Category: Environment and Wildlife
POEA is an acronym which stands for polyoxyethylene amine. This is a surfactant mixture that is included in some glyphosate-based herbicides to enhance uptake of the active ingredient (glyphosate) across the waxy layers and membranes of plants. It is well known from laboratory studies that POEA can cause toxic effects in sensitive aquatic organisms. Because of this known risk, more in depth studies have specifically examined the toxicity of formulated products which may contain POEA or other types of surfactants. These studies show that when used under typical conditions for forest management in Canada, these products pose a minimal risk to aquatic organisms, largely because surfactants such as POEA rapidly absorbs to sediments and quickly degrades therein.
Glyphosate is a highly water-soluble compound that does not cross waxy surfaces or biological membranes well. In order for the active compound to be taken up effectively by plants, surfactants are typically added to the formulation to facilitate the transfer across those barriers. POEA is a mixture of several compounds rendered from animal fat that have soap-like properties and are very effective in the facilitated transfer of glyphosate into plants. Unfortunately, surfactants such as POEA, also affect membranes in animals resulting in relatively greater toxicity of end-use products to organisms such as fish and amphibians that have exposed membranes or permeable skin. This fact has been recognized for many years and is one example of why higher tier pesticide ecotoxicology studies are conducted on end-use products rather than glyphosate alone. Using this approach ensures that the toxicity of the formulated product, inclusive of potential effects of the surfactant, are captured in the evaluation. Similarly, regulatory agencies specifically incorporate fate and effects of POEA and end-use products containing these surfactants in their risk analyses (e.g. PMRA 2015). This Canadian regulatory agency noted that all glyphosate-based herbicide products currently registered in Canada contain less than 20% POEA by weight and when used in accordance with their product labels, do not pose an unacceptable risk to wildlife including sensitive aquatic organisms. The relative sensitivity of aquatic plants, fish and amphibians to products containing POEA surfactants is the fundamental reason why intentional direct application of such products to water bodies is prohibited and why ponds, streams and lakes receive additional protection through the requirement for no-spray buffers as stated on glyphosate product labels.
PMRA (2015) notes that in general glyphosate formulations that contain POEA are more toxic to freshwater organisms than formulations that do not but do not pose an unacceptable risk to the environment when used as directed on the label. Multiple laboratory studies, extending at least as far back as 1979 (Folmar et al. 1979) have documented the fact that POEA is largely responsible for acute toxicity in fish and amphibians exposed to glyphosate-based herbicide formulations containing this surfactant (e.g. Folmar et al. 1979; Wan et al. 1989; Howe et al. 2004; Edginton et al. 2004; Moore et al. 2011). However the degree of toxicity observed in laboratory studies is typically much greater than that observed in field studies. The general lack of effect observed in field studies is largely attributable to reduced exposure which results from the rapid dissipation of both glyphosate and POEA from the water column via both microbial degradation and strong sorption to sediments (Legris and Couture 1990; Couture et al. 1995; Goldsborough and Beck 1989; Goldsborough and Brown 1993; Wojtaszek et al. 2004; Newton et al. 1994; Edge et al. 2014; Wang et al. 2005; Rodriguez 2015). Results from the latter two studies indicate that aquatic organisms are unlikely to be exposed to POEA in aqueous phase for a period of more than a few hours and that sediments are a primary sink for POEA. In sediments POEA concentrations decline through time following a biphasic process which is initially fast but slower over the second phase, presumably due to limited bioavailability for microbial degradation.
PMRA (Pest Management Regulatory Agency). Proposed re-evaluation decision – Glyphosate. PRCD2015-01. 13 April 2015. Available electronically at: firstname.lastname@example.org
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