Our previous study reported that the Ca-dependent aggregation of polyacrylate-coated TiO2 nanoparticles (PAA-TiO2-NPs) determines their routes of uptake by the waterflea Daphnia magna. Besides the ...effects of aggregation on NP bioaccumulation, how this process may influence the bioavailability of NP-adsorbed pollutants remains obscure. In the present study, the aggregation of PAA-TiO2-NPs was also adjusted through Ca. Then the accumulation and toxicity of Cd in D. magna were investigated in the presence and absence of the NPs. Although PAA-TiO2-NPs ameliorated Cd toxicity at both low and high Ca concentrations, the underlying mechanisms differed completely. At low Ca, the metal-NP complexes were accumulated by endocytosis and passive drinking, with both pollutants distributed throughout the daphnid. Nevertheless, Cd accumulation was reduced due to its rapid dissociation from the NPs during the endocytosis of the metal-NP complexes. At high Ca, the metal-NP complexes were actively ingested, Cd accumulation was induced, and both pollutants were concentrated in the daphnid gut. The aggregation-dependent effects of PAA-TiO2-NPs on Cd bioaccumulation were further evidenced by the distinct patterns of metal efflux from D. magna at different Ca concentrations. Overall, Cd adsorption by PAA-TiO2-NPs may either increase or reduce its bioaccumulation, as determined by the aggregation of the NPs.
Fullerenols have wide application in the field of life sciences as a result of their extensive biocompatibility and biofunctionality. However, their environmental fate and ecotoxicological risks are ...largely unknown. In this study, stable isotope (13C) labeling was applied to investigate the bioaccumulation and depuration of fullerenols in Daphnia magna. By incorporation of 13C on the skeleton of fullerenols, the concentrations of fullerenols in the samples could be precisely determined on the basis of carbon isotope ratios (13C/12C). After exposure to 13C-labeled fullerenols in artificial freshwater for 48 h, the steady concentrations of fullerenols in D. magna were nearly 0.39 and 1.37% of the dry body weight in the 0.1 and 1.0 mg/L exposure groups, respectively. After 48 h of depuration, D. magna could excrete 97.34 and 89.56% of the accumulated fullerenols in 0.1 and 1.0 mg/L exposure group, respectively. The depuration of fullerenols from D. magna followed first-order kinetics. Moreover, accumulated fullerenols in gravid D. magna could be transferred to the next generation of neonates. The results in present study demonstrated that stable isotope (13C) labeling is a powerful tool to investigate the environmental fate and the potential impacts of fullerenols in ecological systems.
Mycotoxins are low molecular weight compounds present in food and feed. Although their effects on human health have been widely described, their mechanisms of action are still undefined. Gliotoxin ...(GTX) and ochratoxin A (OTA) are among the most dangerous mycotoxins produced by Aspergillus spp. Therefore, their toxicity was studied in the Daphnia magna model, which has high capacity to predict cytotoxicity and assess ecotoxicity, comparable to mammalian models. The study consisted of a series of tests to evaluate the effects of mycotoxins GTX, OTA and their combinations at different dilutions on Daphnia magna that were conducted according to standardized OECD 202 and 211 guidelines. The following assays were carried out: acute toxicity test, heartbeat, delayed toxicity test, reproduction, growth rate test. Reproducibility was determined by observing the offspring after 21 days of GTX exposure. In acute and delayed toxicity transcript levels of genes involved in xenobiotic metabolism (mox, gst, abcb1, and abcc5), and oxidative stress (vtg-SOD) were analyzed by qPCR. GTX showed acute toxicity and decreased heart rate in D. magna compared to OTA. On the other hand, OTA showed a delayed effect as evidenced by the immobility test. Both mycotoxins showed to increase genes involved in xenobiotic metabolism, while only the mycotoxin mixture increased oxidative stress. These results suggest that the mycotoxins tested could have negative impact on the environment and human health.
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The amount of nano- and microplastic in the aquatic environment rises due to the industrial production of plastic and the degradation of plastic into smaller particles. Concerns have been raised ...about their incorporation into food webs. Little is known about the fate and effects of nanoplastic, especially for the freshwater environment. In this study, effects of nano-polystyrene (nano-PS) on the growth and photosynthesis of the green alga Scenedesmus obliquus and the growth, mortality, neonate production, and malformations of the zooplankter Daphnia magna were assessed. Nano-PS reduced population growth and reduced chlorophyll concentrations in the algae. Exposed Daphnia showed a reduced body size and severe alterations in reproduction. Numbers and body size of neonates were lower, while the number of neonate malformations among neonates rose to 68% of the individuals. These effects of nano-PS were observed between 0.22 and 103 mg nano-PS/L. Malformations occurred from 30 mg of nano-PS/L onward. Such plastic concentrations are much higher than presently reported for marine waters as well as freshwater, but may eventually occur in sediment pore waters. As far as we know, these results are the first to show that direct life history shifts in algae and Daphnia populations may occur as a result of exposure to nanoplastic.
This study demonstrates the acute toxicity of lanthanum oxide nanoparticles (La sub(2)O sub(3) NP) on two sentinel aquatic species, fresh-water microalgae Chlorellasp. and the crustacean Daphnia ...magna. The morphology, size and charge of the nanoparticles were systematically studied. The algal growth inhibition assay confirmed absence of toxic effects of La sub(2)O sub(3) NP on Chlorellasp., even at higher concentration (1000 mg L super(-1)) after 72 h exposure. Similarly, no significant toxic effects were observed on D. magnaat concentrations of 250 mg L super(-1) or less, and considerable toxic effects were noted in higher concentrations (effective concentration EC sub(50) 500 mg L super(-1); lethal dose LD sub(50) 1000 mg L super(-1)). In addition, attachment of La sub(2)O sub(3) NP on aquatic species was demonstrated using microscopy analysis. This study proved to be beneficial in understanding acute toxicity in order to provide environmental protection as part of risk assessment strategies.
Tioxazafen (TXF) is the first 1,2,4-oxadiazole nematicide. In the present study, the aqueous degradation of TXF was investigated in terms of hydrolysis and photolysis. Under the irradiation of ...simulated sunlight, TXF degraded very fast in ultrapure water and buffers with half-lives (t1/2s) <8.3 min. A sole photoproduct (PP) PP228a was isolated, and identified by spectroscopic means (UV, IR, HRMS, and 1H NMR) to be the thiophen-3-yl isomer converted from its thiophen-2-yl parent. Comparing with TXF, PP228a had quite extended t1/2s ranging from 6.9 to 7.9 d. The photolysis kinetics of TXF and PP228a showed no pH-dependence, and varied for each individual compound as affected by nitrate, fulvic acid, and humic acid. Besides, both compounds were hydrolytically stable. 6 PPs of PP228a were identified, with two of them being its isomers. The mechanisms involved in the process included the biradical photosensitization, photoinduced electron transfer, and ring contraction-ring expansion reactions. The 48 h-EC50 to Daphnia magna was 0.808 mg/L for PP228a comparing to >1.12 mg/L for TXF, while the results of Vibrio fischeri assays indicated that one or more PPs of PP228a might have higher toxicity.
We investigate the distribution and effects of polystyrene microplastic (MP) particles in exposure experiments with the ecotoxicology model organism Daphnia magna. The aim was to investigate the ...short and long-term toxicity of MP at different concentrations. To achieve this goal, the effects of 6 μm commercially available polystyrene beads on two different life-stages of D. magna: < 24 h old juveniles and 9 days old adults was assessed. The following end points in test animals were measured: (1) survival, (2) growth, (3) individual and population fecundity, (4) age at maturation and (5) body size of newborn offspring. These response variables were followed in two acute and two chronic experiments. The acute experiments showed that MP is not acutely toxic to D. magna within 48 h, but cause added mortality within 120 h. The juveniles were about 50% more sensitive than the adults tested. In life-cycle experiments testing chronic exposure to MP, again, animals exposed as juveniles at relatively high concentrations, i.e. > 30 μg ml−1 showed higher sensitivity. We observed slightly increased mortality, reduced growth and stimulation of early reproduction at the cost of later reproduction. Animals exposed after reaching adulthood did not show increased mortality and showed a stimulation response with higher reproductive rates than the control group. However, both the growth rate of mother animals and the body size of newborn declined with increasing dose of MP. We conclude that these effects indicate a role of MP in mechanical interaction/interference with the animal on the level of feeding (clogging filtering functions), digestion (gut filled with plastic particles), and/or other animal behavior. The study also illustrates how MP with slow break-down rates may accumulate in the environment and enter the food-chain as obstructing non-food particles in filter-feeding organisms.
•Microplastic shows toxicity after long time exposure.•Effects are significantly different between juvenile and adult.•Microplastic show significant effects on second generation.
Microplastics could act as vectors for the transport of harmful bacteria, such as pathogens and antibiotic resistance bacteria (ARB), but their combined effects have not been reported yet. Here, ARB ...Shigella flexneri with sulfonamides resistance and micro-polystyrene (micro-PS) were used to investigate their possible combined effects on the growth and expression of functional genes in Daphnia magna. Results showed that micro-PS colonized with S. flexneri were ingested by D. magna and blocked in their intestine after 24 h exposure. Changes were observed in the life history and morphology of D. magna, as well as the expression of functional genes in all treatments, but with no difference in the survival rate. We also determined the expression of six functional genes involved in energy and metabolism (arginine kinase, AK) and oxidative stress response (thioredoxin reductase, TRxR, catalase, CAT, and glutathione S-transferases, GSTs), as well as in growth, development and reproduction (vitellogenin, Vtg1 and ecdysone receptor, EcR). AK and Vtg1 did not show significant differences, however, EcR was down-regulated and the other three genes (TRxR, CAT, GSTs) were up-regulated in the combined-treated group. Antibiotic resistance gene (ARGs) sul1 was detected when exposed to micro-PS colonized with S. flexneri., suggesting that D. magna could acquire resistance genes through microplastic biofilms. These results indicated that MPs could act as a carrier of ARB to transfer ARGs into D. magna, and affect the life history, morphology, and the expression of related functional genes of D. magna, to adapt to the stress caused by MPs and ARB.
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•The colonization of antibiotic-resistant bacteria (ARB) on microplastics is investigated.•Microplastics block in the intestine of D. magna.•The life history and morphology of D. magna were changed by the microplastics and ARB.•Microplastics and ARB caused effects on the expression of functional genes in D. magna.•Microplastics affect the integration of antibiotic resistance genes carried by ARB.
Calcium plays versatile roles in aquatic ecosystems. In this study, we investigated its effects on the uptake of polyacrylate-coated TiO sub( 2) nanoparticles (PAA-TiO2-NPs) by the water flea ...(cladoceran) Daphnia magna. Particle distribution in these daphnids was also visualized using synchrotron radiation-based micro X-ray fluorescence spectroscopy, transmission electron microscopy, and scanning electron microscopy. At low ambient Ca concentrations in the experimental medium (Ca sub( dis)), PAA-TiO sub( 2)-NPs were well dispersed and distributed throughout the daphnid; the particle concentration was highest in the abdominal zone and the gut, as a result of endocytosis and passive drinking of the nanoparticles, respectively. Further, Ca induced PAA-TiO sub( 2)-NP uptake as a result of the increased Ca influx. At a high Ca sub( dis), the PAA-TiO sub( 2)-NPs formed micrometer-sized aggregates that were ingested by D. magna and concentrated only in its gut, independent of the Ca influx. Our results demonstrated the multiple effects of Ca on nanoparticle bioaccumulation. Specifically, well-dispersed nanoparticles were taken up by D. magna through endocytosis and passive drinking whereas the uptake of micrometer-sized aggregates relied on active ingestion.
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