Leaching and sorption of neonicotinoid insecticides and fungicides from seed coatings

Abstract

Seed coatings are a treatment used on a variety of crops to improve production and offer protection against pests and fungal outbreaks. The leaching of the active ingredients associated with the seed coatings and the sorption to soil was evaluated under laboratory conditions using commercially available corn and soybean seeds to study the fate and transport of these pesticides under controlled conditions. The active ingredients (AI) included one neonicotinoid insecticide (thiamethoxam) and five fungicides (azoxystrobin, fludioxonil, metalaxyl, sedaxane thiabendazole). An aqueous leaching experiment was conducted with treated corn and soybean seeds. Leaching potential was a function of solubility and seed type. The leaching of fludioxonil, was dependent on seed type with a shorter time to equilibrium on the corn compared to the soybean seeds. Sorption experiments with the treated seeds and a solution of the AIs were conducted using three different soil types. Sorption behavior was a function of soil organic matter as well as seed type. For most AIs, a negative relationship was observed between the aqueous concentration and the log K. Sorption to all soils tested was limited for the hydrophilic pesticides thiamethoxam and metalaxyl. However, partitioning for the more hydrophobic fungicides was dependent on both seed type and soil properties. The mobility of fludioxonil in the sorption experiment varied by seed type indicating that the adjuvants associated with the seed coating could potentially play a role in the environmental fate of fludioxonil. This is the first study to assess, under laboratory conditions, the fate of pesticides associated with seed coatings using commercially available treated seeds. This information can be used to understand how alterations in agricultural practices (e.g., increasing use of seed treatments) can impact the exposure (concentration and duration) and potential effects of these chemicals to aquatic and terrestrial organisms.

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

“…Given the high summer temperatures and precipitation in Maryland, the low levels of neonicotinoid residues in our plots could be caused by rapid microbial and photolytic breakdown of residues, or by leaching and run‐off. Soil testing prior to the start of the study indicated that our plots had low organic matter content, which is correlated with reduced sorption of neonicotinoids, another potential cause for low residue levels (Smalling et al, 2018). We found relatively low residue levels compared to some other studies (Bonmatin et al, 2015), and the levels we found were below the known acute toxicity thresholds for various terrestrial arthropods (Douglas & Tooker, 2016; Pisa et al, 2015).…”

“…High moisture content, temperature and sunlight are all positively correlated with neonicotinoid breakdown, and thiamethoxam and imidacloprid also have high leaching potential (Smalling, Hladik, Sanders, & Kuivila, 2018). Given the high summer temperatures and precipitation in Maryland, the low levels of neonicotinoid residues in our plots could be caused by rapid microbial and photolytic breakdown of residues, or by leaching and run‐off.…”

“…To the best of our knowledge, few studies have evaluated the persistence of seed applied fungicides in agroecosystems, or their impact on the arthropod community, even though they can be moderately toxic to arthropods (Minnesota Department of Agriculture, 2012) and vary in their mobility as well as likelihood for leaching (Smalling et al, 2018). Given that the fungicide treatments consist of several active ingredients, those ingredients could interact synergistically with each other or with the insecticides to impact the arthropod community.…”

Pesticides from the EU First and Second Watch Lists in the Water Environment

“…), pH value, soil microbial activity, and temperature . The sorption of neonicotinoids on soils is generally low and is mainly influenced by the soil organic carbon content …”

Combining Culture-Dependent and Independent Approaches for the Optimization of Epoxiconazole and Fludioxonil-Degrading Bacterial Consortia

“…Epoxiconazole (EPO) and fludioxonil (FLU) ( Figure S1 ) are two examples of fluorinated pesticides not readily degraded in the natural environment, as shown by their typically high half-lives in soils (over 353 and 218 days for EPO and FLU, respectively) [ 6 ] and by the scant literature reporting their productive biodegradation [ 7 , 8 ]. As a result, both these compounds have been reported to persist and accumulate in aquatic and terrestrial ecosystems [ 9 , 10 , 11 , 12 ]. We recently reported the successful enrichment of two bacterial consortia obtained from an agricultural soil with high capacity for the complete removal and defluorination of EPO and FLU (one consortium for each pesticide) in a wide range of pesticide concentrations, after 21 to 28 days of incubation [ 7 ].…”