The use of gene expression to unravel the single and mixture toxicity of abamectin and difenoconazole on survival and reproduction of the springtail Folsomia candida

Abstract

Pesticides risk assessments have traditionally focused on the effects on standard parameters, such as mortality, reproduction and development. However, one of the first signs of adverse effects that occur in organisms exposed to stress conditions is an alteration in their genomic expression, which is specific to the type of stress, sensitive to very low contaminant concentrations and responsive in a few hours. The aim of the present study was to evaluate the single and binary mixture toxicity of commercial products of abamectin (Kraft ® 36 EC) and difenoconazole (Score ® 250 EC) to Folsomia candida. Laboratory toxicity tests were conducted to access the effects of these pesticides on springtail survival, reproduction and gene expression. The reproduction assays gave EC 50 and EC 10 values, respectively, of 6.3 and 1.4 mg a.s./ kg dry soil for abamectin; 1.0 and 0.12 mg a.s./kg dry soil for Kraft ® 36 EC; and 54 and 23 mg a.s./kg dry soil for Score ® 250 EC. Technical difenoconazole did not have any effect at the concentrations tested. No significant differences in gene expression were found between the abamectin concentrations tested (EC 10 and EC 50) and the solvent control. Exposure to Kraft ® 36 EC, however, significantly induced Cyp6 expression at the EC 50 level, while VgR was significantly downregulated at both the EC 10 and EC 50. Exposure to the simple pesticide mixture of Kraft ® 36 EC þ Score ® 250 EC caused significant up regulation of ABC transporter, and significant down regulation of VgR relative to the controls. GABA receptor also showed significant down-regulation between the EC 10 and EC 50 mixture treatments. Results of the present study demonstrate that pesticide-induced gene expression effects precede and occur at lower concentrations than organism-level responses. Integrating "omic" endpoints in traditional bioassays may thus be a promising way forward in pesticide toxicity evaluations.

Impact of temperature on the toxicity of Kraft 36 EC® (a.s. abamectin) and Score 250 EC® (a.s. difenoconazole) to soil organisms under realistic environmental exposure scenarios

“…The fungicide Score 250 EC® had no effects on F. candida at both temperatures tested (23 and 33°C). Oliveira et al (2018) determined an EC 50 for F. candida of this compound of 28.9 mg a.s./kg soil. F. candida was clearly less sensitive to difenoconazole than to abamectin.…”

“…Previous studies revealed a rather large variation in the toxicity of abamectin to collembolans. Oliveira et al (2018), for example, noted a 50% reduction in F. candida when exposed to 0.06 mg a.s./kg in a natural Brazilian soil (15% organic matter content; CEC 3.33 (meq/ 100 g); 48% clay; 12% silt; and 19, 11, and 10% of fine, medium, and coarse sand, respectively) in the laboratory. However, Diao et al (2007) reported such a reduction at a ten-fold higher concentration in a natural (York, England) sandy-loamy soil (21% clay, 12% silt, 67% sand, 2.22% organic carbon and a pH of 7.0) (EC 50 F. candida = 0.68 mg a.s./kg).…”

“…F. candida was clearly less sensitive to difenoconazole than to abamectin. Given the mode-of-action of these compounds, collembolans may indeed be expected to be more sensitive to insecticides like abamectin than to fungicides like difenoconazole (Daam et al, 2011;Oliveira et al, 2018;Pitombeira de Figueirêdo et al, 2019). The toxicity of difenoconazole to invertebrates, such as F. candida, remains unknown, since few studies have been carried out with this group of organisms (US Environmental Protection Agency, 2016).…”

“…In recent years, studies have demonstrated a high toxicity of Score 250 EC® and especially Kraft 36 EC® to non-target organisms https://doi.org/10.1016/j.ecoenv.2020.110446 (Moreira et al, 2017;Nunes et al, 2016;Nunes and Espíndola, 2012;Pitombeira de Figueirêdo et al, 2019). For example, Oliveira et al (2018), evaluating their toxicity to the potworm Enchytraeus crypticus, the collembolan Folsomia candida, and the mite Hypoaspis aculeifer, concluded that environmentally relevant concentrations of both pesticides may significantly affect the reproduction of Collembola (Oliveira et al, 2018). In addition, mixtures of the two pesticides showed synergistic effects on aquatic organisms, indicating that environmental risk evaluations based on individual compounds may not adequately protect aquatic ecosystems (Moreira et al, 2017;Sanches et al, 2017).…”

Toxicity of pesticides with fungicide and fungicide + insecticide effects to Eisenia andrei

“…Fipronil is an insecticide of contact and ingestion, belonging to the chemical group of the pyrazoles, indicated for an extensive range of applications from plants to animals (EC, 2011;Brasil, 2020). Studies demonstrating the ecotoxicological potential of pesticides on non-target species, such as bees, earthworms and collembolans, include the death of these individuals, possibly leading to a population decline, even at recommended or very low concentrations (Pitombeira de Figueirêdo et al, 2019;Sánchez-Bayo et al, 2016;Yang et al, 2017).…”