by Sarah Janes Ugoretz
This week we return to our Silent Spring series with a two-part feature on neonicotinoids or neonics, as they’re commonly called. The toxicity of these insecticides to insects and bees—paired with their widespread, global use—has fueled ongoing regulatory discussion and, in some cases, country-wide bans. Here in the U.S., the Environmental Protection Agency has recently refocused its attention on the environmental safety concerns associated with neonics, primarily honing in on insect pollinators. However, as researchers with the American Bird Conservancy point out, “much more is at stake,” as the environmental implications tied to the use of neonics “go well beyond bees” (Mineau & Palmer, 2013, p. 3). We’ll begin unpacking this warning here, as we explore what neonics are and how they’re being utilized. In the subsequent article, we’ll apply this understanding as we consider the various arguments for and against neonics.
In 1991, Bayer Cropscience introduced imidacloprid, the first of seven commercially available neonic compounds that today make up 24 percent of the global insecticide market (Bittel, 2014). Unsurprisingly, neonics are the fastest growing class of pesticides here in the U.S. (Bittel, 2014). Last year, 146 million acres of U.S. crops were verifiably treated with neonics—including virtually our entire corn crop and half of our soybean crop (Stockstad, 2013). To give you an idea, this area represents about 45 percent of our country’s cropland (Stockstad, 2012). However, as Stevens and Jenkins (2013) point out, this total doesn’t necessarily include acreage under insecticidal treatments such as neonic seed coatings, which alone account for 60 percent of neonic applications. We must also consider the widespread non-agricultural uses of neonics. For instance, in a recent study, nearly 60 percent of all turf and ornamental professionals polled named neonics as their “most used” insecticide (Growing Indiana, 2015).
So what exactly are these pervasive compounds? Put simply, they are insecticides that work as nerve poisons. By binding to receptors of the enzyme nicotinic acetylcholine, they disrupt nerve function—a process that leads to paralysis and, ultimately, to death (Leu, 2014). The degree to which neonics bind to these receptors is especially high within insects, a consideration that regulators have viewed favorably (Quarles, 2014). As we know, however, insects are not alone in their vulnerability to neonics. Bees are also highly at risk due to their having a large number of these particular receptors (Pesticide Action Network, 2015). As Quarles (2014) discusses, just 3-4 billionths of a gram of imidacloprid is enough to kill a honeybee. Meanwhile, smaller amounts can produce sublethal effects. In one particular study, Henry et al. (2012) found that 10 percent of bees that had ingested contaminated pollen and nectar in familiar areas failed to make it back to their hives. This number rose to 32 percent among bees in unfamiliar areas. Those that are able to return to their hives introduce larvae to contaminated pollen, which is seven times more toxic to them than it is to mature bees (Zhu, Schmehl, Mullin, & Frazier, 2014).
On top of their lethal capabilities, users find neonics’ versatility in application appealing. Apart from more commonly utilized foliar sprays, neonics can be delivered in what have been described as more targeted ways via soil drenches, granules, tree injections, and as seed treatments. Overall, proponents have heralded these delivery mechanisms as being not only more environmentally friendly, but more effective as well (Simon-Delso et al., 2015).
As the Pesticide Action Network (PAN) (2015) has pointed out, the environmental risks associated with neonics remain poorly understood. One of the primary drivers of these risks is another characteristic that has made neonics highly attractive—their systemic nature. Neonics are classified as systemic agents in that, rather than remain confined to the plant’s exterior (as is the case with contact insecticides), they instead permeate the entire organism. Take seeds that have been treated with a neonic coating, for instance. Once planted, the neonic compound is essentially incorporated into every tissue and “every bud and branch, effectively turning the plant itself into a pest-killing machine” (Bittel, 2014). As Quarles (2014) comments, this feature makes it impossible for neonics to be applied in a way that mitigates their impact on organisms because “systemics are always present.”
Now let’s consider neonics’ systemic properties in relation to another fundamental characteristic—their persistence. Whereas older insecticides such as organophosphates tend to degrade somewhat rapidly following application (though we by no means advocate for their use), neonics can remain in the environment for well beyond one year (Goulson, 2013). What this means is that the window of exposure for non-target organisms, like various species of birds and butterflies, is huge (Quarles, 2014).
Keeping this in mind, and using seed treatments as an example, let’s consider the various pathways neonics can take from a single point of origin. Starting with the mechanized planting process, seed coatings may be aerially dispersed, along with talc and poisoned dust generated by planting machines (Quarles, 2014). With airborne particles, it becomes impossible to prevent the contamination of non-target organisms and soil. This side effect—albeit unintended—is essentially pesticide drift, one of the primary consequences proponents cite as not being associated with seed treatment applications (PAN, 2015). Meanwhile, seeds that are successfully planted—or unintentionally spilled—may now be consumed by various organisms prior to or during the germination process. As Quarles (2014, p. 8), drawing from the work of Mineau and Palmer (2013), points out, “…one imidacloprid treated corn seed can be lethal to the average bird…[and] about 1/10 of a lethal dose can cause chronic and reproductive effects.”
The seeds that do remain in the ground go on to take up anywhere from 2 to 20 percent of the neonic compound they’ve been treated with (Quarles, 2014). The remaining 80 to 98 percent either becomes airborne via seed drills and other soil disruptions or remains in the soil. Apart from the negative implications this has on ground-dwelling species, we must consider the fact that neonics are water-soluble. It is therefore not uncommon for these compounds to leach into ground and surface water, where non-target contamination continues (Goulson, 2013). Finally, secondary exposure—whereby a non-target predator consumes poisoned prey—is also a possibility. Keep in mind this prey may have been exposed to neonic compounds via airborne particles, treated seeds, the leaves, nectar or pollen of a treated or unintentionally polluted plant, via contaminated water, or even through organisms that it itself has preyed upon (Quarles, 2014).
As researchers and activists with PAN (2015) state, the rate at which neonics are used, along with “their unplanned presence paints a worrying picture of low level but continued exposure.” Given that even miniscule amounts of neonic compounds can cause lethal or sublethal effects—and considering that the toxicity of these compounds is cumulative—we indeed are validated in our concerns. Bittel (2014) recognizes that a number of the effects associated with neonics are similar to those of organophosphates, which were meticulously observed and discussed by biologist Rachel Carson back in the 1960s. Unfortunately, it appears that we “didn’t learn our lessons” (Bittel, 2014).
Watch for more on the ill effects of neonics in the coming weeks, as we dig deeper into some of these issues.
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