environment have decreased significantly over the past 20 years. Today, studies indicate that the largest sources of these chemicals in the U.S. are backyard trash burning and forest fires.

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What is the problem with dioxins?

Dioxins are not soluble in water and are highly soluble in fat. This means that they bind to sediment and organic matter in the environment and are absorbed in animal and human fatty tissue. Moreover, they are not biodegradable, so they are persistent and bio-accumulate in the food chain. This means that once released into the environment, via air or via water, they pile up in the fat tissue of animals and humans.

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What are the sources of human exposure to dioxin?

Dioxins are ubiquitous in the environment. They are found throughout the world in air, water and soil. Although dioxin can come through industrial exposure by contact with the skin or inhalation, overall, this represents very small sources of dioxin exposure.

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How does dioxin get into food chain?

Dioxin can enter the food supply through a number of different routes. The contamination of the environment by dioxins is primarily caused by the aerial transportation and deposition of emissions from various sources (waste incineration, production of chemicals, traffic, etc.). The use and disposal of chemicals can contribute to more severe localized contamination.

Soil is a natural sink for dioxins. Apart from atmospheric deposition, soils may be polluted by sewage sludge or composts, spills and erosion from nearby contaminated areas. Soil is absorbed directly or indirectly via dust deposits on vegetables; by free-range grazing cattle, goats, sheep and chicken; and by burrowing or grazing pig and wild boar.

Aerial transport and deposition of dioxins and dioxin-like PCBs are also the main sources of contamination of leafy vegetables, pastures and roughages. Leaves are either directly grazed by free-ranging animals, or cropped and then preserved under dried form (hay) or silage. The spreading of sewage sludge on vegetation can increase to a limited extent the exposure of livestock.

Dioxins and dioxin-like PCBs are poorly soluble in water, but are absorbed onto mineral or organic particles in suspension in water. When dioxin emissions are transported by air to the surface of oceans and seas, they end up concentrating along the aquatic food chain.

Dioxin concentrates in the fatty tissues of beef and dairy cattle, poultry, pork or seafood. Theoretically, the longer the lifespan of an animal, the higher potential accumulation of dioxin in its adipose tissue.

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Which food products are most affected?

In general, food of animal origin contributes to about 90 percent of the overall human exposure. The contamination can vary widely depending on the origin of the foodstuff. Meat, eggs, milk, farmed fish and other food products may be contaminated above background levels by dioxins from feeding stuffs. Such contamination may be due to a high level of local environmental contamination, for example from a local waste incinerator, to incidents, or to a high content of dioxins in fishmeal, fish oil and tallow (animal fat). Wild fish from certain polluted areas may be highly contaminated.

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How does dioxin get into our bodies?

We accumulate dioxins in our bodies mostly by eating dioxin-contaminated food. As in animals, dioxin is stored in human adipose tissue. Certain population groups, such as nursing babies and people who eat a diet high in animal fat or in contaminated foods because of their proximity to dioxin release sites, are exposed to higher than average levels of dioxin.

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What is the dioxin body burden?

Toxicity of dioxins is related to the amount accumulated in the body during lifetime, the so-called body burden. It is used for the assessment of toxic effects of dioxins as it is a much better estimate of the continuous exposure than the daily intake.

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What is the health impact of eating food contaminated with dioxins?

Dioxins have a broad series of toxic and biochemical effects and some of them are classified as known human carcinogen. In laboratory animals they have been linked to endometriosis (severe effects on the uterus), developmental and neurobehavioral effects (learning disabilities), developmental reproductive effects (low sperm count, genital malformation), and immunotoxic effects. These effects occur at much lower levels of exposure than carcinogenic effects.

A few cases of intentional human poisoning have been reported. The most notable incident is the 2004 case of Ukraine President Viktor Yushchenko, whose face was disfigured by chloracne.

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What about dioxin in mother's milk and breast-feeding? Is it a health threat to nursing infants?

Mother's milk does contain elevated dioxin levels. Some dioxin is known to pass from the mother's body to the infant during lactation. However, breast-feeding is restricted to a relatively short period. What is relevant for children, and not not only breast-fed babies, is the amount of dioxin they received from their mothers as an embryo.

In this context, the Scientific Committee for Food (SCF) has reiterated the conclusions of the WHO meetings on the health significance of contamination of human milk with dioxins and PCBs since current evidence does not justify altering recommendations on the promotion of, and support for, breast-feeding. Health experts recognize that breastfeeding provides many nutritional, immunologic and other benefits to the infant in the first months of life.

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How is dioxin contamination of food and feed detected?

The quantitative chemical analysis of dioxins requires sophisticated methods that are available only in a limited number of laboratories around the world. These are mostly in individualized countries. The analysis costs are very high and vary according to the type of sample, but range from over US$ 1,700 for the analysis of a single biological sample to several thousand US dollars for the comprehensive assessment of release from a waste incinerator.

Increasingly, biological-based screening methods, either cell-based or antibody-based, are being developed. The use of such methods for food samples is not yet sufficiently validated. Nevertheless, such screening methods will allow more analyses at lower cost. In case of a positive screening test, confirmation of results must be carried out via more complex chemical analysis.

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What are the current legislative rules on dioxin in feed?

The Philippines does not have any prescribed standards for dioxin emissions for the different environmental media (soil, water and land). The country also does not have any capacity to monitor and test the dioxin emissions. There is very little data about dioxin contamination of the environment and human population of the Philippines.

In response to the Belgian dioxin crisis in 1999 which involved dioxin contamination of Belgian food products via PCB contaminated feed, the EU imposed temporary restrictions on the intra  and extra community trade in milk and dairy products, beef, pork, poultry, eggs and egg derivatives (mayonnaise, prepared dishes, for examples), and cattle feed.

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Are there currently any limits on dioxins in animal feed?

Specific maximum limits for dioxins (dioxins and furans, not for dioxin-like PCBs) have been established fo citrus pulp and kaolinitic clay. These limits were established on a provisional basis in 1998 and 1999, respectively and have to be reviewed in the light of the Scientific Committee on Animal Nutrition (SCAN) opinion of November 2000. The SCAN opinion deals with dioxin and PCB contamination of animal feed, the likely exposure of food-producing animals (mammals, birds and fish) and the carry-over of this contamination to food products.

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How do you prevent and control dioxin exposure?

Proper incineration of contaminated material is the best available method of preventing and controlling exposure to dioxins. It can also destroy PCB-based waste oils. The incineration requires high temperatures over 850 degrees centigrade. For the destruction of large amounts of contaminated material, even higher temperatures (1,000 degrees centigrade or more) are required.

Prevention or reduction of human exposure is best done via source-directed measures like strict control of industrial processes to reduce formation of dioxins as much as possible. This is the responsibility of national governments. But the Codes Alimentarius Commission has recognized the importance of this approach, so it has adopted in 2001 a Code of Practice for Source Directed Measures to Reduce Contamination of Foods with Chemicals, and a Code of Practice for the Prevention and Reduction of Dioxin and Dioxin-like PCB Contamination in Food and Feeds.

More than 90 percent of human exposure to dioxins is through the food supply, mainly meat and dairy products, fish and shellfish. Consequently, protecting the food supply is critical. One approach includes, as mentioned above, source-directed measures to reduce dioxin emissions. Secondary contamination of the food supply needs to be provided throughout the food chain. Good controls and practices during primary production, processing, distribution and sale are all essential to the production of safe food.

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What should consumers do to reduce their risk of exposure?

Trimming fat from meat and consuming low fat dairy products may decrease the exposure to dioxin compounds. Also, a balanced diet (including adequate amounts of fruits, vegetables and cereals) will help to avoid excessive exposure from a single source.

This is a long term strategy to reduce body burdens and is probably most relevant for girls and young women to reduce exposure of the developing fetus and when breastfeeding infants later on in life. However, the possibility for consumers to reduce their own exposure is somewhat limited.

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