Herbicides biodegradation

Casida, J.E., Gray, R.A., and Tides, H. Thiocarbamate sulfoxides potent, selective, and biodegradable herbicides. Science (Washington, DC), 184(4136) 573-574, 1974. 

Marsh and Pond S ediments. Herbicides and pesticides are detectable ia marsh and pond sediments, but intrinsic biodegradation is usually found to be occurting. Littie work has yet been presented where the biodegradation of these compounds has been successfully stimulated by a bioremediation approach. 

Although the antibacterial and antifungal activities of bialaphos and phosphinothricin were not found to be usehil, the two agents were later used as biodegradeable, relatively nonselective, postemergent herbicides. Glutamine synthetase inhibition is toxic to plants because the enzyme is key to ammonia assimilation. There is some selectivity for individual plant species as shown by the LD for bialaphos ranging from 0.125 to 8.5 kg/ha (301—303). 

Pesticides include the broad categories of insecticides, fungicides, rodenticides, and herbicides. Insecticides in common use fall into three categories. The chloroinsec-ticides have chlorine in their structure. They are less soluble than the other insecticide forms and much less biodegradable (i.e., more persistent). While they are less acutely toxic, several have been identified as potential carcinogens. Carbamatea are a relatively new form of pesticide. They are less persistent and less... 

The concept of fibrous polymer formulations was extended to the delivery of aquatic herbicides (56). Several herbicides including Diquat, Fluridone, and Endothal were spun into biodegradable poly-caprolactone. Monolithic fibers and a modified monolithic system were produced with levels of herbicide from 5 to 60% by weight. Laboratory and field trials showed efficacious delivery of the active agent. Fibers provided both targeted localized delivery and controlled release of the herbicide to the aquatic weed. 

Topp E, L Xun, CS Orser (1992) Biodegradation of the herbicide bromoxynil (3,5-dibromo-4-hydroxybenzo-nitrile) by purified pentachlorophenol hydroxylase and whole cells of Flavobacterium sp. strain ATCC 39723 is accompanied by cyanogenesis. Appl Environ Microbiol 58 502-506. 

A number of substituted triazines are used as herbicides, and their biodegradation has been discussed in Chapter 10, Part 1. Treatment of soil contaminated with atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-l,3,5-triazine) illustrated a number of significant features. Although the soil that was used had the potential for degradation, a laboratory experiment with Pseudomonas sp. strain ADP that had an established potential for atrazine degradation revealed important limitations. There was a substantial decline in the numbers of Pseudomonas sp. strain ADP and only limited mineralization. Supplementation with citrate or succinate increased the survival of the strain, and successful mineralization was dependent on the preservation of a carbon/nitrogen ratio >10 (Silva et al. 2004). The last would apply generally to substrates with a low C/N ratio such as triazines. 

Schneiderheinze, J.M., Armstrong, D.W., Berthod, A. (1999). Plant and soil enantioselective biodegradation of racemic phenoxyalkanoic herbicides. Chirality 11, 330-337. 

Holtze, M.S., Sorensen, J., Christian, H. and Aamand, J. (2006) Transformation of the herbicide 2,6-dichlorobenzonitrile to the persistent metabolite 2,6-dichlorobenzamide (BAM) by soil bacteria known to harbor nitrile hydratase or nitrilase. Biodegradation, 17, 503—510. 

Biodegradation can only take place if the sorbed pollutants can be rapidly released from the organoclay complex as is the case with naphthalene (Crocker et al. 1995) and the herbicide fenamiphos (Singh et al. 2003). 

StrauberH, Muller RH, Babel W (2003) Evidence of cytochrome P450-catalyzed cleavage of the ether bond of phenoxybutyrate herbicides in Rhodococcus erythropolis K2-3. Biodegradation 14 41-50... 

McCormick, C.L., D.K. Lichatowich, and M.M. Fooladi, "Controlled Activity Pendant Herbicide Systems Utilizing Chitin and Other Biodegradable Polymers," Proceedings of the 5th International Symposium on Controlled Release of Bioactive Materials, pp. 3.6-3.17, Gaithersburg, MD (1978). 

Fig. 5. Polymerization reactions that occur with the herbicide Propanil during biodegradation...

Benzoic acid, a common food preservative, may be a suitable substrate to achieve biostimulation. It is a relatively inexpensive, harmless aromatic compound that has been previously used in analogue enrichment1 schemes to enhance biodegradation of the aromatic herbicide, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) [336]. Benzoate ion is also an intermediate in the toluene pathway and it can induce related enzymes involved in the degradation of toluene and m-and p-xylenes [336]. In addition, the anionic nature of benzoic acid would minimize its retardation and facilitate its distribution when injected into an... 

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