RESUMO
The adenosine A2A receptor (A2AR) engages several G proteins, notably Go and its cognate Gs protein. This coupling promiscuity is facilitated by a dynamic ensemble, revealed by 19F nuclear magnetic resonance imaging of A2AR and G protein. Two transmembrane helix 6 (TM6) activation states, formerly associated with partial and full agonism, accommodate the differing volumes of Gs and Go. While nucleotide depletion biases TM7 toward a fully active state in A2AR-Gs, A2AR-Go is characterized by a dynamic inactive/intermediate fraction. Molecular dynamics simulations reveal that the NPxxY motif, a highly conserved switch, establishes a unique configuration in the A2AR-Go complex, failing to stabilize the helix-8 interface with Gs, and adoption of the active state. The resulting TM7 dynamics hamper G protein coupling, suggesting kinetic gating may be responsible for reduced efficacy in the noncognate G protein complex. Thus, dual TM6 activation states enable greater diversity of coupling partners while TM7 dynamics dictate coupling efficacy.
RESUMO
Standard toxicological test methods with Hyalella azteca incorporate both lethal and sublethal (growth, reproduction) endpoints, although lethal endpoints are often favored in routine testing. However, sublethal endpoints are important to consider because they are ecologically relevant and are often more sensitive than lethality. It is difficult to achieve robust data for reproduction in H. azteca because high biological variability is associated with reproductive yield, likely due to complex interactions in mate selection, which can add to the variability in brood sizes that females produce. In addition, effects on reproduction often co-occur with effects on growth, making it difficult to differentiate effects on growth from those on reproduction in standard tests initiated with juveniles. The present study characterized the reproductive capacity of H. azteca by investigating the role of sex ratios in reproductive yield. Experiments were initiated in the absence of toxicants with sexually mature (6-8-week-old) individuals that were placed in different female-to-male ratios (1:1, 2:3, 3:2, and 7:3). Reproduction was monitored during weekly static renewals for 7 weeks. The results indicated that a higher female:male ratio (seven females to three males) improved reproductive success and lowered biological variability in reproduction. In addition, the body lengths and weights of newly mature amphipods were used to create a size distribution to aid in the identification of small female amphipods. Based on the results of our study, a novel reproductive toxicity test method is proposed that begins with sexually mature amphipods in a ratio of seven females to three males to minimize reproductive variability in amphipods and to enable a more effective assessment of contaminants using reproduction as a highly sensitive endpoint. However, evaluation of this novel method with toxicants is needed to demonstrate that results are comparable to standard methods. Environ Toxicol Chem 2024;43:712-722. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Assuntos
Anfípodes , Formigas , Poluentes Químicos da Água , Humanos , Animais , Feminino , Masculino , Razão de Masculinidade , Testes de Toxicidade/métodos , Reprodução , Poluentes Químicos da Água/toxicidadeRESUMO
The antioxidant N-(1,3-Dimethylbutyl)-N'-phenyl-p- phenylenediamine (6PPD) is used to protect the rubber in tires from oxidation, which extends the life of the tire. When oxidized, 6PPD is transformed into 6PPD-quinone (6PPDQ). 6PPDQ, along with other tire ingredients, can enter aquatic ecosystems through the transport of tire wear particles in runoff during a precipitation event. The mass mortality of coho salmon following precipitation events in urban areas lead to the discovery that 6PPDQ is the likely cause due to coho salmon's relatively high sensitivity to 6PPDQ. The assessment of 6PPDQ toxicity to other aquatic species has expanded, but it has focused on fish. This study investigated the toxicity of 6PPDQ to four freshwater invertebrate species, larval burrowing mayfly (Hexagenia spp.), juvenile cladoceran (Daphnia magna), file ramshorn snail embryo (Planorbella pilsbryi), and adult washboard mussel (Megalonaias nervosa). For all four species, the highest concentration of 6PPDQ tested did not result in significant mortality. This translated into the determination of the highest concentration that did not cause significant mortality (NOEC) for Hexagenia spp., D. magna, P. pilsbryi, and M. nervosa of 232.0, 42.0, 11.7, and 17.9 µg/L, respectively. The data from this study indicate that freshwater invertebrates are not as sensitive to 6PPDQ as some salmonid species (e.g., coho salmon Oncorhynchus kisutch). This study also analyzed 6PPDQ in road runoff from around the city of Guelph in Ontario, Canada. 6PPQ was detected in all samples but the concentration was two orders of magnitude lower than the NOECs for the four tested species of freshwater invertebrate.
Assuntos
Benzoquinonas , Água Doce , Invertebrados , Fenilenodiaminas , Animais , Ecossistema , Ephemeroptera/efeitos dos fármacos , Água Doce/química , Invertebrados/efeitos dos fármacos , Oncorhynchus kisutch , Ontário , Fenilenodiaminas/análise , Fenilenodiaminas/toxicidade , Benzoquinonas/análise , Benzoquinonas/toxicidadeRESUMO
19F NMR provides a way of monitoring conformational dynamics of G-protein coupled receptors (GPCRs) from the perspective of an ensemble. While X-ray crystallography provides exquisitely resolved high-resolution structures of specific states, it generally does not recapitulate the true ensemble of functional states. Fluorine (19F) NMR provides a highly sensitive spectroscopic window into the conformational ensemble, generally permitting the direct quantification of resolvable states. Moreover, straightforward T1- and T2-based relaxation experiments allow for the study of fluctuations within a given state and exchange between states, on timescales spanning nanoseconds to seconds. Conveniently, most biological systems are free of fluorine. Thus, via fluorinated amino acid analogues or thiol-reactive fluorinated tags, F or CF3 reporters can be site specifically incorporated into proteins of interest. In this review, fluorine labeling protocols and 19F NMR experiments will be presented, from the perspective of small molecule NMR (i.e. drug or small molecule interactions with receptors) or macromolecular NMR (i.e. conformational dynamics of receptors and receptor-G-protein complexes).
Assuntos
Flúor , Receptores Acoplados a Proteínas G , Humanos , Cinética , Membrana Celular , AminoácidosRESUMO
Early life stages are commonly thought to be highly sensitive to environmental contaminants and may offer insight into the future health of a population. Despite the importance of studying early life stages, very few standard protocols for benthic invertebrates commonly used in ecotoxicological assessments measure developmental endpoints. The goal of the present study was to develop and optimize a robust standard protocol for studying embryonic endpoints in freshwater gastropods. The developed method was then used to characterize the sensitivity of four embryonic endpoints (viability, hatching, deformities, and biomass production), in conjunction with juvenile and adult mortality, for the snail Planorbella pilsbryi exposed to three metals (copper [Cu], cadmium [Cd], and nickel [Ni]). Biomass production was typically the most sensitive endpoint but was relatively variable, while embryo hatching was slightly less sensitive but highly consistent for all three metals. However, no single embryonic endpoint was consistently the most sensitive, which demonstrates the importance of assessing a broad range of endpoints and life stages in ecotoxicological risk assessment. Interestingly, the embryonic life stage of P. pilsbryi was considerably less sensitive to Cu exposure compared with juvenile and adult mortality. However, for Cd exposure, embryonic endpoints were the most sensitive, and for Ni exposure, embryonic endpoints were similar in sensitivity to juvenile and adult mortality. The present study has valuable applications in conducting developmental toxicity research with organisms lacking standardized testing protocol as well as future applications in multigenerational and in silico toxicity research. Environ Toxicol Chem 2023;42:1791-1805. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Assuntos
Gastrópodes , Metais , Testes de Toxicidade , Poluentes Químicos da Água , Embrião não Mamífero , Água Doce , Metais/toxicidade , Animais , Cádmio , Cobre/toxicidade , Níquel/toxicidadeRESUMO
Heterotrimeric G proteins serve as membrane-associated signaling hubs, in concert with their cognate G-protein-coupled receptors. Fluorine nuclear magnetic resonance spectroscopy was employed to monitor the conformational equilibria of the human stimulatory G-protein α subunit (Gsα) alone, in the intact Gsαß1γ2 heterotrimer or in complex with membrane-embedded human adenosine A2A receptor (A2AR). The results reveal a concerted equilibrium that is strongly affected by nucleotide and interactions with the ßγ subunit, the lipid bilayer and A2AR. The α1 helix of Gsα exhibits significant intermediate timescale dynamics. The α4ß6 loop and α5 helix undergo membrane/receptor interactions and order-disorder transitions respectively, associated with G-protein activation. The αN helix adopts a key functional state that serves as an allosteric conduit between the ßγ subunit and receptor, while a significant fraction of the ensemble remains tethered to the membrane and receptor upon activation.
Assuntos
Subunidades alfa Gs de Proteínas de Ligação ao GTP , Proteínas Heterotriméricas de Ligação ao GTP , Humanos , Modelos Moleculares , Subunidades alfa Gs de Proteínas de Ligação ao GTP/metabolismo , Conformação Proteica , Proteínas Heterotriméricas de Ligação ao GTP/metabolismo , Subunidades alfa de Proteínas de Ligação ao GTP/química , Subunidades alfa de Proteínas de Ligação ao GTP/metabolismo , Ligação ProteicaRESUMO
The intensity and frequency of forest fires is increasing across the globe due to climate change. Additives are often added to make water more effective at extinguishing fire and preventing re-ignition. This study investigated the toxicity of nine different firefighting water additives to four species of soil invertebrates (Folsomia candida, Porcellio laevis, Porcellio scaber, and Trichorhina tomentosa) and two plant species (Agropyron cristatum and Raphanus sativus). Considerable variation in toxicity was observed among the firefighting products. The toxicity of individual products also varied considerably amongst the tested species. A hazard assessment was conducted by comparing the concentration of firefighting water additive that caused a 50% effect (LC50 or EC50) or a concentration that caused no effect (NOEC) to the concentration recommended by the manufacturer. At a rate of application representative of a forest firefighting scenario, most firefighting water additives tested in this study posed a hazard to F. candida and the three isopod species. The majority of products did not pose a risk to the two plant species included in this study. Consideration of the toxicity of firefighting water additives to terrestrial biota should be considered along with the efficacy of the product to fight fires when deciding which products to use.
Assuntos
Artrópodes , Incêndios , Isópodes , Poluentes do Solo , Animais , Solo , Invertebrados , Poluentes do Solo/toxicidadeRESUMO
In Helicobacter pylori, the nickel-responsive NikR transcription factor plays a key role in regulating intracellular nickel concentrations, which is an essential process for survival of this pathogen in the acidic human stomach. Nickel binding to H. pylori NikR (HpNikR) allosterically activates DNA binding to target promoters encoding genes involved in nickel homeostasis and acid adaptation, to either activate or repress their transcription. We previously showed that HpNikR adopts an equilibrium between an open conformation and DNA-binding competent cis and trans states. Nickel binding slows down conformational exchange between these states and shifts the equilibrium toward the binding-competent states. The protein then becomes stabilized in a cis conformation upon binding the ureA promoter. Here, we investigate how nickel binding creates this response and how it is transmitted to the DNA-binding domains. Through mutagenesis, DNA-binding studies, and computational methods, the allosteric response to nickel was found to be propagated from the nickel-binding sites to the DNA-binding domains via the ß-sheets of the metal-binding domain and a network of residues at the inter-domain interface. Our computational results suggest that nickel binding increases protein rigidity to slow down the conformational exchange. A thymine base in the ureA promoter sequence, known to be critical for high affinity DNA binding by HpNikR, was also found to be important for the allosteric response, while a modified version of this promoter further highlighted the importance of the DNA sequence in modulating the response. Collectively, our results provide insights into regulation of a key protein for H. pylori survival.
Assuntos
Proteínas de Bactérias , Helicobacter pylori , Níquel , Proteínas Repressoras , Humanos , Proteínas de Bactérias/metabolismo , Helicobacter pylori/metabolismo , Níquel/metabolismo , Proteínas Repressoras/metabolismo , Fatores de Transcrição/metabolismoRESUMO
The frequency and severity of forest fires is increasing due to climate change. Consequently, there will be an increased use of forest firefighting additives, which increase the ability of water to extinguish fires and prevent reignition. Increased use will potentially result in increased exposure to aquatic ecosystems within forests. This study examined the toxicity of nine firefighting water additives that are currently on the market to three species of freshwater invertebrates that occupy different niches within freshwater ecosystems. The toxicity of the water additives varied up to three orders of magnitude. Pelagic and epibenthic invertebrates are affected at lower rates of application than endobenthic invertebrates. A field relevant application rate of three of the nine water additives tested represent a hazard to freshwater ecosystems under varies exposure scenarios represented by the depth of a theoretical water body (15-200 cm). This study highlights the importance of application buffers around water bodies and the selection of water additives that pose the lowest hazard to freshwater ecosystem, assuming that the efficacy of the additives in extinguishing fires is similar.
Assuntos
Ecossistema , Água , Animais , Invertebrados , Água Doce , BiotaRESUMO
One-third of current pharmaceuticals target G protein-coupled receptors (GPCRs), the largest receptor superfamily in humans and mediators of diverse physiological processes. This review summarizes the recent progress in GPCR structural dynamics, focusing on class A receptors and insights derived from nuclear magnetic resonance (NMR) and other spectroscopic techniques. We describe the structural aspects of GPCR activation and the various pharmacological models that capture aspects of receptor signaling behavior. Spectroscopic studies revealed that receptors and their signaling complexes are dynamic allosteric systems that sample multiple functional states under basal conditions. The distribution of states within the conformational ensemble and the kinetics of transitions between states are regulated through the binding of ligands, allosteric modulators, and the membrane environment. This ensemble view of GPCRs provides a mechanistic framework for understanding many of the pharmacological phenomena associated with receptor signaling, such as basal activity, efficacy, and functional bias.
Assuntos
Receptores Acoplados a Proteínas G , Transdução de Sinais , Humanos , Ligantes , Espectroscopia de Ressonância Magnética , Conformação Proteica , Receptores Acoplados a Proteínas G/metabolismoRESUMO
Cholesterol is a major component of the cell membrane and commonly regulates membrane protein function. Here, we investigate how cholesterol modulates the conformational equilibria and signaling of the adenosine A2A receptor (A2AR) in reconstituted phospholipid nanodiscs. This model system conveniently excludes possible effects arising from cholesterol-induced phase separation or receptor oligomerization and focuses on the question of allostery. GTP hydrolysis assays show that cholesterol weakly enhances the basal signaling of A2AR while decreasing the agonist EC50. Fluorine nuclear magnetic resonance (19F NMR) spectroscopy shows that this enhancement arises from an increase in the receptor's active state population and a G-protein-bound precoupled state. 19F NMR of fluorinated cholesterol analogs reveals transient interactions with A2AR, indicating a lack of high-affinity binding or direct allosteric modulation. The combined results suggest that the observed allosteric effects are largely indirect and originate from cholesterol-mediated changes in membrane properties, as shown by membrane fluidity measurements and high-pressure NMR.
Assuntos
Regulação Alostérica/efeitos dos fármacos , Colesterol/metabolismo , Receptor A2A de Adenosina/química , Animais , Escherichia coli , Espectroscopia de Ressonância Magnética , Saccharomycetales , Células Sf9 , SpodopteraRESUMO
Thiamethoxam is a neonicotinoid insecticide widely applied in the Canadian Prairies. It has been detected in surface waters of agro-ecosystems, including wetlands, but the potential effects on non-target invertebrate communities in these wetlands have not been well characterized. In an effort to understand better the fate of thiamethoxam in wetlands and the response of invertebrates (zooplankton and emergent insects), model systems were used to mimic wetland flooding into planted fields. Outdoor mesocosms were treated with a single application of thiamethoxam-treated canola seeds at three treatment levels based on a recommended seeding rate (i.e., 6 kg/ha; 1×, 10×, and 100× seeding rate) and monitored over ten weeks. The mean half-life of thiamethoxam in the water column was 6.2 d. There was no ecologically meaningful impact on zooplankton abundances or community structure among treatments. Statistically significant differences were observed in aquatic insect abundance between control mesocosms and the two greatest thiamethoxam treatments (10× and 100× seeding rate). The observed results indicate exposure to thiamethoxam at environmentally relevant concentrations likely does not represent a significant ecological risk to abundance and community structure of wetland zooplankton and emergent insects.
Assuntos
Inseticidas , Tiametoxam , Poluentes Químicos da Água , Animais , Canadá , Ecossistema , Inseticidas/análise , Inseticidas/toxicidade , Invertebrados , Neonicotinoides/toxicidade , Nitrocompostos/toxicidade , Dinâmica Populacional , Tiametoxam/análise , Tiametoxam/toxicidade , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/toxicidadeRESUMO
Membrane proteins work within asymmetric bilayers of lipid molecules that are critical for their biological structures, dynamics and interactions. These properties are lost when detergents dislodge lipids, ligands and subunits, but are maintained in native nanodiscs formed using styrene maleic acid (SMA) and diisobutylene maleic acid (DIBMA) copolymers. These amphipathic polymers allow extraction of multicomponent complexes of post-translationally modified membrane-bound proteins directly from organ homogenates or membranes from diverse types of cells and organelles. Here, we review the structures and mechanisms of transmembrane targets and their interactions with lipids including phosphoinositides (PIs), as resolved using nanodisc systems and methods including cryo-electron microscopy (cryo-EM) and X-ray diffraction (XRD). We focus on therapeutic targets including several G protein-coupled receptors (GPCRs), as well as ion channels and transporters that are driving the development of next-generation native nanodiscs. The design of new synthetic polymers and complementary biophysical tools bodes well for the future of drug discovery and structural biology of native membrane:protein assemblies (memteins).
RESUMO
G protein-coupled receptors (GPCRs) are the largest class of transmembrane proteins, making them an important target for therapeutics. Activation of these receptors is modulated by orthosteric ligands, which stabilize one or several states within a complex conformational ensemble. The intra- and inter-state dynamics, however, is not well documented. Here, we used single-molecule fluorescence to measure ligand-modulated conformational dynamics of the adenosine A2A receptor (A2AR) on nanosecond to millisecond timescales. Experiments were performed on detergent-purified A2R in either the ligand-free (apo) state, or when bound to an inverse, partial or full agonist ligand. Single-molecule Förster resonance energy transfer (smFRET) was performed on detergent-solubilized A2AR to resolve active and inactive states via the separation between transmembrane (TM) helices 4 and 6. The ligand-dependent changes of the smFRET distributions are consistent with conformational selection and with inter-state exchange lifetimes ≥ 3 ms. Local conformational dynamics around residue 2296.31 on TM6 was measured using fluorescence correlation spectroscopy (FCS), which captures dynamic quenching due to photoinduced electron transfer (PET) between a covalently-attached dye and proximal aromatic residues. Global analysis of PET-FCS data revealed fast (150-350 ns), intermediate (50-60 µs) and slow (200-300 µs) conformational dynamics in A2AR, with lifetimes and amplitudes modulated by ligands and a G-protein mimetic (mini-Gs). Most notably, the agonist binding and the coupling to mini-Gs accelerates and increases the relative contribution of the sub-microsecond phase. Molecular dynamics simulations identified three tyrosine residues (Y112, Y2887.53, and Y2907.55) as being responsible for the dynamic quenching observed by PET-FCS and revealed associated helical motions around residue 2296.31 on TM6. This study provides a quantitative description of conformational dynamics in A2AR and supports the idea that ligands bias not only GPCR conformations but also the dynamics within and between distinct conformational states of the receptor.
Assuntos
Ligantes , Conformação Molecular , Simulação de Acoplamento Molecular , Simulação de Dinâmica Molecular , Receptor A2A de Adenosina/química , Receptor A2A de Adenosina/metabolismo , Algoritmos , Fluorescência , Humanos , Modelos Teóricos , Imagem Molecular , Mutação , Ligação Proteica , Imagem Individual de Molécula , Relação Estrutura-AtividadeRESUMO
G-protein-coupled receptors (GPCRs) represent a ubiquitous membrane protein family and are important drug targets. Their diverse signaling pathways are driven by complex pharmacology arising from a conformational ensemble rarely captured by structural methods. Here, fluorine nuclear magnetic resonance spectroscopy (19F NMR) is used to delineate key functional states of the adenosine A2A receptor (A2AR) complexed with heterotrimeric G protein (Gαsß1γ2) in a phospholipid membrane milieu. Analysis of A2AR spectra as a function of ligand, G protein, and nucleotide identifies an ensemble represented by inactive states, a G-protein-bound activation intermediate, and distinct nucleotide-free states associated with either partial- or full-agonist-driven activation. The Gßγ subunit is found to be critical in facilitating ligand-dependent allosteric transmission, as shown by 19F NMR, biochemical, and computational studies. The results provide a mechanistic basis for understanding basal signaling, efficacy, precoupling, and allostery in GPCRs.
Assuntos
Proteínas Heterotriméricas de Ligação ao GTP/química , Receptor A2A de Adenosina/química , Regulação Alostérica , Sítios de Ligação , Proteínas Heterotriméricas de Ligação ao GTP/genética , Proteínas Heterotriméricas de Ligação ao GTP/metabolismo , Humanos , Cinética , Ligantes , Bicamadas Lipídicas/química , Bicamadas Lipídicas/metabolismo , Espectroscopia de Ressonância Magnética , Simulação de Dinâmica Molecular , Nanoestruturas/química , Ligação Proteica , Conformação Proteica , Subunidades Proteicas/química , Subunidades Proteicas/genética , Subunidades Proteicas/metabolismo , Receptor A2A de Adenosina/genética , Receptor A2A de Adenosina/metabolismo , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Transdução de SinaisRESUMO
Naphthalene sulfonic acids (NSAs) are used primarily as additives in a wide range of industrial products (e.g., rubber materials, coatings, sealants, fuels, paints). Based on modeled physicochemical properties, NSAs would likely partition into sediments or the tissues of biota in an aquatic system. This study examined the potential for three NSAs, dinonylnaphthalene disulfonic acid (DNDS), barium dinonylnaphthalene sulfonate (BaDNS), and calcium dinonylnaphthalene sulfonate (CaDNS), to accumulate in the tissue of a freshwater mussel (Lampsilis siliquoidea) and oligochaete worm (Tubifex tubifex). The ability of L. siliquoidea to depurate accumulated chemical was also assessed. Mussels were exposed via sand spiked with CaDNS for 25 d, and then transferred to clean water where their ability to depurate the chemical over an additional 28 d was monitored. Worms were exposed to each of the three NSAs via spiked sediment for 28 d. NSA concentrations were measured separately in gill, foot, and remaining soft tissues (viscera) for mussels and in whole body tissue samples of worms. For L. siliquoidea, the largest concentration of CaDNS was measured in the gill tissue; once removed from CaDNS exposure, mussels were able to depurate up to 87% of the CaDNS from their tissues in 28 days. The biota-sediment accumulation factors (28-d BSAFs) for T. tubifex were 2.8-5.2, 0.53-0.76, and 0.83-1.11 for DNDS, BaDNS, and CaDNS, respectively. For mussel gill and viscera, BCFK values were 14.07 and 16.39, respectively. When BAFKs were calculated using the concentration of CaDNS in sand, they were 1.11 and 1.29 for mussel gill and viscera, respectively. These values are much lower than what would be necessary to classify this chemical as bioaccumulative; however, the BSAFs for DNDS in T. tubifex indicated a potential biomagnification concern if this compound were to occur in the aquatic environment.
Assuntos
Bivalves , Oligoquetos , Unionidae , Poluentes Químicos da Água , Animais , Bioacumulação , Água Doce , Sedimentos Geológicos , Poluentes Químicos da Água/análiseRESUMO
Plastics have a variety of applications due to their versatility, relative cost, and strength-to-weight ratio, and resistance to degradation. As a result, plastic waste can be found in all corners of the Earth. A class of plastic contaminants that have received increasing attention in terms of their potential impact on ecosystems is microplastics (≤5 mm). The greatest attention to date has been on their potential effect in marine ecosystems. However, a growing number of studies are examining their potential impact on soil ecosystems. The data reported in the literature on the environmentally-relevant concentrations of microplastics in soils and the concentration of microplastics that causes an adverse effect in soil biota were used to perform a probabilistic risk assessment of microplastics to soil biota. An environmental exposure distribution was constructed from the concentrations of microplastics reported in soil in the literature. Species sensitivity distributions were constructed using concentration of microplastics in soil that had no adverse effect on soil species (NOEC) or the lowest concentrations that had an adverse effect on soil species (LOEC) reported in the literature. The 95th centile of the environmental exposure distribution (8147 microplastic particles per gram of soil) was greater than 22 and 28% of the species sensitivity distribution constructed using NOECs and LOECs, respectively. The assessment concluded that environmentally relevant concentrations of microplastics reported in the literature could pose a considerable risk to soil biota. It is also important to note that due to the continued production of large quantities of plastic and the persistence of microplastics in the environment, environmentally-relevant concentrations of microplastics in soil are likely to only rise.
RESUMO
Naphthalene sulfonic acids (NSAs) are used extensively in industrial applications as dispersants in dyes, rubbers, and pesticides, and as anti-corrosive agents in coatings, gels, and sealants. This study examined the toxicity of three NSA congeners, barium dinonylnaphthalene sulfonate (BaDNS), calcium dinonylnaphthalene sulfonate (CaDNS), and dinonylnaphthalene disulfonic acid (DNDS), to two benthic species, Tubifex tubifex and Hyalella azteca. Two substrates with different levels of organic carbon (sediment [2%] and sand [0%]) were used in toxicity tests. Juvenile production was the most sensitive endpoint for T. tubifex: the 28-d EC50s were <18.2, 22.2, and 64.0 µg/g dw in sand and 281.3, 361.6, and 218.9 µg/g dw in sediment for BaDNS, CaDNS, and DNDS, respectively. The 28-d LC50s for H. azteca were similar among compounds: 115.3, 82.1, and 49.0 µg/g dry weight (dw) in sand, and 627.3, 757.9, and >188.5 µg/g dw in sediment, for BaDNS, CaDNS, and DNDS, respectively. However, when LC50s were estimated based on concentrations of NSAs measured in overlying water (which can be an important route of exposure for H. azteca), BaDNS and CaDNS were 3-4 orders of magnitude more toxic than DNDS. The NSAs examined were >3-fold more toxic when present in substrates with no organic carbon (e.g., sand) for all H. azteca endpoints where LC/EC50s could be calculated and for sublethal endpoints for T. tubifex. The organic carbon content of the sediment appears to have acted as a sink and reduced NSA toxicity by decreasing bioavailability. Environmental sediment samples were collected from 12 river sites across southern Ontario. The maximum concentration of CaDNS observed in sediment collected from this region was 2.8 µg/g dw in sediment with 2% organic carbon; 100-fold lower than the lowest EC10 in the current study.
Assuntos
Anfípodes , Oligoquetos , Poluentes Químicos da Água , Alcanossulfonatos , Animais , Carbono , Sedimentos Geológicos , Ontário , Ácidos Sulfônicos , Poluentes Químicos da Água/toxicidadeRESUMO
Past firefighting water additives were found to contain perfluorinated compounds that could persist in the environment resulting in potential adverse effects to biota. Since this revelation, manufacturers have introduced alternative firefighting water additives that are fluorine free, but few studies have investigated the fate and effects in the environment of these new additives. Firefighting water additives could enter aquatic ecosystems through run-off, leaching or direct application. Therefore, there is a need to investigate the potential effect that firefighting water additives could have on aquatic biota. This study investigated the toxicity of six firefighting water additives: Eco-Gel™, Thermo-Gel™, FireAde™, Fire-Brake™, Novacool Foam™, and F-500™ to aquatic biota. The toxicities of firefighting water additives to Lemna minor (duckweed), Daphnia magna (water flea), Hexagenia spp. larvae (mayfly), Lampsilis fasciola (wavy-rayed lampmussel) and Oncorhynchus mykiss (rainbow trout) were investigated through acute and chronic static and semi-static tests to estimate LC50 values for survival and EC50 values for immobility and/or reproduction endpoints. A large variation in toxicities among the firefighting water additives and among the test species was observed. Based on a worst-case exposure scenario of direct application, several firefighting water additives were found to pose a hazard to aquatic organisms. An exposure rate representative of a direct overhead application by a water bomber during a forest fire was used in the hazard assessment. For example, the hazard quotients determined for the D. magna acute toxicity tests ranged from 0.20 for Eco-Gel to 317 for F-500 in the forest pool (15 cm) scenario. This study presents the first deterministic risk assessment of firefighting water additives in aquatic ecosystems.
Assuntos
Organismos Aquáticos/efeitos dos fármacos , Poluentes Químicos da Água/toxicidade , Animais , Retardadores de Chama/toxicidade , Medição de Risco , Testes de Toxicidade AgudaRESUMO
The temporal dynamics of pesticide concentrations in streams remains poorly characterized in southwestern Ontario, a region of the province where land use is dominated by agriculture. Understanding the magnitude and duration of pulsed exposures to pesticides in these small streams is critical when estimating the risk of pesticides to these aquatic ecosystems. The present study investigated the application of a high-frequency water sampling approach paired with the collection of flow data to characterize the pulsed exposure of pesticides to small streams in southwestern Ontario. Six sites along 2 different streams with different magnitudes of agricultural land use in their upstream catchments were sampled using half-day composite samples from July to October 2018 and from May to September 2019. A total of 1043 samples were collected over the 2 yr, of which 210 were analyzed. Samples for analysis were chosen based on flow, water level, and precipitation data. Liquid and gas chromatography coupled with tandem mass spectrometry was used to measure >500 pesticides in each water sample. A total of 35 different compounds were detected over the 6 sampling sites. For pesticides that were detected in >10% of water samples above the method quantification limit, a deterministic risk assessment using water quality guidelines and a probabilistic risk assessment using species sensitivity distributions were performed. The calculated hazard quotients showed that 2,4-D, atrazine, metolachlor, and metribuzin exceeded a level of concern of 1 at the highest concentrations detected. In all cases, hazard concentrations that would be protective of 95% of species from the species sensitivity distributions were greater than the 95th centile of the environmental exposure distributions, meaning that the risk from the pesticides was low. Environ Toxicol Chem 2020;39:2570-2587. © 2020 SETAC.