Assessing nanomaterial exposures in aquatic ecotoxicological testing: Framework and case studies based on dispersion and dissolution

Abstract

The unique behavior of engineered nanomaterials (ENM) in aqueous media and dynamic changes in particle settling, agglomeration and dissolution rates is a challenge to the consistency, reliability and interpretation of standard aquatic hazard bioassay results. While the toxicological endpoints (e.g., survival, growth, reproduction, etc.) in ecotoxicity bioassays are largely applicable to ENMs, the standard methods as written for dissolved substances are confounded by the dynamic settling, agglomeration and dissolution of particulate ENMs during the bioassay. A testing framework was designed to serve as a starting point to identify approaches for the consistent conduct of aquatic hazard tests that account for the behavior of ENMs in test media and suitable data collection to support representative exposure metrology. The framework was demonstrated by conducting three case studies testing ENMs with functionally distinct characteristics and behaviors. Pretests with a temporal sampling of particle concentration, agglomeration and dissolution were conducted on each ENM in test media. Results indicated that a silver nanoparticle (AgNP) powder was not dispersible, a nano-TiO 2 powder was dispersible but unstable, and a polyvinylpyrrolidinone-coated AgNP was relatively stable in test media. Based on these functional results, Ceriodaphnia dubia bioassays were conducted to compare different exposure summary methods (nominal, arithmetic average, geometric average, time-weighted average) for calculating and expressing toxicity endpoints. Results indicated that while arithmetic means were effective for expressing the toxicity of more stable materials, time-weighted averaged concentrations were appropriate for the unstable nano-TiO 2 .ARTICLE HISTORY

Nanoecotoxicity assessment of graphene oxide and its relationship with humic acid

“…The Organisation for Economic Co-operation and Development guidance describes how variation in substance concentration greater than AE20% should be addressed using modified experimental procedures or monitoring strategies (Petersen et al 2015). However, in cases where the period of dispersion stability and exposure in the water column is short (<12 h relative to bioassay durations) acute toxicity tests (48-h duration) may be considered relevant and conducted (Kennedy et al 2017).…”

“…In general, humic acid-containing dispersions have remained within (or close to) the limit of the 20% reduction of the nominal concentration. The use of modifications to reduce the strength of ionic testing media and pH alterations must consider the environmental relevance and test organism health and is not always possible (Martinez et al 2014;Kennedy et al 2017).…”

Photocatalytic Degradation of Polycyclic Aromatic Hydrocarbons in Water by 3D Printed TiO2 Composites

“…Additional advantages of incorporating the photocatalyst into a 3D printable polymer includes the ability to augment the density to maintain catalysts in the photoactive zone as buoyant structures to overcome limitations of free powders or "slurries" which would otherwise agglomerate and settle. 28 This would allow the TiO 2 to be easily recoverable from complex environmental media which would prevent legacy contamination and subsequent physical 28 or photocatalytic effects 29 of the material on ecological receptors.…”

“…Recently, pioneering studies have demonstrated the fabrication of a variety of 3D printed TiO 2 composites (e.g., polylactic–hydroxyapatite–TiO 2 ; ceramic–polymer–nano-TiO 2 ; polyetheretherketone (PEEK)–TiO 2 ; polycarbonate (PC)–TiO 2 ). − Recent demonstrated uses of AM structures for wastewater treatment included 3D printed polymer–zeolite composite geometries that successfully reduced ammonia concentrations in water and 3D printed polymer–photocatalyst composites having demonstrated proof-of-efficacy for degrading model organic contaminants. , Therefore, there is a strong technical basis for using AM to develop and test potential photocatalytic reactors to provide proof-of-principle performance and optimization that can aid in developing treatment structures that meet the site-specific demands. Additional advantages of incorporating the photocatalyst into a 3D printable polymer includes the ability to augment the density to maintain catalysts in the photoactive zone as buoyant structures to overcome limitations of free powders or “slurries” which would otherwise agglomerate and settle . This would allow the TiO 2 to be easily recoverable from complex environmental media which would prevent legacy contamination and subsequent physical or photocatalytic effects of the material on ecological receptors.…”

Nanosilver toxicity thresholds estimative for aquatic and sediment environmental safety

“…Before performing the toxicity tests, it should be ensured that the AgNPs can be well dispersed in the culture medium. Therefore, it is recommended to characterize the test nanomaterial, including the degree of aggregation/agglomeration or change of particle size distribution (Kennedy et al 2017;Rasmussen et al 2018). This variation ideally may not be more than ± 20% (Petersen et al 2015).…”