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Do polyethoxylated tallow amine surfactants in herbicides pose a risk to aquatic organisms?

(© iStockphoto.com/ Vesna Sajn)

Some recent studies have raised concerns that the class of Polyoxyethylenealkylamine (POEA), including polyethoxylated tallow amine surfactants contained in some glyphosate-based herbicides, poses risks to aquatic animals. POEA is a non-specific name which covers a whole range of ethoxylated alky amine compounds of which ethoxylated tallow amine are a sub group. In particular, a study published in 2004 by the researcher Rick Relyea 6 and colleagues assessed the potential toxic effects of glyphosate-based herbicides containing polyethoxylated tallow amines on several species of frogs. The results indicated that tallow amine-based surfactants could harm amphibians and lead to increased mortality. Indeed, above a certain threshold, surfactants in water are expected to have negative effects on aquatic organisms by impairing the integrity of cellular membranes.

However, the results of these studies need to be viewed with caution because the animals in the experiments were exposed to unrealistically high concentrations of polyethoxylated tallow amines. Such high concentrations are highly unlikely to be found in the real world for the following reasons:

  • Aquatic organisms may only occasionally be exposed to ethoxylated tallow amines as a consequence of unintentional spray drift or run-off from fields. The predicted concentrations of these substances in water after such events present no significant acute risks to amphibians, fish or invertebrates in water bodies.
  • Ethoxylated tallow amines dissipate rapidly from natural water into sediment. A study has shown that it takes less than a day for half the polyethoxylated tallow amines to dissipate from the water, so aquatic animals should not be exposed to elevated levels of these substances over a longer period 9.

From a regulatory perspective, there are guidelines that define the acceptable level of environmental risk posed by herbicides to aquatic organisms in terms of their “toxicity exposure ratio” (TER). The higher the TER value, the lower the risk of an incident that could cause harm to organisms in wetlands. Substances with acute TER values above 100 for aquatic animals are considered to present a low acute risk in the environment, as defined by regulatory authorities. For the ethoxylated tallow amine still in use in glyphosate based formulations, the calculated acute TER value for different aquatic animals are >100 when following label directions as well as following good agricultural practices are respected which means that the acute risk to amphibians, fish and aquatic invertebrates in real-world situations resulting from exposure to ethoxylated tallow amines is relatively low 1, 2, 7.

 

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Last update: 03 June 2013