Researchers Characterize “Hidden” Dioxins Found in Informal E-Waste Processing

A research team in Ehime University characterized the multifaceted composition of brominated, chlorinated, and mixed halogenated dioxins as well as their main precursors in soils from e-waste burning and disassembling areas in Agbogbloshie (Accra, Ghana), a major center of informal e-waste processing in Africa. The results were published in the February 22nd issue of Environmental Science & Technology.

E-waste, or Waste Electrical and Electronic Equipment (WEEE), denotes end-of-life products such as consumer electronics, communication devices, and home appliances. E-waste contains considerable quantities of valuable metals to recycle, but is also classified as harmful waste because of the presence of poisonous substances such as heavy metals and many different types of plastic additives. A large volume of these unsafe waste materials has been recycled incorrectly, and treated informally in Asian and African developing nations using basic approaches such as circuit board heating and open burning of wires. These informal recycling activities have caused critical environmental pollution due to the emission of not only pollutants contained in e-waste but also inadvertently formed secondary toxic chemicals.

Dioxin-like compounds, or just dioxins, are a family of inadvertent contaminants produced during informal processing of e-waste with a wide variety of potential toxic effects. However, assessment of the health and environmental effects of dioxins from e-waste is difficult because of their complex composition. Chlorinated dioxins such as polychlorinated dibenzo-p-dioxins and dibenzofurans are combustion by-products of polyvinyl chloride (PVC) used in wire coating. Lesser-known brominated dioxins are thermal degradation products of brominated flame retardants (BFRs), which are plastic additives engineered to stop accidental fires. Mixed brominated/chlorinated dioxins are also produced during e-waste burning but have not been properly characterized on account of the difficulties in examining their large number.

The research team in Ehime University used special analytical techniques based on 2D gas chromatography (GC×GC) and time-of-flight mass spectrometry (ToFMS) to carry out a detailed profiling of halogenated contaminants in the soils collected close to e-waste burning and disassembling areas. Polybrominated and mixed halogenated dibenzofurans (PBDFs and PXDFs) were the main dioxins detected. Their composition profiles indicate that PBDFs were produced from polybrominated diphenyl ethers (PBDEs), a family of flame retardants usually found in e-waste plastics; and PXDFs mostly from PBDFs through a consecutive bromine-to-chlorine exchange. High concentrations of PXDFs in e-waste burning areas specify that these "hidden" dioxins may add considerably to the total toxicity of the e-waste-derived dioxin mixture, and have to be added in future human and environmental exposure risk assessment.

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