The biological effects of engineered nanomaterials on soil organisms: surface coating and age matter

Engineered nanomaterials (ENMs) have been increasingly used in various applications. Often, the ENMs are functionalised with a surface coating to enhance their properties. Decades of research has provided information on mostly pristine and unmodified ENMs, while ecotoxicity of coated ENMs and how their hazard changes with age in soils is still uncertain. The thesis aimed to determine the toxic effects and bioaccumulation potential of CuO ENMs and CdTe quantum dots (QDs) with different chemical coatings (carboxylate, COOH; polyethylene glycol, PEG; ammonium, NH4+) on the earthworm (Eisenia fetida), and compare the effects to their metal salt (CuSO4) or micron-sized counterpart. Then, to determine if any observed toxicity was altered after ageing the soils for up to one year. Incidental plant growth was studied in the exposure soils to maximise the scientific value of the earthworm tests. Toxic effects of CuO ENMs were also assessed in Caenorhabditis elegans exposed in liquid and soil media to understand effects of the media and method of dosing on ENM toxicity. CuO ENMs were equally toxic to earthworms, or less toxic to plants than the dissolved Cu; whereas CdTe QD ENMs were more toxic than the micron-sized CdTe QDs. There was a coating effect in both, CuO and CdTe QD ENM experiments, the -COOH coated ENMs were most toxic in the fresh soil study, while -NH4+ coated ENMs were most toxic in the aged soil study. Despite the similarities in the toxicity ranking, the biological effects exerted were different between CuO and CdTe QD ENMs. In C. elegans exposures, the ENMs were more hazardous than dissolved Cu, but ranking of ENMs depended on the media and method of dosing. The results suggest the coating effect is determined by the reactivity of the coating in a given media, and it also depends on the core of the ENMs. As such, coating and ageing effects should be considered in the risk assessment of ENMs

Practical considerations to optimize aquatic testing of particulate material, with focus on nanomaterials

Aquatic testing of particulate materials (PMs), e.g., nanomaterials (NMs) and microplastics (MPs), poses inherent challenges potentially hindering the application of existing test guidelines (TGs). Those TGs are primarily designed for hazard assessment of the dissolvable form of a material, whereas the guidance document on aquatic and sediment toxicological testing of NM (OECD Guidance Document 317) encourages the inclusion of potential colloidal fractions in the assessment. A prerequisite for the testing of PMs is the preparation of stable dispersions. However, testing difficulties may result from the fact that nano-scale PMs are inherently unstable when dispersed in test media, leading to the need for differentiation of potential chemical vs. physical effects caused by the tested material. Aquatic testing of unstable PMs will likely result in inconsistent and non-uniform uptake and exposure scenarios and thus effects observed in the respective test systems. Maintaining stable exposure conditions is often very challenging given the constantly changing size of the PM and its agglomerates, requiring observed endpoints to be based on measured concentrations and particle size distributions present in the water phase, while neglecting agglomerated and settled particulates. In this paper we describe the current state of PM-testing, demonstrate PM-specific challenges in aquatic testing (e.g., test duration, physical effects, instability, biodegradation, bioaccumulation) with a focus on NMs, considering a set of most relevant TGs, and provide proposed testing considerations to optimize aquatic testing of PMs