Formation of polychlorinated phenols from photodegradation of 2,4,5-trichlorophenoxyacetic acid herbicide

R.A.A. Rahim; B.Z. Dlugogorski; E.M. Kennedy; J.C. Mackie

The phenoxyacetic acid type herbicides were used for more than half of the century to control broad leave weeds, brush and certain aquatic weeds. However, the use of 2,4,5-trichlorophenoxyacetic acid herbicide (2,4,5-T) was phased out in the 1970’s once it was established that it was often contaminated with the highly toxic 2,3,7,8-TCDD. Polychlorinated phenols, which are parent chromophores for phenoxyacetic acid type herbicides, are themselves highly toxic compounds. The toxicity of polychlorinated phenols depends on the number of chlorine atoms in the molecule, and their relative position with respect to the hydroxyl group. Most chlorinated phenols are released in natural environment from pulp bleaching process, wood preservative, chemical spillage and illegal dumping of waste disposal. Due to its high persistence and generally high stability, traces of these compounds (with their degradation products) are widespread in soils and water. In addition to concerns about their own toxicity, it has been reported that polychlorinated phenols can act as precursors to PCDD/Fs formation. The formation of PCDD/Fs from polychlorinated phenols has been investigated previously. While the release of PCDD/Fs into the environment is often associated with high temperature thermal processing of commercial materials, it has been speculated that polychlorinated dioxin can be formed from a polychlorinated phenol (pentachlorophenol) via low temperature photolysis in aqueous conditions with or without the aid of a sensitizer. However, previous attempts to establish a mechanism for the formation of dioxin via photodecomposition decomposition of 2,4,5-T were fruitless. The research to be presented in this paper was undertaken in order to assess the formation of polychlorinated phenols from photodecomposition of 2,4,5-T in pure water under UVC radiation at room temperature. The motivation for this study is associated with a desire to understand the sources, transportation and reaction mechanisms involved when toxic materials are released into the natural environment. We report the formation of chlorinated phenols from 2,4,5-T; other photodegradation products, which were also detected, will not be discussed in this paper.

Formation of polychlorinated phenols from photodegradation of 2,4,5-trichlorophenoxyacetic acid herbicide

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