Dioxins are perhaps the most toxic of environmental contaminants. A new survey updates the national picture on levels of dioxins in the Irish environment.
The Environmental Protection Agency (EPA) have just released the latest report on dioxin levels in the Irish environment (based on the levels in cows’ milk in a 2006 survey). The report, entitled Dioxin Levels in the Irish Environment – Fourth Assessment, shows that all of the samples had levels well below the relevant EU limit.
Other key findings were:
All levels recorded compare favourably with those from similar studies in other EU countries and the US;
Some results for the greater Dublin area were higher than elsewhere in Ireland, but nonetheless remained at less than half of the EU limit.
Commenting on the results, EPA Programme Manager Dr. Ciaran O’Donnell said,
"While some dioxin compounds were found in all samples, as expected, the concentrations were low by international standards. The survey confirms the continuing low levels of dioxins and dioxin-like PCBs in the Irish environment."
The principal mechanism for the entry of dioxins into the environment in Ireland is by low-level emission from multiple combustion sources to the atmosphere, with subsequent deposition onto vegetation such as grass. Since any dioxins on grass ingested by cows tend to concentrate in the milk fat, sampling for dioxin levels in the milk of grazing cows is the approach adopted in the assessment of dioxin levels in the Irish environment.
The survey was carried out between late May and early July 2006, during the peak outdoor grazing season, by taking a series of milk samples mainly from representative regional dairies. Additional samples were also taken from localities which might be seen as areas of potential risk of raised dioxin levels.
The results of the survey showed levels for dioxins in milk fat ranging from 0.118 to 1.31 pg WHO-TEQ/g with a mean of 0.275 WHO-TEQ/g (picograms of World Health Organisation Toxic Equivalent per gram of fat; 1 pg is 10-12 of a gram). The WHO Toxic Equivalent is the current internationally recognised system for comparing dioxin toxicities of different samples. These concentrations were uniformly low by international standards. The highest level found was less than 50% of the EU limit of 3.0 pg WHO-TEQ/g for dioxins in milk and milk products.
In view of the increased international awareness of the presence in the environment of brominated flame retardants (BFRs), these were also sampled for in the survey. A broad range of the common BFRs was tested but only Polybrominated Diphenyl Ethers (PBDEs) were found. The range for PBDEs (5 samples) was 150 to 265 nanogram per kilogram (ng/kg) fat with a mean of 200 ng/kg fat. (1 ng = 10-9 of a gram). These levels are relatively low by international standards.
The survey has been repeated in its entirety in 2007 and the indicative results for the greater Dublin area samples show substantially lower levels than in 2006.
The report Dioxin Levels in the Irish Environment – Fourth Assessment is available on the EPA website at: http://www.epa.ie/downloads/pubs/air/quality/
What are Dioxins?
Dioxins form a group of some 210 closely related, complex organic compounds, the vast majority of which are considered to have little environmental significance at the levels normally encountered. However, 17 of these substances have been shown to possess a very high toxicity, particularly in animal tests. The toxic responses include dermal effects, immunotoxicity and carcinogenicity, as well as reproductive and developmental toxicity. Dioxins arise mainly as unintentional by-products of incomplete combustion and from certain chemical processes. Similar effects are caused by some of the dioxin-like polychlorinated biphenyls (PCBs) and in order to conform to current practice, testing for these compounds was also included in this programme.
Sources of Dioxins
Although PCDDs and PCDFs are not produced intentionally except for research and analysis purposes their formation is often a by-product of many activities. Some significant sources internationally are:
- Accidental fires
- Backyard burning of household waste and bonfires
- Cement kilns (especially where hazardous waste is co-incinerated)
- Chlorine bleaching of wood pulp
- Coal fired power plants
- Copper production
- Forest fires and other natural fires
- Incineration of medical waste
- Incineration of municipal or hazardous waste
- Production of steel
- Residential combustion (especially where wood is used)
- Sinter plants
An emerging category of pollutants, brominated flame retardants (BFRs) and brominated dioxins (PBDD/PBDF) were measured for the first time as part of the main survey. Brominated dioxins (PBDDs and PBDFs) are also formed unintentionally, mainly through incineration of wastes or accidental fires that include consumer products containing brominated flame retardants (BFRs). Many of the BFRs have been banned for future use because of their toxicity and environmental persistence but they continue to be found in many consumer products such as furniture, fabrics and electronic products.