Pulse Exposure Research Articles

The impact of repeated pyrethroid pulses on aquatic communities.

Pesticides are considered to be one of the main causes of the decline in macroinvertebrate biodiversity in small streams. In particular, pyrethroids are detected in agricultural surface waters worldwide and pose a high risk to aquatic invertebrates. Due to their knock-down effect, even short pyrethroid exposure pulses can have significant short- and long-term effects on macroinvertebrate communities. Therefore, it is necessary to consider more realistic exposure scenarios for the environmental risk assessment of pyrethroids and, consequently, to obtain more realistic effect data by using multi-stressor test systems. In an experimental setup with artificial indoor streams (AIS), four pyrethroid pulses simulated the exposure scenario of heavy rainfall events. Effects of these 12 h-exposures at different concentrations of deltamethrin (0.64 ng/L, 4 ng/L, 16 ng/L, 64 ng/L) with intervening recovery periods of six days were assessed on an aquatic community consisting of Gammarus pulex, Ephemera danica, Lumbriculus variegatus and Potamopyrgus antipodarum with various lethal and sub-lethal endpoints. The mortality rate of G. pulex significantly increased with increasing deltamethrin concentrations, whereas the mean number of offspring significantly decreased (NOECoffspring: 16 ng/L, LOECoffspring: 64 ng/L). The biomass of L. variegatus decreased with increasing deltamethrin concentrations (NOECdry weight: 16 ng/L, LOECdry weight: 64 ng/L). The findings of this study clearly demonstrate that 12 h-deltamethrin pulses at environmentally relevant concentrations adversely affect an aquatic community. Based on the results of this study a RAC value of 5.33 ng/L is assumed, which is below the concentrations measured in rivers of up to 58.8 ng/L. Unacceptable effects on the entire freshwater environment can therefore not be ruled out. The experimental AIS approach is a useful tool for assessing the effects of repeated pulse exposures that occur during surface runoff events.

Elevated temperature increases the susceptibility of D. magna to environmental mixtures of carbamazepine, tramadol and citalopram

The joint risks assessment of thermal stress and rising loads of pharmaceuticals (PhACs) in surface waters is a relevant topic in aquatic ecotoxicology. This study investigated the relevance of increased water temperature to alter the acute toxicity of environmentally relevant carbamazepine (CBZ), citalopram (CIT) and tramadol (TRA) concentrations as mixtures (ECs) and delayed outcomes in Daphnia magna. Responses of detoxification and antioxidant pathways in premature daphnids post an acute 24 h (pulsed) exposure to the PhACs mixtures and delayed responses as the reproductive output over 14 days recovery were investigated under 21- and 26 °C incubation. Biphasic modulation in glutathione S-transferase (GST) activity and significant inhibition of superoxide dismutase (SOD) activity were observed in both thermal regimes with significant shift in effective thresholds from 10-fold ECs at 21 °C to ECs at 26 °C incubation. Significant induction in catalase (CAT) activity and oxidative stress development were recorded at elevated temperatures from the 10-fold ECs dose onward. Pulsed exposures at 26 °C also led to significant decrease in the reproduction of daphnids above the 10-fold ECs of PhACs. The Integrated Biomarker Response scoring (IBRv2) approach outlined a 1.8-fold increase in alterations of daphnids exposed to 100-fold ECs of PhACs at 26 °C.

Enhanced thermomechanical fatigue resistance in W10Re alloys: Microstructural and surface engineering approaches

Thermomechanical fatigue of refractory metals is commonly observed in high-temperature environments like first walls and divertors for proposed fusion reactors or X-ray anodes for medical imaging. Typically, alloying with rhenium or optimized microstructures are employed to counteract or delay the detrimental effects of fatigue in tungsten. Additionally, a novel concept is the utilization of surface structures to compensate cyclic thermal stresses. This work aimed to investigate the combination of these approaches, by comparing two W10Re alloys with vastly different microstructures, as well as engineered surface conditions of varying scales. Samples were subjected to thermocyclic fatigue under pulsed electron beam exposure, mimicking the surface temperatures typically encountered in a rotating X-ray anode. Analysis of several in-situ data streams, post-mortem investigations by metallography, and finite element methods revealed the interplay between microstructure and surface modifications. The columnar microstructure exhibited higher resistance to severe surface damage compared to the globular one, linked to the deflection of cracks along grain boundaries and subsequent melting. Coarse structuring was found to partly relieve the surface stresses during thermal cycling, preventing most of the damage accumulation. A full damage relief and performance equivalence between columnar and globular microstructure was achieved by engineering fine-structured surfaces, which led to a ten-fold increase in fatigue resistance over the non-structured condition.

Single cell transcriptional changes across the blood stages of artemisinin resistant K13580Y Plasmodium falciparum upon dihydroartemisinin exposure.

Artemisinins have been a cornerstone of malaria control, but resistance in Plasmodium falciparum, due to mutations in the Kelch13 (K13) protein, threaten these advances. Artemisinin exposure results in a dynamic transcriptional response across multiple pathways, but most work has focused on ring stages and ex vivo transcriptional analysis. We applied single cell RNAseq to two unsynchronized coisogenic parasite lines (K13C580 and K13580Y) over 6 hrs after a pulse exposure to dihydroartemisinin (DHA). Transcription was altered across all stages, with the greatest occurring at the trophozoite and ring stage in both lines. This response involved the arrest of metabolic processes, support for a dormancy phenomenon upon treatment, and the enhancement of protein trafficking and the unfolded protein response. While similar, the response was consistent across stages in K13580Y, with enhanced parasite survival to drug induced stress. Increased surface protein expression was seen in K13580Y parasites at baseline and upon drug exposure, highlighted by the increased expression of PfEMP1 and GARP, a potential therapeutic target. Antibody targeting GARP maintained anti-parasitic efficacy in K13580Y parasites. This work provides single cell insight of gene transcription across all life cycle stages revealing transcriptional changes that could initiate a dormancy state and mediate survival upon treatment.

Experimental features of the intense ultra-short electric pulses exposure on similar to biological media

Experimental features of the intense ultra-short electric pulses exposure on similar to biological media

Long-term changes in transmembrane voltage after electroporation are governed by the interplay between nonselective leak current and ion channel activation

Electroporation causes a temporal increase in cell membrane permeability and leads to prolonged changes in transmembrane voltage (TMV) in both excitable and non-excitable cells. However, the mechanisms of these TMV changes remain to be fully elucidated. To this end, we monitored TMV over 30 min after exposing two different cell lines to a single 100 µs electroporation pulse using the FLIPR Membrane Potential dye. In CHO-K1 cells, which express very low levels of endogenous ion channels, membrane depolarization following pulse exposure could be explained by nonselective leak current, which persists until the membrane reseals, enabling the cells to recover their resting TMV. In U-87 MG cells, which express many different ion channels, we unexpectedly observed membrane hyperpolarization following the initial depolarization phase, but only at 33 °C and not at 25 °C. We developed a theoretical model, supported by experiments with ion channel inhibitors, which indicated that hyperpolarization could largely be attributed to the activation of calcium-activated potassium channels. Ion channel activation, coupled with changes in TMV and intracellular calcium, participates in various physiological processes, including cell proliferation, differentiation, migration, and apoptosis. Therefore, our study suggests that ion channels could present a potential target for influencing the biological response after electroporation.

Determining of the effect of reinforcing microrelief guides on the efficiency of folding integrated covers

The object of research is the processes of strengthening the working surfaces of profile folding strips made of stainless steel AISI 347 and carbon steel AISI 1005 using laser formation of microrelief guides. The analytical and experimental studies are based on the technique of laser microrelief formation by pulsed laser effects. The main assumption of the study is that the use of laser microrelief formation could increase the hardness and wear resistance of the folding strips, improving the process of folding integrated covers. Analyzing the effect of different hardening methods on the mechanical properties and wear resistance of the working surfaces of folding strips is necessary to achieve this goal. A methodology for assessing microstructural changes and their impact on the mechanical properties of folding strips during laser hardening has been proposed. It has been shown that the formation of microrelief guides by laser pulse exposure reduces the thermal load on the material, increases the uniformity of hardening and wear resistance. The revealed wear rates calculated for carbon steel AISI 1005 are 0.875, and for stainless steel AISI 347 – 0.345. To improve the accuracy and efficiency of the folding process, a methodology has been devised for calculating the quantitative formation of microrelief guides on the working surface of profile folding strips. This will not only improve the wear resistance and mechanical properties of the strips but also optimize production processes. Differences in the results of hardening for stainless steel AISI 347 and carbon steel AISI 1005 were found: the hardness values for AISI 347 are 3,088–4,904 MPa at a load of 50–350 g with a deviation of 37.1 %, and for AISI 1005 – 2141–1665 MPa with a deviation of 22.3 %

Single-layer encapsulation film with CaO absorbent by solution process

A method for preparing a single-layer encapsulation film using an organic-inorganic hybrid precursor solution processing was investigated. The film was created using a commodity epoxy and graphene oxide to ensure cost-effectiveness. Fast curing and annealing techniques, including microwave and intense pulsed light exposure, were employed. Calcium oxide nanoparticles were incorporated as a special moisture absorbent to improve the film's barrier properties. The barrier performance of the single layer encapsulation film was considerably enhanced by post-treatment of these nanoparticles. The characterization of the calcium oxide nanoparticles after post-treatment was performed using transmission electron microscopy with energy-dispersive X-ray spectroscopy, FT-IR, Brunauer-Emmett-Teller test. The composite epoxy encapsulation film, incorporating graphene oxide and post-treated calcium oxide nanoparticles, reduced water permeability approximately 400 times compared to the neat epoxy encapsulation film. This substantial improvement makes it suitable for use in flexible disposable electronics. The enhanced water vapor blocking efficiency is attributed to the combined effect of pathway block by graphene oxide and moisture absorption by calcium oxide.

Different duration of exposure to a pulsed magnetic field can cause changes in mRNA expression of apoptotic genes in oleic acid-treated neuroblastoma cells

Purpose Neuroblastoma, a prevalent childhood tumor, poses significant challenges in therapeutic interventions, especially for high-risk cases. This study aims to fill a crucial gap in our understanding of neuroblastoma treatment by investigating the potential molecular impacts of short- and long-term pulsed magnetic field exposure on the neuronal apoptosis mechanism in an in vitro model of neuroblastoma treated with oleic acid (OA). Materials and methods Cells were cultured and divided into six following experimental groups: (I) Nontreated group (NT); (II) OA-treated group (OA); (III) Group treated with OA after being exposed to the pulsed magnetic field for 15-min (15 min PEMF + OA); (IV) Group treated with OA after being exposed to the pulsed magnetic field for 12 h (12 h PEMF + OA); (V) Group exposed to the pulsed magnetic field for 15 min (15 min PEMF); and (VI) Group exposed to the pulsed magnetic field for 12 h (12 h PEMF). Cell viability, rates of apoptosis, and mRNA levels of key apoptotic genes (TP53, Bcl2, Bax, and Caspase-3) were assessed. Results Significant reductions in cell viability were observed, particularly in the group treated with OA following long-term pulsed magnetic field exposure. Flow cytometry revealed elevated apoptosis rates, notably in the early stages of apoptosis. qRT-PCR analysis demonstrated increased expression of cleaved Caspase-3, Bax/Bcl2 ratio, and TP53 in cells treated with OA following long-term pulsed magnetic field exposure, signifying enhanced apoptotic pathways. Conclusions The findings indicate that long-term pulsed magnetic field exposure and OA treatment exhibit potential synergistic effects leading to the induction of apoptosis in SH-SY5Y cells. We have concluded that stimulations of pulsed magnetic field have the potential to serve as an adjuvant therapy for oleic acid-based treatment of neuroblastoma.

Interference mechanism of plasma self-organization in transparent dielectrics under the intense femtosecond laser pulse exposure

A new mechanism of plasma self-organization in transparent dielectrics with wide bandgap exposed to the intense tightly focused laser radiation was revealed, which causes the generation of 3D periodic ring structures with subwavelength period both along the laser pulse propagation and in the radial direction. The mechanism involves formation of dense plasma burst in the pre-focal region that provides efficient scattering of the incident wave. The interference of a plane incident laser wave in the focal region and a divergent reflected one will form the standing wave pattern with local minima and maxima of laser field both in the direction of the incident wave propagation and perpendicular to it producing the ring patterns of effective ionization regions in the dielectric volume. Analytical and numerical simulations of the process of laser wave scattering on a near-spherical plasma object with dimensions both smaller and larger than the laser radiation wavelength are performed to verify the proposed model.

Study of genotoxic and cytotoxic effects induced in human fibroblasts by exposure to pulsed and continuous 1.6 GHz radiofrequency.

The widespread use of radiofrequency (RF) sources, ranging from household appliances to telecommunications devices and military equipment, raises concerns among people and regulatory agencies about the potential health risks of RF exposure. Consequently, several in vitro and in vivo studies have been done to investigate the biological effects, in particular non-thermal, of this non-ionizing radiation. To date, this issue is still being debated due to the controversial results that have been reported. Furthermore, the impact of different RF signal modulations on biological systems remains poorly investigated. The present in vitro study aims to evaluate the cytotoxicity and genotoxicity of continuous or pulsed 1.6 GHz RF in human dermal fibroblasts (HDF). HDF cultures were exposed to continuous and pulsed 1.6 GHz RF, for 2 h, with Specific Absorption Rate (SAR) of 0.4 W/kg. The potential biological effects of 1.6 GHz RF on HDF were assessed with a multi-methodological approach, analyzing the effects on cell cycle, ultrastructure, protein expression, mitotic spindle, CREST stained micronuclei, chromosome segregation and γ-H2AX/53BP1 foci. 1.6 GHz RF exposure modified proteins expression and morphology of HDF. Specifically, the expression of different heat-shock proteins (HSP) (i.e., HSP-90, HSP-60, and HSP-25) and phospho-AKT were affected. In addition, both continuous and pulsed RF modified the cytoskeletal organization in HDF and increased the number of lysosomes, while the formation of autophagosomes was observed only after pulsed RF exposure. Mitotic spindle anomalies were also found after exposure. However, no significant effect was observed on cell cycle, chromosome segregation, CREST-stained micronuclei and γ-H2AX/53BP1 foci. The results of the present study show the absence of genotoxic damage in 1.6 GHz RF exposed HDF and, although mitotic spindle alterations were observed, they did not have an aneugenic effect. On the other hand, changes in some proteins expression and cell ultrastructure in exposed HDF suggest that RF can potentially induce cell alterations at the morphological and molecular levels.

Memristor based on carbon nanotube gelatin composite film as artificial optoelectronic synapse for image processing

Photoelectric artificial synapses based on memristors is an effective method to realize neuromorphic computation. This study presents an optoelectronic responsive artificial synapse made of a composite material consisting of gelatin and carbon nanotubes. The memristor demonstrates characteristics of analog resistive switching, the ability to store multiple memory states, and impressive retention properties. It has the capability to induce an excitatory post-synaptic current by means of electrical pulses or pulsed light exposure. The excitatory post-synaptic current can be modulated by the number, amplitude and interval of electrical pulses, as well as the action time, interval and light intensity of optical pulses. The artificial synapse showcases the emulation of fundamental Hebbian learning protocols, including spike timing dependent plasticity and spike amplitude dependent plasticity. In addition, the charge transfer in the carbon nanotube gelatin composite optoelectronic memristor is investigated through first-principles calculations, shedding light on its operational mechanism. Experimental results show that these devices have the potential to be utilized for processing image information, resulting in a significant reduction of input data and training expenses when recognizing handwritten numbers. Overall, the optoelectronic synapse exhibits promising image processing prospects in the field of neuromorphic computing.

Impact of pulse exposure on chimera state in ensemble of FitzHugh-Nagumo systems.

In this article, we consider the influence of a periodic sequence of Gaussian pulses on a chimera state in a ring of coupled FitzHugh-Nagumo systems. We found that on the way to complete spatial synchronization, one can observe a number of variations of chimera states that are not typical for the parameter range under consideration. For example, the following modes were found: breathing chimera, chimera with intermittency in the incoherent part, traveling chimera with strong intermittency, and others. For comparison, here we also consider the impact of a harmonic influence on the same chimera, and to preserve the generality of the conclusions, we compare the regimes caused by both a purely positive harmonic influence and a positive-negative one.

Temporal patterns in multiple stressors shape the vulnerability of overwintering Arctic zooplankton.

The Arctic polar nights bring extreme environmental conditions characterised by cold and darkness, which challenge the survival of organisms in the Arctic. Additionally, multiple anthropogenic stressors can amplify the pressure on the fragile Arctic ecosystems during this period. Determining how multiple anthropogenic stressors may affect the survival of Arctic life is crucial for ecological risk assessments and management, but this topic is understudied. For the first time, our study investigates the complex interactions of multiple stressors, exploring stressor temporal dynamics and exposure duration on a key Arctic copepod Calanus glacialis during the polar nights. We conducted experiments with pulse (intermittent) and press (continuous) exposure scenarios, involving microplastics, pyrene and warming in a fully factorial design. We observed significant effects on copepod survival, with pronounced impacts during later stressor phases. We also detected two-way interactions between microplastics and pyrene, as well as pyrene and warming, further intensified with the presence of a third stressor. Continuous stressor exposure for 9 days (press-temporal scenario) led to greater reductions in copepod survival compared to the pulse-temporal scenario, characterised by two 3-day stressor exposure phases. Notably, the inclusion of recovery phases, free from stressor exposure, positively influenced copepod survival, highlighting the importance of temporal exposure dynamics. We did not find behaviour to be affected by the different treatments. Our findings underscore the intricate interactions amongst multiple stressors and their temporal patterns in shaping the vulnerability of overwintering Arctic copepods with crucial implications for managing Arctic aquatic ecosystems under the fastest rate of ongoing climate change on earth.

Pulsed high power microwave seeds priming modulates germination, growth, redox homeostasis, and hormonal shifts in barley for improved seedling growth: Unleashing the molecular dynamics

Increasing the seed germination potential and seedling growth rates play a pivotal role in increasing overall crop productivity. Seed germination and early vegetative (seedling) growth are critical developmental stages in plants. High-power microwave (HPM) technology has facilitated both the emergence of novel applications and improvements to existing in agriculture. The implications of pulsed HPM on agriculture remain unexplored. In this study, we have investigated the effects of pulsed HPM exposure on barley germination and seedling growth, elucidating the plausible underlying mechanisms. Barley seeds underwent direct HPM irradiation, with 60 pulses by 2.04 mJ/pulse, across three distinct irradiation settings: dry, submerged in deionized (DI) water, and submerged in DI water one day before exposure. Seed germination significantly increased in all HPM-treated groups, where the HPM-dry group exhibited a notable increase, with a 2.48-fold rise at day 2 and a 1.9-fold increment at day 3. Similarly, all HPM-treated groups displayed significant enhancements in water uptake, and seedling growth (weight and length), as well as elevated levels of chlorophyll, carotenoids, and total soluble protein content. The obtained results indicate that when comparing three irradiation setting, HPM-dry showed the most promising effects. Condition HPM seed treatment increases the level of reactive species within the barley seedlings, thereby modulating plant biochemistry, physiology, and different cellular signaling cascades via induced enzymatic activities. Notably, the markers associated with plant growth are upregulated and growth inhibitory markers are downregulated post-HPM exposure. Under optimal HPM-dry treatment, auxin (IAA) levels increased threefold, while ABA levels decreased by up to 65 %. These molecular findings illuminate the intricate regulatory mechanisms governing phenotypic changes in barley seedlings subjected to HPM treatment. The results of this study might play a key role to understand molecular mechanisms after pulsed-HPM irradiation of seeds, contributing significantly to address the global need of sustainable crop yield.

AURKA blockage as a strategy to overcome resistance to olaparib and platinum in high-grade ovarian cancer (HGOC).

e15198 Background: PARP inhibitors (PARPi) as olaparib (OLA) have become the new standard in maintenance treatment in high grade ovarian carcinoma (HGOC). Thus, there is an important need to identify the mechanisms for PARPi resistance and the strategies to overcome them. Our aim is to assess if in vitro inhibition of AURKA, a protein that plays a relevant role in centrosome spindle formation and mitotic regulation, might overcome olaparib resistance mechanisms in HGOC. Methods: Three HGOC cell lines (PEO1, Kuramochi and SKOV3) were selected, and isogenic resistant pairs generated in vitro, by pulsed exposure to OLA (PEO1-R) or by exposure to growing concentrations of OLA (Kuramochi-R and SKOV-R). AURKA expression was assessed by PCR and Western blot (WB). Cells were OLA-treated before and after the downregulation of AURKA expression by a specific small inhibitor RNA (siRNA) and by pharmacologic inhibition with alisertib. Cell viability was assessed by MTT assay and DNA damage by the evaluation of markers by WB. Combination index of the combo OLA+alisertib was assessed by Chou-Talalay method. Results: AURKA expression was lower at gene and protein levels in resistant cell lines compared to parental. Upon AURKA silencing (Si) of parental (OLA-sensitive) cell lines, no differences in the OLA IC50 values between AURKA-Si and control cells were seen. However AURKA-Si of the OLA-resistant cell lines was associated with a decreased in OLA IC50 as follows: 1) In PEO1R control scramble siRNA (sc) was 226 mM vs SI 128 mM, p < 0.0001; 2) In Kuramochi-R scRNA 268.4 mM vs si 130.2 mM p < 0.0001 and 3) in SKOV3-R scRNA 187 mM vs si 74.7 mM, p < 0.0001 suggesting a role of AURKA-si in overcoming OLA-resistance. Pharmacologic AURKA targeting with the inhibitor alisertib in all 3 sensitive and resistant cell lines showed an increase of DNA damage measured by the expression of H2AX protein by WB. Combination index of the OLA+alisertib in all resistant cell lines showed a synergistic effect of the combination with PEO1-R FA50 = 0.25 (FA25-75 0.2-0.31), Kuramochi-R FA50 = 0.29 (0.19-9.36) and SKOV3-R FA50 = 0.24 (0.19-0.36). Conclusions: AURKA targeting either by silencing or pharmacologic inhibition increased OLA-induced apoptosis or had a synergistic effect in OLA-resistant cell lines suggesting AURKA as a potential target for overcoming OLA resistance.

Engineering 3D microenvironments with femtosecond laser-fabricated microtubes to direct neuronal network formation

The regulation of cell growth characteristics through physical structures on material surfaces plays a crucial role in advancing our understanding of cell behavior. Three-dimensional (3D) microstructures, offering multidimensional growth space and a richer nutrient environment compared to their two-dimensional counterparts, have attracted significant attention from researchers. However, the fabrication of high-precision 3D microstructures, especially those with a high aspect ratio (H-AR), remains challenging. In this study, we employ femtosecond laser to achieve exceptional precision and patterning capabilities in fabricating 3D microstructures. To enhance the manufacturing efficiency of axial 3D structures, we introduce a novel single pulse multi-photon polymerization (SP-MPP) method for efficient fabrication of H-AR micropillar and microtube structures. Our innovative approach involves a dual-aperture optical modulation method that effectively modulates the annular energy distribution, enabling the creation of H-AR microstructures. We can achieve a maximum processing height of up to 130 μm with an aspect ratio of 16 within single pulse exposure of 217 fs. Compared to the layer-by-layer scanning method, our proposed approach enhances the axial manufacturing efficiency of 3D structures by 1–2 orders of magnitude. Through experimentation, we validate the applicability of microtube structures for guiding neuronal orientation by utilizing microtube arrays in hippocampal neuronal cell culture. Our results demonstrate that neurons not only grow along the patterned microtubes but also exhibit preliminary synaptic differentiation. Furthermore, we effectively regulate the 3D patterning of neuronal growth by implementing diverse patterned microtube arrays. This proposed method enables the rapid construction of a large-scale 3D cell growth environment, offering significant advantages in inducing neuronal orientation. Consequently, this technique holds immense potential for diverse applications in biomedicine and tissue engineering, including the establishment of isolated neural networks.

Electric pulse exposure reduces AAV8 dosage required to transduce HepG2 cells.

We demonstrate that applying electric field pulses to hepatocytes, in vitro, in the presence of enhanced green fluorescent protein (EGFP)-expressing adeno-associated virus (AAV8) vectors reduces the viral dosage required for a given transduction level by more than 50-fold, compared to hepatocytes exposed to AAV8-EGFP vectors without electric field pulse exposure. We conducted 48 experimental observations across 8 exposure conditions in standard well plates. The electric pulse exposures involved single 80-ms pulses with 375 V/cm field intensity. Our study suggests that electric pulse exposure results in enhanced EGFP expression in cells, indicative of increased transduction efficiency. The enhanced transduction observed in our study, if translated successfully to an in vivo setting, would be a promising indication of potential reduction in the required dose of AAV vectors. Understanding the effects of electric field pulses on AAV transduction in vitro is an important preliminary step.

Understanding the toxicity risk of antibiotic emissions of aquaculture from the perspective of fluctuations concentration

Organisms are generally exposed to target contaminant with stable concentrations in traditional ecotoxicological studies. However, it is difficult to truly represent the dynamics and complexity of actual aquatic pollution for risk management. Contaminants may enter nearby aquatic systems in pulsed exposure, thus resulting in that aquatic organisms will be exposed to contaminants at fluctuating concentrations. Especially during the season of summer, due to the changes in displacement or periodic emissions of veterinary antibiotics in aquaculture, algal blooms occur frequently in surrounding waters, thus leading to eutrophication of the water. Florfenicol (FFC) is currently widely used as a veterinary antibiotic, but the aquatic ecological risks of FFC under concentration fluctuations are still unknown. Therefore, the acute exposure, chronic exposure and pulsed exposure effects of FFC on Microcystis aeruginosa were investigated to comprehensively evaluate the ecological risk of FFC and raise awareness of the pulsed exposure mode. Results indicated that the toxic effects of FFC on M. aeruginosa were dominated by exposure mode, exposure duration, exposure frequency, and exposure concentration. The maximum growth inhibition rate of the 10 μg/L FFC treatment amounted to 4.07% during chronic exposure of 18 days. However, the growth inhibition rate decreased from 55.1% to 19.31% when algae was exposure to 10 μg/L FFC during the first pulsed exposure (8 h). Therefore, when the concentration of FFC was equal under chronic and pulsed exposure, FFC exhibited greater toxicity on M. aeruginosa in short pulsed exposure than in continuous exposure. In addition, repetitive pulsed exposure strengthened the resistance of M. aeruginosa on FFC. The adaptive regulation of algae was related to the duration and frequency of exposure. Above results suggested that traditional toxicity assessments lacked consideration for fluctuating concentrations during pollutant emissions, thus underestimating the environmental risk of contaminant. This investigation aims to facilitate the standardization of pulsed exposure.

Modeling temperature-dependent life-cycle toxicity of thiamethoxam in Chironomus riparius using a DEB-TKTD model

The neonicotinoid insecticide thiamethoxam (TMX) is widely used to protect crops against insect pests. Despite some desirable properties such as its low toxicity to birds and mammals, concerns have been raised about its toxicity to non-target arthropods, including freshwater insects like chironomids. Whereas multiple studies have investigated chronic effects of neonicotinoids in chironomid larvae at standardized laboratory conditions, a better understanding of their chronic toxicity under variable temperatures and exposure is needed for coherent extrapolation from the laboratory to the field. Here, we developed a quantitative mechanistic effect model for Chironomus riparius, to simulate the species’ life history under dynamic temperatures and exposure concentrations of TMX. Laboratory experiments at four different temperatures (12, 15, 20, 23 °C) and TMX concentrations between 4 and 51 µg/L were used to calibrate the model. Observed concentration-dependent effects of TMX in C. riparius included slower growth, later emergence, and higher mortality rates with increasing concentrations. Furthermore, besides a typical accelerating effect on the organisms’ growth and development, higher temperatures further increased the effects associated with TMX. With some data-informed modeling decisions, most prominently the inclusion of a size dependence that makes larger animals more sensitive to TMX, the model was parametrized to convincingly reproduce the data. Experiments at both a constant (20 °C) and a dynamically increasing temperature (15–23 °C) with pulsed exposure were used to validate the model. Finally, the model was used to simulate realistic exposure conditions using two reference exposure scenarios measured in Missouri and Nebraska, utilizing a moving time window (MTW) and either a constant temperature (20 °C) or the measured temperature profiles belonging to each respective scenario. Minimum exposure multiplication factors leading to a 10% effect (EP10) in the survival at pupation, i.e., the most sensitive endpoint found in this study, were 25.67 and 21.87 for the Missouri scenario and 38.58 and 44.64 for the Nebraska scenario, when using the respective temperature assumptions. While the results illustrate that the use of real temperature scenarios does not systematically modify the EPx in the same direction (making it either more or less conservative when used as a risk indicator), the advantage of this approach is that it increases the realism and thus reduces the uncertainty associated with the model predictions.