Dioxin Data Report
There are 210 congeners for mono thru octa chlorodibenzo(p)dioxin (75) and chlorodibenzofuran (135), however only the toxic congeners - those with chlorine in the 2,3,7,8- position - are reported. In your report, you will find a concentration for all 2,3,7,8- congeners for dibenzo(p)dioixn (7) and dibenzofuran (10) expressed in units of ng/kg (nanograms per kilogram, parts per trillion) or pg/L (picograms per litre, parts per quadrillion) and a detection limit. A total concentration for each homologue series is also calculated. This total includes the contribution from the corresponding 2,3,7,8- congener.
Each toxic congener has been assigned a toxic equivalency factor (TEF) relevant to 2,3,7,8-TCDD. The individual concentrations multiplied by their corresponding TEF and then summed together give a Toxic Equivalency (TEQ). Both International TEQs and WHO-TEQs are reported.
All samples are spiked with fifteen carbon-13 labelled surrogates prior to extraction. The recovery of these surrogates are monitored and reported.
Toxic Equivalency Factors
It has been well established that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is carcinogenic, and that other chlorinated dioxins and furans with the same 2,3,7,8- backbone are also toxic. However, each of these 2,3,7,8- congeners do not exhibit the same degree of toxicity.
A number of systems have been developed to express the total toxic contribution from dioxins and furans. In each system, the toxicity of each congener is weighted relative to 2,3,7,8-TCDD. This is called a Toxic Equivalency Factor or TEF. When results are reported, the concentration of each congener is multiplied by the corresponding TEF. These values are then summed together to give a total toxic equivalency or TEQ.
The two most common systems for determining TEQs are the World Health Organization TEQ (WHO-TEQ) and the International TEQ (ITEQ). They are for the most part the same, with the exception of 1,2,3,7,8-PeCDD – WHO assigns a TEF of 1, while the ITEF is 0.5 – and OCDD/F – WHO-TEF is 0.0001, while ITEF is 0.001.
ITEQs are most common in North America, while Asia and Europe tend to use WHO-TEQs. Revised WHO TEFs were released in 2006. Most, but not all regulations, that use WHO-TEQs have been converted to require the 2006 version.
To obtain a complete dioxin TEQ value, PCBs values must also be included. Twelve of the 209 PCB congeners have been assigned TEFs by the WHO. As per the dioxins, the concentration of each congener is multiplied by the corresponding TEF. These values are then summed together to give a PCB-TEQ. New WHO TEFs were released in 2006. They are in limited use at the present time, but should be expected to increase in popularity as more data is produced.
Upper and Lower Bound TEQ
There are many conventions for how to calculate TEQ values for compounds that are not detected. Regulatory jurisdictions typically substitute zero (0) into the formula for any non-detectable compound. This result is call a lower bound TEQ. Due to the toxicity of dioxins, many agencies have opted to report the worst case scenario for TEQ values. In this case, any result that is not detected substitutes the detection limit into the formula. The resulting TEQ is called an upper bound TEQ. In reality, the actual value is somewhere between the Upper Bound and Lower Bound TEQ, but we do not know where.