Safety for the Environment

When pyrethroids were first introduced, another factor which hastened their wide adoption was their environmental profile. The same general pattern of behavior is seen across all of the modern pyrethroid active ingredients.

The compounds degrade relatively quickly in soil and slightly less so in sediment. They degrade largely to the same non-toxic degradates as are found in mammalian systems.

They are extremely tightly adsorbed to any type of organic matter to set up an equilibrium between the organic matter and any surrounding water phase such that the vast majority of the chemical is adsorbed to the organic matter at any given moment but the adsorbed material remains available to re-equilibrate (i.e. this is not a matter of chemical binding).

Although much more stable to light than the original pyrethrin natural products, the modern pyrethroids tend to be degraded slowly by sunlight which tends to reduce their longevity on treated crops.

The strong adsorption means that pyrethroids do not leach to ground water which is a benefit when compared to several other classes of insecticide. However, they can be eroded from soil or concreted surfaces by irrigation or rainfall runoff (often attached to soil or dust particles) and this is the major mechanism of transport to natural water bodies.  In common with all pesticides, when applied as fine sprays, drift to natural waters is also possible.

The relatively low mammalian toxicity indicates that, generally, the compounds are not particularly hazardous to small mammals via off-target transport.  The toxicity to birds is also lower than many other insecticides.  However, as a result of their high toxicity to target insects, non-target insects such as pollinators and the wide range of aquatic invertebrates are potentially at some risk if exposed to non-target transport of pyrethroids.

This is the potential area where, understandably, regulatory authorities have focused their attention when examining pyrethroid uses. This led PWG, government scientists and regulators as well as academics across the world to generate a remarkable body of data on these topics.

The aquatic fate and effects of pyrethroids is the most carefully researched and well understood area of insecticide science and PWG has tracked and documented all of this research (databases available from PWG upon request).  US EPA recently performed a registration review of the pyrethroids to ensure that any risks associated with their use were understood and mitigated to meet current, more stringent, regulations. The EPA focused on aquatic fate and effects and mandated considerably more strict specifications for use to reduce any risks to acceptable levels.