Assessment of the persistence of hexachlorobenzene in the ecosphere

Various degradation tests were carried out to assess the persistence of hexachlorobenzene (HCB) in the ecosphere. HCB was irradiated with light of various wave-lengths in organic solvents and in water, partly after addition of H2O2 or metal oxides. Photolysis to various dehalogenated products occurred at different rates, depending on concentration and irradiation time; HCB adsorbed on a silica gel was mineralized by light to CO2. A negligible amount of 14C-labelled HCB was mineralized to 14CO2 in various biodegradation tests. In an outdoor lysimeter experiment, 14C residues were found in all parts of wheat plants grown from seeds treated with 14C-HCB. Besides the parent compound and bound residues in plants and soil, very small amounts of soluble polar metabolites were present in the plants; the main product of this group, isolated from roots, was conjugated pentachlorothiophenol. Wheat grown in soil with 14C-HCB residues contained unchanged HCB and bound residues.