Phototoxicity and oxidative stress responses in Daphnia magna under exposure to sulfathiazole and environmental level ultraviolet B irradiation

Ecotoxicological, ecophysiological, and mechanistic studies on zinc oxide (ZnO) toxicity in freshwater environment

The world has faced climate change that affects hydrology and thermal systems in the aquatic environment resulting in temperature changes, which directly affect the aquatic ecosystem. Elevated water temperature influences the physico-chemical properties of chemicals in freshwater ecosystems leading to disturbing living organisms. Owing to the industrial revolution, the mass production of zinc oxide (ZnO) has been led to contaminated environments, and therefore, the toxicological effects of ZnO become more concerning under climate change scenarios. A comprehensive understanding of its toxicity influenced by main factors driven by climate change is indispensable. This review summarized the detrimental effects of ZnO with a single ZnO exposure and combined it with key climate change-associated factors in many aspects (i.e., oxidative stress, energy reserves, behavior and life history traits). Moreover, this review tried to point out ZnO kinetic behavior and corresponding mechanisms which pose a problem of observed detrimental effects correlated with the alteration of elevated temperature.

Physiological response and molecular mechanisms against UV-B radiation in Brachionus asplanchnoidis (Rotifera)

Ultraviolet B (UV-B, 280-320 nm) radiation is a major environmental stressor for aquatic organisms on Earth's surface. Its effects on biological systems are well known, but the mechanisms by which organisms respond and adapt to UV-B radiation are still being explored. In this study, we investigated the effects of UV-B radiation on the monogonont rotifer Brachionus asplanchnoidis, focusing on physiological parameters, antioxidant systems, DNA damage, and DNA repair-related molecular mechanism. Our results showed that the LD50 was at 28.53 kJ/m2, indicating strong tolerance to UV-B. However, UV-B radiation caused adverse effects on growth and reproduction, with shortened reproductive period and longevity, decreased fecundity and hatchability, and inhibition of population growth. Biochemical analyses revealed severe oxidative damage and lipid peroxidation, with increased ROS and MDA levels. Activities of antioxidant enzymes were highly induced at low doses but decreased at high doses. DNA damage also occurred in UV-B-exposed rotifers. Furthermore, selected DNA repair-related genes were up-regulated in a dose-dependent manner. These findings provide a comprehensive understanding of the effects of UV-B radiation on rotifers and highlight the importance of considering both ecological and molecular responses in assessing the impact of UV-B radiation on aquatic organisms.

Ecotoxicological Effects of Four Commonly Used Organic Solvents on the Scleractinian Coral Montipora digitata

Organic solvents are often used in aquatic toxicity tests to facilitate the testing of hydrophobic or poorly water-soluble substances such as ultraviolet (UV) filters, pesticides, or polycyclic aromatic hydrocarbons (PAHs). Knowledge of intrinsic effects (i.e., measured as standardized and non-standardized endpoints) of such carrier solvents in non-standardized organisms (i.e., corals), is critical to regulatory processes. Therefore, we exposed the reef-building coral Montipora digitata to the most commonly used carrier solvents ethanol, methanol, dimethyl sulfoxide, and dimethylformamide in the range of 10-100 µL L^-1 for 16 days. The effects on mortality, photobiological, morphological, and oxidative stress markers were evaluated. In our study, all solvents resulted in significant morphological and/or oxidative stress responses, but not in mortality. Moreover, ethanol led to a rapid increase in turbidity, thus questioning its suitability as a carrier solvent in aquatic studies in general. Based on our observations, we could rank the solvent effects as follows: dimethylformamide < dimethyl sulfoxide ≈ methanol ≤ ethanol, with dimethylformamide showing the least and ethanol the most pronounced effects. We conclude that the use of solvents in toxicity studies with corals, particularly by examining non-standardized (e.g., morphological, physiological) endpoints, should be taken with caution and requires further elaboration.

Freshwater crustacean exposed to active pharmaceutical ingredients: ecotoxicological effects and mechanisms

Concerns over the ecotoxicological effects of active pharmaceutical ingredients (APIs) on aquatic invertebrates have been raised in the last decade. While numerous studies have reported the toxicity of APIs in invertebrates, no attempt has been made to synthesize and interpret this dataset in terms of different exposure scenarios (acute, chronic, multigenerational), multiple crustacean species, and the toxic mechanisms. In this study, a thorough literature review was performed to summarize the ecotoxicological data of APIs tested on a range of invertebrates. Therapeutic classes including antidepressants, anti-infectives, antineoplastic agents, hormonal contraceptives, immunosuppressants, and neuro-active drugs exhibited higher toxicity to crustaceans than other API groups. The species sensitivity towards APIs exposure is compared in D. magna and other crustacean species. In the case of acute and chronic bioassays, ecotoxicological studies mainly focus on the apical endpoints including growth and reproduction, whereas sex ratio and molting frequency are commonly used for evaluating the substances with endocrine-disrupting properties. The multigenerational and "Omics" studies, primarily transcriptomics and metabolomics, were confined to a few API groups including beta-blocking agents, blood lipid-lowing agents, neuroactive agents, anticancer drugs, and synthetic hormones. We emphasize that in-depth studies on the multigenerational effects and the toxic mechanisms of APIs on the endocrine systems of freshwater crustacean are warranted.

Antibiotic Pollution of Planktonic Ecosystems: A Review Focused on Community Analysis and the Causal Chain Linking Individual- and Community-Level Responses

Antibiotic pollution has become one of the most challenging environmental issues in aquatic ecosystems, with adverse effects on planktonic organisms that occupy the base of the aquatic food chain. However, research regarding this topic has not been systematically reviewed, especially in terms of community-level responses. In this review, we provide an overview of current antibiotic pollution in aquatic environments worldwide. Then, we summarize recent studies concerning the responses of planktonic communities to antibiotics, ranging from individual- to community-level responses. Studies have shown that extremely high concentrations of antibiotics can directly harm the growth and survival of plankton; however, such concentrations are rarely found in natural freshwater. It is more likely that environmentally relevant concentrations of antibiotics will affect the physiological, morphological, and behavioral characteristics of planktonic organisms; influence interspecific interactions among plankton species via asymmetrical responses in species traits; and thus alter the structure and function of the entire planktonic ecosystem. This review highlights the importance of community analysis in revealing antibiotic toxicity. We also encourage the establishment of the causal relationships between impacts at multiple scales in the future for predicting the community-level consequences of antibiotics based on the currently available individual-level evidence.

Occurrence and ecotoxicity of sulfonamides in the aquatic environment: A review

Rapid population growth and increasing demand for animal protein food have led to a continuous increase in global utilization of antibiotic. Sulfonamides (SAs) are ubiquitous in aquatic environments and pose an ecological risk owing to their large consumption and strong environmental persistence. Hence, this review focuses on the recent publications on 12 different SAs and provides a detailed summary of selected antibiotic concentrations in various water systems. We evaluated the ecotoxicity of SAs on organisms at different trophic level organisms and the environmental risks regarding aquatic systems. The results indicated that SA antibiotics were ubiquitous in aquatic environments at concentrations ranging from ng/L to μg/L. According to the data using standard ecotoxicity bioassays, algae were the most susceptible aquatic organisms for selected antibiotics, followed by crustaceans and fish. The risk data suggested that some antibiotics, such as sulfadiazine (SDZ), sulfamethoxazole (SMX), and sulfamethazine (SMZ) pose a great risk to the aquatic system. Based on the present review, it is necessary to strengthen the research into their ecotoxicity to marine systems and the chronic toxicity of antibiotic mixtures.

Effects of chronic sublethal progestogen exposure on development, reproduction, and detoxification system of water flea, Daphnia magna

The presence of sex steroid hormones in aquatic ecosystems is of rapidly growing concern worldwide since they can affect the different non-target species including cladocerans. Although data are available on the effects of estrogens on the well-established ecotoxicological model organism Daphnia magna, the molecular or behavioural alterations induced by environmentally relevant concentrations (from a few ng L^-1 to a few hundred ng L^-1 in average) of progestogens have not been investigated on this species. In the present study, we exposed neonates of D. magna to relevant equi-concentrations (1, 10, 100, 500 ng L^-1) of mixtures of four progestogens (progesterone, drospirenone, gestodene, levonorgestrel) in short-term (6 days) and long-term (21 days) experiments. Significant alterations were observed at the molecular, cellular, and individual levels. During the short-term exposure, all of the mixtures increased the gene expression of glutathione S-transferase (GST) detoxification enzyme, moreover, the activity of GST was also significantly increased at the concentrations of 10, 100, and 500 ng L^-1. In long-term exposure, the number of days until production of the first eggs was reduced at the 10 ng L^-1 concentration compared to control, furthermore, the maximum egg number per individual increased at the concentrations of 1 and 10 ng L^-1. Based on the authors' best knowledge, this is the first study to investigate the effects of progestogens in mixtures and at environmentally relevant concentrations on D. magna. Our findings contribute to the understanding of the possible physiological effects of human progestogens. Future research should be aimed at understanding the potential mechanisms (e.g., perception) underlying the changes induced by progestogens.

Fenton-like degradation of sulfathiazole using copper-modified MgFe-CO3 layered double hydroxide

The catalytic activity of layered double hydroxides, with and without insertion of copper, was evaluated in a heterogeneous Fenton process for degradation of the antibiotic sulfathiazole (STZ). The characterizations with different techniques revealed lamellar structures formed by stacking of layers containing magnesium, iron, and copper cations. The insertion of copper in the lamellar structure increased the specific area of the material and the degradation kinetics, achieving complete STZ removal after 90 min. X-ray photoelectron spectroscopy analysis showed the presence of Cu(II) and Cu(I) surface sites, which contributed to the generation of hydroxyl and hydroperoxyl/superoxide radicals. It also indicated an increase of Cu(I) content after use. For both materials, but specially for LDH without copper, addition of tert-butyl alcohol and p-benzoquinone hindered STZ degradation, indicating the importance of hydroxyl and hydroperoxyl/superoxide radicals in the degradation process, respectively. These results demonstrated the potential of copper-modified MgFe-CO₃ as a catalyst for the degradation of emerging contaminants, offering the benefits of easy preparation and high efficiency in the Fenton process.

Uptake of microalgae as sublethal biomarker reveals phototoxicity of oxytetracycline to the crustacean Daphnia magna

Antibiotics are considered emerging pollutants as their presence in the environment is increasingly common. Although their environmental concentrations are generally low, they can pose risk to organisms through bioaccumulation, causing sublethal effects. Furthermore, solar radiation can trigger reactions in certain compounds after their accumulation within organisms or in the environment. Toxicity and photoinduced toxicity of oxytetracycline (OTC, widely used antibiotic in salmon aquaculture) on Daphnia magna (Crustacea, Cladocera) and microalgae Raphidocelis subcapitata (Chlorophyceae) as its food source was assessed via aqueous exposure. Also, the impact via diet (microalga) to the crustacean was examined. In addition to lethal (immobility) effect, in vivo chlorophyll fluorescence techniques were used to determine food ingestion (gut content as a biomarker of physiological health) in D. magna and physiological status of microalgae. OTC (≤10 mg L ^- 1) was not acutely (24 h) toxic to R. subcapitata when measured as maximum quantum yield (F_v/F_m) in darkness. However, under short (1 h) UV exposure OTC caused irreversible decrease of F_v/F_m (50%) at ≥0.5 mg L ^- 1. OTC was not acutely lethal to D. magna (≤10 mg L ^- 1), however, sublethal effects (43% decrease in food ingestion) at 10 mg L ^- 1 were demonstrated. UV exposure (4.5 h) strongly exacerbated toxicity of OTC, leading to lethal (87% immobility) and sublethal (81% decrease of feeding in survived individuals) effects. Uptake of OTC (aqueous exposure) and its photosensitization in tissues of D. magna under UV exposure was confirmed. On the other hand, rapid bioadsorption of OTC on cell surface was evident in R. subcapitata. Uptake of OTC in D. magna through diet could not be confirmed at short-term. Photomodification of OTC under UV exposure was observed through changes in its absorption spectrum. The results show that short exposure to summer UV levels of southern Chile can rapidly induce phototoxicity of OTC, suggesting a potential risk to aquatic organisms.

Effect of sulfonamide pollution on the growth of manure management candidate Hermetia illucens

Antibiotics are commonly used in livestock and poultry farming. Residual antibiotics in manure may lead to antibiotic pollution of soil, surface water, and groundwater through land application and run-off rainfall. The black soldier fly (BSF) Hermetia illucens is a good candidate for manure management. We evaluated the effect of sulfonamide pollution on the growth of H. illucens. Four treatments were considered with a sulfonamide content in the feed of 0 (control group), 0.1, 1, and 10 mg/kg. The control larvae were fed without sulfonamide. Survival and development status of the individuals were recorded daily. The weights of the fifth instar larvae, prepupae, and pupae were checked. Antioxidant enzyme activity was determined with the fifth instar larvae. The results showed that a low (0.1 and 1 mg/kg) concentration of sulfonamides had no effects on larval survival, pupation, and eclosion of BSFs. A high sulfonamide concentration of 10 mg/kg had a significant effect on the survival of larvae and pupae and on the body weight of larvae, prepupae and pupae. Peak of the cumulated pupation rate and eclosion rate in the sulfonamide treatment of 10 mg/kg was very low. Pupation and eclosion in this group peaked later than that of the control and low sulfonamide concentration treatment groups (0.1 mg/kg and 1 mg/kg). Larvae from the sulfonamides group showed lower antioxidase activities than that of the control. In sulfonamide groups, the activity of peroxidase and superoxide dismutase was reduced in a concentration-dependent manner. Sulfamonomethoxine, sulfamethoxazole, and sulfamethazine were not detected in the harvested prepupae. Only sulfadiazine was discovered in the sulfonamide treatments of 1 and 10 mg/kg. In conclusion, BSFs can tolerate certain concentrations of sulfonamide contamination.

Effects of lomefloxacin on survival, growth and reproduction of Daphnia magna under simulated sunlight radiation

Lomefloxacin, an antibacterial agent with known photo-induced toxicity in clinical studies, is frequently detected in aquatic environments. Investigating the photo-induced toxicity of lomefloxacin in aquatic organisms is therefore of importance for assessing its ecological risks. In this study, the effects of lomefloxacin on survival, growth and reproduction of Daphnia magna under simulated sunlight radiation (SSR) were investigated, and the mechanism of action was revealed. Results indicated that SSR containing UV radiation increased the acute toxicity of lomefloxacin to Daphnia magna relative to white fluorescent light irradiation. Under SSR, 100 μM lomefloxacin significantly enhanced reactive oxygen species (ROS) generation and lipid peroxidation, and decreased activities of superoxide dismutase and catalase. The biochemical observations and apparent effects on the organism indicate that oxidative stress plays a central role in the acute photo-induced toxicity. Chronic toxicity results showed that SSR significantly affected growth and reproduction of Daphnia magna, whereas lomefloxacin reduced the damage of UV radiation in SSR through light shielding. This study provides insight into the mechanism of photo-induced toxicity and can support the risk assessment of chemicals in the aquatic environment by including the impacts of sunlight irradiation on toxicity.

Investigation of antibiotics in sea cucumbers: occurrence, pollution characteristics, and human risk assessment

Occurrence and distribution of 24 antibiotics from 7 categories were screened in sea cucumbers (Echinodermata: Holothuroidea) collected from different coastal regions of China. The samples were simultaneously extracted and purified using accelerated solvent extraction with in-cell clean-up and analyzed by ultra-performance liquid chromatography-tandem mass spectrometry. A total of ten antibiotics were detected in the sea cucumbers with concentrations ranging from not detected to 32.8 μg/kg (dry weight). Sulfonamides are predominant antibiotics with a mean concentration of 11.5 μg/kg (dry weight), followed by macrolides (11.3 μg/kg, dry weight) and fluoroquinolones (11.2 μg/kg, dry weight). High concentrations of the antibiotics were found in the samples from the South China Sea, implying that the antibiotic pollution in sea cucumbers was geographical region-dependent, which was further confirmed by principal component analysis. It was also found that the antibiotic levels are slightly higher in instant sea cucumbers than in the dried ones. Hazard quotient calculation suggested no obvious human health risks associated with the consumption of sea cucumbers regarding antibiotics.

Size dependent oxidative stress response of the gut of Daphnia magna to functionalized nanodiamond particles

Nanodiamonds are a type of engineered nanomaterial with high surface area that is highly tunable and are being proposed for use as a material for medical imaging or drug delivery to composites. With their potential for widespread use they may potentially be released into the aquatic environment as are many chemicals used for these purposes. It is generally thought that nanodiamonds are innocuous, but toxicity may occur due to surface functionalization. This study investigated the potential oxidative stress and antioxidant response of enterocytes in a freshwater invertebrate, Daphnia magna, a common aquatic invertebrate for ecotoxicological studies, in response to two types of functionalized nanodiamonds (polyallylamine and oxidized). We also examined how the size of the nanomaterial may influence toxicity by testing two different sizes (5 nm and 15 nm) of nanodiamonds with the same functionalization. Adults of Daphnia magna were exposed to three concentrations of each of the nanodiamonds for 24 h. We found that both 5 and 15 nm polyallylamine nanodiamond and oxidized nanodiamond induced the production of reactive oxygen species in tissues. The smaller 5 nm nanodiamond induced a significant change in the expression of heat shock protein 70 and glutathione-S-transferase. This may suggest that daphnids mounted an antioxidant response to the oxidative effects of 5 nm nanodiamonds but not the comparative 15 nm nanodiamonds with either surface chemistry. Outcomes of this study reveal that functionalized nanodiamond may cause oxidative stress and may potentially initiate lipid peroxidation of enterocyte cell membranes in freshwater organisms, but the impact of the exposure depends on the particle size.

Protective effects of compatible solute ectoine against ethanol-induced toxic alterations in Daphnia magna

Ectoine (ECT) is a compatible solute synthesized mostly by halophilic microorganisms subjected to various stressful factors. Its protective properties in bacteria and some populations of isolated cells subjected to different stressors are reported; however, little is known on its effects against a commonly used compound, ethanol (ETH). The purpose of our study was to determine the effects of ETH alone (at 20 and 60 g/L) and in the combination with various concentrations of ECT (5, 10, and 25 mg/L) at various times of exposure on behavioural, physiological, and biochemical parameters of a model invertebrate Daphnia magna. In the present study, we determined the following parameters: immobilisation, heart rate, thoracic limb movement, catalase (CAT) activity, and nitric oxide species (NOx) level. Our study revealed that both concentrations of ETH alone induced immobilisation and decrease of swimming velocity, heart rate, and thoracic limb activity; however, catalase activity and NOx levels were increased. On the other hand, the animals exposed to the combinations of ETH + ECT showed a reduced immobilisation and alleviated inhibition of heart rate and thoracic limb activity, lower increase of CAT activity, and NOx level when compared to the crustaceans subjected to ETH alone. The most distinct alleviation of toxic effects was noted in the combinations in which the highest concentration of ECT were used. The results suggest that ETH may induce oxidative stress in daphnids and attenuating effects of ECT probably result from its antioxidative properties.

Identification of differentially expressed proteins in Ostrinia furnacalis adults after exposure to ultraviolet A

Ultraviolet A (UVA), the major component of solar UV irradiation, is an important environmental factor inducing damage to insects including cell death, photoreceptor damage, and oxidative stress. In order to improve understanding of the adaptation mechanisms of insect after UVA exposure, a comparative proteomic analysis was carried out to reveal differential protein expression in Ostrinia furnacalis. Three-day-old adults were treated with UVA for 1 h. Total proteins of control and UVA-treated insects were examined using two-dimensional electrophoresis (2-DE). 2-DE analysis demonstrated that 19 proteins were increased and 18 proteins were decreased significantly in O. furnacalis after UVA exposure, respectively. Thirty differentially expressed proteins were successfully identified by mass spectrometry. The identified proteins were involved in diverse biological processes, such as signal transduction, transport processing, cellular stress, metabolisms, and cytoskeleton organization. Our results reveal that the response patterns of O. furnacalis to UVA irradiation are complex and provide novel insights into the adaptation response to UVA irradiation stress.

Cyanobacterium removal and control of algal organic matter (AOM) release by UV/H2O2 pre-oxidation enhanced Fe(II) coagulation

Harmful algal blooms in source water are a worldwide issue for drinking water production and safety. UV/H₂O₂, a pre-oxidation process, was firstly applied to enhance Fe(II) coagulation for the removal of Microcystis aeruginosa [M. aeruginosa, 2.0 (±0.5) × 10⁶ cell/mL] in bench scale. It significantly improved both algae cells removal and algal organic matter (AOM) control, compared with UV irradiation alone (254 nm UVC, 5.4 mJ/cm²). About 94.7% of algae cells were removed after 5 min UV/H₂O₂ pre-treatment with H₂O₂ dose 375 μmol/L, FeSO₄ coagulation (dose 125 μmol/L). It was also certified that low residue Fe level and AOM control was simultaneously achieved due to low dose of Fe(II) to settle down the cells as well as the AOM. The result of L₉(3)⁴ orthogonal experiment demonstrated that H₂O₂ and FeSO₄ dose was significantly influenced the algae removal. UV/H₂O₂ induced an increase of intracellular reactive oxidant species (ROS) and a decrease in zeta potential, which might contribute to the algae removal. The total microcystins (MCs) concentration was 1.5 μg/L after UV/H₂O₂ pre-oxidation, however, it could be removed simultaneously with the algae cells and AOM. This study suggested a novel application of UV/H₂O₂-Fe(II) process to promote algae removal and simultaneously control AOM release in source waters, which is a green and promising technology without secondary pollution.

Disrupting effects of antibiotic sulfathiazole on developmental process during sensitive life-cycle stage of Chironomus riparius

Antibiotics in the environment are a concern due to their potential to harm humans and interrupt ecosystems. Sulfathiazole (STZ), a sulfonamide antibiotic, is commonly used in aquaculture and is typically found in aquatic ecosystems. We evaluated the ecological risk of STZ by examining biological, molecular and biochemical response in Chironomus riparius. Samples were exposed to STZ for 12, 24 and 96 h, and effects of STZ were evaluated at the molecular level by analyzing changes in gene expression related to the endocrine system, cellular stress response and enzyme activity of genes on antioxidant and detoxification pathways. STZ exposure induced significant effects on survival, growth and sex ratio of emergent adults and mouthpart deformity in C. riparius. STZ caused concentration and time-dependent toxicity in most of the selected biomarkers. STZ exposure leads to significant heat-shock response of protein genes (HSP70, HSP40, HSP90 and HSP27) and to disruption by up-regulating selected genes, including the ecdysone receptor gene, estrogen-related receptors, ultraspiracle and E74 early ecdysone-responsive gene. Furthermore, STZ induced alteration of enzyme activities on antioxidant and detoxification responses (catalase, superoxide dismutase, glutathione peroxidase and peroxidase) in C. riparius. By inducing oxidative stress, antibiotic STZ disturbs the endocrine system and produces adverse effects in growth processes of invertebrates.

The heat is on: Genetic adaptation to urbanization mediated by thermal tolerance and body size

Worldwide, urbanization leads to tremendous anthropogenic environmental alterations, causing strong selection pressures on populations of animals and plants. Although a key feature of urban areas is their higher temperature ("urban heat islands"), adaptive thermal evolution in organisms inhabiting urban areas has rarely been studied. We tested for evolution of a higher heat tolerance (CT_MAX ) in urban populations of the water flea Daphnia magna, a keystone grazer in freshwater ecosystems, by carrying out a common garden experiment at two temperatures (20°C and 24°C) with genotypes of 13 natural populations ordered along a well-defined urbanization gradient. We also assessed body size and haemoglobin concentration to identify underlying physiological drivers of responses in CT_MAX . We found a higher CT_MAX in animals isolated from urban compared to rural habitats and in animals reared at higher temperatures. We also observed substantial genetic variation in thermal tolerance within populations. Overall, smaller animals were more heat tolerant. While urban animals mature at smaller size, the effect of urbanization on thermal tolerance is only in part caused by reductions in body size. Although urban Daphnia contained higher concentrations of haemoglobin, this did not contribute to their higher CT_MAX . Our results provide evidence of adaptive thermal evolution to urbanization in the water flea Daphnia. In addition, our results show both evolutionary potential and adaptive plasticity in rural as well as urban Daphnia populations, facilitating responses to warming. Given the important ecological role of Daphnia in ponds and lakes, these adaptive responses likely impact food web dynamics, top-down control of algae, water quality, and the socio-economic value of urban ponds.

Do microplastic particles affect Daphnia magna at the morphological, life history and molecular level?

Microplastic particles are ubiquitous not only in marine but also in freshwater ecosystems. However, the impacts of microplastics, consisting of a large variety of synthetic polymers, on freshwater organisms remains poorly understood. We examined the effects of two polymer mixtures on the morphology, life history and on the molecular level of the waterflea Daphnia magna (three different clones). Microplastic particles of ~40 μm were supplied at a low concentration (1% of the food particles) leading to an average of ~30 particles in the digestive tract which reflects a high microplastic contamination but still resembles a natural situation. Neither increased mortality nor changes on the morphological (body length, width and tail spine length) or reproductive parameters were observed for adult Daphnia. The analyses of juvenile Daphnia revealed a variety of small and rather subtle responses of morphological traits (body length, width and tail spine length). For adult Daphnia, alterations in expression of genes related to stress responses (i.e. HSP60, HSP70 & GST) as well as of other genes involved in body function and body composition (i.e. SERCA) were observed already 48h after exposure. We anticipate that the adverse effects of microplastic might be influenced by many additional factors like size, shape, type and even age of the particles and that the rather weak effects, as detected in a laboratory, may lead to reduced fitness in a natural multi-stressor environment.

Is A/A/O process effective in toxicity removal? Case study with coking wastewater

The anaerobic-anoxic-oxic (A/A/O) process is the commonly used biological wastewater treatment process, especially for the coking wastewater. However, limit is known about its ability in bio-toxicity removal from wastewater. In this study, we evaluated the performance of A/A/O process in bio-toxicity removal from the coking wastewater, using two test species (i.e. crustacean (Daphnia magna) and zebra fish (Danio rerio)) in respect of acute toxicity, oxidative damage and genotoxicity. Our results showed that the acute toxicity of raw influent was reduced gradually along with A/A/O process and the effluent presented no acute toxicity to Daphnia magna (D. magna) and zebra fish. The reactive oxygen species (ROS) level in D. magna and zebra fish was promoted by the effluent from each tank of A/A/O process, showing that coking wastewater induced oxidative damage. Herein, the oxidative damage to D. magna was mitigated in the oxic tank, while the toxicity to zebra fish was reduced in the anoxic tank. The comet assays showed that genotoxicity to zebra fish was removed stepwise by A/A/O process, although the final effluent still presented genotoxicity to zebra fish. Our results indicated that the A/A/O process was efficient in acute toxicity removal, but not so effective in the removal of other toxicity (e.g. oxidative damage and genotoxicity). Considering the potential risks of wastewater discharge, further advanced toxicity mitigation technology should be applied in the conventional biological treatment process, and the toxicity index should be introduced in the regulation system of wastewater discharge.

Phototoxicity and chronic toxicity of methyl paraben and 1,2-hexanediol in Daphnia magna

Parabens are used as antimicrobial preservatives in consumer products. Exposure to methylparaben (MP) has been associated with adverse health outcomes, therefore, an alternative compound, 1,2-hexanediol (1,2-H), has been applied for cosmetics. In the present study, the phototoxicity of MP and 1,2-H, as well as the toxic effect caused by chronic exposure, were investigated using Daphnia magna. The 48 h acute toxicity tests with D. magna were conducted under indoor or ultraviolet (UV) light irradiation conditions, i.e., exposure to 4 h/d sunlight. Changes in the transcription of genes related to oxidative stress were determined in D. magna juveniles, to investigate the underlying mechanism of phototoxicity. The 21 d chronic toxicity tests of MP and 1,2-H were performed under indoor light irradiation. Exposure to MP under environmental level of UV light was more detrimental to D. magna. Transcripts of catalase and glutathione-S-transferase genes in D. magna was significantly increased by co-exposure to MP and UV light. After 21 d of chronic exposure to MP and 1,2-H, the reproduction no-observed effect concentrations for D. magna were 1 and >10 mg/L, respectively. The present study showed that exposure to UV could magnify the toxicity of MP on daphnids. Although acute and chronic toxicities of 1,2-H were generally lower than those of MP, its effects on other aquatic organisms should not be ignored. Further studies are needed to identify other mechanisms of MP phototoxicity.

Endocrine-disruption potential of perfluoroethylcyclohexane sulfonate (PFECHS) in chronically exposed Daphnia magna

Perfluoroethylcyclohexane sulfonate (PFECHS), mainly used in hydraulic fluids in aircrafts, is a member of the perfluoroalkyl sulfonate family which includes the regulated perfluorooctane sulfonate (PFOS). PFECHS has been reported in environmental samples but its toxicity to aquatic organisms is unknown. The objectives of this study were to identify biological pathways altered by sublethal exposure (12 d) of D. magna to PFECHS (0.06, 0.6, and 6 mg/L) using microarray and quantitative real-time PCR and to identify potential biomarkers to link transcriptomic to phenotypic responses. PFECHS was also quantified in surface water samples (1.04-1.38 ng/L) collected from the St. Lawrence River, Canada. Transcriptomic analyses indicated the under-regulation of vitellogenin-related genes (VTG1) in PFECHS-exposed groups. PFECHS exposure also led to the up-regulation of genes related to cuticle. VTG was selected as a potential cellular marker and identified in D. magna using an immuno-specific assay and quantified using Western blot and LC/MS/MS. Results indicated a decrease of VTG content in exposed D. magna which was in concordance with the transcription of VTG-related genes. No effects were observed on survival, molting, or reproduction at the individual/population levels. Overall, results suggest endocrine disruption potential for PFECHS in D. magna at concentrations higher than levels reported in the aquatic environment.

Influence of temperature on toxicity of single pharmaceuticals and mixtures, in the crustacean A. desmarestii

Lethal and sublethal responses of the shrimp Atyaephyra desmarestii exposed to three pharmaceutical compounds, Diclofenac (DF), Ibuprofen (IB) and Carbamazepine (CBZ), individually and in mixtures, were evaluated under two temperature scenarios. LC50 (96h) values were obtained individually at 20° and 25°C. At 25°C, mortality in binary and ternary mixtures is higher than at 20°C. The toxicity of the mixtures was predicted on the basis of individual mortality data using two toxicity models: Concentration addition (CA) and Independent action (IA). Our results showed that neither CA nor IA unequivocally predicted the observed toxicity of binary and ternary mixtures. For sublethal toxicity, selected endpoints were: ingestion rate, osmoregulatory capacity and respiration rate. Regarding osmoregulatory capacity, no significant differences were found. The highest ingestion rates were recorded in organisms exposed at 25°C, irrespective of the compound, after 30 and 60min of exposure. At 20°C, there was a significant decrease in respiration rate (Dunnett́s test p<0.05) under conditions of severe anoxia (1mg O2L(-1)) in organisms exposed to 13.3μgL(-1) of DF. At 25°C a significantly lower respiration rate with respect to the control (Dunnett́s test p<0.05) was found in organisms exposed to 13.8μgL(-1) of CBZ under conditions of moderate hypoxia and well-oxygenated water (3 and 5mg O2L(-1), respectively). The respiratory independence of organisms exposed to the higher temperature (25°C) also decreased. This study shows that CBZ and DF individually, even at relatively low concentrations, may produce respiratory deficiencies in the freshwater shrimp, Atyaephyra desmarestii under certain temperature and water oxygenation conditions, thus reducing its ability to function.

Rapid evolution of antioxidant defence in a natural population of Daphnia magna

Natural populations can cope with rapid changes in stressors by relying on sets of physiological defence mechanisms. Little is known onto what extent these physiological responses reflect plasticity and/or genetic adaptation, evolve in the same direction and result in an increased defence ability. Using resurrection ecology, we studied how a natural Daphnia magna population adjusted its antioxidant defence to ultraviolet radiation (UVR) during a period with increasing incident UVR reaching the water surface. We demonstrate a rapid evolution of the induction patterns of key antioxidant enzymes under UVR exposure in the laboratory. Notably, evolutionary changes strongly differed among enzymes and mainly involved the evolution of UV-induced plasticity. Whereas D. magna evolved a strong plastic up-regulation of glutathione peroxidase under UVR, it evolved a lower plastic up-regulation of glutathione S-transferase and superoxide dismutase and a plastic down-regulation of catalase. The differentially evolved antioxidant strategies were collectively equally effective in dealing with oxidative stress because they resulted in the same high levels of oxidative damage (to lipids, proteins and DNA) and lowered fitness (intrinsic growth rate) under UVR exposure. The lack of better protection against UVR may suggest that the UVR exposure did not increase between both periods. Predator-induced evolution to migrate to lower depths that occurred during the same period may have contributed to the evolved defence strategy. Our results highlight the need for a multiple trait approach when focusing on the evolution of defence mechanisms.

Evaluation of a drinking water treatment process involving directly recycling filter backwash water using physico-chemical analysis and toxicity assay

Recycling the filter backwash water of a drinking water treatment plant (DWTP) was considered as a feasible method to enhance the efficiencies of pollutant removal and water conservation.

Is UV radiation changing the toxicity of compounds to zebrafish embryos?

At ecosystems level, environmental parameters such as temperature, pH, dissolved oxygen concentration and intensity of UV radiation (UVR) have an important role on the efficiency of organisms' physiological and behavioral performances and consequently on the capacity of response to contaminants. Insignificant alterations of these parameters may compromise this response. In addition, these parameters can additionally alter chemical compounds by inducing their degradation, producing thereafter other metabolites. Understanding the combined effects of chemicals and environmental parameters is absolutely necessary for an adequate prediction of risk in aquatic environments. According to this scenario, this work aims at studying the combined toxicity of UVR and three xenobiotics: the biocide triclosan (TCS), the metal chromium (as potassium dichromate, PD) and the fungicide prochloraz (PCZ). To achieve this goal zebrafish (Danio rerio) embryos (3h post fertilization (hpf)) were exposed to several concentrations of each chemical combined with different UV intensities; mortality and eggs were recorded every 24h for the all test duration (96 h). Results showed different response patterns depending on the toxicant, stress levels and duration of exposure. The combination of UVR and TCS indicated a dose ratio deviation where synergism was observed when UVR was the dominant stressor (day 2). The combination of UVR and PD presented a dose level dependency at day 3 indicating antagonism at low stress levels, changing with time where at day 4, a dose ratio deviation showed statistically that synergism occurred at higher PD concentrations. Finally, UVR combined with PCZ indicated a dose ratio at day 3 and dose level deviation at day 4 of exposure, suggesting a synergistic response when PCZ is the dominant stressor in the combination. The obtained results in this study highlighted the importance of taking into account the possible interaction of stressors and time of exposure to better predict environmental risk.

Combining physico-chemical analysis with a Daphnia magna bioassay to evaluate a recycling technology for drinking water treatment plant waste residuals

Recycling water treatment plant (WTP) waste residuals is considered to be a feasible method to enhance the efficiency of pollutant removal. This study also evaluated the safety and water quality of a pilot-DWTP waste residuals recycling technology by combining physical-chemistry analysis with a Daphnia magna assay. The water samples taken from each treatment step were extracted and concentrated by XAD-2 resin and were then analyzed for immobilization and enzyme activity with D. magna. The measured parameters, such as the dissolve organic carbon (DOC), UV254 and THM formation potential (THMFPs) of the recycling process, did not obviously increase over 15 days of continuous operation and were even lower than typical values from a conventional process. The extract concentration ranged from 0 to 2 Leq/ml as measured on the 7th and 15th days and the immobilization of D. magna exposed to water treated by the recycling process was nearly equivalent to that of the conventional process. Both the superoxide dismutase (SOD) and the catalase (CAT) activity assay indicated that a lower dose of water extract (0.5, 1, 1.5 Leq/ml) could stimulate the enzyme activity of D. magna, whereas a higher dose (2 Leq/ml at the sampling point C3, R3, R4 ) inhibits the activity. Moreover, the SOD and CAT activity of D. magna with DOC and UV254 showed a strong concentration-effect relationship, where the concentration range of DOC and UV254 were 4.1-16.2 mg/L and 0.071-4.382 cm(-1), respectively. The results showed that there was no statistically significant difference (p>0.05) between the conventional and recycling treatment processes and the toxicity of water samples in the recycling process did not increase during the 15-day continuous recycling trial.

Combined Effects from γ Radiation and Fluoranthene Exposure on Carbon Transfer from Phytoplankton to Zooplankton

Risk assessment does not usually take into account mixtures of contaminants, thus potentially under- or overestimating environmental effects. We investigated how the transfer of carbon between a primary producer, Pseudokirchneriella subcapitata, and a consumer, Daphnia magna, is affected by acute exposure of γ radiation (GR) in combination with the polycyclic aromatic hydrocarbon fluoranthene (FA). We exposed D. magna to five concentrations of FA and five acute doses of GR as single contaminants and in nine binary combinations. We compared the observed data for three end points (incorporation of carbon by D. magna, D. magna ingestion rates, and growth) to the predicted joint effects of the mixed stressors based on the independent action (IA) concept. There were deviations from the IA predictions, especially for ingestion rates and carbon incorporation by D. magna, where antagonistic effects were observed at the lower doses, while synergism was seen at the highest doses. Our results highlight the importance of investigating the effects of exposure to GR in a multistressor context. In mixtures of GR and FA, the IA-predicted effects seem to be conservative as antagonism between the two stressors was the dominant pattern, possibly due to stimulation of cellular antioxidative stress mechanisms.

Protective effects of ectoine on behavioral, physiological and biochemical parameters of Daphnia magna subjected to hydrogen peroxide

Ectoine (ECT) is an osmoprotectant produced by halophilic microorganisms inducing protective effects against various stressful factors. However, little is known about its influence on aquatic invertebrates subjected to hydrogen peroxide (H2O2)-a commonly used oxidative disinfectant. Therefore, the aim of our study was to determine the effects of H2O2 alone (at 5 and 10 mg/L) and in the combination with various concentrations of ECT (5, 10 and 25 mg/L) on behavioral, physiological and biochemical parameters of Daphnia magna. The following endpoints were determined: mortality, heart rate, thoracic limb movement, total glutathione (GSH)/oxidized glutathione (GSSG) ratio, catalase (CAT) activity and nitric oxide (NOx) level. The study showed that daphnids exposed to the combination of H2O2+ECT showed decreased mortality, attenuated inhibition of heart rate and thoracic limb activity, less decreased GSH/GSSG ratio, lower stimulation of CAT activity and NOx level when compared to the crustaceans exposed to H2O2 alone. The most pronounced alleviation of toxic effects was observed in the combination of 5 mg/L H2O2+25 mg/L ECT. The results suggest that protective effects of ECT in D. magna subjected to H2O2 may be related to antioxidative properties of the osmoprotectant.

The HR97 (NR1L) group of nuclear receptors: a new group of nuclear receptors discovered in Daphnia species

The recently sequenced Daphnia pulex genome revealed the NR1L nuclear receptor group consisting of three novel receptors. Phylogenetic studies show that this group is related to the NR1I group (CAR/PXR/VDR) and the NR1J group (HR96), and were subsequently named HR97a/b/g. Each of the HR97 paralogs from Daphnia magna, a commonly used crustacean in toxicity testing, was cloned, sequenced, and partially characterized. Phylogenetic analysis indicates that the HR97 receptors are present in primitive arthropods such as the chelicerates but lost in insects. qPCR and immunohistochemistry demonstrate that each of the receptors is expressed near or at reproductive maturity, and that HR97g, the most ancient of the HR97 receptors, is primarily expressed in the gastrointestinal tract, mandibular region, and ovaries, consistent with a role in reproduction. Transactivation assays using an HR97a/b/g-GAL4 chimera indicate that unlike Daphnia HR96 that is promiscuous with respect to ligand recognition, the HR97 receptors do not respond to many of the ligands that activate CAR/PXR/HR96 nuclear receptors. Only three putative ligands of HR97 receptors were identified in this study: pyriproxyfen, methyl farnesoate, and arachidonic acid. Only arachidonic acid, which acts as an inverse agonist, alters HR97g activity at concentrations that would be considered within physiologically relevant ranges. Overall, this study demonstrates that, although closely related to the promiscuous receptors in the NR1I and NR1J groups, the HR97 receptors are mostly likely not multi-xenobiotic sensors, but rather may perform physiological functions, potentially in reproduction, unique to crustaceans and other non-insect arthropod groups.

Tissue-specific antioxidant responses in pale chub (Zacco platypus) exposed to copper and benzo[a]pyrene

In this study, antioxidant responses including lipid peroxidation (LPO), superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), were evaluated in the liver, gill and muscle tissues of pale chub (Zacco platypus) exposed to copper (Cu) and benzo[a]pyrene (BaP). Cu exposure induced significant antioxidant responses in Z. platypus, particularly in the liver, whereas BaP exposure had a negligible effect. Following Cu exposure, both SOD and CAT activity increased in a concentration-dependent manner, showing significant correlations with malondialdehyde (MDA) levels as a measure of LPO (r = 0.646 and 0.663, respectively). SOD, CAT and GST mRNA levels were also enhanced following Cu exposure, except at 20 μg L(-1), although significant correlations with antioxidant enzyme activities were not found. The results of this study suggest that combined information on SOD and CAT activities together with LPO levels in the liver could be a useful indicator for assessing oxidative stress in freshwater fish.

The influence of sulfathiazole on the macroalgae Ulva lactuca

Sulfonamides (SA) are a class of antibiotics routinely found in environmental matrices and therefore their role as contaminants should be investigated in non-target organisms. With this purpose the present experimental work has evaluated the exposure of the chlorophycean Ulva lactuca L. to sulfathiazole (STZ), a SA drug commonly used in aquaculture, at two concentrations representing prophylactic (25 μg mL(-1)) and therapeutic (50 μg mL(-1)) administrations. Results showed that STZ exhibits high stability in seawater with only 18% degradation over the 5d assay at both dosages tested. Also, macroalgae demonstrated an efficient uptake capacity with constant internal concentrations after 24h regardless of the external solutions and thus should be considered as a bioindicator species in risk assessment. Both STZ concentrations induced a slight inhibition of the macroalgae growth after 96 h.

Non-monotonic concentration-response relationship of TiO(2) nanoparticles in freshwater cladocerans under environmentally relevant UV-A light

The effects of UV-A on the toxicity of TiO2 nano-particles (NPs) were evaluated using Moina macrocopa and Daphnia magna under environmentally relevant level of UV-A. The waterfleas were exposed to TiO2 NPs with different sizes of ~298nm, ~132nm, or ~72nm for up to 48h, with or without UV-A light. Whole body reactive oxygen species and transcription of antioxidant enzyme genes were measured, as well as the survival of the waterflea. In the presence of UV-A, the survival rates of M. macrocopa significantly decreased in concentration dependent way until ~1mg/L TiO2 NPs, but the survivals were reversed at greater concentrations. This peculiar non-monotonic trend of concentration-response relationship might be explained by changes of particle size under different light conditions. TiO2 NPs within a certain size range could be trapped in the filter apparatus and exert toxicity, and the NPs of greater size were subject to either precipitation or ingestion leading to no or little toxicity. Observed TiO2 toxicity was associated with oxidative stress in the filter apparatus. The results of this study showed that the size change due to UV-A irradiation should be considered in evaluation of ecological risks of TiO2 NP.

Oxidative degradation of sulfathiazole by Fenton and photo-Fenton reactions

This article presents experimental results on 47 μmol L(-1) sulfathiazole (STZ) degradation by Fenton and photo-Fenton reactions using multivariate analysis. The optimal experimental conditions for reactions were obtained by Response Surface Methodology (RSM). In the case of the Fenton reactions there were 192 μmol L(-1) ferrous ions (Fe(II)) and 1856 μmol L(-1) hydrogen peroxide (H2O2), as compared with 157 μmol L(-1) (Fe(II)) and 1219 μmol L(-1) (H2O2) for photo-Fenton reactions. Under these conditions, around 90% of STZ degradation were achieved after 8 minutes treatment by Fenton and photo-Fenton reactions, respectively. Moreover, a marked difference was observed in the total organic carbon (TOC) removal after 60-min treatment, achieving 30% and 75% for the Fenton and photo-Fenton reactions, respectively. Acetic, maleic, succinic and oxamic acids could be identified as main Fenton oxidation intermediates. A similar pattern was found in the case of photo-Fenton reaction, including the presence of oxalic acid and ammonia at short periods of irradiation with UV-A. The calculated values of Average Oxidation State (AOS) corroborate the formation of oxidized products from the initial steps of the reaction.

Adaptive phenotypic plasticity and local adaptation for temperature tolerance in freshwater zooplankton

Many organisms have geographical distributions extending from the tropics to near polar regions or can experience up to 30°C temperature variation within the lifespan of an individual. Two forms of evolutionary adaptation to such wide ranges in ambient temperatures are frequently discussed: local adaptation and phenotypic plasticity. The freshwater planktonic crustacean Daphnia magna, whose range extends from South Africa to near arctic sites, shows strong phenotypic and genotypic variation in response to temperature. In this study, we use D. magna clones from 22 populations (one clone per population) ranging from latitude 0° (Kenya) to 66° North (White Sea) to explore the contributions of phenotypic plasticity and local adaptation to high temperature tolerance. Temperature tolerance was studied as knockout time (time until immobilization, T(imm)) at 37°C in clones acclimatized to either 20°C or 28°C. Acclimatization to 28°C strongly increased T(imm), testifying to adaptive phenotypic plasticity. At the same time, Timm significantly correlated with average high temperature at the clones' sites of origin, suggesting local adaptation. As earlier studies have found that haemoglobin expression contributes to temperature tolerance, we also quantified haemoglobin concentration in experimental animals and found that both acclimatization temperature (AccT) and temperature at the site of origin are positively correlated with haemoglobin concentration. Furthermore, Daphnia from warmer climates upregulate haemoglobin much more strongly in response to AccT, suggesting local adaptation for plasticity in haemoglobin expression. Our results show that both local adaptation and phenotypic plasticity contribute to temperature tolerance, and elucidate a possible role of haemoglobin in mediating these effects that differs along a cold-warm gradient.

Low concentrations, potential ecological consequences: synthetic estrogens alter life-history and demographic structures of aquatic invertebrates

Contraceptive drugs are nowadays found in aquatic environments around the globe. Particularly, 17α-ethinylestradiol (EE2) may act even at low concentrations, such as those recorded in natural ecosystems. We evaluated the physiological effects of EE2 on cyclopoids and calanoids, common copepods in both marine and freshwater communities. We used three EE2 concentrations and assessed its impact on activity of different physiological endpoints: Acetylcholinesterase (neurotransmission), Glutathione S-transferase (detoxifying system), and Caspase-3 (apoptosis). While EE2 exerts, distinctive effect on detoxifying and apoptotic systems, no effect on AChE was observed at environmental doses. Our results show that EE2 exposure affects differently copepod physiology endpoints, altering moulting process, adult recruitment in calanoids and calanoid to cyclopoid ratio. The ecological consequences of this underlying physiological process may affect since life history to population and community structures, and this represent a new aspects of this xenobiotic in natural systems.

Toxicity of four sulfonamide antibiotics to the freshwater amphipod Hyalella azteca

Sulfonamides are a widely used class of antibiotics; however, there are few toxicological data available with which to conduct environmental risk assessments for these compounds. Therefore, the toxicity of four sulfonamides (sulfaguanidine, sulfathiazole, sulfamerazine, and sulfasalazine) to Hyalella azteca was assessed in chronic (four-week), water-only exposures. Survival was evaluated weekly, and growth was measured at the end of the test. Four-week lethal concentrations associated with 50% mortality (LC50s) for sulfaguanidine, sulfathiazole, and sulfamerazine were 0.90, 1.6, and 3.9 µM, respectively. Sulfaguanidine caused effects on survival more quickly and at lower concentrations than sulfathiazole or sulfamerazine. These differences were more pronounced at week 1 than week 4, when sulfaguanidine LC50s were 8 to 20 times lower and 2 to 4 times lower, respectively. Growth was affected by sulfathiazole but was a less sensitive end point than survival, with an effective concentration associated with 50% reduction in growth (EC50) of 13 µM, whereas sulfaguanidine and sulfamerazine caused negligible effects on growth. Sulfasalazine had no effect on survival or growth at any concentration tested, up to 13 µM. The effects observed in the present study occurred at concentrations exceeding those typically found in environmental waters. However, given that LC50s decreased with exposure duration (except for sulfasalazine), the present study demonstrates the importance of conducting longer-term tests to adequately assess the environmental toxicity of sulfonamides.

Do UK coastal and estuarine water samples pose a phototoxic threat?

Many studies have investigated phototoxicity under controlled laboratory conditions, however, few have actually demonstrated it occurring in environmental samples. Here we report on the potential for UK marine coastal waters to demonstrate phototoxicity when tested using the oyster embryo (Crassostrea gigas) bioassay in the presence UV light. Subsurface water, sea surface microlayer samples and subsurface water samples that had been extracted through solid phase extraction (SPE) columns were analysed. Results demonstrated that the majority of samples failed to display any phototoxic potential. However, those collected from Belfast Lough did display an increase in toxicity when bioassays were performed in the presence of UV light when compared to identical samples assayed in the absence of UV light. Analysis of water samples at this location identified known phototoxic PAHs, pyrene and fluoranthene. These findings suggest the need to consider the potential UV light has when determining the toxicity of environmental samples.

Risk assessment of chlortetracycline, oxytetracycline, sulfamethazine, sulfathiazole, and erythromycin in aquatic environment: are the current environmental concentrations safe?

To understand potential risks of major pharmaceutical residues in waters, we evaluated ecotoxicities of five major veterinary pharmaceuticals, i.e., chlortetracycline, oxytetracycline, sulfamethazine, sulfathiazole, and erythromycin, which have been frequently detected in freshwater environment worldwide. We conducted acute and chronic toxicity tests using two freshwater invertebrates (Daphnia magna and Moina macrocopa) and a fish (Oryzias latipes). In general, D. magna exhibited greater sensitivity than M. macrocopa, and chronic reproduction was the most sensitive endpoints for both organisms. The population growth rate was adversely influenced by exposure to chlortetracycline, sulfamethazine, or sulfathiazole in water fleas, but reduction in population size was not expected. In O. latipes, the tested pharmaceuticals affected several reproduction related endpoints including time to hatch and growth. Based on the toxicity values from the present study and literature, algae appeared to be the most sensitive organism, followed by Daphnia and fish. Hazard quotients derived from measured environmental concentrations (MECs) and predicted no effect concentrations (PNECs) for erythromycin and oxytetracycline exceeded unity, suggesting that potential ecological effects at highly contaminated sites cannot be ruled out. Long-term consequences of veterinary pharmaceutical contamination in the environment deserve further investigation.

Photocatalytic reactive oxygen species production and phototoxicity of titanium dioxide nanoparticles are dependent on the solar ultraviolet radiation spectrum

Generation of reactive oxygen species (ROS) by titanium dioxide nanoparticles (nano-TiO(2)) and its consequent phototoxicity to Daphnia magna were measured under different solar ultraviolet (UV) spectra by applying a series of optical filters in a solar simulator. Removing UV-B (280-320 nm) from solar radiation had no significant impact on photocatalytic ROS production of nano-TiO(2), whereas removal of UV-A (320-400 nm) decreased ROS production remarkably. Removal of wavelengths below 400 nm resulted in negligible ROS production. A linear correlation between ROS production and D. magna immobilization suggests that photocatalytic ROS production may be a predictor of phototoxicity for nano-TiO(2). Intracellular ROS production within D. magna was consistent with the immobilization of the organism under different solar UV spectra, indicating that oxidative stress was involved in phototoxicity. The dependence of nano-TiO(2) phototoxicity on environmentally realistic variations in solar radiation suggests that risk assessment of these nanomaterials requires careful evaluation of exposure conditions in the environment.

Gamma irradiation-induced oxidative stress and developmental impairment in the hermaphroditic fish, Kryptolebias marmoratus embryo

This study investigated the effects of gamma radiation on the early developmental stages in hermaphroditic fish embryos of Kryptolebias marmoratus. The authors measured reactive oxygen species (ROS) level and antioxidant enzyme activities with the endpoint hatching rate after gamma irradiation of different embryonic stages. Then, the transcriptional changes of antioxidant enzyme-coding genes were evaluated by quantitative real-time reverse transcription polymerase chain reaction in response to gamma radiation on embryonic stages. Gamma radiation inhibited hatching rate and caused developmental impairment in a dose-dependent manner. Embryos showed tolerances in a developmental stage-dependent manner, indicating that early embryonic stages were more sensitive to the negative effects of gamma radiation than were later stages. After 5 Gy rate of radiation, the ROS level increased significantly at embryonic stages 2, 3, and 4 with a significant induction of all antioxidant enzyme activities. The expressions of glutathione S-transferase isoforms, catalase, superoxide dismutase (Mn-SOD, Cu/Zn-SOD), glutathione reductase, and glutathione peroxidase mRNA were upregulated in a dose-and-developmental stage-dependent manner. This finding indicates that gamma radiation can induce oxidative stress and subsequently modulates the expression of antioxidant enzyme-coding genes as one of the defense mechanisms. Interestingly, embryonic stage 1 exposed to gamma radiation showed a decreased expression in most antioxidant enzyme-coding genes, suggesting that this is also related to a lower hatching rate and developmental impairment. The results of this study provide a better understanding of the molecular mode of action of gamma radiation in aquatic organisms.

The transcriptome and proteome are altered in marine polychaetes (Annelida) exposed to elevated metal levels

Polychaetes are often used in toxicological studies to understand mechanisms of resistance and for biomarker detection, however, we know of only a few genetic pathways involved in resistance. We found the marine polychaete Ophelina sp.1 (Opheliidae) in sediment containing high copper levels and investigated this phenomenon by measuring metal accumulation in the worms and changes in gene and protein expression. We sequenced the transcriptome of Ophelina sp.1 from both the impacted and reference sediments using 454-sequencing and analysed their proteomes using differential in gel electrophoresis (DIGE). We used the sequenced transcriptome to guide protein identification. Transcripts coding for the copper chaperone, Atox1, were up-regulated in the worms inhabiting the high copper sediment. In addition, genes coding for respiratory proteins, detoxification proteins and cytoskeletal proteins were significantly altered in metal-exposed worms; many of these changes were also detected in the proteome. This dual approach has provided a better understanding of heavy metal resistance in polychaetes and we now have a wider range of suitable indicator genes and proteins for future biomarker development.

Comparative phototoxicity of nanoparticulate and bulk ZnO to a free-living nematode Caenorhabditis elegans: the importance of illumination mode and primary particle size

The present study evaluated phototoxicity of nanoparticulate ZnO and bulk-ZnO under natural sunlight (NSL) versus ambient artificial laboratory light (AALL) illumination to a free-living nematode Caenorhabditis elegans. Phototoxicity of nano-ZnO and bulk-ZnO was largely dependent on illumination method as 2-h exposure under NSL caused significantly greater mortality in C. elegans than under AALL. This phototoxicity was closely related to photocatalytic reactive oxygen species (ROS) generation by the ZnO particles as indicated by concomitant methylene blue photodegradation. Both materials caused mortality in C. elegans under AALL during 24-h exposure although neither degraded methylene blue, suggesting mechanisms of toxicity other than photocatalytic ROS generation were involved. Particle dissolution of ZnO did not appear to play an important role in the toxicity observed in this study. Nano-ZnO showed greater phototoxicity than bulk-ZnO despite their similar size of aggregates, suggesting primary particle size is more important than aggregate size in determining phototoxicity.

Ultraviolet B retards growth, induces oxidative stress, and modulates DNA repair-related gene and heat shock protein gene expression in the monogonont rotifer, Brachionus sp

Ultraviolet B (UV-B) radiation causes direct cellular damage by breakage of DNA strands and oxidative stress induction in aquatic organisms. To understand the effect of UV-B radiation on the rotifer, Brachionus sp., several parameters including 24-h survival rate, population growth rate, and ROS level were measured after exposure to a wide range of UV-B doses. To check the expression of other important inducible genes such as replication protein A (RPA), DNA-dependent protein kinase (DNA-PK), Ku70, Ku80, and heat shock proteins (hsps) after UV-B radiation, we observed dose- and time-dependency at 2kJ/m(2). We also examined 13 hsp genes for their roles in the UV-B damaged rotifer. Results showed that UV-B remarkably inhibited the population growth of Brachionus sp. The level of intracellular reactive oxygen species (ROS) was high at 2kJ/m(2), suggesting that 2kJ/m(2) would already be toxic. This result was supported by other enzymatic activities, such as GSH levels, glutathione peroxidase, glutathione S-transferase, and glutathione reductase. For dose dependency, low doses of UV-B radiation (2, 4, and 6kJ/m(2)) significantly up-regulated the examined genes (e.g. RPA, DNA-PK, Ku70, and Ku80). For the time course study, RPA genes showed immediate up-regulation but returned to basal or lower expression levels compared to the control 3h after UV-B exposure. The DNA-PK and Ku70/80 genes significantly increased, indicating that they may be involved in repairing processes against a low dose of UV-B exposure (2kJ/m(2)). At the basal level, the hsp90α1 gene showed the highest expression, and followed by hsp10, hsp30, hsp60, and hsc70, and hsp90β in adults (w/o egg). In eggs, the hsp10 gene was expressed the highest, and followed by hsp30, hsp27, hsp90α1, and hsp60 genes. In real-time RT-PCR array on rotifer hsp genes, low doses of UV-B radiation (2 and 4kJ/m(2)) showed up-regulation of several hsp genes but most of the hsp genes showed down-regulation at 8kJ/m(2) and higher, indicating that significant Hsp-mediated cellular damage already occurred at low doses. For the time course study of four hsp genes (hsp20, hsp27, hsp70, hsp90α1), they showed a significant correlation for UV-B radiation (2kJ/m(2)). In this paper, we demonstrated that UV-B radiation would affect growth retardation with up- or down-regulation of some important genes in DNA replication, repair process, and chaperoning. This finding provides a better understanding of molecular mechanisms involved in UV-B-mediated cellular damage in the rotifer, Brachionus sp.

Solvatochromic and fluorescence behavior of sulfisoxazole

The Fluorescence spectroscopic and solvatochromic behavior of Sulfisoxazole, a sulfa drug with antimicrobial activities, in various pure solvents of different polarity and hydrogen bonding capability is reported. The fluorescence emission spectrum of sulfisoxazole was found to be solvent polarity dependent, where a notable red shift in emission maximum was observed with increasing solvent polarity as well as hydrogen bonding capability. The effects of the latter two solvent parameters were quantitatively investigated using the methods of Lippert-Mataga and solvatochromic comparison method (SCM) that is based on the Kamlet-Taft equation. Particularly, the Lippert-Mataga method was applied to estimate the dipole moment of the excited state (μ(e)) upon plotting Stokes shift versus solvent polarizability (Δf), where a value of 11.54 Debye was obtained. On the other hand, applying the multiple regression analysis to the SCM method revealed that solvent polarizability (π*) and hydrogen-bond donor capability (α) approximately equally stabilize sulfisoxazole in the excited state with minor destabilization contribution by the hydrogen-bond acceptor capability (β). These findings revealed that the excited state of sulfisoxazole is stabilized by polar solvents, indicating that this drug molecules exhibit larger dipole moment in the excited state than in the ground state, which in turn implies that a potential intramolecular charge transfer (ICT) occurs after excitation.

Molecular cloning of Daphnia magna catalase and its biomarker potential against oxidative stresses

Catalase (EC 1.11.1.6) is an important antioxidant enzyme that protects aerobic organisms against oxidative damage by degrading hydrogen peroxide to oxygen and water. Catalase mRNAs have been cloned from many species and employed as useful biomarkers of oxidative stress. In the present study, we cloned the cDNA from the catalase gene in Daphnia magna, analyzed its catalytic properties, and investigated mRNA expression patterns after the exposure to known oxidative stressors. The catalase proximal heme-ligand signature sequence, FDRERISERVVHAKGSGA, and the proximal active site signature, RLFSYTDTH, are highly conserved. The variation of catalase mRNA expression in D. magna was quantified by real-time PCR, and the results indicated that catalase expression was up-regulated after exposure to UV-B light or cadmium (Cd). The activity of catalase enzyme also showed a similar increasing pattern when exposed to these model stressors. The full-length catalase cDNA of D. magna was cloned using mixed primers by the method of 3' and 5' rapid amplification of cDNA ends PCR. The cDNA sequence consists of 1515 nucleotides, encoding 504 amino acids. Sequence comparison showed that the deduced amino acid sequence of D. magna shared 73%, 72%, 71% and 70% identity with that of Chlamys farreri, Fenneropenaeus chinensis, Litopenaeus vannamei and Anopheles gambiae, respectively. This study shows that the catalase mRNA from D. magna could be successfully employed as a biomarker of oxidative stress, which is a common mode of toxicity for many water contaminants.

Detection of reactive oxygen species (ROS) by the oxidant-sensing probe 2',7'-dichlorodihydrofluorescein diacetate in the cyanobacterium Anabaena variabilis PCC 7937

The generation of reactive oxygen species (ROS) under simulated solar radiation (UV-B: 0.30Wm(-2), UV-A: 25.70Wm(-2) and PAR: 118.06Wm(-2)) was studied in the cyanobacterium Anabaena variabilis PCC 7937 using the oxidant-sensing fluorescent probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). DCFH-DA is a nonpolar dye, converted into the polar derivative DCFH by cellular esterases that are nonfluorescent but switched to highly fluorescent DCF when oxidized by intracellular ROS and other peroxides. The images obtained from the fluorescence microscope after 12h of irradiation showed green fluorescence from cells covered with 295, 320 or 395nm cut-off filters, indicating the generation of ROS in all treatments. However, the green/red fluorescence ratio obtained from fluorescence microscopic analysis showed the highest generation of ROS after UV-B radiation in comparison to PAR or UV-A radiation. Production of ROS was also measured by a spectrofluorophotometer and results obtained supported the results of fluorescence microscopy. Low levels of ROS were detected at the start (0h) of the experiment showing that they are generated even during normal metabolism. This study also showed that UV-B radiation causes the fragmentation of the cyanobacterial filaments which could be due to the observed oxidative stress. This is the first report for the detection of intracellular ROS in a cyanobacterium by fluorescence microscopy using DCFH-DA and thereby suggesting the applicability of this method in the study of in vivo generation of ROS.