Strategies for robust and accurate experimental approaches to quantify nanomaterial bioaccumulation across a broad range of organisms

Abstract

One of the key components for environmental risk assessment of engineered nanomaterials (ENMs) is data on bioaccumulation potential. Accurately measuring bioaccumulation can be critical for regulatory decision making regarding material hazard and risk, and for understanding the mechanism of toxicity. This perspective provides expert guidance for performing ENM bioaccumulation measurements across a broad range of test organisms and species. To accomplish this aim, we critically evaluated ENM bioaccumulation within three categories of organisms: single-celled species, multicellular species excluding plants, and multicellular plants. For aqueous exposures of suspended single-celled and small multicellular species, it is critical to perform a robust procedure to separate suspended ENMs and small organisms to avoid overestimating bioaccumulation. For many multicellular organisms, it is essential to differentiate between the ENMs adsorbed to external surfaces or in the digestive tract and the amount absorbed across epithelial tissues. For multicellular plants, key considerations include how exposure route and the role of the rhizosphere may affect the quantitative measurement of uptake, and that the efficiency of washing procedures to remove loosely attached ENMs to the roots is not well understood. Within each organism category, case studies are provided to illustrate key methodological considerations for conducting robust bioaccumulation experiments for different species within each major group. The full scope of ENM bioaccumulation measurements and interpretations are discussed including conducting the organism exposure, separating organisms from the ENMs in the test media after exposure, analytical methods to quantify ENMs in the tissues or cells, and modeling the ENM bioaccumulation results. One key finding to improve bioaccumulation measurements was the critical need for further analytical method development to identify and quantify ENMs in complex matrices. Overall, the discussion, suggestions, and case studies described herein will help improve the robustness of ENM bioaccumulation studies.

Toward an Improved Understanding of the Ingestion and Trophic Transfer of Microplastic Particles: Critical Review and Implications for Future Research

“…Concerns related to the potential for bioaccumulation are not necessarily limited to chemical contaminants but have recently been raised with respect to poorly soluble particulates such as engineered nanomaterials (ENMs; Hou et al 2013; Martirosyan and Schneider 2014; Lead et al 2018; Petersen et al 2019) and microplastic particles (Watts et al 2014; Van Cauwenberghe et al 2015; Karlsson et al 2017; Barboza et al 2018; Carbery et al 2018; Dawson et al 2018). A fundamental challenge in assessing the bioaccumulation of poorly soluble particulates is that the accumulation process is not driven by thermodynamic energy gradients, but by physical processes (Petersen et al 2019). For soluble chemicals, bioaccumulation can be perceived as a pseudo‐intrinsic property (Mackay et al 2001), and is thus not dependent on parameters such as external concentration.…”

“…The interaction between organisms and particulates such as ENMs and microplastic particles is thus dynamic, not steady state, and the processes for uptake and elimination are driven by various endocytosis‐related mechanisms (Felix et al 2017), not by passive diffusion through tissues or via solute transporters as they are for soluble chemicals (Schultz 1976; DeVito 2000). Consequently, the assessment of poorly soluble particulates with respect to their potential to bioaccumulate may require the development of new test systems, models, and mechanistic understanding (Handy et al 2018; European Centre for Ecotoxicology and Toxicology of Chemicals 2019; Petersen et al 2019; Roch et al 2020).…”

“…Caution has been suggested, however, regarding the potential for translocation of microplastic particles based on observations utilizing fluorescence, because the results may be characteristic of a study artifact (i.e., lipid accumulation of the leached fraction of hydrophobic fluorescent dye), as opposed to actual particle translocation (Schur et al 2019). Consequently, quantifying and characterizing the bioaccumulation potential of microplastic particles within the tissues of organisms would benefit from the adoption of a mass balance approach, aimed at assessing adsorption, distribution, metabolism, and excretion (Gobas and Morrison 2000; Al‐Sid‐Cheikh et al 2018; Diepens and Koelmans 2018; Petersen et al 2019).…”

Comparative biokinetics of pristine and sulfidized Ag nanoparticles in two arthropod species exposed to different field soils

“…their accumulation in or on organisms, depends on their bioavailability, defined as the ability to interact with an organism. 1 The bioavailable fraction of Ag NPs is lower than their total concentration in most natural environments, particularly in soils, 2 where it is affected by a complex interplay of soil properties and interactions with other ligands present in the soil solution. Ag NPs that reach the soil are mostly transformed by the environment and lose their pristine characteristics.…”

Risk Management Framework for Nano-Biomaterials Used in Medical Devices and Advanced Therapy Medicinal Products

“…Therefore, the bioaccumulation/trophic transfer potential is not well understood for nanomaterials and hence also not for NBMs used in medicine. Although substantial research efforts have focused on bioaccumulation [ 84 ] there are currently no good models available, partly because nanomaterials are difficult to detect in complex media, partly because nanomaterials are not assumed to follow equilibrium paradigms, which hampers the estimation of bioaccumulation factors.…”