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Frederick M. Fishel2 1. This document is PI-89, one of a series of the Pesticide Information Office, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date November 2005. Revised May 2011. Visit the EDIS website at http://edis.ifas.ufl.edu. 2. Frederick M. Fishel, Associate Professor, Agronomy Department, and Director, Pesticide Information Office; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611. The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label. This document provides a general overview of human toxicity, provides a listing of laboratory animal and wildlife toxicities and a cross reference of chemical, common, and trade names of the arsenical herbicides registered for use in Florida. The arsenical herbicides are a group of older herbicides, having been in use since the 1950s. There are currently three arsenical herbicide active ingredients registered for use in Florida: cacodylic acid, disodium methanearsonate, and monosodium methanearsonate (DSMA and MSMA, respectively). Many arsenic compounds have been discontinued in the United States because of regulatory reasons. They are applied as postemergence or directed sprays acting primarily as contact materials with limited translocation. Their mode of action is to inhibit plant growth by uncoupling phosphorylation. Their initial plant injury symptoms are chlorosis caused by a loss of chlorophyll. Their phytotoxic activities are inactivated upon soil contact. They have been historically useful for grass control in turfgrass sites, cotton, citrus, rights-of-way, and other industrial and non-crop sites. Commercial products are readily available and numerous. They are formulated as liquids. The EPA has reached an agreement in principle with the major manufacturers of the organic arsenicals MSMA, DSMA, and cacodylic acid. This voluntary agreement steadily removes all organic arsenical pesticide uses, except the use of MSMA on cotton, from the market and implements new restrictions to better protect drinking water resources. Phasing out these uses is expected to accelerate the transition to new, lower risk herbicides. The arsenical active ingredients remaining on the market in the U.S. are the organic methylated compounds which are considered to present less toxic hazard than other forms (arsines or arsenites). Acute poisoning symptoms and signs usually appear within one hour, if ingested. Cacodylic acid is absorbed into the bloodstream more readily through inhalation than through ingestion or dermal exposure. With severe cases, garlicky odor of the breath and feces are noticeable. There may also be a salty, metallic taste in
Pesticide Toxicity Profile: Arsenical Herbicides 2 the mouth, along with abdominal discomfort. The central nervous system is also commonly affected with acute exposures, beginning with dizziness, headache, drowsiness, and confusion. Symptoms may progress with weakened muscles, spasms, coma, and convulsions. Death usually occurs one to three days following onset of symptoms and is often the result of circulatory failure, but renal injury may also contribute. Chronic exposures are more difficult to determine; but, neurological symptoms are usually more common than gastrointestinal effects which are more closely associated with acute poisoning. A sign of exposure is the formation of white bands across the nails. Mammalian toxicities for the arsenical herbicides are shown in Table 1. Table 2 lists the toxicities to wildlife by the common name of the pesticide. Table 3 provides a cross listing of many of the trade names that these products are registered and sold by in Florida. Crop Protection Handbook. 2005. vol. 91. Willoughby, Ohio: Meister Publishing Co. http://www.meistermedia.com/publications/ handbook.html Extension toxicology network (EXTOXNET). Cornell University and Michigan State University. http://extoxnet.orst.edu/index.html. Visited November 2005. Nesheim, O.N., F. M. Fishel, and M. A. Mossler. 2005. Toxicity of pesticides. UF/IFAS EDIS Document PI-13. http://edis.ifas.ufl.edu/PI008. Ware, G.W. 2000. The pesticide book. 5th edition. Thomson Publications.
Pesticide Toxicity Profile: Arsenical Herbicides 3 Arsenical herbicide mammalian toxicities (mg/kg of body weight). Cacodylic acid (sodium salt) 2,756 --DSMA 600 236 325 MSMA 1,700 >2,500 Arsenical herbicide wildlife toxicity ranges. Cacodylic acid (sodium salt) PNT ST PNT PNT DSMA ST PNT PNT MSMA PNT PNT PNT *Bird LD50: Practically nontoxic (PNT) = >2,000; slightly toxic (ST) = 501 2,000; moderately toxic (MT) = 51 500; highly toxic (HT) = 10 50; very highly toxic (VHT) = <10. **Fish LC50: PNT = >100; ST = 10 100; MT = 1 10; HT = 0.1 1; VHT = <0.1. Bee: HT = highly toxic (kills upon contact as well as residues); MT = moderately toxic (kills if applied over bees); PNT = relatively nontoxic (relatively few precautions necessary). Cross reference list of common, trade, and chemical names of arsenical herbicides. Cacodylic acid (sodium salt) Liquid Edger Hydroxydimethylarsine oxide DSMA Bonide Disodium methanearsonate MSMA Ansar, Bueno, MSMA, others Monosodium methanearsonate Does not include manufacturers' prepackaged mixtures.