New approach methods (NAMs) are increasingly important to help accelerate the pace of ecological risk assessment and offer more ethical, affordable, and efficient alternatives to traditional toxicity tests. In the present study, we describe the development, technical characterization, and initial testing of a toxicogenomics tool, EcoToxChip (384-well quantitative polymerase chain reaction [qPCR] array), to support chemical management and environmental monitoring for three laboratory model species—fathead minnow (Pimephales promelas), African clawed frog (Xenopus laevis), and Japanese quail (Coturnix japonica). Chip design, including gene selection, was informed by a diverse end-user group and quality control metrics (e.g., primer assay, reverse transcription, and PCR efficiency) performed well based on a priori established criteria. Correlation with RNA sequencing (seq) data provided additional confidence in this novel toxicogenomics tool. Although the present study represents an initial testing of only 24 EcoToxChips for each of the model species, the results provide increased confidence in the robustness/reproducibility of EcoToxChips for evaluating perturbations in gene expression associated with chemical exposure and thus, this NAM, combined with early-life stage toxicity testing, could augment current efforts for chemical prioritization and environmental management. Environ Toxicol Chem 2023;42:1763–1771. © 2023 SETAC

When performing basic and translational laboratory studies with aquatic organisms, particularly for bioaccumulation, toxicity, or biotransformation experiments, it is imperative to control the route and dose of exposure. Contamination of feed and the organisms prior to study could alter the results of an experiment. Furthermore, if organisms not exposed in the lab are used for quality assurance/quality control, then blank levels, method detection limits, and limits of quantitation can be affected. In an effort to determine the magnitude of this potential issue for exposure studies involving Pimephales promelas, we analyzed a suite of 24 per- and polyfluoroalkyl substances (PFAS) in four types of feed from three different companies and in organisms from five aquaculture facilities. Contamination with PFAS was found in all types of materials and organisms from all aquaculture farms. The most frequently detected PFAS in fish feed and aquaculture fathead minnows were perfluorocarboxylic acids and perfluorooctane sulfonate (PFOS). Concentrations of total and individual PFAS in feed ranged from nondetect to 76 ng/g and from nondetect to 60 ng/g, respectively. Fathead minnows were contaminated with PFOS and perfluorohexane sulfonate as well as several perflourocarboxylic acids. Concentrations of total and individual PFAS ranged from 1.4 to 351 ng/g and from nondetect to 328 ng/g, respectively. The PFOS measured in food was primarily the linear isomer, consistent with greater bioaccumulation of that isomer in organisms raised as fish food. Future studies are necessary to define the extent of PFAS contamination in aquatic culture facilities and aquaculture production operations. Environ Toxicol Chem 2023;42:1463–1471. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Amphetamine (AMP) is a chiral psychoactive substance that exhibits enantioselectivity in its pharmacological properties. It has been detected in wastewaters and surface waters and can occur as enantiomeric mixtures, but little is known about its environmental risk and potential enantioselective toxicity to aquatic organisms. Our study aimed to target enantioselectivity in AMP toxicity to the freshwater invertebrate Daphnia magna. Daphnids were subchronically exposed to the racemate (rac-AMP: 0.1, 1.0, and 10 µg/L) and pure enantiomers, (R)-AMP and (S)-AMP (0.1, and 1.0 µg/L, respectively), for 8 days. Morphophysiological, swimming behavior, reproductive and biochemical variables were evaluated during critical life stages (juveniles vs. adults). Some responses were context-dependent and often enantioselective, varying between racemate and enantiomers and across the life stage of the organisms. Overall, rac-AMP stimulated D. magna growth, decreased heart rate and area, affected behavior, and stimulated reproduction. The effect of enantiomers was totally or partially concordant with rac-AMP, except for swimming behavior and reproduction. Enantioselectivity was observed for body size, number of eggs/daphnia, and heart rate (steeper decrease caused by (R)-AMP on day 3). Changes in biochemical parameters were also observed: AMP caused a significant decrease in catalase activity as racemate or pure enantiomers, whereas a decrease in acetylcholinesterase activity was found only for rac-AMP. Evidence for oxidative stress was contradictory, although both enantiomers caused a significant decrease in reactive oxygen species (unlike rac-AMP). Overall, these results show that AMP can interfere in an enantioselective way with aquatic organisms at low concentrations (e.g., 0.1 µg/L), demonstrating the relevance of this kind of study to an accurate environmental risk assessment regarding medium- to long-term exposure to this psychoactive drug. Environ Toxicol Chem 2023;42:1743–1754. © 2023 SETAC.

While salinity can alter the photodegradation of hydrophobic organic compounds (HOCs), the cause of their altered kinetics in seawater is not well understood. Because HOC intermediate photoproducts are often more toxic than their parent compounds, characterizing the generation of intermediates in saline environments is needed to accurately predict their health effects. The present study investigated the influence of salinity on the generation of anthraquinone through the photolysis of anthracene and the generation of anthrone and 1-hydroxyanthraquinone from the photolysis of anthraquinone as well as their reactivities with hydroxyl radicals. This was conducted by measuring the photolysis rates of anthracene and anthraquinone and characterizing their product formation in buffered deionized water, artificial seawater, individual seawater halides (bromide, chloride, and iodide), dimethyl sulfoxide, furfuryl alcohol, and solutions of hydrogen peroxide. Salinity enhanced the persistence of anthraquinone by a factor >10 and altered its product formation, including the generation of the suspected carcinogen 1-hydroxyanthraquinone. In part, this was attributed to reactive oxygen species (ROS) scavenging by the seawater constituents chloride and bromide. In addition, anthraquinone and its hydroxylated products were found to be moderately to highly reactive with hydroxyl radicals, further illustrating their tendency to react with ROS in aqueous environments. The present study emphasizes the importance of considering the effects of salinity on organic contaminant degradation; it can significantly enhance the persistence of HOCs and alter their intermediate formation, subsequently impacting chemical exposure times and potential toxic effects on estuarine/marine organisms. Environ Toxicol Chem 2023;42:1721–1729. © 2023 SETAC.

Plastic - related contaminants in the environment have attracted increasing attentions as plastic pollution becoming a serious issue globally. This work investigated potential of bioaccumulation and biotransfer of bisphenol compounds that are widely added in various products such as plastics and other products in a freshwater ecosystem, China. Among commonly applied 14 bisphenol analogues (BPs), bisphenol A (BPA), bisphenol F (BPF) and bisphenol S (BPS) were predominant, representing 64-100% of the total concentrations of bisphenols (ΣBPs) in the freshwater wildlife. Both the concentrations and analogue profiles in the fish showed seasonal differences and species dependence. Higher BP concentrations were observed in the fish collected during dry season than wet season. Higher percentages of non-BPA analogues (e.g. BPS and BPF) were observed in the fish of wet season. The pelagic species accumulated obviously higher BPs than the midwater and bottom species. The liver generally contained the highest ΣBPs, followed successively by the swimming bladder, belly fat, and dorsal muscle. The analogue profile also showed somewhat differences among tissues, varying by species and season. Lower ΣBPs but higher percentages of non-BPA analogues were observed in the female than male common carp. Time trends of the BPA concentration in the fish varied by species, probably related with habitats and diets of the fish. Habitats, feeding behaviors, and trophic transfer may have significant impacts on exposure of the wildlife to the BPs in natural ecosystems. The BPs did not demonstrate strong potential of bioaccumulation. More research is warranted about metabolism and transgenerational transfer of the BPs in wildlife in order to fully reveal bioaccumulation and consequently ecological risks of these chemicals in the environment.

The effects of silver nanoparticles (Ag NPs) on the soil environment have attracted considerable research attention. Previous studies mainly focused on agent-coated Ag NPs, which inevitably introduce additional disturbance of chemical agents to the intrinsic property of Ag NPs. We investigated the environmental effects induced by pure surfactant-free Ag NPs (SF-Ag NPs), including soil enzyme activities (urease, sucrase, phosphatase, and β-glucosidase), bacterial community structure, and functional profile, over different exposure periods in the present study. The results indicated that these enzymes, especially urease and phosphatases, exhibit different responses to SF-Ag NPs and are more susceptible to SF-Ag NPs than other enzymes. Surfactant-free Ag NPs can also induce a decrease in bacterial diversity and a change of bacterial community structure. The abundance of SF-Ag NPs in Proteobacteria increased, but decreased in Acidobacteria after 14 days of exposure. Moreover, the abundance of genus Cupriavidus was significantly higher than those of the respective controls. By contrast, SF-Ag NP exposure for 30 days could attenuate these negative effects. The phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) prediction revealed that SF-Ag NPs exert a negligible effect on bacterial function, thereby suggesting that functional redundancy is conduced to bacterial community tolerance to SF-Ag NPs. These findings will help us further understand the environmental toxicity of Ag NPs. Environ Toxicol Chem 2023;42:1685–1695. © 2023 SETAC

Effects of Ethiprole on Nuclear Acid Methylation of Apis mellifera ligustica Worker Larvae Honeybees are an important bioindicator for environmental pollutants (see Figure 1). As a substitute for fipronil, ethiprole is still a high risk to honeybees. In this study, the authors evaluated the effects of ethiprole at sublethal concentrations (10−5, 10−4, 10−3, and 10−2 mg/L) on the DNA and RNA methylation by continuous exposure of Apis mellifera ligustica worker larvae to it. The results showed significant hypomethylation of DNA 5mC and down-regulation of Dnmt3 expression level under all test concentrations. Compared with DNA, RNA methylation, including total RNA and mRNA, was more marked. In all of the treatments, the total RNA methylation in m5C and m3C, and mRNA m6A and m3C methylation were significantly up-regulated; the expression of ALKBH1 that encoding RNA m6A demethylase was significantly down-regulated (p < 0.01); whereas the NSUN4 encoding RNA m5C methyltransferase was significantly up-regulated (P < 0.01). In conclusion, Dnmt3, ALKBH1, and NSUN4 are sensitive enough to sublethal doses of ethiprole, suggesting their potential as risk evaluators for ethiprole. This study provides a new perspective and technic for the assessment of pesticide risk. Figure 1Open in figure viewerPowerPoint Alvéole d'abeilles et larves by Shocky. Photo by Adobe Images. Man, F., Suzhen, Q., Miao, W., & Shaokang H. (2023). Effects of ethiprole on nuclear acid methylation of Apis mellifera ligustica worker larvae. Asian Journal of Ecotoxicology, 1, 68–77. http://doi.org/10.7524/AJE.1673-5897.20220511001. http://www.stdlxb.cn/article/doi/10.7524/AJE.1673-5897.20220511001 Research Progress on Immunotoxic Mechanism of Dioxins and Dioxin-Like Pollutants Dioxins are highly potent exogenous ligands of the aryl hydrocarbon receptor (AHR), which are known to exert immunotoxic effects through AHR. The canonical AHR toxicity pathway is that activated AHR enters the nucleus and forms a complex with the AHR nuclear translocator (ARNT), inducing the expression of downstream immune-related genes controlled by dioxin response element (DRE). However, new studies have shown that non-canonical AHR pathways are responsible for dioxin-induced immunotoxicity to some extent. Non-canonical AHR pathways refer to that activated AHR crosstalk with key proteins in other signaling pathways (such as inflammation, cell cycle, and signal transduction), affecting cell function. In this process, AHR directly or in the form of the AhR-ARNT complex interacts with other transcription factors, and they are collaboratively recruited and bind to consensus or non-consensus DRE sites, that then affect the transcription and expression of key molecules. At present, many substances with similar structure to dioxins have been proved to have dioxin-like AHR activation activity, including some polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and polybrominated diphenyl ethers, which are called dioxin-like compounds. Dioxin-like compounds can affect the immune system by activating the AHR. In addition, in some research, AHR-independent pathways could include cause cells to oxidative stress, affect respiratory burst responses, interfere with mitochondrial function, promoting cell apoptosis, and so on. In conclusion, compared with dioxins, the immunotoxic mechanism of dioxin-like compounds is not clear, and more systematic studies are needed. Xinge, W., Na, L., Yingnan, H., Mei, M., Xinghua, W., Chong, L., & Dianchang W. (2023). Research progress on immunotoxic mechanism of dioxins and dioxin-like pollutants. Asian Journal of Ecotoxicology, 1, 138–148. http://doi.org/10.7524/AJE.1673-5897.20220805003. http://www.stdlxb.cn/article/doi/10.7524/AJE.1673-5897.20220805003

Environmental risk assessment (ERA) of pharmaceuticals relies on available measured environmental concentrations, but often such data are sparse. Predicted environmental concentrations (PECs), calculated from sales weights, are an attractive alternative but often cover only prescription sales. We aimed to rank, by environmental risk in Norway, approximately 200 active pharmaceutical ingredients (APIs) over 2016–2019, based on sales PECs. To assess the added value of wholesale and veterinary data, we compared exposure and risk predictions with and without these additional sources. Finally, we aimed to characterize the persistence, mobility, and bioaccumulation of these APIs. We compared our PECs to available Norwegian measurements, then, using public predicted-no-effect concentrations, we calculated risk quotients (RQs) and appended experimental and predicted persistence and bioaccumulation. Our approach overestimated environmental concentrations compared with measurements for 18 of 20 APIs with comparable predictions and measurements. Seventeen APIs had mean RQs >1, indicating potential risk, while the mean RQ was 2.05 and the median 0.001, driven by sex hormones, antibiotics, the antineoplastic abiraterone, and common painkillers. Some high-risk APIs were also potentially persistent or bioaccumulative (e.g., levonorgestrel [RQ = 220] and ciprofloxacin [RQ = 56]), raising the possibility of impacts beyond their RQs. Exposure and risk were also calculated with and without over-the-counter sales, showing that prescriptions explained 70% of PEC magnitude. Likewise, human sales, compared with veterinary, explained 85%. Sales PECs provide an efficient option for ERA, designed to overestimate compared with analytical techniques and potentially held back by limited data availability and an inability to quantify uncertainty but, nevertheless, an ideal initial approach for identification and ranking of risks. Environ Toxicol Chem 2023;00:1–18. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Parasites can affect their hosts in various ways, and this implies that parasites may act as additional biotic stressors in a multiple-stressor scenario, resembling conditions often found in the field if, for example, pollutants and parasites occur simultaneously. Therefore, parasites represent important modulators of host reactions in ecotoxicological studies when measuring the response of organisms to stressors such as pollutants. In the present study, we introduce the most important groups of parasites occurring in organisms commonly used in ecotoxicological studies ranging from laboratory to field investigations. After briefly explaining their life cycles, we focus on parasite stages affecting selected ecotoxicologically relevant target species belonging to crustaceans, molluscs, and fish. We included ecotoxicological studies that consider the combination of effects of parasites and pollutants on the respective model organism with respect to aquatic host–parasite systems. We show that parasites from different taxonomic groups (e.g., Microsporidia, Monogenea, Trematoda, Cestoda, Acanthocephala, and Nematoda) clearly modulate the response to stressors in their hosts. The combined effects of environmental stressors and parasites can range from additive, antagonistic to synergistic. Our study points to potential drawbacks of ecotoxicological tests if parasite infections of test organisms, especially from the field, remain undetected and unaddressed. If these parasites are not detected and quantified, their physiological effects on the host cannot be separated from the ecotoxicological effects. This may render this type of ecotoxicological test erroneous. In laboratory tests, for example to determine effect or lethal concentrations, the presence of a parasite can also have a direct effect on the concentrations to be determined and thus on the subsequently determined security levels, such as predicted no-effect concentrations. Environ Toxicol Chem 2023;00:1–14. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Pesticides and climate change are both thought to contribute to the global amphibian decline, yet their combined effects are still poorly understood. Metolachlor is a widespread herbicide applied across North America, but little is known about its effects on amphibians. We used a replicated mesocosm experimental design with different levels of drying (i.e., no drying and medium and rapid drying) and metolachlor concentrations (0, 0.8, 8, and 80 µg/L) to assess their respective and combined effects on wood frog (Lithobates sylvaticus) larvae throughout metamorphosis. Metolachlor had no significant effect on survival and development of tadpoles. However, metolachlor significantly interacted with drying levels to reduce the growth of tadpoles, which was mainly due to a difference detected among metolachlor concentrations under the rapid drying treatment. Drying also directly reduced growth and body mass at metamorphosis. Our results suggest that environmental stressors, such as drying, should be considered in toxicological experiments to provide relevant exposure conditions to pesticides for ephemeral pond species in the context of global climate change. Environ Toxicol Chem 2023;42:1772–1781. © 2023 SETAC

Polycyclic aromatic compounds (PACs) present in the water column are considered to be one of the primary contaminant groups contributing to the toxicity of a crude oil spill. Because crude oil is a complex mixture composed of thousands of different compounds, oil spill models rely on quantitative structure activity relationships (QSARs) like the target lipid model (TLM) to predict the effects of crude oil exposure on aquatic life. These models rely on input provided by single species toxicity studies which remain insufficient. Though the toxicity of select PACs have been well studied, there is little data available for many, including transformation products like oxidized hydrocarbons. In addition, the effect of environmental influencing factors like temperature, on PAC toxicity is a wide data gap. In response to these needs, in the present study, stage I lobster larvae were exposed to 6 different understudied PACs (naphthalene, fluorenone, methylnaphthalene, phenanthrene, dibenzothiophene, and fluoranthene) at 3 different relevant temperatures (10, 15 and 20°C) all within the biological norms for the species during summer when larval releases occur. Lobster larvae were assessed for immobilization as a sublethal effect and mortality following 3, 6, 12, 24, and 48 h of exposure. Higher temperatures increased the rate at which immobilization and morality was observed for each of the compounds tested and also altered the predicted critical target lipid body burden (CTLBB), incipient LC50, and elimination rate. Our results demonstrate that temperature has an important influence on PAC toxicity for this species and we provide critical data for oil spill modeling. More studies are needed so oil spill models can be appropriately calibrated and improve their predictive ability.

Maternal transfer of selenium (Se) to developing fish eggs during vitellogenesis can cause larval deformity and mortality. Previous studies have shown wide variation among fish species in both the magnitude of maternal transfer (exposure) and the egg Se concentration causing effects (sensitivity). We studied maternal transfer and effects of Se on early life stage development, survival, and growth of redside shiner (Richardsonius balteatus), a small-bodied cyprinid that has been reported to have relatively high ovary:muscle Se concentration ratios. Gametes were collected from lentic areas in southeast British Columbia with a range of dietary Se concentrations related to weathering of waste rock from coal mining. Eggs were fertilized and reared in the laboratory from hatch to the onset of exogenous feeding. Larvae were assessed for survival, length, weight, Se-characteristic deformities, and edema. Eggs from a total of 56 females were collected, with egg Se concentrations from 0.7 to 28 mg/kg dry weight. Maternal transfer varied among sites, with egg:muscle Se concentration ratios ranging from 4. We also found that sampling residual ovaries can overestimate Se concentrations in ripe eggs by up to a factor of 5.7. A correlation between larval weight and egg Se concentration was identified, although the relationship was weak (r228 mg/kg dw in eggs. These data indicate that redside shiner is less sensitive to maternally transferred Se than most other tested fish species.

WINNER OF THE 2022 BEST PAPER AWARD Tackling the challenge of extracting microplastics from soils: A protocol to purify soil samples for spectroscopic analysis Julia N. Möller, Ingrid Heisel, Anna Satzger, Eva C. Vizsolyi, S.D. Jakob Oster, Seema Agarwal, Christian Laforsch, and Martin G.J. Löder DOI: 10.1002/etc.5024 Understanding the occurrence of microplastics in various environmental media is critical for assessing their environmental impact. Soil is one of the hotspots within which microplastics accumulate and reside. Nonetheless, analysis and characterization of microplastics in soil are highly challenging, due to the complexity and heterogeneity of natural soils. Möller et al. (2022) tackles the challenge of extracting microplastics from soil samples for the subsequent micro-Fourier-transform infrared spectroscopy (µ-FTIR) analysis, one of the very few currently available methods for microplastics characterization. The combination of freeze-drying, sieving, density separation, and sequential enzymatic-oxidative digestion allows for the successful recovery of microplastic fibers and fragments of polyamide, polyethylene, polyethylene terephthalate, and polyvinyl chloride, down to a size of 10 µm. Even though the protocol works less well for biodegradable microplastics, the protocol highlighted here may shed light on future research aiming to improve the analytical sensitivity and resolution, and to expand the method applications. REFERENCE Möller, J. N., Heisel, I., Satzger, A., Vizsolyi, E. C., Oster, S. D. J., Agarwal, S., Laforsch, C., & Löder, M. G. J. (2022). Tackling the challenge of extracting microplastics from soils: A protocol to purify soil samples for spectroscopic analysis. Environmental Toxicology and Chemistry, 41, 844−857. Wei Chen College of Environmental Science and Engineering Nankai University China Best Paper Award winner Julia N. Möller.

Antibiotic resistance is one of the most serious threats to human health and food safety, carrying a dramatic cost to society both financially and in terms of human suffering. The Organisation for Economic Co-operation and Development (OECD) has estimated that over the next 30 years, infections involving resistant bacteria could cost the lives of 2.4 million people in Europe, North America, and Australia, at an estimated cost of 3.5 billion dollars a year (OECD, 2018). Because antibiotics are natural or synthetic chemical compounds that inhibit the development or cause the death of microorganisms, they are widely used (and sometimes overused) in human healthcare for the treatment of bacterial infections; in animal care they are employed to prevent disease and promote livestock growth. Antibiotics utilized in animal farm production constitute the greatest use worldwide; it has been estimated that more than 130 000 t were used for this purpose in 2013, an amount that could exceed 200 000 t in 2030 (Boeckel et al., 2017). Even though the available data are incomplete, this number would be significantly increased with the inclusion of human therapeutic use. These antibiotics reach the environment at different stages of an organism's life cycle and through different routes (manufacturing efflux, excretion after consumption and metabolization, inappropriate disposal or recycling, etc.). This continuous release leads to the detection of antibiotics in surface waters and estuarine areas, where they have been measured at concentrations ranging from 10 ng/L to μg/L, depending on the location; traces have also been detected in drinking water (Zheng et al., 2021). Such contamination is a driving factor in the development of bacterial resistance. Even if the acquisition of resistance is a natural adaptive mechanism, increased acquisition can be seen in response to an increase in antibiotic use, while at the same time the efficiency of newly developed antibiotics rapidly decreases. Bacteria may become resistant to antibiotics via mutations, leading to the establishment of mechanisms that inactivate the antibiotic, increase the efflux of the molecule outside the bacterial cell, or modify the target protein. The second resistance strategy consists of the acquisition of genetic material through horizontal gene transfer (HGT); if the antibiotic resistance gene (ARG) is transferred, it confers a new function (resistance) on the target bacteria. Thus antibiotics are a gold standard for exerting high selection pressure on bacteria and triggering the occurrence of specific ARGs. However, environmental pollutants such as metals, polycyclic aromatic hydrocarbons, or pesticides have also been shown to exert selection pressure by causing cross-resistance to antibiotics or inducing HGT. In most cases, these xenobiotics, which originate from industrial and agricultural activities, are more prevalent than antibiotics in ecosystems and are able to activate genes encoding for efflux pumps, which in turn cause a decrease in the active concentration of compounds (including antibiotics) inside the bacterial cell (Blanco et al., 2016). Thus we urgently need to decipher the role of nonantibiotic contaminants in the induction of ubiquitous resistance to molecules that the bacteria might never have been exposed to. In the environment, aquatic ecosystems are thought to constitute major reservoirs of resistance genes and to favor their spread into other ecosystems, including estuarine areas. In particular, it is now recognized that wastewater treatment plants (WWTPs) constitute hotspots for environmental diffusion of pollutants and antibiotic-resistant bacteria (ARBs), which may be only partially eliminated during treatment, depending on the facility's level of technology. This leads to discharge into aquatic ecosystems through effluents and also into terrestrial ecosystems following the spread of sewage sludge or manure from farm animals. Thus resistant bacteria are detected downstream of WWTPs worldwide (Grenni, 2022). Runoff and transport via rivers and streams allow these contaminants to reach estuaries. An understanding of the development, retention, and diffusion of antimicrobial resistance (AMR) in estuaries is critical because they act as natural filtering points for chemical and biological pollutants at the boundary between terrestrial/freshwater and marine ecosystems. In addition, estuarine areas are highly productive systems; they supply resources for natural living populations and also for human consumption. Liguori et al. (2022) have laid out a framework for monitoring water environments and standardizing methods. However, most of the studies on the occurrence of ARGs consist of gene quantification in biota such as water columns or sediment while the role of other microbiological compartments with a high potential to act as incubators of AMR is often not considered. In particular, the commensal microbiotas of organisms that encourage auspicious conditions such as high microbial diversity and density can facilitate AMR and HGT, as observed in the human intestine after medical treatment. Thus particular attention should be paid to such microbiological niches, which are poorly investigated and may contribute to environmental dissemination of ARGs through release of feces or trophic transfer between organisms. In addition, it has been suggested that microplastics also contribute to the antibiotic resistance crisis, in a different manner. Microplastics are found downstream of WWTPs, emptying into the oceans and threatening the ecological functioning of both stream and estuarine ecosystems. They may be potential carriers of AMR because they provide new ecological niches for the development of ARG-containing biofilms, facilitating the spread of resistance into an environment (Bank et al., 2020). Thus, concomitantly with the general study of ARGs, monitoring the dynamics of microplastics could help us to better understand and characterize the spread of ARGs along the land–sea continuum and to define the risk associated with microplastic-transported ARGs in aquatic environments. These microplastics might contribute to human exposure because they are accumulated by multiple organisms, including living resources consumed by humans. In particular, organisms such as oysters, which are often eaten raw, are species of interest for the monitoring of AMR because their contamination by ARBs involves food safety and human health, exposing humans to unaltered AMR-containing microbiomes. Ingestion of contaminated food may lead to colonization of the human digestive tract by resistant bacteria. Because HGT may occur between phylogenetically distant prokaryote cells from different niches (von Wintersdorff et al., 2016), resistance may therefore be acquired by bacteria from the human gut microbiota. If the bacterium receiving the gene is pathogenic, then the related infection could be untreatable. In this context, we urgently need to improve our understanding of how aquatic and estuarine environments are involved in this crisis of antibiotic resistance, to help stakeholders improve environmental management and mitigate the spread of AMR and to prevent or reduce transmission to human populations; otherwise the action plans to counter the expansion of such resistance may not achieve their objectives.

Recovery, recolonization, and adaptation in a chemical stress context are processes that regenerate local populations and communities as well as the functions these communities perform. Recolonization, either by species previously present or by new species able to occupy the niches left empty, refers to a metacommunity process with stressed ecosystems benefiting from the dispersal of organisms from other areas. A potential consequence of recolonization is a limited capacity of local populations to adapt to potentially repeating events of chemical stress exposure when their niches have been effectively occupied by the new colonizers or by new genetic lineages of the taxa previously present. Recovery, instead, is an internal process occurring within stressed ecosystems. More specifically, the impact of a stressor on a community benefits less sensitive individuals of a local population as well as less sensitive taxa within a community. Finally, adaptation refers to phenotypic and, sometimes, genetic changes at the individual and population levels, allowing the permanence of individuals of previously existing taxa without necessarily changing the community taxonomic composition (i.e., not replacing sensitive species). Because these processes are usually operating in parallel in nature, though at different degrees, it seems relevant to try to understand their relative importance for the regeneration of community structure and ecosystem functioning after chemical exposure. In the present critical perspective, we employed case studies supporting our understanding of the underlying processes with the hope to provide a theoretical framework to disentangle the relevance of the three processes for the regeneration of a biological community after chemical exposure. Finally, we provide some recommendations to experimentally compare their relative importance so that the net effects of these processes can be used to parameterize risk-assessment models and inform ecosystem management. Environ Toxicol Chem 2023;00:1–10. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

While it is recognized that groundwater contaminant plumes can impact surface waters, there remains little information on the magnitude, spatial extent, and especially temporal variability of the resulting exposure to the variety of aquatic organisms, particularly for stagnant surface waters (e.g., ponds). The present study of a historic landfill plume discharging to a pond investigated contaminant exposure to multiple aquatic zones (endobenthic, epibenthic, pelagic) over approximately 1 year within a temperate climate. Landfill tracers included the artificial sweetener saccharin, ammonium, chloride, and specific conductance. Sampling of pond sediment porewater (upwelling groundwater) and continuous geophysical imaging of the subsurface showed a relatively stable plume footprint covering approximately 26% of the pond, although with spatially varying leachate composition, revealing year-round exposure to endobenthic (within sediments) organisms. Substantial and variable contaminant exposure to epibenthic organisms within the plume footprint was shown by elevated specific conductance measured directly above the sediment interface. Exposure varied daily at times and increased through winter to values representing undiluted plume groundwater. Exposure to pelagic organisms (overlying water) covered a larger area (~50%) due to in-pond circulation. The stream outlet concentrations were stable at approximately 10 times dilution for chloride and saccharin, but were substantially less in summer for ammonium due to in-pond processes. Whereas groundwater contaminants are typically assumed elevated at base flows, the outlet stream contaminant mass discharges to downstream receptors were notably higher in winter than summer, following stream flow patterns. Insights from the present study into the timings and locations of contaminant plume exposure to multiple ecological zones of a pond can provide guidance to contaminated site and aquatic ecosystem managers on improved monitoring, assessment, and remediation protocols. Environ Toxicol Chem 2023;42:1667–1684. © 2023 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Proposed development of a mine within Alaska's Bristol Bay watershed has raised concerns about the potential impact of copper (Cu) on Pacific salmon (Oncorhynchus spp.). We conducted 96-hour flow-through bioassays using low-hardness and low-dissolved organic carbon water to determine the acute lethal toxicity of Cu to sockeye (O. nerka), Chinook (O. tshawytscha), and coho salmon (O. kisutch) fry. We aimed to determine Cu toxicity under field-relevant water quality conditions and to assess three methods of calculating ambient Cu criteria: the USEPA-endorsed biotic ligand model (BLM), a multiple linear regression model, and the hardness-based model currently used by the State of Alaska. The criteria generated by all models were below 20% lethal Cu concentrations by factors ranging from 2.2 to 54.3, indicating that all criteria would be protective against mortality. The multiple linear regression-based criteria were the most conservative and comparable to BLM-based criteria. The median lethal concentrations (LC50s) for sockeye, Chinook, and coho, were 35.2, 23.9, and 6.3 µg Cu/L, respectively. We also used the BLM to predict LC50s for each species. Model-predictions differed from empirical LC50s by factors of 0.7 for sockeye and Chinook salmon, and 1.1 for coho salmon. These differences fell within the acceptable range of ± 2, indicating the model's accuracy. We calculated critical lethal Cu accumulation values for each species to account for differing water chemistry in each bioassay, revealing that coho salmon were most sensitive to Cu, followed by sockeye, and Chinook salmon. Our findings underscore the importance of considering site- and species-specific factors when modeling Cu toxicity. The empirical data presented in this study may enhance Cu risk assessments for Pacific salmon.

Imidacloprid (IM) has emerged as a contaminant of concern in several areas within the United States due to its frequent detection in aquatic ecosystems and its pseudo-persistence, which pose potential risks to nontarget species. We evaluated the sublethal toxicity of IM to fathead minnow larvae following chronic exposure beginning just after fertilization. Our in silico analysis and in vivo bioassays suggest that IM has a low binding affinity for the vertebrate nicotinate acetylcholine receptor (nAChR), as expected. However, chronic exposure to ≥0.16 µg IM/L reduced survival by 10%, and exposure to ≥18 µg IM/L reduced survival by approximately 20%–40%. Surviving fish exposed to ≥0.16 µg IM/L showed reduced growth, altered embryonic motor activity, and premature hatching. Furthermore, a significant proportion of fish exposed to ≥0.16 µg IM/L were slower to respond to vibrational stimuli and slower to swim away, indicating that chronic exposure to IM has the potential to impair the ability of larvae to escape predation. The adverse health effects we observed indicate that chronic exposure to environmentally relevant concentrations of IM may elicit sublethal responses that culminate in a significant increase in mortality during early life stages, ultimately translating to reduced recruitment in wild fish populations. Environ Toxicol Chem 2023;00:1–9. © 2023 SETAC

The present study used diffusive gradients in thin film (DGT) samplers deployed in situ at a wastewater-impacted site (Clarkboro Ferry) for 20 days to develop a predictive model between time-weighted mean concentrations of seven selected antipsychotic compounds in water and those in resident benthic invertebrates, specifically crayfish (Faxonius virilis). The model was further combined with a model of desorption of antipsychotic compounds to predict kinetics at the sediment–water interface. Antipsychotic compounds were mostly detected in adult crayfish and internal concentrations were similar among targeted compounds, except for lesser concentrations of duloxetine. The model, based on the mass balance of organic chemicals, to predict uptake by organisms exhibited good agreement with measured values (R2 = 0.53−0.88), except for venlafaxine (R2 = 0.35). At the sediment–water interface, positive fluxes were observed for antipsychotic compounds and the results from DGT-induced fluxes in sediments (DIFS) coupled with equilibrium hydroxyl-β-cyclodextrin extraction further indicated partial resupply of antipsychotic compounds from sediments to the aqueous phase, despite the labile pool being relatively limited. The results of the present study affirm that DGT techniques can be used as a predictive tool for contamination in benthic invertebrates and can simulate the ability of contaminant resupply from sediments. Environ Toxicol Chem 2023;42:1696–1708. © 2023 SETAC.

Phosphorus (P) is critical for algal growth and resistance to environmental stress. However, little is known about the effects of P supply on the lead (Pb) toxicity and accumulation in microalgae. We set up two P concentrations, 315 (PL) and 3150 μg L−1 (PH), in algal culture, and the responses of Chlamydomonas reinhardtii to various Pb treatments (0, 200, 500, 1000, 2000, and 5000 μg L−1) were investigated. Compared with the PL condition, PH promoted cell growth but reduced cellular respiration by approximately 50%. Moreover, PH alleviated damage to the photosynthetic system in algal cells after Pb stress. After exposure to 200–2000 μg L−1 Pb, higher Pb2+ concentrations and Pb removal were observed in the PL medium. However, under exposure to 5000 μg L−1 Pb, less Pb2+ was present but more Pb was removed by the algal cells in the PH medium. More P supply enhanced the secretion of extracellular fluorescent substances by C. reinhardtii. Transcriptomic analysis showed that genes associated with synthesis of phospholipids, tyrosine-like proteins, ferredoxin, and RuBisCO were up-regulated after Pb exposure. Together the findings of our study demonstrated the critical roles of P in Pb accumulation and resistance in C. reinhardtii. Environ Toxicol Chem 2023;00:1–11. © 2023 SETAC