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3 Why We Should Take Action on Dioxin
3.1 Health effects
In the last 30 years dioxin has been widely studied. Despite this, there is still much we do not know about its effects on human health. However, animal studies show that dioxin is an extremely toxic chemical capable of causing a wide range of effects. It is generally assumed that dioxin has the potential to cause these effects in people.
Effects on animals
Dioxin is a very potent animal carcinogen that can cause a wide range of cancers. Other adverse effects seen in animals include neurobehavioural, development, reproductive and immunotoxic effects.
Characteristic signs of lethal exposure to dioxin are severe weight loss and atrophy of the thymus gland. Non-lethal doses can lead to weight loss, and biochemical and degenerative changes in the liver. Reproductive damage includes decreases in fertility, changes in sex hormone levels, reduced sperm production and increased rates of miscarriage. Birth defects include cleft palate and kidney damage.
Effects on humans
Scientific understanding of the human health effects of dioxin is incomplete, especially for effects other than cancer. Direct evidence of adverse effects in humans is limited. Some effects have been observed in people exposed to relatively high levels of dioxin, the most obvious of which is chloracne, a severe skin disease characterised by acne-like lesions.
Several studies of industrial workers exposed to high levels of dioxin have shown increased risks of cancer. As a result, the World Health Organization (WHO) and the United States National Toxicology Programme both list dioxin as a human carcinogen. In New Zealand the Ministry for the Environment estimates that up to 50 cancers each year may be due to dioxin.
Non-cancer effects, such as immunotoxicity and neurobehavioural and reproductive effects, might turn out to be the most important in terms of their overall health impact. The margin of safety between the current body burdens in New Zealanders and body burdens known to cause adverse health effects in animals is considered to be small.(See footnote 9)
3.2 Exposure of New Zealanders to dioxin
Dioxin exposure for the general population has been assessed in two ways: measuring the levels in food, and measuring the levels already present in people's bodies. Dioxin exposure can be measured in units of picograms per kilogram of body weight per day (pg/kg bw/day).(See footnote 10) Both measurement methods have provided similar estimates of exposure.
From the first method, a dietary survey, the current dioxin intake of New Zealanders has been estimated to be approximately 0.5 pg/kg bw/day. The dioxin intake of people in industrialised northern hemisphere countries is between two and five times as great (Figure 1).
See figure at its full size (including text description).The second method, a study of concentrations of dioxin in blood, suggests that over the last 25 to 40 years the average exposure has been about three times higher - 1.4 pg/kg bw/day in comparison with the current 0.5 pg/kg bw/day from the dietary study. Because dioxin is only slowly excreted from the body, levels in blood reflect both current and historical exposures.
The amount of dioxin present in people's bodies rises markedly with age. This is because dioxin accumulates throughout life. It also suggests that in the past New Zealanders were exposed to more dioxin than they are now. Other evidence for falling exposures comes from studies of dioxin in breast milk, which suggest that exposure has decreased by about 70% in the last decade (Figure 2). Decreasing exposure has also been reported in several European countries, in Canada and the United States.
See figure at its full size (including text description).Despite encouraging signs of comparatively low dioxin intake and decreasing exposures, the existing average level of human exposure in New Zealand is still close to the WHO tolerable daily intake of 1 pg/kg bw/day.(See footnote 11) Some members of the population will exceed this WHO value. The New Zealand exposure is also about 100 times greater than the safe measurement of exposure set by the United States Environmental Protection Agency of 0.006 pg/kg bw/day.
To improve the margin of safety between New Zealanders' intake of dioxin and levels that may cause adverse effects in humans, actions should be taken so that people's exposure continues to trend downward over time.(See footnote 12)
3.3 How dioxin travels from air into humans
Over 90% of the dioxin entering the body of the typical New Zealander is thought to have come from eating animal foods. For discharges to air, exposure takes the following pathway:
Variations to the dietary exposure pathway include:
- the discharge of dioxin-containing effluent to waterways and consequent bioaccumulation in fish and shellfish
- the application of solid waste, such as sewage sludge, to agricultural soil and consequent ingestion by grazing animals.
Exposure also occurs from the inadvertent ingestion of soil containing dioxin, and from inhalation.
Because contamination of food is the primary route for human exposure, people who live near a major point source are not likely to have a higher than average body burden of dioxin, unless most of the food they eat is grown locally and contaminated by the discharge source. In fact, the level of exposure to dioxin will be similar for the majority of New Zealanders, because most people eat foods produced commercially across the country.
3.4 Economic considerations
New Zealand increasingly uses its clean green image for marketing biologically based products in export markets and tourism,(See footnote 13) as well as for other economic activities. Dioxin discharges are low compared with other countries, because New Zealand is not heavily industrialised and population density is low. Despite this, if no action is taken to reduce discharges of a toxin of such international concern, then our clean green image will be undermined.
A clean green image should be supported by a clean green reality. Increasingly, non-tariff barriers to trade are environmental. Meat and dairy products are both New Zealand's largest export earners and the products most susceptible to dioxin contamination. Dioxin is measured in our foods only at very low levels, if at all, so it is important that actions are taken to ensure that this favourable position is maintained. Overseas experience has shown the negative effect on a region's and country's economy if dioxin contamination of food occurs.
No residue limits have yet been established for dioxin in food with respect to overseas trade, although the WHO and the Food and Agriculture Organization of the United Nations have begun discussions. The European Commission has recently proposed maximum limits for dioxin levels in animal foods, with the intention of regulation from 2002 onwards. The first World Trade Organization notification of maximum dioxin levels in agricultural products has also been made. Other countries can be expected to follow, and monitoring of dioxin residues in New Zealand agricultural exports appears inevitable.
Given the growing export market for demonstrably 'pure' agricultural produce that sells at high prices, there is potential for economic advantage from demonstrating the continued absence of dioxin in New Zealand's exports.
3.5 A preventive and proactive response
New Zealand action on dioxin should be seen as both preventive and proactive.
A preventive measure is justified in view of the potential health effects, recognising the goal of New Zealand's dioxin policy is to protect human health and the environment. Preventive action will also protect the quality of our foods and reduce any potential for damage to the economy.
Initiatives on dioxin are already happening in other countries. A proactive response to these global initiatives will help to maintain New Zealand's comparative clean green advantage. Action should also be proactive in the expectation of new dioxin sources (such as municipal waste incineration) being established in New Zealand.
Footnotes:
9 Evaluation of the Toxicity of Dioxins and Dioxin-like PCBs: A
Health Risk Appraisal for the New Zealand Population. Ministry
for the Environment, Wellington, February 2001.
10 A picogram is a trillionth of a gram.
11 Established as a range of 1-4 pg/kg bw/day, with a target tolerable
daily intake of 1 pg/kg bw/day.
12 The situation is similar in other countries, and is the reason why
global (i.e. the Stockholm Convention), regional and countrywide initiatives
are being taken.
13 For example, the slogan of the Tourism Board is '100% Pure New Zealand'.
