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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] 12
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 (
