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narrative_review·ecotoxicology, environmental health, nanotoxicology, aquatic toxicology, regulatory toxicology·PMC10140508

Daphnia as a model organism to probe biological responses to nanomaterials—from individual to population effects via adverse outcome pathways

Frontiers in Toxicology · 9 authors, 2 centres

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This review examines Daphnia as a model organism for assessing nanomaterial and microplastic toxicity, highlighting its advantages including filter-feeding, transparent body, and parthenogenetic reproduction. The paper synthesizes evidence on nanomaterial transformations in the environment, enzyme biomarkers, multigenerational effects, and emerging technologies like microfluidics and adverse outcome pathways. Key findings indicate that standard OECD tests may underestimate toxicity by not accounting for environmental transformations, multigenerational effects, or particle-specific uptake mechanisms.

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{"Background": "Daphnia are well-established model organisms for freshwater toxicity testing due to their rapid parthenogenetic reproduction, sensitivity to xenobiotics, and non-sentient status aligning with NC3Rs principles. Standardized protocols (OECD 202 acute, OECD 211 chronic) evaluate endpoints like immobilization, lethality, reproduction, and growth. Nanomaterials (NMs, <100 nm) and microplastics (MPs, <5 mm per NOAA) present unique challenges due to their physical nature, surface reactivity, and dynamic transformations in environmental and biological systems. The review addresses how Daphnia can bridge mechanistic understanding from molecular initiating events to population-level effects.", "Methods": "This is a narrative review synthesizing literature on Daphnia nanoecotoxicology, covering nanomaterial transformations (chemical, physical, biological), enzyme biomarkers (digestive and antioxidant), multigenerational studies, genomic approaches, adverse outcome pathways (AOPs), and microfluidic technologies. The authors draw on data from OECD guideline studies, published experimental research, and ongoing EU projects (RiskGONE, NanoSolveIT, CompSafeNano).", "Key Results": "Nanomaterials undergo dissolution, sulfidation, agglomeration, and eco-corona formation in environmental media, altering toxicity. Standard OECD media may overestimate NM toxicity compared to environmentally realistic conditions. Multigenerational studies show increased sensitivity in offspring generations not predicted by single-generation tests. Enzyme biomarkers (SOD, CAT, GST, GPx, trypsin, amylase, esterase) reveal sublethal effects at concentrations below OECD endpoint thresholds. Only 8 of 331 AOPs in the AOP-Wiki (2.4%) are NM-specific as of 2022. Microfluidic devices enable real-time monitoring and automated data collection but remain underutilized for NM studies with Daphnia. The Daphnia genome (D. pulex and D. magna sequenced) shows conserved ancestral gene families shared with humans, including those linked to disease pathways.", "Clinical Implications": "Daphnia-based assays can inform human health risk assessment through conserved biochemical pathways and genomic homology, supporting New Approach Methodologies that reduce mammalian testing. Findings highlight the need to update regulatory frameworks to incorporate particle-specific considerations: environmental transformation, multigenerational effects, and internalized dose quantification. Microfluidic and omics technologies offer pathways to higher-throughput, more environmentally relevant toxicity screening. The review emphasizes that current standardized tests may underestimate ecological risks by not accounting for transgenerational effects or particle surface dynamics."}

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narrative_review

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ecotoxicology

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ORIGINAL PAPER

PMC10140508

Daphnia as a model organism to probe biological responses to nanomaterials—from individual to population effects via adverse outcome pathways

Frontiers in Toxicology

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ABSTRACT

Abstract The importance of the cladoceran Daphnia as a model organism for ecotoxicity testing has been well-established since the 1980s. Daphnia have been increasingly used in standardised testing of chemicals as they are well characterised and show sensitivity to pollutants, making them an essential indicator species for environmental stress. The mapping of the genomes of D. pulex in 2012 and D. magna in 2017 further consolidated their utility for ecotoxicity testing, including demonstrating the responsiveness of the Daphnia genome to environmental stressors. The short lifecycle and parthenogenetic reproduction make Daphnia useful for assessment of developmental toxicity and adaption to stress. The emergence of nanomaterials (NMs) and their safety assessment has introduced some challenges to the use of standard toxicity tests which were developed for soluble chemicals. NMs have enormous reactive surface areas resulting in dynamic interactions with dissolved organic carbon, proteins and other biomolecules in their surroundings leading to a myriad of physical, chemical, biological, and macromolecular transformations of the NMs and thus changes in their bioavailability to, and impacts on, daphnids. However, NM safety assessments are also driving innovations in our approaches to toxicity testing, for both chemicals and other emerging contaminants such as microplastics (MPs). These advances include establishing more realistic environmental exposures via medium composition tuning including pre-conditioning by the organisms to provide relevant biomolecules as background, development of microfluidics approaches to mimic environmental flow conditions typical in streams, utilisation of field daphnids cultured in the lab to assess adaption and impacts of pre-exposure to pollution gradients, and of course development of mechanistic insights to connect the first encounter with NMs or MPs to an adverse outcome, via the key events in an adverse outcome pathway. Insights into these developments are presented below to inspire further advances and utilisation of these important organisms as part of an overall environmental risk assessment of NMs and MPs impacts, including in mixture exposure scenarios. Keywords: ecotoxicity, high throughput, microfluidics, nanosafety assessment, standardised testing, nanomaterials (A)

CITATION EXPORT

Katie Reilly, Laura-Jayne A Ellis, Hossein Hayat Davoudi et al.. Daphnia as a model organism to probe biological responses to nanomaterials—from individual to population effects via adverse outcome pathways. Frontiers in Toxicology. (2023). https://doi.org/10.3389/ftox.2023.1178482

AUTHORS

9 · 2 CENTRES

Katie Reilly, Laura-Jayne A Ellis, Hossein Hayat Davoudi, Suffeiya Supian, Marcella T Maia, Gabriela H Silva, Zhiling Guo, Diego Stéfani T Martinez, Iseult Lynch

1 School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
2 Brazilian Nanotechnology National Laboratory (LNNano), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, Brazil