TEF's - TEQ's

The EPA and the MI DEQ have established 90 ppt Toxic Equivalency Quantity (TEQ) as being an acceptable limit for residential contamination and 330 ppt TEQ as being an acceptable limit for recreational contamination. The Center for Disease Control (Atlanta) has established 1,000 ppt TEQ as being the maximum allowable level of dioxin contamination permitted before some form of corrective action must be taken to mitigate TEQ exposure.

While the 90, 330 and 1,000 ppt TEQ may seem to be very precise levels, it must be noted that there is not a great deal of scientific data to support that these levels are without appreciable risk.

The TEQ system was developed to be able to compare the relative risk of exposure in areas of contamination that vary widely in the composition and level of most toxic dioxins and furans. Each of the seventeen highly dioxins/furans are assigned a Toxic Equivalency Factor (TEF) based on a particular chemical’s toxicity relative to 2378-TCDD, with the toxicity of TCDD being equal to 1.0.

The concentration of each dioxin/furan is multiplied by its respective TEF and the results are summed. The added results are known as the TEQ of the sample.

While the TEQ system works relatively well from a regulatory point of view, there is very little data to support that 200 ppt TEQ, for example, is actually as toxic as is 200 ppt of 2378-TCDD.

Perhaps, an example will help to illustrate the problem between actual 2378-TCDD exposure and TEQ exposure. In September, 1996, the US EPA analyzed some of the soils of Midland to determine the levels of the seventeen most toxic dioxins and furans.  The table blow is a summary of the dioxin analysis for two locations.
 

Midland, MI - Soil Analysis

(1)  Intersection of Saginaw Road and Bay City Road
(2)  Intersection of Salzburg Road and Rockwell Drive

Based on the TEQ criteria, dioxin contamination in the two locations (~600ppt) would be equivalent -- at least from a regulatory standpoint.

Note that both locations exceed the EPA maximum allowable TEQ level of 90 ppt for residential areas. However, because the TEQ levels are below 1000 ppt, neither site will require any mandatory corrective action.

However, the actual TCDD level (288 ppt) in the NE-47 location is more than three times the actual TCDD level (86ppt) in the other location. The total levels of dioxins and furans in the NE-47 location are 74,659 ppt, more than twice the level of 30,116 ppt found in the other location.

Even though the TCDD-TEQ levels are approximately the same, the locations have unique levels of the seventeen most toxic dioxins and furans.

There may be doubts about some dioxin matters but your author can guarantee one thing: there is absolutely no human health information – whether from epidemiology studies or from laboratory toxicity studies – about exposure to the specific mix of dioxins and furans found in these two locations. The assumption is that the overall toxicity is equivalent to approximately 600 ppt of 2378-TCDD for both locations. There is no data to support this assumption about the two locations.

As can be seen from this example, there is a considerable difference between actual levels of dioxins and furans and “equivalent” levels of TCDD. The human body is not exposed to “equivalent amounts of TCDD”. The human body is besieged by actual molecules of dioxin and dibenzofurans. The “equivalent amount of TCDD” is a regulatory convenience, it may not be an accurate measure of actual toxicity.


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