Polyethoxylated tallow amine

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General structure

Polyethoxylated tallow amine (POEA) is a surfactant that enhances the activity of herbicides such as glyphosate. The role of a surfactant in a herbicide product is to improve wettability of the hydrophobic surface of plants for maximum coverage and aid penetration through the plant surface.[1][2]

Use and composition[edit]

The polyethoxylated tallow amine used as a surfactant in Roundup is referred to in the literature as MON 0139 or polyoxyethyleneamine (POEA). According to a 1997 review, "presumably, the Roundup surfactant is a derivative of tallow, a complex mixture of fat from the fatty tissue of cattle or sheep. Tallow contains a variety of fatty acids including oleic (37–43%), palmitic (24–32%), stearic (20–25%), myristic (3–6%), and linoleic (2–3%) acids as well as small amounts of cholesterol, arachidonic, elaidic, and vaccenic acids (Budavari 1989). An ethoxylated tallow amine (CAS No. 61791-26-2), is on the U.S. EPA List 3 of Inert Ingredients of Pesticides."[3]:14 Roundup Pro is a formulation of glyphosate that contains a phosphate ester neutralized polyethoxylated tallow amine surfactant; as of 1997 there was no published information regarding the chemical differences between the surfactant in Roundup and Roundup Pro.[3]:14

POEA is 15% of Roundup formulations and the phosphate ester neutralized polyethoxylated tallow amine surfactant is 14.5% of Roundup Pro.[3]:14

Surfactants are generally required to be used with glyphosate to allow effective uptake of glyphosate, which is hydrophilic, across plant cuticles, which are hydrophobic, and reduces the amount of glyphosate washed off plants by rain.[4]:96

Environmental effects[edit]

The chemical complexity of POEA makes it difficult to study in the environment.[4]:96

Laboratory experiments show that POEA has a half-life in soils of less than 7 days, that washout from soil is likely to be minimal, and that the estimated half-life in bodies of water would be about 2 weeks. Field experiments have shown that the half-life of POEA in shallow waters is about 13 hours, "further supporting the concept that any potential direct effects of formulated products on organisms in natural waters are likely to occur very shortly post-treatment rather than as a result of chronic or delayed toxicity."[4]:96

A review of the literature provided to the EPA in 1997 found that POEA was generally more potent in causing toxicity to aquatic organisms than glyphosate and that POEA becomes more potent in more alkaline environments. (Potency is measured by the median lethal dose (LD50); a low LC50 means that just a little of the substance is lethal; a high LC50 means that it takes a high dose to kill.) Glyphosate has an LC50 ranging from 4.2 that of POEA for midge larvae at pH 6.5, to 369 times that of POEA for rainbow trout at pH 9.5 (for comparison, at pH 6.5 the LC50 of glyphosate was 70 times that of POEA for rainbow trout).[3]:18 The pH value of most freshwater streams and lakes is between 6.0 and 9.0; fish species are harmed by water having a pH value outside of this range.[5]

Human toxicity[edit]

Two reviews have been published on the toxicity of POEA to humans. The earlier, published in 2000,[6] evaluated studies that were performed for regulatory purposes as well as published research reports. It found that "no significant toxicity occurred in acute, subchronic, and chronic studies. Direct ocular exposure to the concentrated Roundup formulation can result in transient irritation, while normal spray dilutions cause, at most, only minimal effects. The genotoxicity data for glyphosate and Roundup were assessed using a weight-of-evidence approach and standard evaluation criteria. There was no convincing evidence for direct DNA damage in vitro or in vivo, and it was concluded that Roundup and its components do not pose a risk for the production of heritable/somatic mutations in humans. ...Glyphosate, AMPA, and POEA were not teratogenic or developmentally toxic....Likewise there were no adverse effects in reproductive tissues from animals treated with glyphosate, AMPA, or POEA in chronic and/or subchronic studies. Results from standard studies with these materials also failed to show any effects indicative of endocrine modulation. Therefore, it is concluded that the use of Roundup herbicide does not result in adverse effects on development, reproduction, or endocrine systems in humans and other mammals. ... It was concluded that, under present and expected conditions of use, Roundup herbicide does not pose a health risk to humans."

The later, published in 2004,[7] said that with respect to glyphosate formulations, "experimental studies suggest that the toxicity of the surfactant, polyoxyethyleneamine (POEA), is greater than the toxicity of glyphosate alone and commercial formulations alone. There is insufficient evidence to conclude that glyphosate preparations containing POEA are more toxic than those containing alternative surfactants. Although surfactants probably contribute to the acute toxicity of glyphosate formulations, the weight of evidence is against surfactants potentiating the toxicity of glyphosate. Accidental ingestion of glyphosate formulations is generally associated with only mild, transient, gastrointestinal features. Most reported cases have followed the deliberate ingestion of the concentrated formulation of Roundup (The use of trade names is for product identification purposes only and does not imply endorsement.) (41% glyphosate as the IPA salt and 15% POEA). There is a reasonable correlation between the amount ingested and the likelihood of serious systemic sequelae or death. Advancing age is also associated with a less favourable prognosis. Ingestion of >85 mL of the concentrated formulation is likely to cause significant toxicity in adults. Gastrointestinal corrosive effects, with mouth, throat and epigastric pain and dysphagia are common. Renal and hepatic impairment are also frequent and usually reflect reduced organ perfusion. Respiratory distress, impaired consciousness, pulmonary oedema, infiltration on chest x-ray, shock, arrythmias, renal failure requiring haemodialysis, metabolic acidosis and hyperkalaemia may supervene in severe cases. Bradycardia and ventricular arrhythmias are often present pre-terminally. Dermal exposure to ready-to-use glyphosate formulations can cause irritation and photo-contact dermatitis has been reported occasionally; these effects are probably due to the preservative Proxel (benzisothiazolin-3-one). Severe skin burns are very rare. Inhalation is a minor route of exposure but spray mist may cause oral or nasal discomfort, an unpleasant taste in the mouth, tingling and throat irritation. Eye exposure may lead to mild conjunctivitis, and superficial corneal injury is possible if irrigation is delayed or inadequate. Management is symptomatic and supportive, and skin decontamination with soap and water after removal of contaminated clothing should be undertaken in cases of dermal exposure."

References[edit]

  1. ^ http://www.epa.gov/espp/litstatus/effects/redleg-frog/glyphosate/appendix-b.pdf
  2. ^ U.S. Patent 4,528,023
  3. ^ a b c d Gary L. Diamond and Patrick R. Durkin February 6, 1997 Effects of Surfactants on the Toxicitiy of Glyphosate, with Specific Reference to RODEO Report submitted to Leslie Rubin, COTR, Animal and Plant Health Inspection Service (APHIS). Biotechnology, Biologics and Environmental Protection, Environmental Analysis and Documentation, United States Department of Agriculture
  4. ^ a b c Dean G. Thompson Ecological Impacts of Major Forest-Use Pesticides Ecological Impacts of Toxic Chemicals, 2011, 88-110
  5. ^ "Technical Memorandum pH Requirements of Freshwater Aquatic Life". 
  6. ^ Williams GM, Kroes R, Munro IC. Safety evaluation and risk assessment of the herbicide Roundup and its active ingredient, glyphosate, for humans Regul Toxicol Pharmacol. 2000 Apr;31(2 Pt 1):117-65. Review.
  7. ^ Bradberry SM, Proudfoot AT, Vale JA. Glyphosate poisoning Toxicol Rev. 2004;23(3):159-67. Review.