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Environmental fate & pathways

Biodegradation in soil

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Description of key information

All of the available studies were assigned a reliability rating of 2, according to the criteria of Klimisch, 1997 as the studies well conducted and documented. The two Bentley studies followed guidelines for pesticide testing and were field studies conducted with a commercial formulation of dinoseb. The other studies had no information on guidelines or GLP. 
The Bentley, 1986 study in peanuts was selected as the key study as it is a robust study adequately addressing the endpoint of concern.

Key value for chemical safety assessment

Additional information

The Bentley,1986 study was selected as the key study. In the study, peanuts were treated with 12 lbs active ingredient of a 51.0% formulation of dinoseb 2 -sec butyl 4,6, dinitrophenol (Dynamyte 3). Dinoseb was applied to the crop and bare-ground plots with a CO2 back-pack sprayer.

 

Results:

Half-life (DT50): 237 d (Peanut cropped soil) & 162 d (Bare-ground soil)

Evaporation of parent compound: not measured

Volatile metabolites: not measured

Residues: not measured

Metabolites: Not measured

 

Four supporting studies were provided for this endpoint:

- In the Bentley, 1986 study, potatoes were treated with 2.5 lbs active ingredient of a 54.4% formulation of dinoseb 4,6-dinitro-o-sec-butylphenol (Dynamyte 5). Dinoseb was applied to the crop and bare-ground plots with a CO2 back-pack sprayer.

Results:

Half-life (DT50): 172 d (Potato cropped soil) & 340 d (Bare-ground soil)

Evaporation of parent compound: not measured

Volatile metabolites: not measured

Residues: not measured

Metabolites: Not measured

 

- In the Stevens et al report, the ability of native microorganisms in various Idaho soils to degrade dinoseb was studied, in addition to some physical and chemical soil characteristics which might affect the biodegradation process.

Results: Dinoseb biodegradation rates were higher in silt-loam soils than in loamy-sand soils. Biodegradation rates were not influenced by previous exposure of the soils to dinoseb. It was shown that biodegradation of dinoseb can occur in soil and is not dependent on long term acclimation to the substance.

 

- In the Kaake et al report, the degradation pathway for dinoseb (2-sec-butyl-4,6-dinitrophenol) under reducing conditions was investigated. Cultures were inoculated with a dinoseb-degrading anaerobic enrichment culture used in field studies. Biotransformation intermediates were extracted with ethyl acetate and analyzed by high pressure liquid chromatography, gas chromatography, and mass spectrometry. Dinoseb degradation involves reduction of the nitro groups to amino groups followed by replacement with hydroxyl groups. Depending on the pH and redox potential in the culture, these intermediates may exist as quinones or hydroquinones.

 

- In the Hammill & Crawford report, a strain of Clostridium bifermentans, KMR-1, degraded 2-sec-butyl-4,6-dinitrophenol (dinoseb) to a level below the limit of detection by high-performance liquid chromatography (0.5 mg/liter) within 96 h, with no accumulation of aromatic intermediates. KMR-1 could not utilize dinoseb as a sole carbon or energy source, and degradation occurred via co-metabolism in the presence of a fermentable carbon source. KMR-1 mineralized some dinoseb in anaerobic cultures, evolving 7.2% of the radioactive label in U-ring 14C-labeled dinoseb as 14CO2. The remaining anaerobic degradation products were incubated with aerobic soil bacteria, and 35.4% of this residual radioactive label was evolved as 14CO2. During this mineralization experiment, 38.9% of the initial label was evolved as 14CO2 after both anaerobic and aerobic phases. This is the first demonstration of dinoseb degradation by a pure microbial culture.