International audience | The silverleaf whitefly Bemisia tabaci (Gennadius, 1889) (Homoptera: Aleyrodidae) is a serious invasive herbivorous insect pest worldwide. The excessive use of pesticides has progressively selected B. tabaci specimens, reducing the effectiveness of the treatments, and ultimately ending in the selection of pesticide-resistant strains. The management of this crop pest has thus become challenging owing to the level of resistance to all major classes of recommended insecticides. Here, we used in silico techniques for detecting sequence polymorphisms in ace1 gene from naturally occurring B. tabaci variants, and monitor the presence and frequency of the detected putative mutations from 30 populations of the silverleaf whitefly from Egypt and Pakistan. We found several point mutations in ace1-type acetylcholinesterase (ace1) in the studied B. tabaci variants naturally occurring in the field. By comparing ace1 sequence data from an organophosphate-susceptible and an organophosphate-resistant strains of B. tabaci to ace1 sequence data retrieved from GenBank for that species and to nucleotide polymorphisms from other arthropods, we identified novel mutations that could potentially influence insecticide resistance. Homology modeling and molecular docking analyses were performed to determine if the mutation-induced changes in form 1 acetylcholinesterase (AChE1) structure could confer resistance to carbamate and organophosphate insecticides. Mutations had small effects on binding energy (Delta G(b)) interactions between mutant AChE1 and insecticides; they altered the conformation of the peripheral anionic site of AChE1, and modified the enzyme surface, and these changes have potential effects on the target-site sensitivity. Altogether, the results from this study provide information on genic variants of B. tabaci ace1 for future monitoring insecticide resistance development and report a potential case of environmentally driven gene variations.

International audience | The silverleaf whitefly Bemisia tabaci (Gennadius, 1889) (Homoptera: Aleyrodidae) is a serious invasive herbivorous insect pest worldwide. The excessive use of pesticides has progressively selected B. tabaci specimens, reducing the effectiveness of the treatments, and ultimately ending in the selection of pesticide-resistant strains. The management of this crop pest has thus become challenging owing to the level of resistance to all major classes of recommended insecticides. Here, we used in silico techniques for detecting sequence polymorphisms in ace1 gene from naturally occurring B. tabaci variants, and monitor the presence and frequency of the detected putative mutations from 30 populations of the silverleaf whitefly from Egypt and Pakistan. We found several point mutations in ace1-type acetylcholinesterase (ace1) in the studied B. tabaci variants naturally occurring in the field. By comparing ace1 sequence data from an organophosphate-susceptible and an organophosphate-resistant strains of B. tabaci to ace1 sequence data retrieved from GenBank for that species and to nucleotide polymorphisms from other arthropods, we identified novel mutations that could potentially influence insecticide resistance. Homology modeling and molecular docking analyses were performed to determine if the mutation-induced changes in form 1 acetylcholinesterase (AChE1) structure could confer resistance to carbamate and organophosphate insecticides. Mutations had small effects on binding energy (Delta G(b)) interactions between mutant AChE1 and insecticides; they altered the conformation of the peripheral anionic site of AChE1, and modified the enzyme surface, and these changes have potential effects on the target-site sensitivity. Altogether, the results from this study provide information on genic variants of B. tabaci ace1 for future monitoring insecticide resistance development and report a potential case of environmentally driven gene variations.

Ecotoxicological effects of photolytic degradation mixtures of the two brominated flame retardants PolymericFR and Tetrabromobisphenol A-bis (2,3-dibrom-2-methyl-propyl) Ether (TBBPA-BDBMPE) have been studied in vitro and in vivo. Both substances were experimentally degraded separately by exposure to artificial UV-light and the resulting degradation mixtures from different time points during the UV-exposure were applied in ecotoxicological tests. The in vitro investigation showed no effects of the degraded flame retardants on the estrogenic and androgenic receptors via the CALUX (chemically activated luciferase gene expression) assay. Short-term exposures (up to 96 h) of Lumbriculus variegatus lead to temporary physiological reactions of the annelid. The exposure to degraded PolymericFR lead to an increased activity of Catalase, while the degradation mixture of TBBPA-BDBMPE caused increases of Glutathione-S-transferase and Acetylcholine esterase activities. Following a chronic exposure (28 d) of L. variegatus, no effects on the growth, reproduction, fragmentation and energy storage of the annelid were detected. The results indicate that the experimental degradation of the two flame retardants causes changes in their ecotoxicological potential. This might lead to acute physiological effects on aquatic annelids, which, however, do not affect the animals chronically according to our results.

The use of reclaimed water in agriculture represents a promising alternative to relieve pressure on freshwater supplies, especially in arid or semiarid regions facing water scarcity. However, this implies introducing micropollutants such as pharmaceutical residues into the environment. The fate and the ecotoxicological impact of valsartan, an antihypertensive drug frequently detected in wastewater effluents, were evaluated in soil-earthworm microcosms. Valsartan dissipation in the soil was concomitant with valsartan acid formation. Although both valsartan and valsartan acid accumulated in earthworms, no effect was observed on biomarkers of exposure (acetylcholinesterase, glutathione S-transferase and carboxylesterase activities). The geometric mean index of soil enzyme activity increased in the soils containing earthworms, regardless of the presence of valsartan. Therefore, earthworms increased soil carboxylesterase, dehydrogenase, alkaline phosphatase, β-glucosidase, urease and protease activities. Although bacterial richness significantly decreased following valsartan exposure, this trend was enhanced in the presence of earthworms with a significant impact on both alpha and beta microbial diversity. The operational taxonomic units involved in these changes were related to four (Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes) of the eight most abundant phyla. Their relative abundances significantly increased in the valsartan-treated soils containing earthworms, suggesting the presence of potential valsartan degraders. The ecotoxicological effect of valsartan on microbes was strongly altered in the earthworm-added soils, hence the importance of considering synergistic effects of different soil organisms in the environmental risk assessment of pharmaceutical active compounds.

The flame retardants hexabromobenzene (HBB) and pentabromobenzene (PBB) have been extensively used and become ubiquitous pollutants in the aquatic environment and biota, but their potential toxic effects on wildlife remained unknown. In this study, by using zebrafish (Danio rerio) as a model, the bioconcentration and developmental neurotoxicity were investigated. Zebrafish embryos were exposed to HBB and PBB (0, 30, 100 and 300 μg/L) from 2 until 144 h post-fertilization (hpf). Chemical analysis showed bioconcentrations of both chemicals, while HBB is readily metabolized to PBB in zebrafish larvae. Embryonic exposure to both chemicals did not cause developmental toxicity, but induced locomotor behavioral anomalies in larvae. Molecular docking results indicated that both chemicals could bind to zebrafish acetylcholinesterase (AChE). Furthermore, HBB and PBB significantly inhibited AChE activities, accompanied by increased contents of acetylcholine and decreased choline in larvae. Downregulation of the genes associated with central nervous system (CNS) development (e.g., mbp, α1-tubulin, gfap, shha) as well as the corresponding proteins (e.g., Mbp, α1-Tubulin) was observed, but gap-43 was upregulated at both gene and protein levels. Together, our results indicate that both HBB and PBB exhibit developmental neurotoxicity by affecting various parameters related to CNS development and indications for future toxicological research and risk assessment of the novel brominated flame retardants.

Although many polymers are known by their toxicity, we know nothing about the impact of polyethylene glycol (PEG) on anurofauna. Its presence in different products and disposal in aquatic environments turn assessments about its impact on amphibians an urgent matter. Accordingly, we tested the hypothesis that short-time exposure (72 h) of tadpoles belonging to the species Physalaemus cuvieri (Anura, Leptodactylidae) to PEG induces oxidative stress and neurotoxicity on them. We observed that polymer uptake in P. cuvieri occurred after exposure to 5 and 10 mg/L of PEG without inducing changes in their nitrite levels neither at the levels of substances reactive to thiobarbituric acid. However, hydrogen peroxide and reactive oxygen species production was higher in animals exposed to PEG, whose catalase and superoxide dismutase levels were not enough to counterbalance the production of these reactive species. Therefore, this finding suggests physiological changes altering REDOX homeostasis into oxidative stress. In addition, the increased activity of acetylcholinesterase and butyrylcholinesterase, and reduction in superficial neuromasts, confirmed PEG’s neurotoxic potential. To the best of our knowledge, this is the first report on PEG’s biological impact on a particular amphibian species. The study has broadened the understanding about ecotoxicological risks associated with water pollution by these polymers, as well as motivated further investigations on its impacts on amphibians’ health and on the dynamics of their natural populations.

Given extensive use of pesticides in agriculture, there is concern for unintended consequences to non-target species. The non-target freshwater amphipod, Hyalella azteca has been found to show resistance to the organophosphate (OP) pesticide, chlorpyrifos, resulting from an amino acid substitution in acetylcholinesterase (AChE), suggesting a selective pressure of unintended pesticide exposure. Since resistant organisms can survive in contaminated habitats, there is potential for them to accumulate higher concentrations of insecticides, increasing the risk for trophic transfer. In the present study, we estimated the uptake and elimination of chlorpyrifos in non-resistant US Lab, and resistant Ulatis Creek (ULC Resistant), H. azteca populations by conducting 24-h uptake and 48-h elimination toxicokinetic experiments with ¹⁴C-chlorpyrifos. Our results indicated that non-resistant H. azteca had a larger uptake clearance coefficient (1467 mL g⁻¹ h⁻¹) than resistant animals (557 mL g⁻¹ h⁻¹). The half-life derived from the toxicokinetic models also estimated that steady state conditions were reached at 13.5 and 32.5 h for US Lab and ULC, respectively. Bioaccumulation was compared between non-resistant and resistant H. azteca by exposing animals to six different environmentally relevant concentrations for 28 h. Detection of chlorpyrifos in animal tissues indicated that resistant animals exposed to high concentrations of chlorpyrifos were capable of accumulating the insecticide up to 10-fold higher compared to non-resistant animals. Metabolite analysis from the 28-h concentration experiments showed that between 20 and 50 % parent compound was detected in H. azteca. These results imply that bioaccumulation potential can be more significant in chlorpyrifos resistant H. azteca and may be an essential factor in assessing the full impacts of toxicants on critical food webs, especially in the face of increasing pesticide and chemical runoff.

In ecological risk assessment, acute to chronic ratio (ACR) uncertainty factors are routinely applied to acute mortality benchmarks to estimate chronic toxicity thresholds. To investigate variability of aquatic ACRs, we first compiled and compared 56 and 150 pairs of acute and subchronic/chronic growth/reproductive toxicity data for fishes (Pimephales promelas (53), Danio rerio (2), and Oryzias latipes (1)) and the crustacean Daphnia magna, respectively, for 172 chemicals with different modes of action (MOA). We found that there were only significant relationships between P. promelas acute median lethal concentrations and growth lowest-observed effect concentrations for class 1 (nonpolar narcosis) chemicals, though significant relationships were demonstrated for D. magna to all Verhaar et al. MOA classes (Class 1: nonpolar narcosis, Class 2: polar narcosis, Class 3: reactive chemicals, and Class 4: AChE inhibitors and estrogenics). Probabilistic ecological hazard assessment using chemical toxicity distributions was subsequently employed for each MOA class to estimate acute and chronic thresholds, respectively, to identify MOA and species specific ecological thresholds of toxicological concern. Finally, novel MOA and species specific ACRs using both chemical toxicity distribution comparison and individual ACR probability distribution approaches were identified using representative MOA and chemical categories. Our data-driven approaches and newly identified ACR values represent robust alternatives to application of default ACR values, and can also support future research and risk assessment and management activities for other chemical classes when toxicity information is limited for chemicals with specific MOAs within invertebrates and fish.

While extreme high temperatures are an important aspect of global warming, their effects on organisms are relatively understudied, especially in ecotoxicology. Sequential exposure to heat spikes and pesticides is a realistic scenario as both are typically transient stressors and are expected to further increase in frequency under global warming. We tested the effects of exposure to a lethal heat spike and subsequently to an ecologically relevant lethal pulse exposure of the pesticide chlorpyrifos in the larvae of mosquito Culex pipiens. The heat spike caused direct and delayed mortality, and resulted in a higher heat tolerance and activity of acetylcholinesterase, and a lower fat content in the survivors. The chlorpyrifos exposure caused mortality, accelerated growth rate, and decreased the heat tolerance and the activity of acetylcholinesterase. The preceding heat spike did not change how chlorpyrifos reduced the heat tolerance. Notably, the preceding heat spike did lower the lethal effect of the pesticide, which makes an important novel finding at the interface of ecotoxicology and global change biology, and adds a new dimension to the “climate-induced toxicant sensitivity” (CITS) concept. This may be due to both survival selection and cross-tolerance, and therefore likely a widespread phenomenon. Our results emphasize the importance of including extreme high temperatures as an important transient global change stressor in ecotoxicology.