Major Pathways of Exposure

Food

UPDATE: In June 1998, the World Health Organisation re-evaluated the health risks from dioxins and agreed on a new tolerable daily intake (TDI) range of 1-4 picogrammes/kilogramme bodyweight, to take into account new epidemiological data that has emerged, notably concerning dioxins' effects on neurological development and the endocrine system. The previous TDI was 10 pc/kg/bw per day.

It is estimated that 98% of our dioxin intake comes from food, with milk and milk products representing one third of the total intake. Animal fat in meat, poultry and fish also contribute a large fraction of dioxins in diet. In a recent Dutch study these products represented one third of the total intake and the final third came from various types of oil and fat added to processed food items. Fish oil only represented 15% of the oils which were used for this purpose but contributed to 90-95% of PCDD/Fs in the products.

Unusually high concentrations of dioxins in milk and animal fats has been reported to occur near to sources of dioxin emission from industrial processes that generate or use organochlorines. Ingestion of both soil and plants by cattle in such areas can t hen lead to elevated levels of dioxins in milk or animal fat. For example, a study of dioxin contamination in cow's milk from dairy farms located in the vicinity of municipal waste incinerators in the Netherlands, led to the restriction of milk and chees e consumption in the area.

Contamination can also occur remote from industrial sources of dioxin, as it can be distributed globally via the atmosphere, and can accumulate in the food chain in colder regions of the earth such as the Arctic.

Sewage Sludge

Sewage sludges will be contaminated with dioxins if industries which generate dioxins as by-products discharge to the sewer system - which is usually the case. The use of sludges on agricultural land used for grazing can increase human exposure because l ivestock can ingest the sludge adhered to the vegetation. The World Health Organization has advised that sewage sludge application to agricultural land should be banned where there is potential for bioaccumulation in the food chain and human exposure. Giv en the tendency of dioxins to persist and become redistributed through the environment, spreading of dioxin contaminated sludge should not be permitted under any circumstances.

Soil and Sediments

The occurrence of elevated levels of dioxins in soil has been considered to be a potentially significant public health concern since 1980. Exposure can occur through skin contact and soil ingestion. Agricultural and building workers may have a higher expo sure to dioxin from these routes than the general population. Also, children are likely to have more contact with than adults. This is an important point for consideration when setting levels for remediation of residential sites and in some instances levels of less than 1 part per billion of TCDD in soil have been set to limit human exposure.

In industrialised areas, PCDD/Fs discharged into rivers reach high levels in sediments, and thereby contaminate the aquatic foodchain. Humans who eat significant quantities of fish, especially indigenous people and sporting fishermen are at risk.

Breast Milk and Placenta

Human milk dioxin levels are of particular concern because newborns are believed to be highly sensitive to dioxins and will ingest far more than the World Health Organization's 'Tolerable Daily Inktake' (TDI) of 1-4 pg TEQ /kg/body weight per day (dioxins).

Studies on levels of breast milk in many industrialized countries indicate the average daily intake for breast-fed infants between 0 and 6 months of age is estimated to be 13pg 2,3,7,8 TCDD/kg/body weight (or 90pg TEQ/kg body weight). However, WHO stated that the TDI should not be applied to breast-fed infants since the TDI concept for these substances is based on lifetime intake. It was still recommended however, that lactating mothers should not try to l ose weight intentionally since dioxins could be mobilised from their own bodyfat.

Current levels of dioxins in human milk mean that the margin of safety for breast-fed babies calculated by risk assessments in Europe is very low. This becomes of greater concern because health risk assessments of dioxins do not take other chemicals into account and the effects of such compounds could be additive. Dioxins are also transferred to the foetus via the placenta and health risks to h umans appear to be particularly great in this early developmental stage.

WHO recommends that the benefits of breast feeding outweigh the risks and recent assessments in some countries have revealed a decline in dioxin contamination of human milk -- probably due to the reduction of some pesticide use and incinerator emissions. WHO notes, however, that the issue of hormone disruption needs to be factored into future risk assessments and "tolerable daily intake" advisories.