Appendix A
Herbicide Selection



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 237
Appendix A Herbicide Selection 

OCR for page 237
 APPENDIX A Herbicidea Classificationb ACCase inhibitors (A(1)) Haloxyfop (aryloxyphenoxypropionates) Clethodim (cyclohexanediones) Pinoxaden (phenylpyrazolines) Mitosis inhibitors (K3(15)) Alachlor (chloroacetanilides) Diphenamid (acetamides) Flufenacet (oxyacetamides) Fentrazamide (tetrazolinones) ALS inhibitors (B(2)) Bensulfuron-methyl (sulfonylureas) Imazethapyr (imidazolinones) Cloransulam-methyl (triazolopyrimidines) Photosynthesis II inhibitors (C1(5)) Atrazine (symmetrical triazines) Synthetic auxins (O(4)) Dicamba (benzoic acids) Glutamine synthetase inhibitor (H(10)) Glufosinate (organophosphorus) Glyphosate (organophosphorus) Enolpyruvyl shikimate-3-phosphate (EPSP) synthase inhibitor (G(9)) *Reference dose. †Lethal dose. §Lethal concentration.

OCR for page 237
 APPENDIX A Mode of Actionc Relative Toxicity Inhibitor of acetyl coenzyme-A Varies based on specific chemical carboxylase (ACCase), a pivotal enzyme compound; likely to be carcinogenic to in plant fatty acid biosynthesis. humans according to EPA Proposed EPA Weight-of-the-Eidence Categories (US-EPA, 2009a). Inhibition of cell division (long-chain Slightly toxic; oral RfD* of 1 × 10–2 mg/kg-day. Critical effects: fatty acid inhibitor). hemosiderosis, hemolytic anemia (US-EPA, 2009b). Inhibition of the acetolactate synthase Varied; generally low acute and chronic (ALS) enzyme resulting in cessation of toxicity to humans and not likely to be the biosynthesis of essential branched carcinogenic. chain amino acids (leucine, valine, and isoleucine). Inhibit photosynthesis by binding with Slightly to moderately toxic; oral RfD of 3.5 × 10–2 mg/kg-day. Critical effects: a specific protein in the photosystem II complex. decreased body weight gain (other effect: cardiac toxicity and moderate-to-severe dilation of the right atrium (EXTOXNET, 2009a; US-EPA, 2009c)). Relatively nontoxic. Acute oral LD50† The specific mode of action is not well in rats is 1707 mg/kg, dermal LC50§ in defined, however these herbicides mimic the endogenous auxin rabbits is >2000 mg/kg. However, eye indoleacetic acid, a plant hormone irritation in rabbit is extreme. that stimulates growth and appears to negatively affect cell wall plasticity and nucleic acid metabolism. Inhibits the activity of glutamine Practically nontoxic by ingestion; synthetase, which causes ammonia some increase in absolute and buildup in the cell. The ammonia relative kidney weights in males. No destroys cell membranes. observed carcinogenesis. Oral RfD of 4 × 10–4 mg/kg-day (NPIC, 2009; US-EPA, 2009d). Inhibits the EPSP synthase, which Generally nontoxic. Increased incidence leads to depletion of essential aromatic of renal tubular dilation in third amino acids (tryptophan, tyrosine, and generation weanlings. Oral RfD of 1 × 10–1 mg/kg-day (US-EPA, 2009e). phenylalanine). continued

OCR for page 237
0 APPENDIX A Herbicidea Classificationb Amides, pyridiazinones, pyridines, Carotenoid biosynthesis inhibitors isoxazoles, pyrazoles, triazoles, triketones, and others (F1(12)) Fluridone (unclassified) (F2(28)) Mesotrione (triketones) (F3(11)) Amitrole (triazoles) Photosynthesis II inhibitors (C1(5)) Metribuzin (triazinones, asymmetrical triazines) Dicarboximide herbicides, triazolone Protoporphyrinogen Oxidase (PPO) inhibitors (E(14)) herbicides, diphenylethers, N-phenylphthalimides, oxadiazoles, thiadiazoles, triazolinones, and others

OCR for page 237
 APPENDIX A Mode of Actionc Relative Toxicity Inhibit the catabolic degradation of Varied; developmental toxicity, probable tyrosine to plastoquinones (important human carcinogen, phytotoxic (US-EPA, for photosynthesis and carotenoid 2004, 2006, 2009f, 2009g). biosynthesis) and tocopherol (vitamin E, which protects biological membranes against oxidative stress and the photosynthetic apparatus against photo-inactivation). Inhibition of phytoene desaturase, an enzyme essential for carotenoid biosynthesis. Inhibition of hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme involved in the synthesis of plastoquinone (PQ) and tocopherol (vitamin E). Target site is generally considered unknown with the exception of amitrole, which inhibits lycopene cyclase and clomazone that is reported to inhibit an early step in the nonmevalonic acid isoprenoid pathway ultimately leading to carotenoid synthesis. Inhibit photosynthesis by binding with A slightly toxic compound in EPA a specific protein in the photosystem II toxicity class III. Liver and kidney effects, complex. decreased body weight, mortality; no indications of carcinogenic effects. RfD of 2.5 × 10–2 mg/kg-day (EXTOXNET, 2009b; US-EPA, 2009h). Inhibits the protoporphyrinogen Varied; including compounds having: oxidase (PPO) which is in the slight toxicity (EPA category III); classified chlorophyll synthesis pathway. The as a “not likely” human carcinogen PPO inhibition starts a reaction in to “likely to be a human carcinogen” the cell that ultimately causes the (US-EPA, 2001). destruction of cell membranes. The leaking cell membranes rapidly dry and disintegrate. continued

OCR for page 237
 APPENDIX A Herbicidea Classificationb Synthetic auxins (O(4)) 2,4-D (phenoxyacetic herbicide) aHerbicide listed is one example of the herbicide family. bHerbicide mode of action code according to the Herbicide Resistance Action Committee (HRAC, 2010) and the Weed Science Society of America (WSSA) classification (Senseman and Armbrust, 2007). The capitalized letter is the HRAC classification and the superscript number is the WSSA classification. cThe indicated herbicide mode of action is from the HRAC and WSSA descriptions as well as other citations. REFERENCES EXTOXNET (Extension Toxicology Network). 2009a. Atrazine. Corvallis, OR: Oregon State University. Available online at http://extoxnet.orst.edu/pips/atrazine.htm. Accessed November 14, 2009. ———. 2009b. Metribuzin. Corvallis, OR: Oregon State University. Available online at http://extoxnet.orst.edu/pips/metribuz.htm. Accessed November 14, 2009. HRAC (Herbicide Resistance Action Committee). 2010. Classification of herbicides accord- ing to mode of action. Washington, DC. Available online at http://www.hracglobal. com/Publications/ClassificationofHerbicideModeofAction/tabid/222/Default.aspx. Accessed January 21, 2010. NPIC (National Pesticide Information Center). 2009. Glufosinate. Corvallis, OR: Oregon State University. Available online at http://extoxnet.orst.edu/pips/atrazine.htm. Accessed November 14, 2009. Senseman, S.A., and K. Armbrust, eds. 2007. Herbicide handbook. 9th ed., p. 458. Lawrence, KS: Weed Science Society of America. US-EPA (U.S. Environmental Protection Agency). 2001. Pesticide fact sheet: Flumioxazin. 7501C. Office of Prevention, Pesticides, and Toxic Substances. Washington, DC. Avail - able online at http://www.epa.gov/opprd001/factsheets/flumioxazin.pdf. Accessed January 21, 2010. ———. 2004. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and Risk Management Decision (TRED) for Fluridone. 7508C. Office of Pre - vention, Pesticides, and Toxic Substances. Washington, DC.Available online at www. epa.gov/oppsrrd1/REDs/fluridone_tred.pdf. Accessed January 21, 2010. ———. 2006. Pesticide fact sheet: 1,2,4-triazole, triazole alanine, triazole acetic acid: Human health aggregate risk assessment in support of reregistration and registration actions for triazole-derivative fungicide compounds. Office of Prevention, Pesticides, and Toxic Substances. Washington, DC. Available online at www.epa.gov/opprd001/factsheets/ tetraHHRA.pdf. Accessed January 21, 2010. ———. 2009a. User’s manual for RSEI, version 2.2.0 [1996 - 2006 TRI data]. Office of Pre - vention, Pesticides, and Toxic Substances. Washington, DC. Available online at http:// www.epa.gov/oppt/rsei/pubs/RSEI%20Users%20Manual%20V2.2.0.pdf. Accessed June 24, 2009.

OCR for page 237
 APPENDIX A Mode of Actionc Relative Toxicity Mimics a plant growth regulator. The Critical effects include: hematologic, specific mode of action is not well hepatic, and renal toxicity. RfD of 1 × 10–2 mg/kg-day. defined, however these herbicides mimic the endogenous auxin indoleacetic acid, a plant hormone that stimulates growth and appears to negatively affect cell wall plasticity and nucleic acid metabolism. ———. 2009b. Alachlor (CASRN 15972-60-8). National Center for Environmental Assessment. Washington, DC. Available online at http://www.epa.gov/ncea/iris/subst/0129.htm. Accessed January 21, 2010. ———. 2009c. Atrazine (CASRN 1912-24-9). National Center for Environmental Assessment. Washington, DC. Available online at http://www.epa.gov/ncea/iris/subst/0209.htm. Accessed January 21, 2010. ———. 2009d. Glufosinate-ammonium (CASRN 77182-82-2). National Center for Environ - mental Assessment. Washington, DC. Available online at http://www.epa.gov/ncea/ iris/subst/0247.htm. Accessed January 21, 2010. ———. 2009e. Glyphosate (CASRN 1071-83-6). National Center for Environmental Assess - ment. Washington, DC. Available online at http://www.epa.gov/ncea/iris/subst/0057. htm. Accessed January 21, 2010. ———. 2009f. Pesticide fact sheet. Office of Prevention, Pesticides, and Toxic Substances. Washington, DC. Available online at http://www.epa.gov/ncea/iris/subst/0057.htm. Accessed January 21, 2010. ———. 2009g. Tembotrione chemical documents. Office of Prevention, Pesticides, and Toxic Substances. Washington, DC. Available online at http://www.epa.gov/opprd001/fact - sheets/tembotrione.htm. Accessed January 21, 2010. ———. 2009h. Metribuzin (CASRN 21087-64-9). Office of Prevention, Pesticides, and Toxic Substances. Washington, DC. Available online at http://www.epa.gov/NCEA/iris/ subst/0075.htm. Accessed January 21, 2010.

OCR for page 237