Microplastics are emerging contaminants ubiquitously distributed in the environment, with rivers acting as their main mode of transport in surface freshwater systems. However, the relative importance of hydrologic processes and source-related variables for benthic microplastic distribution in river sediments is not well understood. We therefore sampled and characterized microplastics in river sediments across the Meramec River watershed (eastern Missouri, United States) and applied a hydrologic modeling approach to estimate the relative importance of river discharge, river sediment load, land cover, and point source pollution sites to understand how these environmental factors affect microplastic distribution in benthic sediments. We found that the best model for the Meramec River watershed includes both source-related variables (land cover and point sources) but excludes both hydrologic transport-related variables (discharge and sediment load). Prior work has drawn similar and dissimilar conclusions regarding the importance of anthropogenic versus hydrologic variables in microplastic distribution, though we acknowledge that comparisons are limited by methodological differences. Nevertheless, our findings highlight the complexity of microplastic pollution in freshwater systems. While generating a universal predictive model might be challenging to achieve, our study demonstrates the potential of using a modeling approach to determine the controlling factors for benthic microplastic distribution in fluvial systems.

Microplastics (MPs) are an emerging global concern as they are abundant in the environment and can act as vectors of various contaminants. However, whether and how MPs can be vectors of antibiotic resistance genes (ARGs), especially extracellular ARGs (eARGs), remains far from explicit. This study addresses the adsorption of both intracellular ARGs (iARGs) and eARGs by four types of MPs in municipal wastewater, and then explores the potential horizontal gene transfer of iARGs and eARGs exposed to MPs. Results indicate that though MPs significantly adsorbed both iARGs and eARGs, eARGs were adsorbed with a significantly higher fold enrichment (2.0–5.0 log versus 2.0–3.3 log) and rate (0.0056 min⁻¹ versus 0.0037 min⁻¹) than iARGs. While all four types of MPs adsorbed ARGs, polypropylene MPs showed the highest adsorption capacity for ARGs. Background constituents such as humic acid and antibiotics significantly inhibited adsorption of iARGs, but not eARGs on MPs. The presence of sodium chloride didn't significantly affect adsorption of iARGs or eARGs. The adsorption of ARGs was well explained by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) interaction energy profile. Higher eARG adsorption was attributed to a lower energy barrier between MPs and eARGs than that between MPs and iARGs. Exposure to MPs enhanced horizontal gene transfer of both iARGs and eARGs by 1.5 and 2.0 times, respectively. The improved contact potential between donors and recipients, as well as the increased cell permeability of recipients induced the improved horizontal gene transfer by MPs. This study underscores the need to address ARG propagation through adsorption to MPs.

The North Sea and its coastal zones are heavily impacted by anthropogenic activities, which has resulted in significant chemical pollution ever since the beginning of the industrialization in Europe during the 19th century. In order to assess the chemical Anthropocene, natural archives, such as sediment cores, can serve as a valuable data source to reconstruct historical emission trends and to verify the effectiveness of changing environmental legislation. In this study, we investigated 90 contaminants covering inorganic and organic pollutant groups analyzed in a set of sediment cores taken in the North Seas' main sedimentation area (Skagerrak). We thereby develop a chemical pollution fingerprint that records the constant input of pollutants over time and illustrates their continued great relevance for the present. Additionally, samples were radiometrically dated and PAH and PCB levels in porewater were determined using equilibrium passive sampling. Furthermore, we elucidated the origin of lead (Pb) contamination utilizing non-traditional stable isotopic analysis. Our results reveal three main findings: 1. for all organic contaminant groups covered (PAHs, OCPs, PCBs, PBDEs and PFASs) as well as the elements lead (Pb) and titanium (Ti), determined concentrations decreased towards more recent deposited sediment. These decreasing trends could be linked to the time of introductions of restrictions and bans and therefor our results confirm, amongst possible other factors, the effectiveness of environmental legislation by revealing a successive change in contamination levels over the decades. 2. concentration trends for ΣPAH and ΣPCB measured in porewater correspond well with the ones found in sediment which suggests that this method can be a useful expansion to traditional bulk sediment analysis to determine the biologically available pollutant fraction. 3. Arsenic (As) concentrations were higher in younger sediment layers, potentially caused by emissions of corroded warfare material disposed in the study area after WW II.

Plastic pollution in the natural environment is causing increasing concern at both the local and global scale. Understanding the dispersion of plastic through the environment is of key importance for the effective implementation of preventive measures and cleanup strategies. Over the past few years, various models have been developed to estimate the transport of plastics in rivers, using limited plastic observations in river systems. However, there is a large discrepancy between the amount of plastic being modelled to leave the river systems, and the amount of plastic that has been found in the seas and oceans. Here, we investigate one of the possible causes of this mismatch by performing an extensive uncertainty analysis of the riverine plastic export estimates. We examine the uncertainty from the homogenisation of observations, model parameter uncertainty, and underlying assumptions in models. To this end, we use the to-date most complete time-series of macroplastic observations (macroplastics have been found to contain most of the plastic mass transported by rivers), coming from three European rivers. The results show that model structure and parameter uncertainty causes up to four orders of magnitude, while the homogenisation of plastic observations introduces an additional three orders of magnitude uncertainty in the estimates. Additionally, most global models assume that variations in the plastic flux are primarily driven by river discharge. However, we show that correlations between river discharge (and other environmental drivers) and the plastic flux are never above 0.5, and strongly vary between catchments. Overall, we conclude that the yearly plastic load in rivers remains poorly constrained.

Estuaries are considered as important sources of the global emission of greenhouse gases (GHGs). Urbanized estuaries often experience eutrophication under strong anthropogenic activities. Eutrophication can enhance phytoplankton abundance, leading to carbon dioxide (CO₂) consumption in the water column. Only a few studies have evaluated the relationship between GHGs and eutrophication in estuaries. In this study, we assessed the concentrations and fluxes of CO₂, methane (CH₄) and nitrous oxide (N₂O) in combination with a suite of biogeochemical variables in four sampling campaigns over two years in a highly urbanized tropical estuary in Southeast Asia (the Saigon River Estuary, Vietnam). The impact of eutrophication on GHGs was evaluated through several statistical methods and interpreted by biological processes. The average concentrations of CO₂, CH₄ and N₂O at the Saigon River in 2019–2020 were 3174 ± 1725 μgC-CO₂ L⁻¹, 5.9 ± 16.8 μgC-CH₄ L⁻¹ and 3.0 ± 4.8 μgN-N₂O L⁻¹, respectively. Their concentrations were 13–18 times, 52–332 times, and 9–37 times higher than the global mean concentrations of GHGs, respectively. While CO₂ concentration had no clear seasonal pattern, N₂O and CH₄ concentrations significantly differed between the dry and the rainy seasons. The increase in eutrophication status along the dense urban area was linearly correlated with the increase in GHGs concentrations. The presence of both nitrification and denitrification resulted in elevated N₂O concentrations in this urban area of the estuary. The high concentration of CO₂ was contributed by the high concentration of organic carbon and mineralization process. GHGs fluxes at the Saigon River Estuary were comparable to other urbanized estuaries regardless of climatic condition. Control of eutrophication in urbanized estuaries through the implantation of efficient wastewater treatment facilities will be an effective solution in mitigating the global warming potential caused by estuarine emissions.

The intensification of anomalous events of seawater warming and the co-occurrence with local anthropogenic stressors are threatening coastal marine habitats, including seagrasses, which form extensive underwater meadows. Eutrophication highly affects coastal environments, potentially summing up to the widespread effects of global climate changes. In the present study, we investigated for the first time in seagrasses, the transcriptional response of different plant organs (i.e., leaf and shoot apical meristem, SAM) of the Mediterranean seagrass Posidonia oceanica growing in environments with a different history of nutrient enrichment. To this end, a mesocosm experiment exposing plants to single (nutrient enrichment or temperature increase) and multiple stressors (nutrient enrichment plus temperature increase), was performed. Results revealed a differential transcriptome regulation of plants under single and multiple stressors, showing an organ-specific sensitivity depending on plants' origin. While leaf tissues were more responsive to nutrient stress, SAM revealed a higher sensitivity to temperature treatments, especially in plants already impacted in their native environment. The exposure to stress conditions induced the modulation of different biological processes. Plants living in an oligotrophic environment were more responsive to nutrients compared to plants from a eutrophic environment. Evidences that epigenetic mechanisms were involved in the regulation of transcriptional reprogramming were also observed in both plants’ organs. These results represent a further step in the comprehension of seagrass response to abiotic stressors pointing out the importance of local pressures in a global warming scenario.

In fish, the gut microbiome plays a crucial role in homeostasis and health and is affected by several organic and inorganic environmental contaminants. Amphidromous fish are sentinel species, particularly exposed to these stressors. We used whole metagenome sequencing to characterize the gut microbiome of wild European eels (Anguilla anguilla) at a juvenile stage captured from three sites with contrasted pollution levels in term of heavy metals and persistent organic pollutants. The objectives were to identify what parameters could alter the gut microbiome of this catadromous fish and to explore the potential use of microbiota as bioindicators of environment quality. We identified a total of 1079 microbial genera. Overall, gut microbiome was dominated by Proteobacteria, Firmicutes and Actinobacteria. Alpha and beta diversity were different amongst sites and could be explained by a reduced number of environmental and biological factors, specifically the relative abundance of fish preys in eels’ diet, PCB101, γHCH (lindane), transnonachlor and arsenic. Furthermore, we identified a series of indicator taxa with differential abundance between the three sites. Changes in the microbial communities in the gut caused by environmental pollutants were previously undocumented in European eels. Our results indicate that microbiota might represent another route by which pollutants affect the health of these aquatic sentinel organisms.

During the last decades, the coastal areas of Morocco have witnessed an intense socioeconomic development associated with a continuous population growth and urban extension. This has led to an overexploitation of coastal aquifers leading to a degradation of their water quality. In order to obtain large scale overview on the quality status of Morocco's coastal aquifers (MCA) to assist national water managers to make informed decisions, a comprehensive scrutinization of the MCA against common indicators and using unified methods is essential. In this study, databases from thirteen MCA were analyzed, using multivariate statistical approaches and graphical methods in order to investigate the degree of mineralization in each aquifer and to identify the main salinization processes prevailing in groundwater. The results showed that the dominant groundwater types are Na–Cl, Ca–Mg–Cl, Ca–Mg–SO₄, Ca–Mg–HCO₃ and Ca–HCO₃–Cl. The Gibbs diagram and the seawater contribution (0–37%) indicate that the mineralization is mainly due to the seawater intrusion and water-rock interaction. The salinity degree diagram illustrates that almost all groundwater samples are located in the moderate to very saline zone, indicating that MCA are recharged by water from variable sources. The groundwater quality assessment shows a deterioration, particularly by seawater intrusion and significant nitrate pollution. The temporal evolution confirm that the MCA are influenced by seawater namely in the Atlantic part. The Wilcox and USSL diagram indicate that the majority of sampled water are unsuitable for irrigation uses. In addition, and by referring to the WHO and the Moroccan standards for water potability, large number of samples from the groundwaters of the MCA is not fully adequate for drinking purposes. A set of management actions (e,g., artificial recharge) are proposed in order to mitigate the effect of groundwater overexploitation and seawater intrusion to ensure the sustainability of MCA.

Extended-spectrum β-lactamases (ESBL)-producing Enterobacterales have been classified as critical priority pathogens by the World Health Organization (WHO). ESBL are universally distributed and, in 2006, were firstly reported on a wild animal. Understanding the relative contributions of wild animals to ESBL circulation in the environment is urgently needed. In this work, we have conducted a nationwide study in Portugal to investigate the occurrence of bacteria carrying clinically significant antimicrobial resistance genes (ARG), using widely distributed wild ungulates as model species. A total of 151 antimicrobial resistant-Enterobacterales isolates were detected from 181 wild ungulates: 50% (44/88) of isolates from wild boar (Sus scrofa), 40.3% (25/62) from red deer (Cervus elaphus), 41.4% (12/29) from fallow deer (Dama dama) and 100% (2/2) from mouflon (Ovis aries subsp. musimon). Selected isolates showed a diversified resistance profile, with particularly high values corresponding to ampicillin (71.5%) and tetracycline (63.6%). Enterobacterales strains carried blaTEM, tetA, tetB, sul2, sul1 or dfrA1 ARG genes. They also carried blaCTX₋M-type genes, which are prevalent in human infections, namely CTX-M-14, CTX-M-15 and CTX-M-98. Strikingly, this is the first report of CTX-M-98 in wildlife. Almost 40% (n = 59) of Enterobacterales were multi-drug resistant. The diversity of plasmids carried by ESBL isolates was remarkable, including IncF, K and P. This study highlights the potential role of wild ungulates as environmental reservoirs of CTX-M ESBL-producing E. coli and in the spill-over of AMR bacteria and their determinants. Our findings suggest that wild ungulates are useful as strategic sentinel species of AMR in terrestrial environments, especially in response to potential sources of anthropogenic pollution, providing early warning of potential risks to human, animal and environmental health.

The assessment of contaminant exposure in marine organisms often focuses on the most toxic chemical elements from upper trophic level species. Information on mid-trophic level species and particularly on potentially less harmful elements is lacking. Additionally, microplastics have been considered emergent contaminants in aquatic environments which have not been extensively studied in species from mid-trophic levels in food chains. This study aims to contribute to an overall assessment of environmental impacts of such chemicals in a community of small pelagic fish in the North Atlantic. The concentrations of 16 chemical elements, rarely simultaneously quantified (including minerals, trace elements and heavy metals), and the presence of microplastics were analysed in sardines (Sardina pilchardus) and mackerels (Scomber spp. and Trachurus trachurus) sampled along the Portuguese coast. Biochemical stress assessments and stable isotope analyses were also performed. The chemical element concentrations in S. pilchardus, T. trachurus, and Scomber spp. were relatively low and lower than the levels reported for the same species in the North Atlantic and adjacent areas. No clear relationships were found between chemical elements and oxidative damage in fish. However, the concentration of several chemical elements showed differences among species, being related with the species’ habitat use, trophic niches, and specific feeding strategies. The presence of plastic pieces in the stomachs of 29% of the sampled fishes is particularly concerning, as these small pelagic fish from mid-trophic levels compose a significant part of the diet of humans and other top predators. This study highlights the importance of multidisciplinary approaches focusing on the individual, including position data, stable isotopes, and oxidative stress biomarkers as complementary tools in contamination assessment of the marine mid-trophic levels in food chains.