Dioxins
Dioxins are a group of chemicals that share similar structures and ways of affecting the body. Find out about the effects of dioxin exposure, and the health support services available if you have been exposed.
What dioxins are
Dioxin compounds belong to a group of 3 closely related families:
- polychlorinated dibenzo-p-dioxins
- polychlorinated dibenzofurans (furans)
- certain polychlorinated biphenyls PCBs).
All dioxins are very stable. Unlike most other chemicals, they do not quickly decompose or break down in the environment. Some of them have shown adverse health effects in animals at very low levels. For this reason, most countries are trying to reduce:
- the amount of dioxins in the environment
- people's exposure to dioxins.
There are 17 dioxins that are thought to pose a health and environmental risk. The level of harmfulness (toxicity) of the 17 varies. The most toxic and well studied is TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin).
How dioxins get into the environment
There are a few natural sources of dioxins, such as forest fires and volcanic activity. But most dioxins are from man made sources. These are largely the result of formation as byproducts of burning (combustion) and certain industrial processes.
Advances in chemical and environmental management practices since the late 1980s has caused a reduction in dioxin emissions in Aotearoa New Zealand.
In 2004, Aotearoa ratified the Stockholm Convention on Persistent Organic Pollutants. This aims to eliminate dioxins from the environment, where possible.
Stockholm Convention on Persistent Organic Pollutants — Ministry for the Environment (external link)
How dioxins get into your body
Some exposure to dioxins cannot be avoided as they are in the environment and form naturally, as well as by certain industrial processes. Cigarette smoke also contains small amounts of dioxins.
For most people in Aotearoa New Zealand, about 90% of dioxin exposure is through diet. Mainly from foods that have animal fats, such as meat, dairy products, eggs and fish.
Dioxins in food
Dioxins enter food after being deposited onto soil and plant surfaces from the air. They are then eaten by grazing animals.
Dioxins in plants
Plants take up only very small amounts of dioxins through their roots. Small amounts of exposure happen:
- by being breathed in (inhalation)
- through the skin (skin absorption)
- by accidentally eating contaminated soil or dust (ingestion).
Dioxins are broken down by exposure to sunlight. But if they are buried in the soil, they are likely to stay there for a long time. Once they are in the body, they can build up in fat and stay for many years.
Dioxins in people
Typically, lower levels of dioxins are found in:
- people from less industrialised countries
- rangatahi (younger people).
Levels for Aotearoa New Zealand's general population are at the lower end of the range of reported international levels.
In 1996 and 1997, the Ministry for the Environment did a study on the level of dioxin in the blood of 1,834 people in Aotearoa New Zealand.
This study found the average amount of dioxin in the blood was 2.7 pg/g (picograms per gram) for people of the same age and sex as the Paritutu people tested. If this is projected to 2024, this represents a value of 1.7 pg/g. A picogram is a trillionth of a gram (0.000000000001g).
Dioxins in breast milk
A study of the dioxins in the breast milk of a sample of New Zealand women, for the Ministry of Health, found the levels had decreased from an average of 16.4 pg/g of fat in breast milk in 1988 to 5.3 pg/g in 1998. This is a fall of about 70% over the decade. There was a further 40% decline from 1998 to 2008. The study of dioxins in breast milk was for all dioxins, not just the TCDD dioxin found at elevated levels in the Paritutu blood serum study.
Because of concerns by residents that illnesses might be due to dioxin exposures from the former Ivon Watkins-Dow plant in New Plymouth, health authorities commissioned a serum dioxins study of selected residents who live or did live at Paritutu, the nearest suburb to the plant.
The report investigating historical exposures to dioxin among residents of the New Plymouth suburb of Paritutu was released in 2005.
Serum dioxin study in Paritutu — Health New Zealand (external link)
Health effects caused by exposure to dioxins
While there have been many studies, there is still a lot that is not known about:
- how dioxin affects people
- at what level people exposed to dioxin might be likely to have health effects.
How much dioxin a person is exposed to and for how long is important, as well how likely they are to be harmed.
The most well-studied dioxin is TCDD. At very high doses it may case:
- a severe acne-like skin condition (chloracne)
- cancer in some people.
The adverse health effects associated with TCDD exposure are not fully known. Animal studies show immune, reproductive and developmental effects. These animal studies have been used internationally to establish health-based guidelines for exposure to dioxins in soil, air and food.
The first evidence that dioxin may cause cancer was an animal study published in 1978. But it was not until 1997 that dioxin was classified as a human carcinogen (cancer causing agent) by the International Agency for Research on Cancer (IARC).
In animal models TCDD appears to be a strong promoter (helps it along) and weak initiator (starter) in the development of cancer (carcinogenesis). So it is possible that the development of cancer in response to TCDD exposure in humans depends upon exposure to other initiators such as cigarette smoking.
There have been regular reviews of all the evidence (animal and human) by the former Institute of Medicine of the National Academy of Sciences and the National Academies of Sciences, Engineering and Medicine in the United States to create a list of conditions that are accepted as being associated with exposure to TCDD.
The conditions accepted in the sufficient evidence of health effects category are:
- Hodgkin's disease
- non-Hodgkin's lymphoma
- soft tissue cancer (sarcoma)
- chronic lymphocytic leukaemia
- chloracne
- hypertension
- monoclonal gammopathy of undetermined significance (a condition with no symptoms but has abnormal protein in the blood and urine, or both).
Review in 2018
The most recent review in 208 was undecided if Type 2 diabetes should remain in the limited or suggestive evidence category, or move to the sufficient evidence category.
There is limited or suggestive evidence that exposure to dioxins are related to:
- respiratory cancers (lung, bronchus, larynx and trachea)
- prostate cancer
- bladder cancer
- multiple myeloma
- early onset peripheral neuropathy
- porphyria cutanea tarda
- AL amyloidosis
- Parkinson's disease
- ischaemic heart disease
- stroke
- hypothyroidism.
There is no evidence that dioxins cause direct genetic damage. There is a small possibility that dioxin may cause indirect genetic damage.
Genetic testing of people will not provide any useful information in relation to their historic dioxin exposure. The difficulty in interpreting the results of genetic testing, and the inability to connect the results specifically to dioxin exposure need to be considered by people thinking about the test. There are no apparent clinical or prognostic benefits from genetic testing.
Health effects caused by exposure to dioxins
While there have been many studies, there is still a lot that is not known about:
- how dioxin affects people
- at what level people exposed to dioxin might be likely to have health effects.
How much dioxin a person is exposed to and for how long is important, as well how likely they are to be harmed.
The most well-studied dioxin is TCDD. At very high doses it may case:
- a severe acne-like skin condition (chloracne)
- cancer in some people.