The key difference between dioxins and PCBs is that most dioxins are naturally occurring substances and are never synthesized for any purpose, whereas PCBs are substances that were synthesized for various technical purposes.
Dioxins and PCBs are toxic chemical compounds that can persist in the environment, accumulating in the food chain. Therefore, these are harmful chemicals. PCBs are a derivative of dioxins, or we say, PCBs are dioxin-like compounds. Both dioxins and PCBs are considered as environmental pollutants.
CONTENTS
1. Overview and Key Difference
2. What are Dioxins
3. What are PCBs
4. Side by Side Comparison – Dioxins vs PCBs in Tabular Form
5. Summary
What are Dioxins?
Dioxins are a group of chemical compounds that are considered as persistent environmental pollutants. Most members of this group are highly toxic compounds. These compounds are grouped together since their mechanism of action regarding the toxic effect is the same. E.g. these compounds tend to activate aryl hydrocarbon receptor (AH receptor) in different binding affinities depending on the chemical structure of the dioxin compound.
Figure 01: Chemical Structure of 1,4-dioxin
The toxicity of dioxin compounds depends on the number of chlorine atoms in the molecule and their positions. The Toxic Equivalency Factor (TEF) is an important concept regarding the toxicity of dioxin compounds. This factor was developed to facilitate risk assessment and regulatory control.
Dioxin compounds are virtually insoluble in water but are soluble in lipids. Thus, this makes these compounds able to associate with organic matter such as plankton, plant leaves, and animal fat. In addition to that, these compounds tend to be absorbed into inorganic particles, such as ash and soil. These are extremely stable compounds and tend to accumulate through the food chain.
What are PCBs?
PCBs or polychlorinated biphenyl compounds are a group of organic chlorine compounds having the general chemical formula C12H10-xClx. These compounds were once widely deployed as dielectric and coolant fluids in electrical apparatus, carbonless copy paper and in heat transfer fluids. The molar mass of PCBs varies according to the value of the “x” in the chemical formula. However, PCBs appear in light yellow colour or can be colourless. These are thick, oily liquids.
Figure 02: General Structure of PCBs
PCB compounds are considered as organic pollutants that can cause environmental pollution. Due to their characteristic longevity, they are still in use, but their production has been drastically decreased since 1960 due to its environmental toxicity. They are classified as persistent organic pollutants. According to some research studies, PCBs can cause cancer in animals and are probable carcinogens for humans. These compounds can accumulate in the food chain, including many rivers, buildings, parks, and other sites.
PCB compounds are structurally similar to dioxin compounds, and their toxic mode of action is also the same. However, PCBs can cause extra toxic effects, such as endocrine disruption and neurotoxicity.
PCB compounds are slightly soluble in water but are soluble in organic solvents. Therefore, we can categorize these compounds as hydrophobic compounds. PCB compounds are soluble in oils, and fats as well. These compounds exist as pale yellow coloured or colourless viscous liquids having a low vapour pressure at room temperature. These substances show a high thermal conductivity and a high flashpoint.
Similar to most other organic environmental pollutants, PCBs do not break down or undergo degradation easily, making them attractive for industries. These compounds are resistant to acids, bases, oxidation, hydrolysis, and temperature changes as well. Moreover, these compounds can generate extremely toxic compounds such as dibenzodioxins and dibenzofurans through partial oxidation.
More importantly, PCB compounds can easily and readily penetrate our skin, PVC structures, and latex structures; however, there are some PCB resistant materials as well, e.g. Viton, polyethylene, PVA, PTFE, nitrile rubber, Neoprene, etc.
What is the Difference Between Dioxins and PCBs?
Dioxins and PCB compounds are organic pollutants. The key difference between dioxins and PCBs is that most dioxins are naturally occurring substances and are never synthesized for any purpose, whereas PCBs are substances that were synthesized for various technical purposes. Therefore, dioxins already exist in the environment while PCBs are released to the environment due to human activities.
Below is a summary of the difference between dioxins and PCBs in tabular form.
Summary – Dioxins vs PCBs
Dioxins and PCBs are stable compounds containing chlorine atoms attached to hydrocarbon compounds. These are considered as organic pollutants. The key difference between dioxins and PCBs is that most of the dioxins are naturally occurring substances and never synthesized for any purpose, whereas PCBs are substances that were synthesized for various technical purposes.
Reference:
1. “Polychlorinated Biphenyls (PCBs).” Illinois Department of Public Health, Available here.
Image Courtesy:
1. “1,4-Dioxin” By Leyo – Own work, Public Domain) via Commons Wikimedia
2. “Polychlorinated biphenyl structure” By D.328 – Own work (CC BY-SA 3.0) via Commons Wikimedia
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