Zebrafish neuromast sensory system: Is it an emerging target to assess environmental pollution impacts?

Environmental pollution poses risks to ecosystems. Among these risks, one finds neurotoxicity and damage to the lateral line structures of fish, such as the neuromast and its hair cells. Zebrafish (Danio rerio) is recommended as model species to be used in ecotoxicological studies and environmental biomonitoring programs aimed at assessing several biomarkers, such as ototoxicity. However, little is known about the history of and knowledge gaps on zebrafish ototoxicity. Thus, the aim of the current study is to review data available in the scientific literature about using zebrafish as animal model to assess neuromast toxicity. It must be done by analyzing the history and publication category, world production, experimental design, developmental stages, chemical classes, neuromasts and hair cell visualization methods, and zebrafish strains. Based on the results, number, survival and fluorescence intensity of neuromasts, and their hair cells, were the parameters oftentimes used to assess ototoxicity in zebrafish. The wild AB strain was the most used one, and it was followed by Tübingen and transgenic strains with GFP markers. DASPEI was the fluorescent dye most often applied as method to visualize neuromasts, and it was followed by Yo-Pro-1 and GFP transgenic lines. Antibiotics, antitumorals, metals, nanoparticles and plant extracts were the most frequent classes of chemicals used in the analyzed studies. Overall, pollutants can harm zebrafish's mechanosensory system, as well as affect their behavior and survival. Results have shown that zebrafish is a suitable model system to assess ototoxicity induced by environmental pollution.

Influence of temperature on the toxicity of the elutriate from a pesticide contaminated soil to two cladoceran species

Brazil has become one of the largest consumers of pesticides in the world. However, there are still few studies evaluating pesticide toxicity integrating local aquatic and terrestrial environments. In addition, there is growing concern about the influence of temperature conditions related with climate change on contaminants toxicity. The aim of the present study was to evaluate the elutriate toxicity of the insecticide Kraft^® 36 EC (a.i. abamectin), the fungicide Score^® 250 EC (a.i. difenoconazole) and their mixture to the cladocerans Ceriodaphnia silvestrii and Daphnia similis, using model ecosystems (mesocosms). To this end, mesocosms were filled with natural soil and subjected to the following treatments: Control (Milli-Q water), Kraft (10.8 g abamectin ha^-1), Score (20 g difenoconazole ha^-1), and Kraft + Score (10.8 g abamectin ha^-1 + 20 g difenoconazole ha^-1). The experiment lasted 18 days, and the applications were made on days 1, 8, and 15; the occurrence of rainfall was simulated on days 1, 8, and 15 after applications and only rainfall simulation on days 4, 11, and 18. The experiment was conducted under two different temperatures: 23 °C and 33 °C. At 23 °C, single Kraft treatment and in combination with Score showed high toxicity to both cladocerans. At 33 °C, elutriate of the Kraft^® and mixture treatments were highly toxic to D. similis but not to C. silvestrii. The results indicate that while Kraft had higher toxicity than Score to both cladocerans, this toxicity was counteracted at 33 °C only for the exotic species, D. similis. The results portray the complexity of pesticide toxicity when considering realistic experimental settings including different organisms and temperature treatments.

Integrated ecosystem models (soil-water) to analyze pesticide toxicity to aquatic organisms at two different temperature conditions

In order to increase the knowledge about pesticides considering the soil-water interaction, ecosystem models (mesoscosms) were used to analyze the of leachate on the immobility and feeding rate of the cladocerans, Ceriodaphnia silvestrii and D. similis and algae Raphidocelis subcapitata, at two different temperatures. Mesocosm were filled with natural soil (latosolo) that were contaminated with insecticide/acaricide Kraft 36 EC® and fungicide Score 250 EC®, using the recommended concentration for strawberry crops (10.8 g abamectin/ha and 20 g difenoconazole/ha). Pesticides were applied once (hand sprayers) and the precipitation was simulated twice a week (Days 1, 4, 8, 11, 15 and 18). The mesocosm were kept in a room with a controlled temperature (23 and 33 °C) and photoperiod (12h light/12h dark). The Kraft 36 EC® insecticide showed toxicity for both species of cladocerans tested, with effects on immobility and feeding rate, both at 23 and 33 °C. Score 250 EC® showed to be toxic only for the experiments that analyzed the immobility of C. silvestrii at 23 °C and the feeding of D. smilis at 33 °C, demonstrating that the effects are species-specific and related to the temperature at which they are tested. While for species R. subcapitata there was an effect only for mixture treatments of the pesticides analyzed at both temperatures. Thereby, zooplanktonic organisms may be at risk when exposed to this compound even after percolating in a soil column, which could lead to effects on the entire aquatic trophic chain and that temperature can influence the organism response to the contaminant.

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

Pesticides can affect all receiving compartments, especially soils, and their fate and effects may be enhanced by temperature, increasing their risk to ecological functions of soils. In Brazil, the most widely used pesticides are the insecticide Kraft 36 EC® (a.s. abamectin) and the fungicide Score 250 EC® (a.s. difenoconazole), which are commonly used in strawberry, often simultaneously as a mixture. The aim of this study was to evaluate the toxicity of realistic environmental applications, single and in mixtures, for both pesticides to the springtail Folsomia candida and the plant species Allium cepa (onion) and Lycopersicum esculentum (tomato). Mesocosms filled with Brazilian natural soil (lattosolo) were dosed with water (control), Kraft (10.8 g a.s/ha), Score (20 g.a.s/ha) and Kraft + Score (10.8 + 20 g a.s./ha). The applications were repeated every 7 days, during 18 days of experiment, and simulating rainfall twice a week. Collembola reproduction tests were conducted with soils from the first (day 1) and last day (day 18) of experiment for each treatment. Plant toxicity tests were carried out in the experimental units. The experiments were run at 23 °C and 33 °C. Kraft, alone and in the binary mixture, showed high toxicity to the springtails in soils from both days 1 and 18, especially at 23 °C where it caused 100% mortality. Score however, was not toxic to the springtails. Plant growth was reduced by Score, but responses varied depending on temperature. This study indicates a high environmental risk of the insecticide Kraft, particularly at lower temperatures (23 °C), and an influence of temperature on pesticide fate and effects.

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

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 EC₅₀ and EC₁₀ 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 (EC₁₀ and EC₅₀) and the solvent control. Exposure to Kraft^® 36 EC, however, significantly induced Cyp6 expression at the EC₅₀ level, while VgR was significantly downregulated at both the EC₁₀ and EC₅₀. Exposure to the simple pesticide mixture of Kraft^® 36 EC + 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 EC₁₀ and EC₅₀ 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.