An assessment of acute insecticide toxicity loading (AITL) of chemical pesticides used on agricultural land in the United States

Abstract

We present a method for calculating the Acute Insecticide Toxicity Loading (AITL) on US agricultural lands and surrounding areas and an assessment of the changes in AITL from 1992 through 2014. The AITL method accounts for the total mass of insecticides used in the US, acute toxicity to insects using honey bee contact and oral LD 50 as reference values for arthropod toxicity, and the environmental persistence of the pesticides. This screening analysis shows that the types of synthetic insecticides applied to agricultural lands have fundamentally shifted over the last two decades from predominantly organophosphorus and N-methyl carbamate pesticides to a mix dominated by neonicotinoids and pyrethroids. The neonicotinoids are generally applied to US agricultural land at lower application rates per acre; however, they are considerably more toxic to insects and generally persist longer in the environment. We found a 48- and 4-fold increase in AITL from 1992 to 2014 for oral and contact toxicity, respectively. Neonicotinoids are primarily responsible for this increase, representing between 61 to nearly 99 percent of the total toxicity loading in 2014. The crops most responsible for the increase in AITL are corn and soybeans, with particularly large increases in relative soybean contributions to AITL between 2010 and 2014. Oral exposures are of potentially greater concern because of the relatively higher toxicity (low LD 50 s) and greater likelihood of exposure from residues in pollen, nectar, guttation water, and other environmental media. Using AITL to assess oral toxicity by class of pesticide, the neonicotinoids accounted for nearly 92 percent of total AITL from 1992 to 2014. Chlorpyrifos, the fifth most widely used insecticide during this time contributed just 1.4 percent of total AITL based on oral LD 50 s. Although we use some simplifying assumptions, our screening analysis demonstrates an increase in pesticide toxicity loading over the past 26 years, which potentially threatens the health of honey bees and other pollinators and may contribute to declines in beneficial insect populations as well as insectivorous birds and other insect consumers.

Ecological impacts of pesticide seed treatments on arthropod communities in a grain crop rotation

“…Without a corresponding increase in pest pressure , NST-treated maize and soybean acreage has increased, and many of these acres were previously untreated with insecticides. The Acute Insecticide Toxicity Loading on US agricultural lands has increased 48-and 4-fold for oral and contact toxicity from 1992 and 2014, primarily due to the use of neonicotinoids in maize and soybean (DiBartolomeis, Kegley, Mineau, Radford, & Klein, 2019).…”

County-level analysis reveals a rapidly shifting landscape of insecticide hazard to honey bees (Apis mellifera) on US farmland

“…For those fields that are treated, the intensity of insecticide use varies as a function of the application rate (kg active ingredient [AI]/ha) of products applied and the potency (toxicity/kg AI) of those products toward insects, typically measured via the LD 50 (the dose required to kill 50% of a population). These factors jointly determine insect toxic load, the total number of insect lethal doses applied in a given area 18,19 . Because the honey bee (Apis mellifera) is the standard terrestrial insect in regulatory pesticide tests and so has the most comprehensive toxicity data available, thus far, calculations of this or similar metrics have depended on honey bee data 18,19 .…”

“…These factors jointly determine insect toxic load, the total number of insect lethal doses applied in a given area 18,19 . Because the honey bee (Apis mellifera) is the standard terrestrial insect in regulatory pesticide tests and so has the most comprehensive toxicity data available, thus far, calculations of this or similar metrics have depended on honey bee data 18,19 . We have followed this convention and will henceforth refer to this value as "bee toxic load.…”

“…Two recent analyses examined trends in bee toxic load at the national scale in Great Britian 18 and the US 19 . Goulson et al 18 found that in Great Britain, from 1990 to 2015, the quantity (kg) of pesticide applied decreased, but the amount of treated agricultural land (ha) increased and the toxic load to bees increased 6-fold.…”

Extrapolating acute bee sensitivity to insecticides using a phylogenetically informed interspecies scaling framework

“…All reported substance specific LD50 were categorized according to their mode of action (MoA [30]) and the four currently most commonly used insecticides were selected for further analysis [31][32][33][34]. The neonicotinoids were split between cyano-(c-) and nitro-(n-) substituted neonicotinoids, as it is known that bee species' responses can drastically differ between these two classes [22,35,36].…”