The latest Environmental Protection Agency (EPA) report on dioxin levels in the Irish environment (based on dioxin levels measured in cows’ milk in a 2007 survey) shows that all of the samples had dioxin levels well below the relevant EU limits. The report also shows that dioxin levels measured in this survey compare favourably with those taken from similar surveys in EU and other countries.
Commenting on the results, EPA Programme Manager Dr. Ciaran O’Donnell said,
‘The concentrations of dioxins were low by international standards and comparisons. The survey confirms the continuing low levels of dioxins and dioxin-like substances in the Irish environment.’
The principal mechanism for the entry of dioxins into the environment in Ireland is by low-level emissions 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 this as well as in previous assessments of dioxin levels in the Irish environment.
The survey was carried out between late May and early July 2007, 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 that might be seen as areas of potential risk of raised dioxin levels.
The reported ranges for dioxins in milk fat (37 samples) were 0.141 to 0.611 pg WHO-TEQ/g with a mean of 0.225 WHO-TEQ/g. When PCBs (Polychlorinated biphenyls) were included, the ranges are 0.232 to 1.51 pg WHO-TEQ with a mean of 0.425 pg WHO-TEQ/g (picograms of WHO 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 levels are well below the EU limit in milk and milk products of 3.0 pg WHO-TEQ/g for dioxins only, and 6.0 pg WHO-TEQ/g for dioxins and PCBs combined. Some PCB results for the greater Dublin area were higher than previously but nonetheless remained at less than half of the EU action level.
In view of the increased international awareness of the presence in the environment of brominated flame retardants (BFRs) and brominated dioxins (PBDD/PBDF), a broad range of these substances was also tested in the survey. However, only Polybrominated Diphenyl Ethers (PBDEs) were detected. The range for PBDEs (5 samples) was 95 to 279 ng/kg fat with a mean of 152 ng/kg fat, slightly lower than the levels found in 2006 when these substances were included for the first time. These levels are relatively low by international comparisons.
Download the report Dioxin Levels in the Irish Environment – Fifth Assessment.
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.