Attachment Efficiency of Nanomaterials to Algae as an Important Criterion for Ecotoxicity and Grouping

Abstract

Engineered nanomaterials (ENMs) based on CeO2 and TiO2 differ in their effects on the unicellular green alga Raphidocelis subcapitata but these effects do not reflect the physicochemical parameters that characterize such materials in water and other test media. To determine whether interactions with algae can predict the ecotoxicity of ENMs, we studied the attachment of model compounds (three subtypes of CeO2 and five subtypes of TiO2) to algal cells by light microscopy and electron microscopy. We correlated our observations with EC50 values determined in growth inhibition assays carried out according to the Organisation for Economic Co-operation and Development (OECD) test guideline 201. Light microscopy revealed distinct patterns of ENM attachment to algal cells according to the type of compound, with stronger interactions leading to greater toxicity. This was confirmed by electron microscopy, which allowed the quantitative assessment of particle attachment. Our results indicate that algal extracellular polymeric substances play an important role in the attachment of ENMs, influencing the formation of agglomerates. The attachment parameters in short-term tests predicted the toxicity of CeO2 and TiO2 ENMs and can be considered as a valuable tool for the identification of sets of similar nanoforms as requested by the European Chemicals Agency in the context of grouping and read-across.

Prioritising nano- and microparticles: identification of physicochemical properties relevant for toxicity to Raphidocelis subcapitata and Daphnia magna

“…For the green algae R. subcapitata, no relationship between physicochemical properties such as particle size, surface area, agglomeration size, reactivity, crystalline structure and growth inhibition according to OECD Test Guideline (TG) 201 was obvious. However, their attachment to algae was found to be related to their ecotoxicity [27]. The toxicity of particles with high attachment efficiency exceeded the toxicity of particles with a lower tendency for attachment.…”

Too advanced for assessment? Advanced materials, nanomedicine and the environment

“…To address the illustrated gaps, some possible ways forward are emerging. Research is starting to address knowledge gaps, e.g., novel endpoints in ecotoxicological testing like immunotoxicology are considered [ 42 ], as well as effects based on physical interactions [ 43 ]. The fate of water-soluble polymers in the environment is starting to be addressed by monitoring, e.g., for PEG [ 44 ].…”

Long-Term Toxicity of ZnO Nanoparticles on Scenedesmus rubescens Cultivated in Semi-Batch Mode

“…The exposure time of microorganisms on NPs is a factor that has not been extensively investigated, despite the fact that NPs in nature will be present for a long period and the organisms will be exposed for a long time. Especially, metal NPs need further investigation in relation to other NPs as their toxic effect is due to their dissolution in the environment and exposure of organisms to heavy metals [3,14].…”

“…The lipid content of microalgae is an important factor for the choice of suitable algal species for biofuel production. For this reason, many studies have been focused on NPs' effects on microalgae [8,14,[19][20][21] with the latest studies focusing not on the toxic effects of NPs but in the increased lipid accumulation of microalgae due to NPs' presence [10,22]. The effect of NP toxicity on microalgae in short term and batch mode experiments has been investigated by many researchers.…”