Abstract
Silica nanoparticles (SiO2NPs) are one of the most used in commercial products and biomedical tools, however, their environmental effects have not been fully described. Although negative effects of SiO2NPs on the behavior of freshwater invertebrates have been reported, the knowledge is limited, especially the effect of nanopowders in terrestrial organisms. Accordingly, the aim of the present study is to understand the effects of SiO2NPs on the avoidance behavior of five soil species, whose niche may differ thus contributing to differential harmful SiO2NPs effects. Hence, avoidance assays testing SiO2NPs concentrations of 0, 10, 100, 250, 500 and 1000 mg/kg were performed with Enchytraeus crypticus, Folsomia candida, Tenebrio molitor, Porcellionides pruinosus and Eisenia fetida. SiO2NPs induced different behavioral effects, depending on the invertebrate ecology/habitat, exposure route and physiology. T. molitor, P. pruinosus and F. candida did not avoid contaminated soil; however, E. crypticus and E. fetida significantly avoided SiO2NPs spiked soil. Since these terrestrial worms (oligochaetes) live mostly burrowed in the soil, this can provide greater opportunity for SiO2NPs’ uptake. On the other hand, the other tested organisms mainly living on the upper part of the soil did not avoid the SiO2NPs spiked soil. The avoidance data obtained here also highlight the need for further studies to understand whether (or not) the detected behavioral responses are linked to either neurotransmission processes or sensorial aspects of the biological models.
Highlights
Silicon is highly occurring in the earth’s crust in the form of crystalline, poorly crystalline and amorphous mineral phases within a wide range of particle sizes [1]
Enchytraeus crypticus were obtained from a laboratory culture kept in agar, consisting of the Bacti-Agar medium (Agar No 1, Lab M Limited, Lancashire, UK) and a sterilized mixture of four different salt solutions: 2 mM CaCl2·2H2O (Purity: 99.0–105.0%; Panreac, Darmstad, Germany; AppliChem, Barcelona, Spain); 1 mM MgSO4 (Purity: 99.0–105.0%; Panreac, Darmstad, Germany; AppliChem, Barcelona, Spain); 0.08 mM KCl (Purity: 99.5–101.0%; VWR Leuven, Belgium) and 0.75 mM NaHCO3 (Purity: 99.0–105.0%; Panreac, Darmstad, Germany; AppliChem, Barcelona, Spain), at a temperature of 19 ± 1 ◦C with a 16 h:8 h light:dark photoperiod
Folsomia candida were obtained from a laboratory culture kept on a moist substrate of plaster of Paris and activated charcoal (8:1 ratio), at a temperature of 20 ± 1 ◦C, in constant darkness
Summary
Silicon (mostly as SiO2) is (naturally) highly occurring in the earth’s crust (e.g., soils) in the form of crystalline, poorly crystalline and amorphous mineral phases within a wide range of particle sizes [1]. It is expected that soil will be an important reservoir of engineered SiO2 nanopowders in variable states of aggregation and combination, making crucial a correct assessment of potential impacts in terrestrial environments and in the overall soil ecosystem [7]. These are important interdisciplinary approaches, namely because reported studies on engineered nanoparticles, have shown specific abiotic properties (e.g., size, shape, surface-to-volume ratio and silanol group concentration) that modify toxic effects in organisms as compared to bulk silica powders [9]
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