Multi-level ecotoxicity assay on the aquatic midge, Chironomus tentans (Diptera, Chironomidae) exposed to octachlorostyrene

Molecular and biochemical evaluation of effects of malathion, phenanthrene and cadmium on Chironomus sancticaroli (Diptera: Chironomidae) larvae

In-vitro effects of sub-lethal concentrations of malathion, phenanthrene (Phe) and cadmium (Cd) were tested on Chironomus sancticaroli larvae in acute bioassays by measuring biochemical and molecular parameters. Malathion was evaluated at 0.001, 0.0564 and 0.1006 mg L^-1; Phe at 0.0025, 1.25 and 2.44 mg L^-1; and Cd at 0.001, 3.2 and 7.4 mg L^-1. The recovery test carried out at the highest concentration of each compound showed that survival of larvae exposed to Phe ranged from 4% to 5%, while the effects of malathion and Cd were irreversible, not allowing the emergence of adults. Results showed that malathion and Cd inhibited AChE, EST-α and ES-β activities at the two highest concentrations. Phe at 0.0025, 1.25 and 2.44 mg L^-1; and Cd at 3.2 and 7.4 mg L^-1 inhibited glutathione S-transferase activity. Oxidative stress was exclusively induced by the lowest concentration of malathion considering SOD activity once CAT was unaffected by the stressors. Lipid peroxidation was registered exclusively by malathion at the two highest concentrations, and total hemoglobin content was only reduced by Cd at the two highest concentrations. The relationship among biochemical results, examined using the PCA, evidenced that malathion and Cd concentrations were clustered into two groups, while Phe only formed one group. Four hemoglobin genes of C. sancticaroli were tested for the first time in this species, with Hemoglobin-C being upregulated by malathion. The toxicity ranking was malathion > Phe > Cd, while biochemical and molecular results showed the order malathion > Cd > Phe. Our results highlight the importance of combining different markers to understand the effects of the diverse compounds in aquatic organisms.

Multi-Level Gene Expression in Response to Environmental Stress in Aquatic Invertebrate Chironomids: Potential Applications in Water Quality Monitoring

In freshwater ecosystems, aquatic invertebrates are influenced continuously by both physical stress and xenobiotics. Chironomids (Diptera; Chironomidae), or non-biting midges, are the most diverse and abundant invertebrates in freshwater habitats. They are a fundamental link in food chains of aquatic ecosystems. Chironomid larvae tolerate stress factors in their environments via various physiological processes. At the molecular level, environmental pollutants induce multi-level gene responses in Chironomus that regulate cellular protection through the activation of defense processes. This paper reviews literature on the transcriptional responses of biomarker genes to environmental stress in chironomids at the molecular level, in studies conducted from 1991 to 2020 (120 selected literatures of 374 results with the keywords "Chironomus and gene expression" by PubMed search tool). According to these studies, transcriptional responses in chironomids vary depending on the type of stress factor and defensive responses associated with antioxidant activity, the endocrine system, detoxification, homeostasis and stress response, energy metabolism, ribosomal machinery, apoptosis, DNA repair, and epigenetics. These data could provide a comprehensive overview of how Chironomus species respond to pollutants in aquatic environments. Furthermore, the transcriptomic data could facilitate the development of genetic tools for water quality and environmental monitoring based on resident chironomid species.

What types of enzyme activities are useful biomarkers of bifenthrin exposure on Chironomus sp. (Diptera, Chironomidae) larvae under laboratory and field-based microcosm conditions?

Bifenthrin is a second generation synthetic pyrethroid insecticide that is widely used in Australia and worldwide. It is frequently found in urban freshwater sediments at concentrations likely to impact biota as it is highly toxic to fish and macroinvertebrates, such as chironomids. Our main goal was to evaluate if oxidative stress and hydrolase enzymes are useful biomarkers of effect of synthetic pyrethroids exposure under different scenarios. Chironomus tepperi larvae (5 days old) were exposed to sub-lethal sediment concentrations of bifenthrin for 5 days under controlled laboratory conditions. A field-based microcosm exposure with bifenthrin-spiked sediments (using the same concentrations as the laboratory exposure) was carried out at a clean field site for four weeks to allow for colonization and development of resident chironomid larvae. At the end of both experiments, Chironomus larvae (C. tepperi in the laboratory exposures and C. oppositus in the microcosm exposures) were collected and oxidative stress enzymes (Glutathione-s-Transferase, Glutathione Reductase and Glutathione Peroxidase) and hydrolase enzymes (Acetylcholinesterase and Carboxylesterase) were measured. Only the Glutathione Peroxidase activity was significantly impacted in larvae from the laboratory exposure. On the contrary, significant changes were observed in all the measured enzymes from the field-based microcosm exposure. This is likely because exposure was throughout the whole life cycle, from egg mass to fourth instar, showing a more realistic exposure scenario. Furthermore, this is the first time that changes in oxidative stress and hydrolase enzymes have been shown to occur in Australian non-biting midges exposed under field-based microcosm conditions. Thus, this study demonstrated the usefulness of these enzymes as biomarkers of effect following bifenthrin exposure in microcosms. It also highlights the importance of using a range of different biochemical endpoints to get a more holistic understanding of pesticide effects and the pathways involved.

A Multiparametric Approach to Cerium Oxide Nanoparticle Toxicity Assessment in Non-Biting Midges

Cerium oxide nanoparticles (CeO₂ NPs) are included in the Organisation for Economic Co-operation and Development (OECD) priority list of engineered nanomaterials for assessment of their environmental impact. The present study was carried out to assess the CeO₂ NP toxicity to the freshwater midge Chironomus riparius larvae at concentrations of 2.5, 25, 250, and 2500 mg of CeO₂ NP/kg of sediment. Experiments were designed to assess the prolonged exposure of midges to CeO₂ NPs while adhering to OECD test guideline 218. The following parameters were investigated: CeO₂ NP uptake by larvae, oxidative stress parameters, in vivo genotoxic effects, and life trait parameters. Inductively coupled plasma-mass spectrometry analysis showed a significant positive correlation between the concentration of CeO₂ NPs in the sediment and its uptake by the larvae. No significant mortality was observed in C. riparius, and oxidative stress was not detected. The only significantly induced sublethal effect was genotoxicity, which began to manifest at a lowest-observed-effect concentration of 25 mg kg^-1 of sediment and progressively increased at higher concentrations. Our results indicate that exposure to CeO₂ NP-contaminated freshwater sediments does not pose a risk to chironomids at environmentally realistic concentrations. However, the significant accumulation of CeO₂ NPs by chironomid larvae may pose a risk through trophic transfer to organisms further up the food chain. Environ Toxicol Chem 2019;39:131-140. © 2019 SETAC.

Amitraz toxicity to the midge Chironomus riparius: Life-history and biochemical responses

Acute and chronic toxicity of the formamidine pesticide amitraz to the midge Chironomus riparius was assessed using conventional ecotoxicological tests and biochemical approaches (biomarkers). Amitraz is mainly used as an ectoparasiticide in veterinary medicine, but also in agriculture and apiculture. However, information of amitraz toxicity to non-target invertebrates is limited. Besides the impairment of developmental and emergence rates (reduced larval growth, emergence, and delayed development time) caused by chronic exposure to amitraz, acute exposures induced alterations in the antioxidant enzymes glutathione peroxidase (GPx) and catalase (CAT), and in energetic metabolism biomarkers, lactate dehydrogenase (LDH) and electron transport system (ETS) activities. Moreover, lipid peroxidation (LPO) increased by amitraz exposure. Our results reveal potential secondary effects of amitraz to invertebrates and biomarkers that may aid in the interpretation of sub-lethal toxic responses to amitraz. These results add information concerning the potential outcomes of amitraz exposure to freshwater invertebrates underlining the importance of risk assessment studies of formamidine pesticides.

Polybrominated diphenyl ethers (PBDEs) effects on Chironomus sancticaroli larvae after short-term exposure

In-vivo effects of polybrominated diphenyl ethers (PBDEs) containing 3, 4 and 5 bromine atoms were tested on fourth-instar larvae of Chironomus sancticaroli (Diptera: Chironomidae) after 48h of exposure, by measuring the activity of the acetyl cholinesterase, alpha and beta esterases and glutathione S-transferase. The PBDE congeners 2,2',4-triBDE (BDE-17), 2,2',4,4'-tetraBDE (BDE-47) and 2,2',4,4',5-pentaBDE (BDE-99) were evaluated at 0.5, 1.0, 2.0 and 3.0ngmL^-1. Acetyl cholinesterase activity decreased significantly (p≤0.05) at all evaluated concentrations of the three PBDE congeners, except for larvae exposed to BDE-17 at 1.0 and 2.0ngmL^-1. The significant inhibition of acetyl cholinesterase activity ranged from 18% (BDE-47 at 0.5ngmL^-1) to 72% (BDE-47 at 2.0ngmL^-1). The enzymes alpha and beta esterase were also affected by the three congeners, reducing their activity from 14% (BDE-99 at 1.0ngmL^-1) to 52% (BDE-47 at 2.0ngmL^-1) and from 7% (BDE-99 at 2.0ngmL^-1) to 34% (BDE-47 at 3.0ngmL^-1) respectively. Substantial increments in glutathione S-transferase activity were similarly observed, varying from 138% (BDE-99 2.0 at ng mL^-1) to 346% (BDE-17 at 1.0ngmL^-1). DNA strand breaks were detected exclusively in larvae exposed to BDE-99 at 2.0 and 3.0ngmL^-1 (H=11.7, p=0.019). These results showed that C. sancticaroli larvae were sensitive to the PBDEs treatments under the experimental conditions.

Transcriptional deregulation of genetic biomarkers in Chironomus riparius larvae exposed to ecologically relevant concentrations of di(2-ethylhexyl) phthalate (DEHP)

Di(2-ethylhexyl) phthalate (DEHP) is a ubiquitous environmental pollutant used worldwide as a plasticizer and solvent in many formulations. Based on available toxicological data, it has been classified as toxic for reproduction and as an endocrine disruptor. Despite this, ecotoxicological studies in aquatic wildlife organisms are still scarce. In the present work, the toxic molecular alterations caused by DEHP in aquatic larvae of the midge Chironomus riparius have been studied, by analyzing the transcriptional activity of genes related to some vital cellular pathways, such as the ribosomal machinery (rpL4, rpL13), the cell stress response (hsc70, hsp70, hsp40, hsp27), the ecdysone hormone pathway (EcR), the energy metabolism (GAPDH), and detoxication processes (CYP4G). Environmentally relevant concentrations (10-3 to 105 μg/L) and exposure conditions (24 to 96 h) have been tested, as well as the toxic effects after DEHP withdrawal. Although the compound caused no mortality, significant changes were detected in almost all the studied biomarkers: e.g. strong repression of hsp70; general inhibition of EcR; GAPDH activity loss in long exposures; among others. Our data show a general transcriptional downregulation that could be associated with an adaptive response to cell damage. Besides, the activity of the compound as an ecdysone antagonist and its delayed effects over almost all the biomarkers analyzed are described as novel toxic targets in insects.

Genes involved in cysteine metabolism of Chironomus tepperi are regulated differently by copper and by cadmium

Freshwater invertebrates are often exposed to metal contamination, and changes in gene expression patterns can help understand mechanisms underlying toxicity and act as pollutant-specific biomarkers. In this study the expressions of genes involved in cysteine metabolism are characterized in the midge Chironomus tepperi during exposures to sublethal concentrations of cadmium and copper. These metals altered gene expression of the cysteine metabolism differently. Both metals decreased S-adenosylhomocysteine hydrolase expression and did not change the expression of S-adenosylmethionine synthetase. Cadmium exposure likely increased cystathionine production by up-regulating cystathionine-β-synthase (CβS) expression, while maintaining control level cysteine production via cystathionine-γ-lyase (CγL) expression. Conversely, copper down-regulated CβS expression and up-regulated CγL expression, which in turn could diminish cystathionine to favor cysteine production. Both metals up-regulated glutathione related expression (γ-glutamylcysteine synthase and glutathione synthetase). Only cadmium up-regulated metallothionein expression and glutathione S-transferase d1 expression was up-regulated only by copper exposure. These different transcription responses of genes involved in cysteine metabolism in C. tepperi point to metal-specific detoxification pathways and suggest that the transsulfuration pathway could provide biomarkers for identifying specific metals.

A wireless and sensitive detection of octachlorostyrene using modified AuNPs as signal-amplifying tags

A wireless, remote query octachlorostyrene (OCS) biosensor was fabricated by coating a mass-sensitive magnetoelastic ribbon with anti-OCS antibody. In response to a time-varying magnetic field, the magnetoelastic sensor mechanically vibrates at a characteristic resonance frequency which inversely depends on the sensor mass loading. As the magnetoelastic film is magnetostrictive itself, the vibrations launch magnetic flux that can be remotely detected using a pickup coil. Au nanoparticles (NPs) were used to amplify the mass loading. In a sample solution containing OCS target and OCS-modified AuNPs (OCS-AuNPs), both OCS and OCS-AuNPs react with the anti-OCS antibody immobilized on the sensor surface in a competition mode. The bound OCS-AuNPs amount is inversely proportional to the OCS target concentration. The reduction of bound OCS-AuNPs induced by free OCS results in significant change in mass loading, which amplifies the responses. The biosensor demonstrates a linear shift in resonance frequency with OCS concentration between 7.4 μM and 9 nM, with a detection limit of 2.8 nM.