Adverse effects in Daphnia magna exposed to e-waste leachate: Assessment based on life trait changes and responses of detoxification-related genes

Biomarker responses in Danio rerio following an acute exposure (96 h) to e-waste leachate

Electronic waste (e-waste) has been identified as an emerging pollutant and is the fastest growing waste stream at the present time. Significant technological development and modernization within the last decade has led to the rapid accumulation of outdated, broken and unwanted electrical and electronic equipment (EEE). Electronic products mainly consist of a range of metal containing components that, when disposed of improperly, could result in metal constituents leached into the environment and posing a health risk to humans and animals alike. Metal exposure can induce oxidative stress in organisms, which could lead to synergistic, antagonistic and additive effects. The metals found highest in abundance in the simulated e-waste leachate, were nickel (Ni), barium (Ba), zinc (Zn), lithium (Li), iron (Fe), aluminium (Al) and copper (Cu). An acute exposure study was conducted over a 96 h period to determine the potential toxicity of e-waste on the test organism Danio rerio. Biomarker analysis results to assess the biochemical and physiological effects induced by e-waste leachate, showed a statistically significant effect induced on acetylcholinesterase activity, superoxide dismutase, catalase activity, reduced glutathione content, glutathione s-transferase, malondialdehyde and glucose energy available. The Integrated Biomarker Response (IBRv2) analysis revealed a greater biomarker response induced as the exposure concentration of e-waste leachate increased.

Combined exposure of polystyrene microplastics and carbamazepine induced transgenerational effects on the reproduction of Daphnia magna

Polystyrene microplastics (PS MPs) and carbamazepine (CBZ) are frequently detected in freshwater ecosystems. However, the transgenerational effects of PS MPs and CBZ on the reproduction of aquatic organisms and the corresponding mechanisms are still unclear. In the present study, Daphnia magna was used to evaluate the reproductive toxicity in two consecutive generations (F0, F1). The molting and reproduction parameters, the expression of reproduction, and the toxic metabolism genes were examined after 21-day exposure. A significantly enhanced toxicity was observed in the presence of 5 μm PS MPs and CBZ. Chronic exposure results showed that the 5 μm PS MPs alone, CBZ alone, and their mixtures exerted significant reproductive toxicity of D. magna. The results of RT-qPCR showed transcripts of genes related to reproduction (cyp314, ecr-b, cut, vtg1, vtg2, dmrt93b) and toxic metabolism (cyp4, gst) were altered in both the F0 and F1. In addition, for the F0, gene transcriptional changes of reproduction were not fully translated into physiological performance, probably due to the compensatory responses caused by the low dose of PS MPs alone, CBZ alone, and their mixtures. Whereas for the F1, the trade-off between reproduction and toxic metabolism at gene levels was observed, which translated into a significant reduction in the total neonate number of F1. These findings suggest that long-term exposure to MPs and CBZ can cause serious reproduction damage to aquatic animals, which needs to be given sufficient attention.

Fragrance materials affect life history parameters and gene expression in Daphnia magna: An emerging issue for freshwater ecosystems

A chronic toxicity test (21 d exposure) with the model organism Daphnia magna was performed to study the single-compound and combined effects of four fragrance materials (FMs), including musk xylene (MX), Celestolide™ (ADBI), Galaxolide™ (HHCB), and ethylene brassylate (MT). Furthermore, the transcriptional responses of ten target genes related to detoxification, molting and reproduction (DHR96, P-gp, CYP360A8, GST, CYP314, EcRb, Vtg, CAT, GPX, and GCLC) were determined by performing a quantitative real-time polymerase chain reaction (qRT‒PCR) after juvenile D. magna was exposed for 48 h. The results showed that MX, ADBI and HHCB affected development and reproduction after chronic exposure at a concentration of 10 μg L^-1. Conversely, MT did not affect reproduction, growth or molting during the 21 d exposure. In juvenile D. magna, gene expression was significantly altered by ADBI (DHR96, CYP260A8, and GCLC) and MX (DHR96, CYP360A8, EcRb, Vtg, CYP314, and GCLC) but not by HHCB. These results suggest that compared to biochemical measures, conventional biological endpoints provide more informative data regarding the effects of this FM. Compared to single substances in the chronic test, the mixture of the four FMs showed effects at lower concentrations and increased gene expression for EcRb and CYP314 during juvenile exposure, indicating a possible additive or synergistic effect of the four FMs compared to single compound exposure.

Computer-aided toxicity prediction and potential risk assessment of two novel neonicotinoids, paichongding and cycloxaprid, to hydrobionts

Paichongding (IPP) and cycloxaprid (CYC) have been effectively used as the alternative products of imidacloprid (IMI) against IMI-resistant insects and exhibit a great market potential. However, risk assessment of IPP and CYC for non-target organisms, especially ecological risk assessment for non-target aquatic organisms, is still lacking. Here, we predicted the toxicity and potential risks of IPP, CYC, and their transformation products (TPs) to hydrobionts. The results indicated that IPP and CYC could generate 428 and 113 TPs, respectively, via aerobic microbial transformation. Nearly half of the IPP TPs and nearly 41 % of the CYC TPs exhibited high or moderate toxicity to Daphnia or fish. Moreover, we found that IPP, CYC, and 80 TPs of them posed potential risks to aquatic ecosystems. Almost all harmful TPs contained a 6-chloropyridine ring structure, suggesting that this structure may be associated with the strong toxicity of these TPs to aquatic organisms, and these TPs (IPP-TP2 or CYC-TP2, IPP-TP197 or CYC-TP71, IPP-TP198 or CYC-TP72, and IPP-TP212 or CYC-TP80) may appear in aquatic environments as final products. The risks posed by these TPs to aquatic ecosystems require more attention. This study provides insights into the toxicity and ecological risks of IPP and CYC.

Developmental and Reproductive Impacts of Four Bisphenols in Daphnia magna

Bisphenol A (BPA) is a typical endocrine-disrupting chemical (EDC) used worldwide. Considering its adverse effects, BPA has been banned or strictly restricted in some nations, and many analogs have been introduced to the market. In this study, we selected three representative substitutes, BPS, BPF, and BPAF, along with BPA, to assess the developmental and reproductive effects on Daphnia magna. The F0 generation was exposed to bisphenols (BPs) at an environmentally relevant concentration (100 μg/L) for 21 d; then the embryo spawn at day 21 was collected. Behavior traits, the activity of antioxidant enzymes, and gene transcription were evaluated at three developmental stages (days 7, 14, and 21). Notably, body length, heart rate, and thoracic limb beating were significantly decreased, and D. magna behaved more sluggishly in the exposed group. Moreover, exposure to BPs significantly increased the antioxidant enzymatic activities, which indicated that BPs activated the antioxidant defense system. Additionally, gene expression indicated intergenerational effects in larvae, particularly in the BPAF group. In conclusion, BPA analogs such as BPF and BPAF showed similar or stronger reproductive and developmental toxicity than BPA in D. magna. These findings collectively deepen our understanding of the toxicity of BPA analogs and provide empirical evidence for screening safe alternatives to BPA.

Treatment of electropolishing industrial wastewater and its impact on the immobilisation of Daphnia magna

The amount of industrial pollution entering the environment and its impact on living organisms is an ongoing concern. At the same time, due to an increasing awareness, new methods of wastewater treatment are being explored that are not only effective but also environmentally acceptable. Meeting environmental standards for permitted concentrations is a necessity, but investigating the effects of wastewater on living organisms is also an important issue. In this paper, the influence of metal ions (Fe(III), Cr(III), Ni(II), Cu(II)) in industrial wastewater from electropolishing of stainless steel on Daphnia magna has been investigated. Daphnids have been exposed to wastewater both before and after treatment (Ca(OH)₂ precipitation, sorption with peat). Immobilisation in a 48-h acute toxicity test and EC₅₀ has been determined. In the case of studied industrial wastewater, the organic content (expressed as total organic carbon) of the effluent has a positive impact in terms of the survival of D. magna and increases the range of heavy metal concentrations tolerated by them. The application of a two-stage process with Ca(OH)₂ neutralisation followed by sorption with peat allows for the removal of almost 100% of metal ions from the wastewater. The reduction obtained ensured a limited impact on D. magna and a decrease in immobilisation to less than 10%. Proper execution of the wastewater treatment process ensures a reduction of its negative impact on living organisms.

Gene expression changes in Daphnia magna following waterborne exposure to cyanobacterial strains from the genus Nostoc

Cyanobacteria can produce highly potent cyanotoxins, however, limited information is provided about their toxicity mechanisms in exposed aquatic invertebrates at the molecular level. In the present study, the effects of cyanobacterial strains from the genus Nostoc (Nostoc Z1 and Nostoc 2S3B) in Daphnia magna after waterborne exposure were investigated. Examined endpoints included immobilization (survival) in acute toxicity tests and selected gene expression changes (cyp314, cyp360A8, gst, p-gp, vtg) analyzed by the quantitative real-time polymerase chain reaction (RT-PCR). In addition, enzyme-linked immunosorbent assay (ELISA) was performed to determine whether the observed changes could be due to the presence of microcystins, the most widespread group of cyanotoxins. The results of acute toxicity tests have shown only minor changes in survival rates, which have not exceeded 20% after 48 h of exposure to either strain. On the other hand, significant changes were recorded in molecular responses of Daphnia to tested strains. Treatment with the aquatic strain Nostoc Z1 altered the expression levels of all analyzed genes. Both strains caused a significant p-glycoprotein (p-gp) induction at 75 µg ml^-1 which suggests the involvement of p-gp mediated multixenobiotic resistance mechanism (MXR) in facilitating excretion of toxic cyanobacterial compounds in daphnids. Additionally, these strains caused an increase in the expression levels of cyp360A8, indicating that genes related to detoxification processes could be sensitive indicators of cyanobacterial toxicity. Statistically significant induction of cyp314, as well as increases in expression of gst and vtg, were observed only after exposure to Nostoc Z1. This study indicates the potential of certain cyanobacterial metabolites to modify the expression of toxicant responsive genes involved in phase I and phase III of the xenobiotic metabolism, as well as possible interference with growth and reproduction in D. magna. Low microcystin concentrations found in both samples suggest that these cyanotoxins were not responsible for the detected toxic effects.

Effects of polyvinyl chloride microplastics on reproduction, oxidative stress and reproduction and detoxification-related genes in Daphnia magna

The drastic increase of microplastics (MPs) in aquatic environment has become a serious threat to marine and freshwater ecosystems. However, little information is available regarding the potential detrimental effects of polyvinyl chloride microplastics (PVC-MPs) on aquatic organisms. This study investigated the changes of reproduction parameters, oxidative stress and the expression of reproduction and detoxification-related genes in Daphnia magna after exposed to 2 ± 1 and 50 ± 10 μm PVC-MPs. The results showed that chronic exposure to 2 ± 1 μm PVC-MPs prolonged days to the first brood, increased total number of broods per female and frequency of molting per adult, decreased offspring number at first brood and total number of offspring per female in D. magna. Moreover, 2 ± 1 μm PVC-MPs also disturbed the activities of SOD and CAT, increased GSH and MDA levels. The expression of Vtg, SOD, CAT, CYP314 and CYP360A8 genes also exhibited different response patterns depending on exposure time. Furthermore, 50 ± 10 μm PVC-MPs decreased offspring at first brood and Vtg mRNA level, increased the transcription levels and activities of SOD and CAT. These results suggest that the presence of PVC-MPs in aquatic environment may cause reproduction toxicity by disrupting the reproduction and detoxification-related genes expression and inducing oxidative stress in D. magna.

Acute and chronic toxicity of microcystin-LR and phenanthrene alone or in combination to the cladoceran (Daphnia magna)

Hazardous substances, such as microcystin-LR (MC-LR) and phenanthrene (Phe) are ubiquitous co-contaminants in eutrophic freshwaters, which cause harms to aquatic organisms. However, the risks associated with the co-exposure of aquatic biota to these two chemicals in the environment have received little attention. In this study, the single and mixture toxic effects of MC-LR and Phe mixtures were investigated in Daphnia magna after acute and chronic exposure. Acute tests showed that the median effective concentrations (48 h) for MC-LR, Phe and their mixtures were 13.46, 0.57 and 8.84 mg/L, respectively. Mixture toxicity prediction results indicated that the independent action model was more applicable than the concentration addition model. Moreover, combination index method suggested that the mixture toxicity was concentration dependent. Synergism was elicited at low concentrations of MC-LR and Phe exposure (≤4.04 + 0.17 mg/L), whereas antagonistic or additive effects were induced at higher concentrations. The involved mechanism of antagonism was presumably attributable to the protective effects of detoxification genes activated by high concentrations of MC-LR in mixtures. Additionally, chronic results also showed that exposure to a MC-LR and Phe mixture at low concentrations (≤50 +2 μg/L) resulted in greater toxic effects on D. magna life history than either chemical acting alone. The significant inhibition on detoxification genes and increased accumulation of MC-LR could be accounted for their synergistic toxic effects on D. magna. Our findings revealed the exacerbated ecological hazard of MC-LR and Phe at environmental concentrations (≤50 +2 μg/L), and provided new insights to the potential toxic mechanisms of MC-LR and Phe in aquatic animals.

The Potential Risk of Electronic Waste Disposal into Aquatic Media: The Case of Personal Computer Motherboards

Considering that electronic wastes (e-wastes) have been recently recognized as a potent environmental and human threat, the present study aimed to assess the potential risk of personal computer motherboards (PCMBs) leaching into aquatic media, following a real-life scenario. Specifically, PCMBs were submerged for 30 days in both distilled water (DW) and artificial seawater (ASW). Afterwards, PCMBs leachates were chemically characterized (i.e., total organic carbon, ions, and trace elements) and finally used (a) for culturing freshwater (Chlorococcum sp. and Scenedesmus rubescens) and saltwater (Dunaliella tertiolecta and Tisochrysis lutea) microalgae for 10 days (240 h), (b) as the exposure medium for mussel Mytilus galloprovincialis (96 h exposure), and (c) for performing the Cytokinesis Block Micronucleus (CBMN) assay in human lymphocytes cultures. According to the results, PCMBs could mediate both fresh- and marine algae growth rates over time, thus enhancing the cytotoxic, oxidative, and genotoxic effects in the hemocytes of mussels (in terms of lysosomal membrane impairment, lipid peroxidation, and NO content and micronuclei formation, respectively), as well as human lymphocytes (in terms of MN formation and CBPI values, respectively). The current findings clearly revealed that PCMBs leaching into the aquatic media could pose detrimental effects on both aquatic organisms and human cells.