Mixture toxicity of phostebupirim and cyfluthrin: Species-specific responses.

Currently, the potential impact of insecticide mixtures to nontarget organisms is largely unknown, and additional study is needed. The present study investigated the mixture toxicity of the organophosphate insecticide phostebupirim and the pyrethroid insecticide cyfluthrin using 4 nontarget species including Daphnia magna, Hyalella azteca, Pimephales promelas (fathead minnow), and Danio rerio (zebrafish). For each species, the toxicity of equipotent mixtures was compared with the expected toxicity estimated using the independent action (IA) and concentration addition (CA) models. Lethal and sublethal responses to D. magna and H. azteca were best described with the IA model. For both fish species, mixture toxicity was significantly higher than that estimated using either mixture model. The synergism noted in fish exposed to the combination of phostebupirim and cyfluthrin was confirmed by exposing P. promelas larvae to a nontoxic dose of phostebupirim and a range of toxic cyfluthrin concentrations, and vice versa. Sublethal and lethal concentrations to fish were up to 7 times lower for the mixture than in concurrently run individual compound exposures. Potential mechanisms for the synergistic responses found in fish are presented. Environ Toxicol Chem 2017;36:1947-1954. © 2016 SETAC.

Fate and risk of atrazine and sulfentrazone to nontarget species at an agriculture site.

The present study evaluated the risk associated with the application and co-occurrence of 2 herbicides, atrazine and sulfentrazone, applied to a 32-ha corn and soybean rotational field. Field concentrations of the compounds were measured in soil, runoff water, and groundwater, with peak mean atrazine and sulfentrazone concentrations found in the soil (144 ng/g dry wt, and 318 ng/g dry wt, respectively). Individual and mixture laboratory bioassays were conducted to determine the effects of atrazine and sulfentrazone on the survival of Daphnia magna and Pimephales promelas, the germination of Lactuca sativa, and the growth of Pseudokirchneriella subcapita and Lemna minor. Pseudokirchneriella subcapita and L. minor were the most susceptible species tested, and the effects on growth of the herbicides in mixtures best fit an independent action model. Risk quotients and margin of safety of 10% (MOS10) values were used to estimate risk and were calculated using runoff water concentrations. The MOS10 values were more sensitive than risk quotients in estimating risk. The MOS10 value for sulfentrazone runoff water concentration effects on P. subcapita was 7.8, and for L. minor was 1.1, with MOS10 values < 1 indicating potential risk. Overall, the environmentally relevant concentrations fell below the effect concentrations; therefore, atrazine and sulfentrazone posed little to no risk to the nontarget species tested. Environ Toxicol Chem 2017;36:1301-1310. © 2016 SETAC.

Fate and transport of agriculturally applied fungicidal compounds, azoxystrobin and propiconazole.

Fungicidal active ingredients azoxystrobin and propiconazole, individually and in combination, have been marketed worldwide in a range of fungicide treatment products for preventative and curative purposes, respectively. Their presence in streams located throughout the midwestern and southeastern United States warrant the need for research into the potential routes of transport of these fungicides in an agricultural field setting. Potential canopy penetration and drift effects of these fungicides during aerial and ground applications were studied in the current project. Canopy penetration was observed for both application types, however drift was associated only with the aerial application of these fungicides. Azoxystrobin and propiconazole persisted in the soil up to 301 d, with peak concentrations occurring approximately 30 d after application. The predominant mode of transport for these compounds was agricultural runoff water, with the majority of the fungicidal active ingredients leaving the target area during the first rain event following application. The timing of application in relation to the first rain event significantly affected the amount of loss that occurred, implying application practices should follow manufacturer recommended guidelines.

Assessing the fate and effects of an insecticidal formulation.

A 3-yr study was conducted on a corn field in central Illinois, USA, to understand the fate and effects of an insecticidal formulation containing the active ingredients phostebupirim and cyfluthrin. The objectives were to determine the best tillage practice (conventional vs conservation tillage) in terms of grain yields and potential environmental risk, to assess insecticidal exposure using concentrations measured in soil and runoff water and sediments, to compare measured insecticidal concentrations with predicted concentrations from selected risk assessment exposure models, and to calculate toxicity benchmarks from laboratory bioassays performed on reference aquatic and terrestrial nontarget organisms, using individual active ingredients and the formulation. Corn grain yields were not significantly different based on tillage treatment. Similarly, field concentrations of insecticides were not significantly (p > 0.05) different in strip tillage versus conventional tillage, suggesting that neither of the tillage systems would enable greater environmental risk from the insecticidal formulation. Risk quotients were calculated from field concentrations and toxicity data to determine potential risk to nontarget species. The insecticidal formulation used at the recommended rate resulted in soil, sediment, and water concentrations that were potentially harmful to aquatic and terrestrial invertebrates, if exposure occurred, with risk quotients up to 34.

Fate and effects of clothianidin in fields using conservation practices.

Despite the extensive use of the neonicotinoid insecticide clothianidin, and its known toxicity to beneficial insects such as pollinators, little attention has been given to its fate under agricultural field conditions. The present study investigated the fate and toxicity of clothianidin applied every other year as a corn seed-coating at 2 different rates, 0.25 mg/seed and 0.50 mg/seed, in an agricultural field undergoing a corn-soybean annual rotation, and conservation tillage. Concentrations were measured in soil, surface runoff, infiltration, and groundwater from 2011 to 2013. Clothianidin was detected at low concentrations in soil and water throughout the 2-yr corn and soybean rotation. Low and no-tillage had little or no effect on clothianidin concentrations. Laboratory toxicity bioassays were performed on nontarget species, including Daphnia magna, Hyalella azteca, Chironomus dilutus, Pimephales promelas and Eisenia fetida. Risk quotients were calculated from clothianidin concentrations measured in the field and compared with the laboratory toxicity bioassay results to assess the environmental risk of the insecticide. The risk quotient was found to be lower than the level of concern for C. dilutus, which was the most sensitive species tested; therefore, no short-term environmental risk was expected for the species investigated in the present study.