Abstract

In terrestrial ecotoxicological tests, the availability and ecotoxicity of solid nanomaterials may depend on the application technique. We compared five spiking procedures using solid uncoated TiO2 and Ag nanoparticles in standardized OECD tests with earthworms, plants and soil microflora: dry spiking of soil by applying soil or silica sand as a carrier; dry spiking of food without a carrier; and wet spiking of soil and food with an aqueous nanoparticle dispersion. The effects of the nanomaterials were influenced by the application technique. The differences were independent of the test organism (which represented different habitats and exposure pathways) and the specificity of the effect (stimulation or inhibition). Wet spiking resulted in stronger effects than dry spiking, but the bioavailability of the particles appeared to be limited when highly-concentrated nanoparticle suspensions were used for wet spiking. The availability of the nanoparticles was slightly lower when silica sand rather than soil was used as the carrier for dry spiking, but the matrix itself (soil or food) had no effect. There are indications that the concentrations of the stock suspensions influence the test results, so dry spiking is preferred for solid TiO2 and Ag nanoparticles. We achieved satisfactory spiking homogeneity with Ag nanoparticles using soil as a solid carrier. Further experiments with other carriers and soil types are required to confirm that the observed differences are universal in character. There was no difference in effect when TiO2 nanoparticles were applied via food or soil. The spiking of soil instead of food is preferred for TiO2 nanoparticles, as is the case for conventional chemicals.

Highlights

  • In terrestrial ecotoxicological tests, the availability and ecotoxicity of solid nanomaterials may depend on the application technique

  • Our experiments using uncoated TiO2 and Ag nanoparticles showed that the application technique influences the severity of the effects observed in standardized ecotoxicity tests

  • The effects caused by dry spiking were concentration-dependent for the selected test concentrations (3-6 concentrations, depending on the test) whereas there was no such relationship for the two test concentrations when wet spiking methods were applied using water as the carrier

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Summary

Introduction

The availability and ecotoxicity of solid nanomaterials may depend on the application technique. The guidance state that nanomaterials applied to solid test media such as soils and sediments can be introduced by dispersion or in solid form, the application method should be carefully chosen to avoid damaging the test substance. The use of high-energy ultrasonication to achieve homogenous aqueous dispersions, or the use of a mortar and pestle to mix solid material with a solid carrier such as silica sand or soil, may damage or modify the surface, coating or crystalline structure of the nanomaterial. The waterbased dispersion of nanomaterials is recommended to provide comparability between aquatic, terrestrial and sediment tests [2]

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