Individual and combined toxicity of imidacloprid and two seed dressing insecticides on collembolans Folsomia candida

ABSTRACT

The aim of this study was to examine the chronic toxicity of imidacloprid (IMI), clothianidin (CLO) and fipronil (FIP) as a single exposure, as well as binary mixtures of IMI with CLO or FIP toward collembolans Folsomia candida, which are fauna present in the soil. Chronic toxicity assays were performed following an ISO guideline in a Tropical Artificial Soil (TAS), and the influence on the number and growth of the juveniles produced were determined. The range of nominal concentrations used in the tests with the individual compounds was 0.08–1.28 mg/kg (IMI), 0.079–1.264 mg/kg (FIP) and 0.007–0.112 mg/kg (CLO), whereas the mixture assays were performed with half the value used in the tests with individual compounds. Based upon single exposures, IMI produced a similar impact of reducing reproduction by 50% (EC₅₀ ranging from 0.74 to 0.85 mg/kg) compared to FIP (EC₅₀ = 0.78 mg/kg), whereas CLO was the most toxic to F. candida (EC₅₀ = 0.08 mg/kg). Their mixtures generally resulted in a diminished effect on reproduction, as evidenced by the higher EC₅₀ values. In contrast, in the case of the IMI+FIP combination at high concentrations at the EC₅₀ level, a synergistic effect on toxicity was observed. The single exposure to the three insecticides and the mixture of IMI-FIP also decreased the size of generated juveniles, which was evidenced by the reduction in the proportion of large juveniles and increased proportion of small juveniles. However, both binary mixtures (IMI-FIP and IMI-CLO) presented antagonistic effects as evidenced by less than expected reductions in growth. Data on the toxic effects of IMI in a mixture with other seed dressing insecticides to collembolans provides useful information to environmental risk assessors by diminishing the uncertainties on the ecological risk of exposure to pesticides, enabling soil management degradation by utilizing multiple insecticides.

KEYWORDS:

• Mixture toxicity
• neonicotinoids
• phenyl-pyrazoles
• soil fauna
• synergism

Acknowledgments

The authors thank the National Council for Scientific and Technological Development (CNPq) for the research grant (Project 407170/2016-2).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15287394.2023.2174464

Ethics approval

The procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted (Brazilian regimentation for the scientific use of animals – Law no. 11.794). Consent to participate and publication is not applicable once this study does not involve humans.

Data availability statement

The data that support the findings of this study are available in the manuscript, and the raw should be requested by e-mail: [email protected]

Additional information

Funding

This study was supported by the National Council for Scientific and Technological Development (CNPq) (Research Grant - Project 407170/2016-2)