Fate and Effects of an Alkylamine Ethoxylate Surfactant Mixture in Aquatic Systems: Pulsed Exposures, Recovery Capacity and the Importance of Sediment

Alkylamine ethoxylates (ANEOs), such as polyoxyethylene(15)tallow amine (POEA) are com-monly used adjuvants in glyphosate herbicide formulations, such as Roundup® and Vision®. The available data on the toxicological effects of glyphosate formulations and POEA to aquatic organ-isms points to the surfactant as the main driver of toxicity from these formulations and suggest the potential for effects at concentrations close to those estimated to occur in the environment. Tier-1 environmental hazard assessments based on these observations resulted in regulatory au-thorities prohibiting direct over-water application of formulations containing POEA in several countries; still, unintended exposure of aquatic ecosystems to these formulations is possible via spray drift or, particularly in forestry scenarios, via aerial over-spray of small, shallow wetlands. The general goal of this thesis was to refine the risk assessments for a commercial mixture of POEA known as MON 0818 and, by extrapolation, the glyphosate-based herbicide formulations in which they are present. The refinement goal involved developing a better quantitative under-standing of the fate of POEAs in aquatic systems with particular emphasis on sorption to sedi-ment and how the fate of POEAs may influence observed toxicity to non-target aquatic organ-isms. The general conclusion from the work presented in this dissertation is that, under real-world envi-ronmental conditions, unintended exposure of aquatic systems to POEA surfactants will most likely result in short, single-pulse, exposures. These are due to rapid (<24 h) partitioning of the surfactant into sediment and suspended particulates where it will remain strongly adsorbed with low bioavailability. Further, this reduced exposure scenario will result in a reduction in the bio-logical effects observed in the field when compared to those expected from Tier-1 hazard assess-ments based on water-only standard tests and worst-case estimated environmental concentrations. These results highlight the inappropriateness of simple screening-level approaches for the as-sessment of the risk posed by compounds for which the expected exposure regimes may deviate from that more typically used in traditional standard acute laboratory tests.