Polyethoxylated tallow amine
Polyethoxylated tallow amine (POEA) refers to a range of non-ionic surfactants derived from animal fats (tallow). They primarily find used as emulsifiers and wetting agents for agrochemical formulations, such as pesticides and herbicides (e.g. glyphosate).
Synthesis
Animal fat is hydroysed to give the free fatty acids (typically oleic (37–43%), palmitic (24–32%), stearic (20–25%), myristic (3–6%), and linoleic (2–3%)). These are then converted to fatty amines via the nitrile process before being ethoxylated with ethylene oxide; this makes them water soluble and amphiphilic. The length of the fatty tail and degree of exothylation will determine the overall properties of the surfactant. Due to it being synthesized from an impure material POEA is itself a mixture compounds.
Composition and use
The polyethoxylated tallow amine used as a surfactant is referred to in the literature as MON 0139 or polyoxyethyleneamine (POEA). It is contained in the herbicide Roundup. An ethoxylated tallow amine (CAS No. 61791-26-2), is on the U.S. EPA List 3 of Inert Ingredients of Pesticides."[1]: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.[1]:14
POEA concentrations range from <1% in ready-to-use glyphosate formulations to 21% in concentrates.[2] POEA constitutes 15% of Roundup formulations and the phosphate ester neutralized polyethoxylated tallow amine surfactant constitutes 14.5% of Roundup Pro.[1]:14
Surfactants are added to glyphosate to allow effective uptake of water-soluble glyphosate across plant cuticles, which are hydrophobic, and reduces the amount of glyphosate washed off of plants by rain.[3]:96
Environmental effects
The chemical complexity of POEA makes it difficult to study in the environment.[3]:96
POEA is toxic to aquatic species like fish and amphibians. As other surfactants as well, it can affect membrane transport and can often act as a general narcotic.[3]
In laboratory experiments POEA has a half-life in soils of less than 7 days. Washout from soil is assumed to be minimal, and 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."[3]: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 LD50 means that just a little of the substance is lethal; a high LD50 means that it takes a high dose to kill.) Glyphosate has an LD50 ranging from 4.2 times 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).[1]: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.[4]
Human toxicity
Two reviews have been published on the toxicity of POEA to humans. The earlier, published in 2000,[5] 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 review, published in 2004,[2] 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." (41% glyphosate as the IPA salt and 15% POEA).
Ingestion of >85 mL of the concentrated formulation is likely to cause significant toxicity in adults.
References
- 1 2 3 4 Gary L. Diamond and Patrick R. Durkin 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, February 6, 1997
- 1 2 Bradberry SM, Proudfoot AT, Vale JA. Glyphosate poisoning Toxicol Rev. 2004;23(3):159-67. Review. (subscription required)
- 1 2 3 4 Dean G. Thompson Ecological Impacts of Major Forest-Use Pesticides Ecological Impacts of Toxic Chemicals, Bentham Science Publishers Ltd, 2011, Chapter 5, 88-110. quote"...owing to the chemical complexity of the POEA surfactant and resultant difficulty in analysing for it in complex environmental matrices, the environmental behaviour of POEA in natural forest ecosystems has not been specifically studied."
- ↑ Robertson-Bryan, Inc (1 May 2004). "Technical Memorandum pH Requirements of Freshwater Aquatic Life" (pdf). www.waterboards.ca.gov. p. 15.
- ↑ 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.