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Biotransformation of 3,5‐dibromo‐4‐hydroxybenzonitrile under denitrifying, Fe(III)‐reducing, sulfidogenic, and methanogenic conditions
Author(s) -
Knight Victoria K.,
Berman Mitchell H.,
Häggblom Max M.
Publication year - 2003
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620220311
Subject(s) - bromoxynil , chemistry , biodegradation , denitrifying bacteria , anaerobic exercise , biotransformation , hydrolysis , environmental chemistry , organic chemistry , denitrification , agronomy , nitrogen , biology , enzyme , physiology , weed control
Abstract Bromoxynil (3,5‐dibromo‐4‐hydroxybenzonitrile) is a halogenated aromatic nitrile herbicide used on a variety of crops for the postemergence control of annual broad‐leaved weeds. The anaerobic biodegradability of bromoxynil and its aerobic transformation product, 3,5‐dibromo‐4‐hydroxybenzoate, were examined in enrichment cultures established with anaerobic sediment under denitrifying, Fe(III)‐reducing, sulfidogenic, and methanogenic conditions. Bromoxynil (100 μM) was depleted in 20 to 30 d in the methanogenic, sulfidogenic, and Fe(III)‐reducing enrichments but was stable under denitrifying conditions. The 3,5‐dibromo‐4‐hydroxybenzoate (100 μM) was depleted within 20 to 35 d under all four anaerobic conditions. Both compounds were stable in sterile controls. Bromoxynil and 3,5‐dibromo‐4‐hydroxybenzoate were readily utilized upon respiking of the cultures. During utilization of bromoxynil, stoichiometric release of bromide was observed with transient accumulation of metabolites identified as bromocyanophenol, cyanophenol, and phenol. Bromoxynil heptanoate and octanoate were rapidly hydrolyzed to bromoxynil, which was further degraded. These results indicate that bromoxynil and 3,5‐dibromo‐4‐hydroxybenzoate are degraded under different anaerobic conditions. Anaerobic degradation of bromoxynil proceeds via reductive debromination to 4‐cyanophenol, which is further transformed to phenol and can ultimately be degraded to carbon dioxide.