Herbicides environmental fate

Degradation or Transformation. Degradation or transformation of a herbicide by soil microbes or by abiotic means has a significant influence not only on the herbicide s fate in the environment but also on the compound s efficacy. Herbicides that are readily degraded by soil microbes or other means may have a reduced environmental impact but may not be efficacious. Consider the phenomenon of herbicide-resistant soils. In these cases, repeated application of a given herbicide has led to a microbial population with an enhanced ability to degrade that herbicide (252,253). This results in a decrease or total loss of the ability of the herbicide to control the weed species in question in a cost-effective manner. 

Then there are a number of pesticides, e.g. the phenolic herbicide dinoseb and the fungicide pentachlorophenol, whose speciation varies strongly in the environmental pH-range. For this reason, one has to consider the pwhen estimating their environmental fate. Structures of the compounds discussed in this section are depicted in Table 1, together with a listing of their pand octanol-water partition coefficients, Kow, of the neutral species (unless otherwise indicated). Typical basic pollutants include the industrial chemicals aniline and jV.jV-dimethylaniline. 

Herbicides, 11 868 13 281-345 13 524. See also Environmental fate of herbicides Growth retardants Herbicide action modes Herbicide groups... 

Triazacyclononane derivatives, 24 56 Triazine-based antibiotics, 26 799 Triazine herbicides, 13 284, 321-322 Triazines, 18 769, 9 290-291 Triazines. See also, Environmental fate of triazines... 

Tremblay, 1978. "The Toxicology, Environmental Fate and Human Risk of Herbicide Orange and Its Associated Dioxin." Air Force Technical Report OEHL-TR-78-92. 247p. Document... 

This study will provide fundamental information on the effect of stereoisomerism on the environmental fate of a widely used chloroacetanilide herbicide, metolachlor. Metolachlor is classified as a potential carcinogen and is the second most extensively used herbicide in the United States (7). Biological dechlorination of metolachlor leads to the formation of more polar metabolites (8), metolachlor oxanilic acid (OXA), and metolachlor ethanesulfonic acid (ESA) (Figure 3). Metolachlor OXA and metolachlor ESA are found at higher concentrations and are more frequently detected in surface and ground water than their parent compound (9). 

Bacci, E., A. Renzoni, C. Gaggi, D. Calamari, A. Franchi, M. Vighi, and A. Seven (1989). Models, field studies, laboratory experiments An integrated approach to evaluate the environmental fate of atrazine (s-triazine herbicide). Agric. Ecosys. Environ., 27 513-522. Baker, J.L. and J.M. Laflen (1979). Runoff losses of surface-applied herbicides as affected by wheel tracks and incorporation../. Environ. Qual., 8 602-607. 

Weinhold, B J., Gish, TJ. (1994) Chemical properties influencing rate of release of starch encapsulated herbicides Implications for modifying environmental fate. Chemosphere 28(5), 1035-1046. 

C.S. Helling, Environmental Fate of Herbicides in Hawaii, Peru and Panama, in Proceedings of a Symposium Environmental Behavior of Crop Protection Chemicals, IAEA-SM-343/7, 1997, Vienna, Austria, pp. 389-406. 

Provides chemical, physical, analytical, use, and toxicity data for nearly 1200 pesticides, herbicides, and other agricultural chemicals. Contains The Agrochemicals Handbook from the Royal Society of Chemistry. Environmental fate/transport, resistance information, and lists of manufacturers are also included. A companion tool from the Royal Society of Chemistry is the 3rd edition of the World Directory of Pesticide Control Organizations (ISBN 0-85404437X), which gives sources of contacts in over 160 organizations worldwide involved in the control of pesticides. 

PBO is known to enhance the activity of several herbicides, but when this action was first described detailed studies on the metabolic fate of PBO in plants had not been undertaken, nor had a full evaluation been made of its environmental fate, all essential for commercial use. Consideration has also been given to using PBO to overcome resistance in herbicides. 

Herbicide fates, environmental, 13 307—313 Herbicide formulations, encapsulated, 16 458-459... 

Polychlorinated Dibenzo-(p)-Dioxins and Dibenzo-Furans. Another group of compounds that we need to specifically address are the polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzo-furans (PCDFs) (Fig. 2.15). The PCDDs and PCDFs are not intentionally produced but are released into the environment from various combustion processes and as a result of their occurrence as unwanted byproducts in various chlorinated chemical formulations (e.g., chlorinated phenols, chlorinated phenoxy herbicides see Alcock and Jones, 1996). Because some of the PCDD and PCDF congeners are very toxic (e.g., 2,3,7,8-tetrachloro dibenzo-p-dioxin, see margin), there have been and still are considerable efforts to assess their sources, distribution, and fate in the environment. Similarly to the PCBs or DDT (see above), the PCDDs and PCDFs are highly hydrophobic and very persistent in the environment. It is therefore not surprising that they have also been detected everywhere on earth (Brzuzy and Hites, 1996 Lohmann and Jones, 1998 Vallack et al., 1998). Finally, we should note that polybrominated diphenylethers (PBDEs, see margin) that, like the PBBs (see above), are used as flame retardants, are of increasing environmental concern (de Boer et al., 2000). 

---