The group of chemicals known as dioxins have sparked numerous health scares in the last few years, having accumulated in the food chain thereby contaminating meat, fish, fruit and vegetables. Just how dangerous are they? And is there anything consumers can do to protect against the harmful chemicals? Alan Osborn investigates.
A recent discovery of high levels of dioxins in people in Paritutu, New Zealand, has prompted renewed speculation about this infamous family of chemicals. Why do dioxins appear in some places and not others that seem just as unhygienic, or even more polluted? How dangerous are they and what can we as consumers do to keep ourselves from ingesting them? What can and should the food industry be doing? As it happens, the affected people in Paritutu lived next to a plant that made powerful herbicides, and produced dioxin as a by-product so there are probably not universal lessons to be drawn from this. But the fact that it caused something of a stir shows how ready people are to believe in dioxin scare stories.
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A lot is known in a purely scientific sense about dioxins. Broadly speaking we know what they are, how they are carried and what they can do. As the European Food Safety Authority (EFSA) said in its introduction to a recent colloquium on the subject in Brussels, there have been numerous assessments of the risk in recent years – by the World Health Organisation (WHO), the European Union (EU) and various national authorities. But, the EFSA added, “there are some differences in approaches used by various authorities for the assessment of dioxins and dioxin-like compounds to human health risk including extrapolation from effects in the observable high dose range to background dietary exposure.” This is a field, in short, where judgement as well as scientific fact is called for.
Nevertheless some facts hold good for all authorities. Dioxins comprise a group of several hundred chemical compounds that share certain chemical structures and biological characteristics. Among the most toxic and best-known is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Dioxins are formed during combustion processes like commercial or municipal waste incineration and from burning fuels like wood, coal or oil. Chlorine bleaching of pulp and paper, certain types of chemical manufacturing and processing, and other industrial processes can all create dioxins.
Accumulation in the food chain
A characteristic of dioxins is that they are not soluble in water but highly soluble in fat, which means they are absorbed in animal and human fatty tissue. They are not biodegradable and so accumulate in the food chain. Once released into the air or water environment they accumulate in the fat tissue of animals, including fish, and humans. Airborne dioxin particles settle on forage or feed which is eaten by animals and the chemical is then passed into the fatty tissues of beef and dairy cattle, poultry, pork or seafood. Airborne dioxin particles settling on fruits and vegetables can be removed by washing though not after the chemical has entered a plant’s system.
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By GlobalDataA survey released in 2001 by the EU’s Scientific Committee for Food found that food of animal origin contributed to about 80% of human exposure to dioxins but the contamination could vary 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,” said the SCF. Wild fish from certain polluted areas like the Baltic could be highly contaminated. Human breast milk was generally a source of dioxins, though usually only for a short time.
Carcinogenic
Dioxins have several toxic and biochemical effects and some are carcinogenic. The US Environmental Protection Agency (EPA) says “several studies suggest that workers exposed to high levels of dioxins at their workplace over many years have an increased risk of cancer. Animal studies have also shown an increased risk of cancer from long-term exposure to dioxins.”
However the most common health effect in people exposed to dioxin is chloracne, a severe skin disease with acne-like lesions, says the EPA. Other effects include skin rashes and discoloration, excessive body hair, and possibly mild liver damage, while data from animal studies prompts concern that “exposure to low levels of dioxins over long periods (or high level exposures at sensitive times) might result in reproductive or developmental effects.”
EFSA’s colloquium in June agreed that though there was “general consensus on the science of dioxin toxicology, with respect to the state of knowledge and research needs,” there were uncertainties in the interpretation of data and work should be done to reduce these and to explore further “possible human health effects”.
One of the most significant dioxin researches of recent years has been last year’s reassessment by the American EPA of the risks of dioxin and dioxin-like compounds, which gave rise to the warnings about cancer and other “adverse health effects”. This has just been submitted to the National Academy of Sciences to see if the findings can be substantiated and if so what action the American agencies should take, though it will not be until 2006 that the panel gives its opinion. Research in this area, at least in America, moves slowly. As the EPA says, “development of the dioxin reassessment has taken longer than expected.” It took substantial time to collect, assess, and portray the significant and latest evolving data on dioxin (12 years in fact!) and “in addition, there has been significant controversy surrounding the science of dioxin.”
Declining threat
For all the apparent caution there are broad signs that the global threat from dioxin is abating though two “freak” occurrences stand out in recent years. First was the contamination of animal feed in the US in 1997 that was traced to clay from a single mine in Mississippi and second was the dioxin outbreak in Belgium in 1999 when animal feed was enriched with old used engine oil with catastrophic results.
The EPA nevertheless says that “known and quantifiable industrial emissions of dioxin in the United States have been reduced significantly since 1987 and dioxin levels in our bodies are also going down.” The European Commission said in 2001 that “from the available data it appears that the background exposure to dioxin and dioxin-like PCBs of the European population has decreased over the last ten years.”
This is reassuring, since a common finding of recent surveys is that there is little the ordinary consumer can normally do by way of diet control or food hygiene to protect against dioxin if it is present locally.
