Efficient Decomposition of Environmentally Persistent and Bioaccumulative Organofluorine Compound "PFOS" by Use of Sub-Critical Water with Iron

The National Institute for Advanced Industrial Science and Technology (AIST) has succeeded in the development of an efficient method to decompose environmentally persistent and bioaccumulative perfluorooctane sulfonate (PFOS) and related compounds to fluoride ions.

Organofluorine compounds have been widely used in many industries as surfactants because they have excellent properties such as heat and chemical resistance, light transparency, etc. However, some of them show high environmental persistence and bioaccumulation so that the development of effective waste treatment methods is desired. PFOS is has been globally detected in environmental waters and wildlife and its long-term toxicity (negative health effects caused by continued intake of the substance) is suspected. PFOS shows very high chemical and thermal stability; it cannot be decomposed even if it is boiled in sulfuric acid.

AIST has achieved highly efficient decomposition of PFOS into fluoride ions by adding iron powder to water containing PFOS and taking the sample to sub-critical water state at 250-350°C. The produced fluoride ions may be recycled as a source of fluorine using an established processing method for fluoride ions. This method was successfully applied to decompose other related fluorochemicals and to decompose PFOS contained in a coating agent used in electronic industry.

Details of this method were published in the February issue (No. 3) of Environmental Science & Technology, Vol. 40, published by the American Chemical Society.

Background

Organofluorine compounds have unique characteristics (repulsion to water and oil, resistance to heat and to chemical substances, non-absorption of light) so that they have been used as surfactants such as surface treatment agents, emulsifiers, coatings, etc. However, it has been recently reported that some of them are persist in the environment and accumulate in wildlife. PFOS is a representative example. Because of the environmental persistence and bioaccumulation of PFOS, the United States Environmental Protection Agency (USEPA) established regulations controlling the use of PFOS in April 2002, and in November of the same year, the Organization for Economic Cooperation and Development (OECD) published a hazard assessment of PFOS. In December of the same year, PFOS became a designated compound according to the Chemical Substances Control Law (currently class II specified chemical substance) in Japan. In June of 2005, PFOS was nominated at the Stockholm Convention, where international regulations are being examined.

Therefore, it is extensively desired to develop effective waste treatment techniques for PFOS and related compounds with low energy costs.

Key Points

  • Perfluorooctane sulfonate (PFOS), a highly bioaccumulative organofluorine compound, can be effectively decomposed to fluoride ions by use of water and iron.
  • The high stability (difficulty of decomposition) of organofluorine compounds hinders their waste treatment. In particular, PFOS is highly stable and there have been no effective methods for its decomposition, except for incinerating at high temperature.
  • Further studies will be conducted to the decomposition and recycling of organofluorine compounds of larger molecular weights.

http://www.aist.go.jp

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