Environmental risks and challenges associated with neonicotinoid

Feb 26, 2018 - Neonicotinoid use has increased rapidly in recent years, with a global shift towards insecticide applications as seed coatings rather t...
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Environmental risks and challenges associated with neonicotinoid insecticides Michelle L Hladik, Anson Main, and Dave Goulson Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b06388 • Publication Date (Web): 26 Feb 2018 Downloaded from http://pubs.acs.org on February 27, 2018

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Feature Article

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Environmental risks and challenges associated with neonicotinoid insecticides

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Michelle L. Hladik,*,1 Anson R. Main,2 and Dave Goulson3

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School of Natural Resources, University of Missouri, Columbia, Missouri 65211 United States

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School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom

USGS Geological Survey, California Water Science Center, Sacramento, California 95819, United States

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*Corresponding author:

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M.L. Hladik, phone: (916) 278-3183; email: [email protected]

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Total number of word-equivalents: 4406 (including table and figures)

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Number of pages: 23

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Number of words in main text: 3206

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Number of tables: 1 (300 word-equivalents)

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Numbers of figures: 2 (300/600 word-equivalents)

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TOC ART

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ABSTRACT Neonicotinoid use has increased rapidly in recent years, with a global shift towards

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insecticide applications as seed coatings rather than aerial spraying. While the use of seed

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coatings can lessen the amount of overspray and drift, the near universal and prophylactic use of

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neonicotinoid seed coatings on major agricultural crops has led to widespread detections in the

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environment (pollen, soil, water, honey). Pollinators and aquatic insects appear to be especially

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susceptible to the effects of neonicotinoids with current research suggesting that chronic sub-

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lethal effects are more prevalent than acute toxicity. Meanwhile, evidence of clear and consistent

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yield benefits from the use of neonicotinoids remains elusive for most crops. Future decisions on

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neonicotinoid use will benefit from weighing crop yield benefits versus environmental impacts to

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non-target organisms and considering whether there are more environmentally benign

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alternatives.

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BACKGROUND ON NEONICOTINOIDS

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Neonicotinoid insecticides have been in use for over two decades. The first

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neonicotinoid, imidacloprid, was registered for use in 1991. From 1995 to 2002 more

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neonicotinoids were introduced to the market: nitenpyram and acetamiprid in 1995,

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thiamethoxam in 1998, thiacloprid and clothianidin in 2001, and dinotefuran in 2002.1 In the

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mid-2000s, neonicotinoid use increased rapidly due to changes in application techniques through

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the increased use of coated seeds and with increasing insect resistance and/or concern over the

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high mammalian toxicity of other insecticides previously used such as the organophosphates

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(e.g., chlorpyrifos), carbamates (e.g., carbaryl), and pyrethroids (e.g,. bifenthrin).2,3,4

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Neonicotinoid use has continued to increase both in the United States5 and worldwide.3,6

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Currently, neonicotinoids are the most widely used insecticides in the world representing 25% of

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the global insecticide market.1

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Neonicotinoids are synthetic compounds similar in structure to nicotine (Figure 1). They

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have a common mode of action that affects the central nervous system of insects (binding to

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nicotinic acetylcholine receptors) making them active against a broad spectrum of insects. They

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are also systemic insecticides,6 which means they can be taken up through the roots of plants and

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translocated to their leaves, flowers, and pollen, making them ideal candidates for seed coatings.

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Seed coatings in this instance refer to the application of chemical products to the seed prior to

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sowing to suppress, control, or repel insects and other pests such as fungi that attack seeds,

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seedlings, or plants.7 Seed coatings are used for a variety of crops including maize (corn),

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soybeans, sunflowers, oilseed rape (canola), and cotton.

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In addition to their use as seed coatings, neonicotinoids are also applied in agricultural

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areas as foliar sprays, in-furrow treatments (e.g., soil drenches), and granules. However,

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neonicotinoid use is not restricted to the agricultural environment. In urban or forested areas,

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neonicotinoids are applied as tree soil drenches or injections (e.g., for the control of emerald ash

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borer and hemlock wooly adelgid8). Plants grown in garden centers and nurseries are often

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protected via neonicotinoid foliar sprays, drenches, and/or granular applications.9,10 Imidacloprid

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also has a variety of other home uses including lawn and garden applications, and topical flea

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medicines.3

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ENVIRONMENTAL FATE

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Neonicotinoids are highly soluble in water (log Kow 0.55 to 1.26; log Koc 1.4 to 2.3),

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somewhat persistent in water and soils (aqueous dissipation half-lives of 4.7 to 40.3 days; soil

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degradation half-lives of 3 to >1,000 days) and not volatile (