Hexachlorobutadiene
What is Hexachlorobutadiene (HCBD)?
Hexachlorobutadiene (HCBD) is a halogenated aliphatic hydrocarbon, which is mostly unintentionally formed as by-product in the manufacturing of chlorinated hydrocarbons. It can be transported via air over long ranges and is hardly biological degradable. It can be traced in surface water, drinking water, ambient air and in water and terrestrial organisms.
Properties
HCBD has low water solubility, is lipophilic and has a high vapour pressure. Because of its Henry constant, it can volatilise from wet surfaces and water into the atmosphere.
Usage and applications
In 1982, the worldwide production of HCBD was 10’000 tons – but as by-product it exceeded even that. In the USA alone 14’000 tons of HCBD were produced in 1981. This huge amount of HCBD as by-product gave incentives to find usage of it in the industry. This included being used as a solvent for rubber and other polymers, as a “scrubber” for the recovery of chlorine-containing gas or to remove volatile organic components from gas; as hydraulic heat transfer or as a transformer fluid and it was also used in the production of aluminum and graphite rods. In addition, it was used primarily in the Soviet Union as an insecticide and fungicide, but less so in Europe.
Some examples of applications:
- Solvent
- Hydraulic heat transfer
- Transformation fluids
- Insecticides and fungicides
Risks
HCBD is persistent and bioaccumulative and enriches itself in the food chain. Reactive compounds can be formed by biotransformation, which can lead to organ toxicity, genotoxicity and carcinogenicity. It is also highly toxic to birds and aquatic organisms. As for humans, HCBD has been shown to cause irritation, nervous system depression and kidney damage. It can also have adverse effects to fatty liver degeneration and according to the EPA, it is classified as a possible human carcinogen.
Laws and regulations
Unfortunately, there are no clear laws or regulations which would restrict HCBD in the ambient air. The USA stopped their production in 1970, and Europe did the same at the end of 1970. However, HCBD is still formed as a by-product during different chemical processes and it can also occur as chemical contamination in other substances. HCBD belongs to the group of persistent organic pollutants (POPs). The EU and its member states proposed HCBD to be listed in Annexes A, B or C of the Stockholm Convention.