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Module 6: Air Pollutants and Control Techniques - Dioxins and Furans - Characteristics
Contents
Lesson Material
Practice Problems
Objective
- Describe the basic characteristics of dioxin and furan compounds.
Sources of dioxins and furans include waste incinerators, cement production, fossil-fuel-fired combustors, and forest fires.
Dioxins and furans are compounds with the general chemical structure
shown in Figure 1 . There are a large number of individual
dioxin and furan compounds called congeners.
There can be as few as one or as many as eight chlorine atoms substituted
on the dioxin or furan ring compound.
The dioxin and furan compounds having from four to eight chlorine atoms are considered especially toxic. All of the dioxin and furan compounds are considered potentially toxic.
Dioxin and furan compound emissions are calculated and regulated in two different ways:
- As the total dioxin and furan compound concentrations
- As the Toxic Equivalency Quotient (TEQ) concentration
The TEQ value for dioxin and furan emission is calculated according to a toxicity weighting scale. The compound 2,3,7,8 tetrachlorinated dibenzo-p-dioxin is usually considered the most toxic compound and is assigned a weighting factor of 1.0. Sixteen other dioxin-furan compounds are assigned weighting factors ranging from 0.5 down to 0.001. The observed concentrations of these seventeen dioxin-furan congeners are multiplied by these weighting factors to determine the total concentration of dioxin-furan compounds that have a toxic equivalent to 2,3,7,8 tetrachlorinated dibenzo-p-dioxin. This concentration is usually expressed as dioxin-furan compounds in TEQ nanograms per cubic meter.
The TEQ value is often used in regulatory limits because it is most closely related to the adverse health effects believed to be associated with dioxin and furan compounds.
Procedures for calculating the TEQ values are discussed in the lesson on Concentration in Module 2.
Practice Problems
Dioxins and Furans - Characteristics
- Instructions:
- Complete the Practice Problems before proceeding to the next section. Click on the button below.