Contribution of combined stressors on density and gene expression dynamics of the copepod Temora longicornis in the North Sea.

The impact of multiple environmental and anthropogenic stressors on the marine environment remains poorly understood. Therefore, we studied the contribution of environmental variables to the densities and gene expression of the dominant zooplankton species in the Belgian part of the North Sea, the calanoid copepod Temora longicornis. We observed a reduced density of copepods, which were also smaller in size, in samples taken from nearshore locations when compared to those obtained from offshore stations. To assess the factors influencing the population dynamics of this species, we applied generalised additive models. These models allowed us to quantify the relative contribution of temperature, nutrient levels, salinity, turbidity, concentrations of photosynthetic pigments, as well as chemical pollutants such as polychlorinated biphenyls and polycyclic aromatic hydrocarbons (PAHs), on copepod density. Temperature and Secchi depth, a proxy for turbidity, were the most important environmental variables predicting the densities of T. longicornis, followed by summed PAH and chlorophyll concentrations. Analysing gene expression in field-collected adults, we observed significant variation in metabolic and stress-response genes. Temperature correlated significantly with genes involved in proteolytic activities, and encoding heat shock proteins. Yet, concentrations of anthropogenic chemicals did not induce significant differences in the gene expression of genes involved in the copepod's fatty acid metabolism or well-known stress-related genes, such as glutathione transferases or cytochrome P450. Our study highlights the potential of gene expression biomonitoring and underscores the significance of a changing environment in future studies.

Probing Long-Term Impacts: Low-Dose Polystyrene Nanoplastics Exacerbate Mitochondrial Health and Evoke Secondary Glycolysis via Repeated and Single Dosing.

Nanoplastics (NPs) are omnipresent in the environment and contribute to human exposure. However, little is known regarding the long-term effects of NPs on human health. In this study, human intestinal Caco-2 cells were exposed to polystyrene nanoplastics (nanoPS) in an environmentally relevant concentration range (102-109 particles/mL) under two realistic exposure scenarios. In the first scenario, cells were repeatedly exposed to nanoPS every 2 days for 12 days to study the long-term effects. In the second scenario, only nanoPS was added once and Caco-2 cells were cultured for 12 days to study the duration of the initial effects of NPs. Under repeated dosing, initial subtle effects on mitochondria induced by low concentrations would accrue over consistent exposure to nanoPS and finally lead to significant impairment of mitochondrial respiration, mitochondrial mass, and cell differentiation process at the end of prolonged exposure, accompanied by significantly increased glycolysis over the whole exposure period. Single dosing of nanoPS elicited transient effects on mitochondrial and glycolytic functions, as well as increased reactive oxygen species (ROS) production in the early phase of exposure, but the self-recovery capacity of cells mitigated these effects at intermediate culture times. Notably, secondary effects on glycolysis and ROS production were observed during the late culture period, while the cell differentiation process and mitochondrial mass were not affected at the end. These long-term effects are of crucial importance for comprehensively evaluating the health hazards arising from lifetime exposure to NPs, complementing the extensively observed acute effects associated with prevalent short-term exposure to high concentrations. Our study underlines the need to study the toxicity of NPs in realistic long-term exposure scenarios such as repeated dosing.

Accelerated fragmentation of two thermoplastics (polylactic acid and polypropylene) into microplastics after UV radiation and seawater immersion.

To better understand the fate and assess the ingestible fraction of microplastics (by aquatic organisms), it is essential to quantify and characterize of their released from larger items under environmental realistic conditions. However, the current information on the fragmentation and size-based characteristics of released microplastics, for example from bio-based thermoplastics, is largely unknown. The goal of our work was to assess the fragmentation and release of microplastics, under ultraviolet (UV) radiation and in seawater, from polylactic acid (PLA) items, a bio-based polymer, and from polypropylene (PP) items, a petroleum-based polymer. To do so, we exposed pristine items of PLA and PP, immersed in filtered natural seawater, to accelerated UV radiation for 57 and 76 days, simulating 18 and 24 months of mean natural solar irradiance in Europe. Our results indicated that 76-day UV radiation induced the fragmentation of parent plastic items and the microplastics (50 - 5000 µm) formation from both PP and PLA items. The PP samples (48 ± 26 microplastics / cm2) released up to nine times more microplastics than PLA samples (5 ± 2 microplastics / cm2) after a 76-day UV exposure, implying that the PLA tested items had a lower fragmentation rate than PP. The particles' length of released microplastics was parameterized using a power law exponent (α), to assess their size distribution. The obtained α values were 3.04 ± 0.11 and 2.54 ± 0.06 (-) for 76-day UV weathered PP and PLA, respectively, meaning that PLA microplastics had a larger sized microplastics fraction than PP particles. With respect to their two-dimensional shape, PLA microplastics also had lower width-to-length ratio (0.51 ± 0.17) and greater fiber-shaped fractions (16%) than PP microplastics (0.57 ± 0.17% and 11%, respectively). Overall, the bio-based PLA items under study were more resistant to fragmentation and release of microplastics than the petroleum-based PP tested items, and the parameterized characteristics of released microplastics were polymer-dependent. Our work indicates that even though bio-based plastics may have a slower release of fragmented particles under UV radiation compared to conventional polymer types, they still have the potential to act as a source of microplastics in the marine environment, with particles being available to biota within ingestible size fractions, if not removed before major fragmentation processes.

A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins.

Phycotoxin-Enriched Sea Spray Aerosols: Methods, Mechanisms, and Human Exposure.

To date, few studies have examined the role of sea spray aerosols (SSAs) in human exposure to harmful and beneficial marine compounds. Two groups of phycotoxins (brevetoxins and ovatoxins) have been reported to induce respiratory syndromes during harmful algal blooms. The aerosolization and coastal air concentrations of other common marine phycotoxins have, however, never been examined. This study provides the first (experimental) evidence and characterization of the aerosolization of okadaic acid (OA), homoyessotoxin, and dinophysistoxin-1 using seawater spiked with toxic algae combined with the realistic SSA production in a marine aerosol reference tank (MART). The potential for aerosolization of these phycotoxins was highlighted by their 78- to 1769-fold enrichment in SSAs relative to the subsurface water. To obtain and support these results, we first developed an analytical method for the determination of phycotoxin concentrations in SSAs, which showed good linearity (R2 > 0.99), recovery (85.3-101.8%), and precision (RSDs ≤ 17.2%). We also investigated natural phycotoxin air concentrations by means of in situ SSA sampling with concurrent aerosolization experiments using natural seawater in the MART. This approach allowed us to indirectly quantify the (harmless) magnitude of OA concentrations (0.6-51 pg m-3) in Belgium's coastal air. Overall, this study provides new insights into the enriched aerosolization of marine compounds and proposes a framework to assess their airborne exposure and effects on human health.

Sea Spray Aerosols Contain the Major Component of Human Lung Surfactant.

Marine phytoplankton influence the composition of sea spray aerosols (SSAs) by releasing various compounds. The biogenic surfactant dipalmitoylphosphatidylcholine (DPPC) is known to accumulate in the sea surface microlayer, but its aerosolization has never been confirmed. We conducted a 1 year SSA sampling campaign at the Belgian coast and analyzed the SSA composition. We quantified DPPC at a median and maximum air concentration of 7.1 and 33 pg m-3, respectively. This discovery may be of great importance for the field linking ocean processes to human health as DPPC is the major component of human lung surfactant and is used as excipient in medical aerosol therapy. The natural airborne exposure to DPPC seems too low to induce direct human health effects but may facilitate the effects of other marine bioactive compounds. By analyzing various environmental variables in relation to the DPPC air concentration, using a generalized linear model, we established that wave height is a key environmental predictor and that it has an inverse relationship. We also demonstrated that DPPC content in SSAs is positively correlated with enriched aerosolization of Mg2+ and Ca2+. In conclusion, our findings are not only important from a human health perspective but they also advance our understanding of the production and composition of SSAs.

Reduced stress defence responses contribute to the higher toxicity of a pesticide under warming.

There is a pressing need to identify the molecular mechanisms underlying the, often magnifying, interactive effects between contaminants and natural stressors. Here we test our hypothesis that lower general stress defence responses contribute to synergistic interactions between stressors. We focus on the widespread pattern that many contaminants are more toxic at higher temperatures. Specifically, we tested the effects of an environmentally realistic low-effect and high-effect concentration of the pesticide chlorpyrifos under warming at the gene expression level in the northern house mosquito Culex pipiens molestus (Forskal, 1775). By applying the independent action model for combined stressors on RNA-sequencing data, we identified interactive gene expression patterns under combined exposure to chlorpyrifos and warming for general stress defence responses: protection of macromolecules, antioxidant processes, detoxification and energy metabolism/allocation. Most of these general stress defence response genes showed upregulated antagonistic interactions (i.e., were less upregulated than expected under the independent action model). This indicates that when pesticide exposure was combined with warming, the general stress defence responses were no longer buffering increased stress levels, which may contribute to a higher sensitivity to toxicants under warming. These upregulated antagonistic interactions were stronger for the high-effect chlorpyrifos concentration, indicating that exposure to this concentration under warming was most stressful. Our results highlight that quantitative analysis of the frequency and strength of the interaction types of general stress defence response genes, specifically focusing on antagonistic upregulations and synergistic downregulations, may advance our understanding of how natural stressors modify the toxicity of contaminants.

Aerosolizable Marine Phycotoxins and Human Health Effects: In Vitro Support for the Biogenics Hypothesis.

Respiratory exposure to marine phycotoxins is of increasing concern. Inhalation of sea spray aerosols (SSAs), during harmful Karenia brevis and Ostreopsis ovata blooms induces respiratory distress among others. The biogenics hypothesis, however, suggests that regular airborne exposure to natural products is health promoting via a downregulation of the mechanistic target of rapamycin (mTOR) pathway. Until now, little scientific evidence supported this hypothesis. The current explorative in vitro study investigated both health-affecting and potential health-promoting mechanisms of airborne phycotoxin exposure, by analyzing cell viability effects via cytotoxicity assays and effects on the mTOR pathway via western blotting. To that end, A549 and BEAS-2B lung cells were exposed to increasing concentrations (ng·L-1 - mg·L-1) of (1) pure phycotoxins and (2) an extract of experimental aerosolized homoyessotoxin (hYTX). The lowest cell viability effect concentrations were found for the examined yessotoxins (YTXs). Contradictory to the other phycotoxins, these YTXs only induced a partial cell viability decrease at the highest test concentrations. Growth inhibition and apoptosis, both linked to mTOR pathway activity, may explain these effects, as both YTXs were shown to downregulate this pathway. This proof-of-principle study supports the biogenics hypothesis, as specific aerosolizable marine products (e.g., YTXs) can downregulate the mTOR pathway.

Genome-Wide Stress Responses to Copper and Arsenic in a Field Population of Daphnia.

Over the past decade, significant advances have been made to unravel molecular mechanisms of stress response in different ecotoxicological model species. Within this study, we focus on population level transcriptomic responses of a natural population of Daphnia magna Straus, (1820), to heavy metals. We aim to characterize the population level transcriptomic responses, which include standing genetic variation, and improve our understanding on how populations respond to environmental stress at a molecular level. We studied population level responses to two heavy metals, copper and arsenic, and their binary mixture across time. Transcriptomic patterns identified significantly regulated gene families and genes at the population level including cuticle proteins and resilins. Furthermore, some of these differentially regulated gene families, such as cuticle proteins, were also significantly enriched for genetic variations including SNPs and MNPs. In general, genetic variation was observed in specific gene families, many of which are known to be involved in stress response. Overall, our results indicate that molecular stress responses can be identified within natural populations and that linking molecular mechanisms with genetic variation at the population level could contribute significantly to adverse outcome frameworks.

Synthesizing the role of epigenetics in the response and adaptation of species to climate change in freshwater ecosystems.

Freshwater ecosystems are amongst the most threatened ecosystems on Earth. Currently, climate change is one of the most important drivers of freshwater transformation and its effects include changes in the composition, biodiversity and functioning of freshwater ecosystems. Understanding the capacity of freshwater species to tolerate the environmental fluctuations induced by climate change is critical to the development of effective conservation strategies. In the last few years, epigenetic mechanisms were increasingly put forward in this context because of their pivotal role in gene-environment interactions. In addition, the evolutionary role of epigenetically inherited phenotypes is a relatively recent but promising field. Here, we examine and synthesize the impacts of climate change on freshwater ecosystems, exploring the potential role of epigenetic mechanisms in both short- and long-term adaptation of species. Following this wrapping-up of current evidence, we particularly focused on bringing together the most promising future research avenues towards a better understanding of the effects of climate change on freshwater biodiversity, specifically highlighting potential molecular targets and the most suitable freshwater species for future epigenetic studies in this context.

Deciphering the Combined Effects of Environmental Stressors on Gene Transcription: A Conceptual Approach.

The use of classical mixture toxicity models to predict the combined effects of environmental stressors based on toxicogenomics (OMICS) data is still in its infancy. Although several studies have made attempts to implement mixture modeling in OMICS analysis to understand the low-dose interactions of stressors, it is not clear how interactions occur at the molecular level and how results generated from such approaches can be better used to inform future studies and cumulative hazard assessment of multiple stressors. The present work was therefore conducted to propose a conceptual approach for combined effect assessment using global gene expression data, as illustrated by a case study on assessment of combined effects of gamma radiation and depleted uranium (DU) on Atlantic salmon ( Salmo salar). Implementation of the independent action (IA) model in reanalysis of a previously published microarray gene expression dataset was performed to describe gene expression patterns of combined effects and identify key gene sets and pathways that were relevant for understanding the interactive effects of these stressors. By using this approach, 3120 differentially expressed genes (DEGs) were found to display additive effects, whereas 279 (273 synergistic, 6 antagonistic) were found to deviate from additivity. Functional analysis further revealed that multiple toxicity pathways, such as oxidative stress responses, cell cycle regulation, lipid metabolism, and immune responses were enriched by DEGs showing synergistic gene expression. A key toxicity pathway of DNA damage leading to enhanced tumorigenesis signaling is highlighted and discussed in detail as an example of how to take advantage of the approach. Furthermore, a conceptual workflow describing the integration of combined effect modeling, OMICS analysis, and bioinformatics is proposed. The present study presents a conceptual framework for utilizing OMICS data in combined effect assessment and may provide novel strategies for dealing with data analysis and interpretation of molecular responses of multiple stressors.

Transgenerational DNA Methylation Changes in Daphnia magna Exposed to Chronic γ Irradiation.

Our aim was to investigate epigenetic changes in Daphnia magna after a 25-day chronic external γ irradiation (generation F0 exposed to 6.5 µGy·h-1 or 41.3 mGy·h-1) and their potential inheritance by subsequent recovering generations, namely, F2 (exposed as germline cells in F1 embryos) and F3 (the first truly unexposed generation). Effects on survival, growth, and reproduction were observed and DNA was extracted for whole-genome bisulfite sequencing in all generations. Results showed effects on reproduction in F0 but no effect in the subsequent generations F1, F2, and F3. In contrast, we observed significant methylation changes at specific CpG positions in every generation independent of dose rate, with a majority of hypomethylation. Some of these changes were shared between dose rates and between generations. Associated gene functions included gene families and genes that were previously shown to play roles during exposure to ionizing radiation. Common methylation changes detected between generations F2 and F3 clearly showed that epigenetic modifications can be transmitted to unexposed generations, most likely through the germline, with potential implications for environmental risk.

Transgenerational Inheritance of DNA Hypomethylation in Daphnia magna in Response to Salinity Stress.

Epigenetic mechanisms have been found to play important roles in environmental stress response and regulation. These can, theoretically, be transmitted to future unexposed generations, yet few studies have shown persisting stress-induced transgenerational effects, particularly in invertebrates. Here, we focus on the aquatic microcrustacean Daphnia, a parthenogenetic model species, and its response to salinity stress. Salinity is a serious threat to freshwater ecosystems and a relevant form of environmental perturbation affecting freshwater ecosystems. We exposed one generation of D. magna to high levels of salinity (F0) and found that the exposure provoked specific methylation patterns that were transferred to the three consequent nonexposed generations (F1, F2, and F3). This was the case for the hypomethylation of six protein-coding genes with important roles in the organisms' response to environmental change: DNA damage repair, cytoskeleton organization, and protein synthesis. This suggests that epigenetic changes in Daphnia are particularly targeted to genes involved in coping with general cellular stress responses. Our results highlight that epigenetic marks are affected by environmental stressors and can be transferred to subsequent unexposed generations. Epigenetic marks could therefore prove to be useful indicators of past or historic pollution in this parthenogenetic model system. Furthermore, no life history costs seem to be associated with the maintenance of hypomethylation across unexposed generations in Daphnia following a single stress exposure.

Multigenerational Effects of the Antibiotic Tetracycline on Transcriptional Responses of Daphnia magna and Its Relationship to Higher Levels of Biological Organizations.

Given the risk of environmental pollution by pharmaceutical compounds and the effects of these compounds on exposed ecosystems, ecologically relevant and realistic assessments are required. However, many studies have been mostly focused on individual responses in a single generation exposed to one-effect concentrations. Here, transcriptional responses of the crustacean Daphnia magna to the antibiotic tetracycline across multiple generations and effect concentrations were investigated. The results demonstrated that tetracycline induced different transcriptional responses of daphnids that were dependent on dose and generation. For example, reproduction-related expressed sequence tags (ESTs), including vitellogenin, were distinctly related to the dose-dependent tetracycline exposure, whereas multigenerational exposure induced significant change of molting-related ESTs such as cuticle protein. A total of 65 ESTs were shared in all contrasts, suggesting a conserved mechanism of tetracycline toxicity regardless of exposure concentration or time. Most of them were associated with general stress responses including translation, protein and carbohydrate metabolism, and oxidative phosphorylation. In addition, effects across the dose-response curve showed higher correlative connections among transcriptional, physiological, and individual responses than multigenerational effects. In the multigenerational exposure, the connectivity between adjacent generations decreased with increasing generation number. The results clearly highlight that exposure concentration and time trigger different mechanisms and functions, providing further evidence that multigenerational and dose-response effects cannot be neglected in environmental risk assessment.

Bisulfite Sequencing with Daphnia Highlights a Role for Epigenetics in Regulating Stress Response to Microcystis through Preferential Differential Methylation of Serine and Threonine Amino Acids.

Little is known about the influence that environmental stressors may have on genome-wide methylation patterns, and to what extent epigenetics may be involved in environmental stress response. Yet, studies of methylation patterns under stress could provide crucial insights on stress response and toxicity pathways. Here, we focus on genome-wide methylation patterns in the microcrustacean Daphnia magna, a model organism in ecotoxicology and risk assessment, exposed to the toxic cyanobacterium Microcystis aeruginosa. Bisulfite sequencing of exposed and control animals highlighted differential methylation patterns in Daphnia upon exposure to Microcystis primarily in exonic regions. These patterns are enriched for serine/threonine amino acid codons and genes related to protein synthesis, transport and degradation. Furthermore, we observed that genes with differential methylation corresponded well with genes susceptible to alternative splicing in response to Microcystis stress. Overall, our results suggest a complex mechanistic response in Daphnia characterized by interactions between DNA methylation and gene regulation mechanisms. These results underscore that DNA methylation is modulated by environmental stress and can also be an integral part of the toxicity response in our study species.

Conserved transcriptional responses to cyanobacterial stressors are mediated by alternate regulation of paralogous genes in Daphnia.

Despite a significant increase in genomic data, our knowledge of gene functions and their transcriptional responses to environmental stimuli remains limited. Here, we use the model keystone species Daphnia pulex to study environmental responses of genes in the context of their gene family history to better understand the relationship between genome structure and gene function in response to environmental stimuli. Daphnia were exposed to five different treatments, each consisting of a diet supplemented with one of five cyanobacterial species, and a control treatment consisting of a diet of only green algae. Differential gene expression profiles of Daphnia exposed to each of these five cyanobacterial species showed that genes with known functions are more likely to be shared by different expression profiles, whereas genes specific to the lineage of Daphnia are more likely to be unique to a given expression profile. Furthermore, while only a small number of nonlineage-specific genes were conserved across treatment type, there was a high degree of overlap in expression profiles at the functional level. The conservation of functional responses across the different cyanobacterial treatments can be attributed to the treatment-specific expression of different paralogous genes within the same gene family. Comparison with available gene expression data in the literature suggests differences in nutritional composition in diets with cyanobacterial species compared to diets of green algae as a primary driver for cyanobacterial effects on Daphnia. We conclude that conserved functional responses in Daphnia across different cyanobacterial treatments are mediated through alternate regulation of paralogous gene families.

Genome-wide transcription profiles reveal genotype-dependent responses of biological pathways and gene-families in Daphnia exposed to single and mixed stressors.

The present study investigated the possibilities and limitations of implementing a genome-wide transcription-based approach that takes into account genetic and environmental variation to better understand the response of natural populations to stressors. When exposing two different Daphnia pulex genotypes (a cadmium-sensitive and a cadmium-tolerant one) to cadmium, the toxic cyanobacteria Microcystis aeruginosa, and their mixture, we found that observations at the transcriptomic level do not always explain observations at a higher level (growth, reproduction). For example, although cadmium elicited an adverse effect at the organismal level, almost no genes were differentially expressed after cadmium exposure. In addition, we identified oxidative stress and polyunsaturated fatty acid metabolism-related pathways, as well as trypsin and neurexin IV gene-families as candidates for the underlying causes of genotypic differences in tolerance to Microcystis. Furthermore, the whole-genome transcriptomic data of a stressor mixture allowed a better understanding of mixture responses by evaluating interactions between two stressors at the gene-expression level against the independent action baseline model. This approach has indicated that ubiquinone pathway and the MAPK serine-threonine protein kinase and collagens gene-families were enriched with genes showing an interactive effect in expression response to exposure to the mixture of the stressors, while transcription and translation-related pathways and gene-families were mostly related with genotypic differences in interactive responses to this mixture. Collectively, our results indicate that the methods we employed may improve further characterization of the possibilities and limitations of transcriptomics approaches in the adverse outcome pathway framework and in predictions of multistressor effects on natural populations.

Effects of ocean warming on the fatty acid and epigenetic profile of Acartia tonsa: A multigenerational approach.

The effects of climate change are becoming more prevalent, and it is important to know how copepods, the most abundant class in zooplankton, will react to changing temperatures as they are the main food source for secondary consumers. They act as key transferers of nutrients from primary producers to organisms higher up the food chain. Little is known about the effects of temperature changes on copepods on the long term, i.e., over several generations. Especially the epigenetic domain seems to be understudied and the question remains whether the nutritional value of copepods will permanently change with rising water temperatures. In this research, the effects of temperature on the fatty acid and epigenetic profiles of the abundant planktonic copepod Acartia tonsa were investigated, since we expect to see a link between these two. Indeed, changing methylation patterns helped copepods to deal with higher temperatures, which is in line with the relative abundance of the most important fatty acids, e.g., DHA. However, this pattern was only observed when temperature increased slowly. A sudden increase in temperature showed the opposite effect; Acartia tonsa did not show deviant methylation patterns and the relative abundance of DHA and other important fatty acids dropped significantly after several generations. These results suggest that local fluctuations in temperature have a greater effect on Acartia tonsa than an elevation of the global mean.

Aerosolization of micro- and nanoplastics via sea spray: Investigating the role of polymer type, size, and concentration, and potential implications for human exposure.

Micro- and nanoplastics (MNPs) can enter the atmosphere via sea spray aerosols (SSAs), but the effects of plastic characteristics on the aerosolization process are unclear. Furthermore, the importance of the transport of MNPs via these SSAs as a possible new exposure route for human health remains unknown. The aim of this study was two-fold: (1) to examine if a selection of factors affects aerosolization processes of MNPs, and (2) to estimate human exposure to MNPs via aerosols inhalation. A laboratory-based bubble bursting mechanism, simulating the aerosolization process at sea, was used to investigate the influence of MNP as well as seawater characteristics. To determine the potential human exposure to microplastics via inhalation of SSAs, the results of the laboratory experiments were extrapolated to the field based on sea surface microplastic concentrations and the volume of inhaled aerosols. Enrichment seemed to be influenced by MNP size, concentration and polymer type. With higher enrichment for smaller particles and denser polymers. Experiments with different concentrations showed a larger range of variability but nonetheless lower concentrations seemed to result in higher enrichment, presumably due to lower aggregation. In addition to the MNP characteristics, the type of seawater used seemed to influence the aerosolization process. Our human exposure estimate to microplastic via inhalation of sea spray aerosols shows that in comparison with reported inhaled concentrations in urban and indoor environments, this exposure route seems negligible for microplastics. Following the business-as-usual scenario on plastic production, the daily plastic inhalation in coastal areas in 2100 is estimated to increase but remain far below 1 particle per day. This study shows that aerosolization of MNPs is a new plastic transport pathway to be considered, but in terms of human exposure it seems negligible compared to other more important sources of MNPs, based on current reported environmental concentrations.

The immunostimulatory activity of sea spray aerosols: bacteria and endotoxins activate TLR4, TLR2/6, NF-κB and IRF in human cells.

Frequent exposure to sea spray aerosols (SSA) containing marine microorganisms and bioactive compounds may influence human health. However, little is known about potential immunostimulation by SSA exposure. This study focuses on the effects of marine bacteria and endotoxins in SSA on several receptors and transcription factors known to play a key role in the human innate immune system. SSA samples were collected in the field (Ostend, Belgium) or generated in the lab using a marine aerosol reference tank (MART). Samples were characterized by their sodium contents, total bacterial counts, and endotoxin concentrations. Human reporter cells were exposed to SSA to investigate the activation of toll-like receptor 4 (TLR4) in HEK-Blue hTLR4 cells and TLR2/6 in HEK-Blue hTLR2/6 cells, as well as the activation of nuclear factor kappa B (NF-κB) and interferon regulatory factors (IRF) in THP1-Dual monocytes. These responses were then correlated to the total bacterial counts and endotoxin concentrations to explore dose-effect relationships. Field SSA contained from 3.0 × 103 to 6.0 × 105 bacteria/m3 air (averaging 2.0 ± 1.9 × 105 bacteria/m3 air) and an endotoxin concentration ranging from 7 to 1217 EU/m3 air (averaging 389 ± 434 EU/m3 air). In contrast, MART SSA exhibited elevated levels of total bacterial count (from 2.0 × 105 to 2.4 × 106, averaging 7.3 ± 5.5 × 105 cells/m3 air) and endotoxin concentration from 536 to 2191 (averaging 1310 ± 513 EU/m3 air). SSA samples differentially activated TLR4, TLR2/6, NF-κB and IRF. These immune responses correlated dose-dependently with the total bacterial counts, endotoxin levels, or both. This study sheds light on the immunostimulatory potential of SSA and its underlying mechanisms, highlighting the need for further research to deepen our understanding of the health implications of SSA exposure.