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

Not Only Toxic but Repellent: What Can Organisms’ Responses Tell Us about Contamination and What Are the Ecological Consequences When They Flee from an Environment?

The ability of aquatic organisms to sense the surrounding environment chemically and interpret such signals correctly is crucial for their ecological niche and survival. Although it is an oversimplification of the ecological interactions, we could consider that a significant part of the decisions taken by organisms are, to some extent, chemically driven. Accordingly, chemical contamination might interfere in the way organisms behave and interact with the environment. Just as any environmental factor, contamination can make a habitat less attractive or even unsuitable to accommodate life, conditioning to some degree the decision of organisms to stay in, or move from, an ecosystem. If we consider that contamination is not always spatially homogeneous and that many organisms can avoid it, the ability of contaminants to repel organisms should also be of concern. Thus, in this critical review, we have discussed the dual role of contamination: toxicity (disruption of the physiological and behavioral homeostasis) vs. repellency (contamination-driven changes in spatial distribution/habitat selection). The discussion is centered on methodologies (forced exposure against non-forced multi-compartmented exposure systems) and conceptual improvements (individual stress due to the toxic effects caused by a continuous exposure against contamination-driven spatial distribution). Finally, we propose an approach in which Stress and Landscape Ecology could be integrated with each other to improve our understanding of the threat contaminants represent to aquatic ecosystems.Versión del edito

Avoidance responses by Danio rerio reveal interactive effects of warming, pesticides and their mixtures

Temperature variations and thermal extremes events caused by climate change can have profound implications for the toxicity of pesticides in aquatic organisms. Using an innovative system (Heterogeneous Multi-Habitat Test System - HeMHAS) that allows the simulation of different scenarios within a spatially heterogeneous landscape, the effects on the habitat selection of Danio rerio fish caused by the pesticides fipronil and 2,4-D were studied as single compounds and in mixture and integrated with air temperature variation (20, 24 and 28 °C). As a result, D. rerio detected and avoided both pesticides at air temperatures of 20 and 24 °C; however, at 28 °C no significant difference was observed in habitat choice by fish. Additionally, when pesticides were mixed in a heterogeneously contaminated landscape, it was observed that D. rerio detected contamination and preferred the clean zone at 20 and 24 °C; however, at 28 °C the potential to escape from the most contaminated areas was impaired. Thus, contamination by both pesticides made the habitat selection behavior of fish at 20 and 24 °C more noticeable. In addition, the association between pesticides and temperature showed negative effects on the response of fish to detect and escape from contaminated environments, suggesting the influence of temperature in altering the ability of the organism to provide an efficient response to stress.R.A. Moreira would like to thank the São Paulo Research Foundation “Fundação de Amparo à Pesquisa do Estado de São Paulo” (FAPESP) for the post doctorate grant to the first author (Process number: 2020/16131-0 and 2017/24126-4). Financial support was also provided by FAPESP (2015/18790-3). C.V.M. Araújo is grateful to the grant (Ramón y Cajal contract: RYC-2017-22324) funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. This research was funded by MCIN/AEI/10.13039/501100011033 (BrEStress project: PID2019-105868RA-I00) and i-COOP2019 program from CSIC (MultiCecotox project: #COOPB20444)

Short and long-term exposure to the pesticides fipronil and 2,4-D: Effects on behavior and life history of Daphnia magna

The high levels of contamination in aquatic ecosystems caused by pesticides and the organisms' consequent continuous exposure to it has made them vulnerable to damage. However, mobile organisms can avoid this continued exposure to contaminants by moving to less disturbed habitats. Therefore, through the use of the Heterogenous Multi-Habitat Assay System (HeMHAS), our objective was to evaluate the ability of Daphnia magna to detect and avoid habitats contaminated by fipronil and 2,4-D, in a spatially connected landscape. Further, the role of contamination by these pesticides, isolated and in mixtures, concerning the colonization of habitats by daphnids was also evaluated. Given that not all organisms successfully escape contamination, the chronic toxicity of the same pesticides using different parameters for D. magna (maternal survival, fecundity and maternal body length) was also evaluated. When evaluating the avoidance response by D. magna exposed to pesticides, there was no preference for the less contaminated areas for both compounds. However, organisms did not move to contaminated zones in the colonization experiments, with no immigration of daphnids to the zones with intermediate and the highest levels of fipronil, nor to the highest concentration of 2,4-D. Finally, the colonization by daphnids was significantly prevented when exposed to a mixture of the pesticides, in which the areas with the highest combinations of pesticide concentrations were not colonized by D. magna. Regarding the long-term chronic effects, negative consequences were observed, particularly for maternal body length, fecundity and maternal survival, due to the exposure to fipronil. Considering that pesticides can limit the areas colonized by organisms by making them unattractive, the risk of local population extinction may be underestimated if only standard endpoints involving forced exposure are studied.R.A. Moreira thanks the São Paulo Research Foundation “Fundação de Amparo à Pesquisa do Estado de São Paulo” (FAPESP) for the post doctoral grant to the first author (Process number: 2020/16131–0 and 2017/24126–4). C.V.M. Araújo is grateful for the grant (Ramón y Cajal contract: RYC-2017-22324) funded by MCIN/AEI / 10.13039/501100011033 and by “ESF Investing in your future”. This research was funded by MCIN/ AEI /10.13039/501100011033 (BrEStress project: PID2019-105868RA-I00) and i-COOP2019 program from CSIC (MultiCecotox project: #COOPB20444).Peer reviewe

Alterations on growth and gill morphology of Danio rerio (Pisces, Ciprinidae) exposed to the toxic sediments

The objective of this work was to assess the toxicity of sediment samples from six cascade reservoirs in Tietê river system, in São Paulo State, Brazil, through chronic-partial toxicity bioassays with Danio rerio larvae as test-organisms. Histology of gills and biometric measurements were used to determine the existence of toxicity problems. The alterations on gill morphology here detected were considered of first stage (hyperplasia, lamellar junction and excess of mucous cells) in the first reservoirs and very slight in the last ones. The biometric analysis pointed to inadequate conditions for the growth of the test-organisms when exposed to the sediment of the rivers and upstream reservoirs and also indicated an improvement of environmental conditions along the system.<br>Os bioensaios de toxicidade com amostras ambientais avaliam as respostas dos organismos teste frente a possíveis poluentes. Ocorrem em complementação às análises limnológicas da água e sedimento, uma vez que estas apenas identificam e quantificam as diferentes substâncias nestes compartimentos aquáticos. O objetivo deste trabalho foi avaliar a toxicidade das amostras de sedimentos dos seis reservatórios em cascata do sistema Tietê (SP) - Brasil, através de bioensaios de toxicidade crônico-parciais utilizando como organismos-teste larvas de Danio rerio. A histologia das brânquias e as medidas biométricas foram as ferramentas utilizadas para averiguar o problema ambiental. As alterações branquiais detectadas foram de primeiro grau (hiperplasia, junção lamelar e excesso de células mucosas) e pouco acentuadas nos últimos reservatórios. As análises biométricas demonstraram condições inadequadas ao desenvolvimento dos organismos testes frente a possíveis poluentes biodisponíveis nos sedimentos dos rios e primeiros reservatórios, confirmando a melhoria das condições ambientais ao longo da cascata. Isto também pode ser confirmado através das análises químicas dos sedimentos deste sistema