The widespread usage of neonicotinoid insecticides has sparked concern over their effects on non-target organisms. While research has largely focused on terrestrial systems, the low soil binding and ...high water solubility of neonicotinoids, paired with their extensive use on the landscape, puts aquatic environments at high risk for contamination via runoff events. We assessed the potential threat of these compounds to wetland communities using a combination of field surveys and experimental exposures including concentrations that are representative of what invertebrates experience in the field. In laboratory toxicity experiments, LC50 values ranged from 0.002 ppm to 1.2 ppm for aquatic invertebrates exposed to clothianidin. However, freshwater snails and amphibian larvae showed high tolerance to the chemical with no mortality observed at the highest dissolvable concentration of the insecticide. We also observed behavioral effects of clothianidin. Water bugs, Belostoma flumineum, displayed a dose-dependent reduction in feeding rate following exposure to clothianidin. Similarly, crayfish, Orconectes propinquus, exhibited reduced responsiveness to stimulus with increasing clothianidin concentration. Using a semi-natural mesocosm experiment, we manipulated clothianidin concentration (0.6, 5, and 352 ppb) and the presence of predatory invertebrates to explore community-level effects. We observed high invertebrate predator mortality with increases in clothianidin concentration. With increased predator mortality, prey survival increased by 50% at the highest clothianidin concentration. Thus, clothianidin contamination can result in a top-down trophic cascade in a community dominated by invertebrate predators. In our Indiana field study, we detected clothianidin (max = 176 ppb), imidacloprid (max = 141 ppb), and acetamiprid (max = 7 ppb) in soil samples. In water samples, we detected clothianidin (max = 0.67 ppb), imidacloprid (max = 0.18 ppb), and thiamethoxam (max = 2,568 ppb). Neonicotinoids were detected in >56% of soil samples and >90% of the water samples, which reflects a growing understanding that neonicotinoids are ubiquitous environmental contaminants. Collectively, our results underscore the need for additional research into the effects of neonicotinoids on aquatic communities and ecosystems.
Nanoparticle production is on the rise due to its many uses in the burgeoning nanotechnology industry. Although nanoparticles have growing applications, there is great concern over their ...environmental impact due to their inevitable release into the environment. With uncertainty of environmental concentration and risk to aquatic organisms, the microcrustacean Daphnia spp. has emerged as an important freshwater model organism for risk assessment of nanoparticles because of its biological properties, including parthenogenetic reproduction; small size and short generation time; wide range of endpoints for ecotoxicological studies; known genome, useful for providing mechanistic information; and high sensitivity to environmental contaminants and other stressors. In this review, we (1) highlight the advantages of using Daphnia as an experimental model organism for nanotoxicity studies, (2) summarize the impacts of nanoparticle physicochemical characteristics on toxicity in relation to Daphnia, and (3) summarize the effects of nanoparticles (including nanoplastics) on Daphnia as well as mechanisms of toxicity, and (4) highlight research uncertainties and recommend future directions necessary to develop a deeper understanding of the fate and toxicity of nanoparticles and for the development of safer and more sustainable nanotechnology.
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•Daphnia are an important model organism for risk assessment of nanoparticles.•Nanoparticle properties and relationship with toxicological effects are summarized.•Nanoparticle mechanisms of toxicity are summarized.•Research directions and uncertainties surrounding fate and toxicity are summarized.
Exposure to perfluorinated and polyfluoroalkyl substances (PFCs/PFASs), endocrine disrupting halogenated pollutants, has been linked to various diseases including thyroid toxicity in human ...populations across the globe. PFASs can compete with thyroxine (T4) for binding to the human thyroid hormone transport protein transthyretin (TTR) which may lead to reduce thyroid hormone levels leading to endocrine disrupting adverse effects. Environmental fate and endocrine-disrupting activity of PFASs has initiated several research projects, but the amount of experimental data available for these pollutants is limited. In this study, experimental data for T4-TTR competing potency of 24 PFASs obtained in a radioligand-binding assay were modeled using classification- and regression-based quantitative structure-activity relationship (QSAR) tools with simple molecular descriptors obtained from chemical structure of these compounds in order to identify the responsible structural features and fragments of the studied PFASs for endocrine disruption activity. Additionally, docking studies were performed employing the crystal structure complex of TTR with bound 2′, 6′-difluorobiphenyl-4-carboxylic acid (PDB: 2F7I) in order to constitute the receptor model for human TTR. The results corroborate evidence for these binding interactions and indicate multiple high-affinity modes of binding. The developed in silico models therefore advance our understanding of important structural attributes of these chemicals and may provide important information for the design of future synthesis of PFASs as well as may serve as an efficient query tool for virtual screening of large PFAS databases to check their endocrine toxicity profile.
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•PFASs can compete with T4 for binding to TTR in resulting endocrine disruption.•The T4-TTR competing potency of 24 PFCs was modeled employing QSAR.•The docking study corroborates evidence of binding interactions with TTR.•Important structural attributes of PFASs for endocrine disruption were identified.•Developed models may serve as an efficient tool for screening of large databases.
Nanoplastics are a growing environmental and public health concern. However, the toxic mechanisms of nanoplastics are poorly understood. Here, we evaluated the effects of spherical polystyrene ...nanoplastics on reproduction of Daphnia pulex and analyzed the proteome of whole animals followed by molecular and biochemical analyses for the development of an adverse outcome pathway (AOP) for these contaminants of emerging concern. Animals were exposed to polystyrene nanoplastics (0, 0.1, 0.5, 1 and 2 mg/L) via water for 21 days. Nanoplastics negatively impacted cumulative offspring production. A total of 327 differentially expressed proteins (DEPs) were identified in response to nanoplastics which were further validated from gene expression and enzyme activity data. Based on these results, we propose an AOP for nanoplastics, including radical oxygen species production and oxidative stress as the molecular initiating event (MIE); followed by changes in specific signaling pathways (Jak-STAT, mTOR and FoxO) and in the metabolism of glutathione, protein, lipids, and molting proteins; with an end result of growth inhibition and decrease reproductive output. This study serves as a foundation for the development of a mechanistic understanding of nanoplastic toxicity in crustaceans and perhaps other aquatic organisms.
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•Spherical polystyrene nanoplastics (0.5–2 mg/L) inhibit Daphnia fecundity and population growth.•Differentially expressed proteins (327) were detected in Daphnia exposed to nanoplastics for 21 d.•ROS production and oxidative stress are major molecular initiating events elicited by nanoplastics.•Pathways targeted by nanoplastics include metabolism of glutathione, proteins, lipids, and molting proteins.
Poly and perfluoroalkyl substances (PFAS) are a large group of emerging organic pollutants that can persist in the environment and bioaccumulate in biota. They are found in complex mixtures, and ...although the exact number of PFAS is unknown, it has been estimated to be in the thousands. The objective of this study was two-fold. First, we examined the cytotoxicity of PFAS singly and in binary mixtures using an amphibian fibroblast cell line. Second, we used this experimental data to develop quantitative structure-activity relationship (QSAR) models for single and binary mixtures. We tested the cytotoxicity of four common PFAS: perfluorooctane sulfonate (PFOS); perfluorooctanoic acid (PFOA); perfluorohexane sulfonate (PFHxS); and perfluorohexanoic acid (PFHxA). PFOS was the most toxic and PFHxA the least cytotoxic. Binary mixtures allowed for the construction of isobolograms to test for additivity, synergism, or antagonism. Using this data, QSAR modeling was used for predicting the toxicity of 24 single and 1380 binary mixtures (theoretically generated). Overall, our experimental and modeling results showed that mixtures were approximately additive, with the exception of PFOS and PFOA, which were found to be weakly synergistic. This data shows that certain mixtures of PFAS may have increased toxicity potential above what the simple sum of PFAS concentrations would suggest. More studies are needed that test the toxicity of PFAS mixtures.
•PFAS binary mixtures were mostly additive.•PFOS + PFAS showed weak synergism.•QSAR modeling can assist testing the effects of PFAS mixtures.
The widespread use of polystyrene (PS) products in a myriad of consumer products has resulted in widespread contamination of PS nanoplastics (PSNPs) in aquatic ecosystems. Fish early life stages are ...exposed to nanoplastics dermally and via gills. Additional routes of exposure include oral via the ingestion of contaminated prey and maternal transfer. However, there is limited amount of work studying the impact of exposure route in the toxicokinetics and toxicodynamics of PSNPs. The objective of this study was to compare the effects of exposure routes (aqueous and microinjection) on the organ distribution and toxicity of PSNPs. We “mimicked” the maternal exposure of PSNPs to zebrafish by injecting a known concentration of fluorescent particles directly into 2-cell stage embryos. Endpoints were collected starting at 96 h post-fertilization until several weeks post-hatch to evaluate depuration. Although both exposure routes led to the accumulation of PSNPs in the yolk sac followed by brain, eyes, gut and swim bladder, the aqueous exposure caused higher PSNP concentrations in the brain and eyes and the injection exposure caused PSNP accumulation mainly in the trunk area. A waterborne exposure also reduced antioxidant gene expression; increased frequency of developmental abnormalities such as bent tails, jaw deformities and pericardial edema; and resulted in lower growth rates and hypoactivity. Overall, a waterborne exposure to PSNPs resulted in higher transfer to the brain and caused greater toxic effects to zebrafish compared to an injection exposure and highlights the key role of exposure routes in the uptake, localization and subsequent distribution of nanoparticles.
Route of exposure affects the distribution of nanoplastics in zebrafish. Display omitted
•Both exposure routes led to the accumulation of PSNPs in the yolk sac.•More PSNPs accumulated in the head of zebrafish under waterborne exposure.•Waterborne exposure caused increased developmental toxicity to zebrafish larva.•Waterborne exposure reduced antioxidant gene expression and hypoactivity.
Offspring survival, cohort performance, and ultimately population dynamics are strongly influenced by maternal characteristics (e.g., fecundity), whereas paternal contribution is often considered ...limited to genetic-driven fitness of males through sexual selection. However, male contribution to reproductive success can be particularly influential in species exhibiting paternal offspring care. Polychlorinated biphenyls (PCBs) are widespread, persistent contaminants that can disrupt maternal reproductive processes and negatively affect offspring. In contrast, how PCBs affect paternal reproductive success is largely unknown, but could ultimately affect population dynamics. We examined the effects of lifelong PCB exposure on the reproductive processes of male fathead minnows (Pimephales promelas), a species exhibiting sole paternal offspring care, by examining endocrine-associated gene expression, testes histology, secondary sexual characteristics, courtship ability, offspring care, and offspring survival. PCBs minimized male secondary sexual characteristics, but did not affect gonadal end points or inhibit ability to court females. Fathers exposed to high concentrations of dioxin-like PCBs had changes in gene expression, reduced offspring care behavior, and higher embryo mortality, possibly due to fathers spending less time within nests and less frequently tending to embryos. Through complex interactions among gene expression, physical characteristics, and behavior, PCBs inhibit paternal reproductive success and have the potential to suppress population size.
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