Does copper contamination change thermotaxis of the soil arthropod Folsomia candida (Collembola)?

Behavioural thermoregulation (thermotaxis) is essential for soil invertebrates to evade thermal extremes in terrestrial environments. Extensive and continuous use of copper (Cu) based products has led to elevated Cu concentration in soils across the globe and in some areas reaching concentrations that are hazardous to soil invertebrates. We hypothesised that environmental stressors, for example, exposure to heavy metals may compromise the adaptive behavioural thermoregulation of organisms, but very little is known of such interactions. In this study, we chose Cu as a model toxicant and investigated the potential effect of Cu-contaminated soils on the behavioural thermoregulation of springtails (Folsomia candida). We measured the distribution of springtails when placed on a temperature gradient ranging from 6 to 46 °C and estimated their thermal preference as an indicator of behavioural thermoregulation. Results showed that within 60 min of being introduced to the thermal gradient, the distribution of springtails was unimodal with slight skewness towards high temperature. Springtails exhibited a consistent preferred temperature range of approximately 21-23 °C across all Cu exposure levels and time points. However, Cu contamination increased the frequency of springtails recorded along the gradient where temperature was above 30 °C. We interpreted this observation as Cu-exposed animals having an elevated risk of entering heat coma and not being able to evade noxious temperatures. We conclude that Cu contamination does not alter the thermal preference of F. candida but compromises their ability to tolerate extreme high temperature. Incorporating behavioural responses into ecotoxicological assessments provides ecologically relevant insights into the impacts of chemical pollution on soil ecosystems.

Locomotion behavior testing as a complementary tool in Collembola avoidance assays with neurotoxic insecticides

This study aimed (1) to assess the ability of collembolans Folsomia candida to avoid soils contaminated with three seed dressing insecticides imidacloprid, clothianidin, and fipronil; (2) to assess the effects of the insecticides on collembolans' locomotion behavior; (3) to check if changes in the locomotion behavior would explain the avoidance/preference responses; and (4) to evaluate the possibility to use locomotion behavior as toxicity biomarker of the tested insecticides. Avoidance and locomotion behavior assays with collembolans F. candida were performed with commercial seed dressing formulations of three insecticides (imidacloprid, clothianidin, and fipronil). Results showed no avoidance behavior at any concentration, while a "preference" was observed with increasing concentrations of the three tested insecticides. Significant reductions in the locomotion of exposed collembolans were observed at ≥ 1 mg kg-1 for imidacloprid (18-38%) and fipronil (29-58%) and ≥ 4 mg kg-1 for clothianidin (10-47%). At the higher insecticide concentrations, the collembolans had their trajectories restricted to smaller areas, with a tendency for circular movements. Our results confirm that the "preference" for contaminated soils with neurotoxic substances is likely due to locomotion inhibition impairing the ability of organisms to escape. This effect highlights that only avoidance assays may be not sufficient to assure the safety of some substances and confirm the potential of locomotion behavior as a sensitive toxicity biomarker for neurotoxic insecticides.

The Recolonization Concentration Concept: Using Avoidance Assays with Soil Organisms to Predict the Recolonization Potential of Contaminated Sites

In this study the recolonization concentration concept for soil organisms is presented and validated. This concept is based on the empirically deduced avoidance–recolonization hypothesis, which shows a negative correlation between avoidance (AC_x) and recolonization (RC_x) (AC_x = RC_100−x) responses. The concept was validated in a two-step approach composed by (i) individual placement tests, to demonstrate the non-influence of individual placement in a dual chamber avoidance test and (ii) small scale gradient tests to demonstrate that the number of colonizers reaching a soil patch with a certain concentration is independent on their previous exposure to lower concentrations. Overall, data show that avoidance data can be used, when framed under the recolonization concentration concept, to evaluate the recolonization potential of contaminated sites. The recolonization concept is an important theoretical concept that when coupled with spatial modelling tools could be used to tackle the spatial and temporal recovery dynamics of contaminated soil.

The inter-individual variance can provide additional information for the ecotoxicologists beside the mean

The hypothesis that the inter-individual parameter variability is an unexploited area of ecotoxicology was proposed several decades ago. Although some illustrative examples were presented to support this hypothesis in the last decades, it has never been tested on an extensive, coherent database. In this study, variance changes of 105 dose-response curves were analysed. All data originated from the same experiment, where the effects of the insecticide Trebon EC were investigated in a dose-response manner on 15 traits of the collembolan Folsomia candida in four subsequent generations and two types of insecticide treatments. A consistent relationship between inter-individual variance and insecticide application was found in 2 (first clutch size and growth-reproduction trade-off) out of the 15 of the parameters. Contrary to the mean, the variance of the first clutch size showed consistent differences compared to the control. Furthermore, the variance of the growth-reproduction trade-off was consistently different from the control except in one case (F3 generation of the transgenerational treatment). Higher first clutch size variances were found in F1 and a lower one in the F2 and F3 generations than in that of the control. This overall pattern of the variance changes of the first clutch size and the trade-off seems to be a quick response to the insecticide application. In the short term, we have found that variance increased with insecticide treatment (P and F1 generation), because phenotypic variance generally increases due to environmental stress. Disruptive selection could be another mechanism between the more detoxification less reproduction strategy and the more reproduction less detoxification strategy. However, in the later generations (F2-F3) the variance decreases compared to the control, which could be because on short term selection stronger on the viability parameters and in long-term selection on reproduction becomes stronger. According to our results, analysis of the variance changes of some parameters may give information about the effects of the pesticide even when the mean does not predict any impact. Testing variance changes are important in ecotoxicology because variance change can signalise toxicant impact even when the mean does not change in certain cases.

Edible size of polyethylene microplastics and their effects on springtail behavior

Many reliable studies have provided evidence of microplastic ingestion by soil organisms. However, further research is required to determine the edible size of microplastics, especially given the ubiquity of microplastics and their adverse effects on the soil environment. Determining the size range of microplastics that can be ingested by soil organisms is crucial for the prediction of the exposure route and toxicity mechanisms of microplastics in soil. Springtails, organisms prevalent in a wide variety of soil ecosystems, can ingest or transport microplastics; however, direct evidence for this has not been reported. To address this knowledge gap, we designed dietary exposure experiments under laboratory conditions, using the springtail species Folsomia candida. The springtails were administered polyethylene microplastics in three different sizes (2, 34, and 66 μm) via their food for a short period of time; we further observed the intestinal presence of microplastics via fluorescence microscopy to determine the maximum edible size. We evaluated the effects of ingested microplastics on springtails by quantifying their moving behavior. The results show that the edible size of microplastics is < 66.0 ± 10.9 μm, and microplastics smaller than this can significantly reduce the velocity and distance of springtail movement by 74% ± 38% compared with the control group. Based on this finding, the broader fate and toxicity of microplastics in soil environments can be estimated. Furthermore, the average velocity and distance of springtail movement decreases in response to microplastic ingestion, highlighting the negative effects of microplastics on soil organisms.

Agricultural trichothecene mycotoxin contamination affects the life-history and reduced glutathione content of Folsomia candida Willem (Collembola)

There is limited data available concerning the effect of T-2/HT-2 toxin or deoxynivalenol (DON) on invertebrates such as springtails, and no data on their life history and oxidative stress. Control maize and DON or T-2 toxin contaminated maize were fed to Folsomia candida with a toxin content of 16324 mg DON kg–1 or 671 mg T-2 kg–1 maize. Ten to twelve days old animals were investigated in a life-history test and a stress protein test.T-2 toxin did not affect Folsomia candida in any measured parameters. The DON exposed group showed decreased growth and reproduction, and a higher survival rate. DON treatment resulted in lower protein content, while reduced glutathione content was higher than in control. It suggests that DON activated the glutathione-related detoxification pathway, which possibly causes a higher survival rate. The results also suggest that the oral toxicity of DON or T-2 is lower than through physical contact.For that reason, DON and T-2 toxin contaminated maize is not suggested to be used as green manure in the native state. Alternative solutions could be using mycotoxin contaminated maize for biogas production, or after decontamination by bacterial strains, it can be used as organic fertilizer.

Transgenerational and multigenerational stress gene responses to the insecticide etofenprox in Folsomia candida (Collembola)

Insecticide exposure may cause both transgenerational and multigenerational effects on populations, but the molecular mechanisms of these changes remain largely unclear. Many studies have focused on either transgenerational or multigenerational mechanisms but did neglect the comparative aspects. This study assessed whether the pyrethroid insecticide etofenprox (formulation Trebon^® 30 EC) shows transgenerational and/or multigenerational effects on the survival and reproduction of Folsomia candida (Collembola). The activation of stress-related genes was studied to detect whether etofenprox modifies the expression of reproduction-associated genes in trans- and multigenerational treatments. A laboratory study was carried out for three generations with five insecticide concentrations in LUFA 2.2 soil. In the transgenerational treatment, only the parent generation (P) was exposed, but the subsequent generations were not. In the multigenerational treatment, all three generations were exposed to the insecticide in the same manner. Multigenerational exposure resulted in reduced reproduction effects over generations, suggesting that F. candida is capable of acclimating to enhanced concentration levels of etofenprox during prolonged exposure over multiple generations. In the transgenerational treatment, the heat shock protein 70 was up-regulated and cytochrome oxidase 6N4v1 expression down-regulated in a dose-dependent manner in the F2 generation. This finding raises the possibility of the epigenetic inheritance of insecticide impacts on parents. Furthermore, CYP6N4v1 expression was oppositely regulated in the trans- and multigenerational treatments. Our results draw attention to the differences in molecular level responses of F. candida to trans- and multigenerational etofenprox exposure.