Environmental safety data on CuO and TiO2 nanoparticles for multiple algal species in natural water: Filling the data gaps for risk assessment.

Most research on nanoparticle (NP) ecotoxicological effects has been conducted on single species in laboratory conditions that are not environmentally representative. We compared the effects of CuO NPs, CuSO4 (ionic control) and TiO2 NPs in nutrient-adjusted natural water (ANW) and in the OECD201 standard medium to four different algal species: green algae Raphidocelis subcapitata and Chlamydomonas reinhardtii, a diatom Fistulifera pelliculosa, and a cyanobacterium Synechocystis sp. Biomass and the effective quantum yield of photosystem II (Fv/Fm) were used as toxicity endpoints. CuO NPs were very toxic across taxa in the OECD201 assay (biomass-based 72 h EC50 0.2-0.9 mg l-1). Toxicity of CuO NPs was explained by shedding of ions from particles as Cu2+ is highly toxic: 72 h EC50 in the OECD201 medium was 0.01-0.03 mg l-1 in three species and 0.003 mg l-1 in the case of the cyanobacterium. Toxicity of copper compounds was overall reduced in ANW, presumably because of reduced bioavailability due to metal ions binding to natural organic matter. Copper compounds were more toxic to the cyanobacterium than to other algae and this effect was not amended in ANW. TiO2 NPs did not inhibit the biomass production and photosynthesis of the diatom or the cyanobacterium up to 100 mg l-1, but inhibited biomass production of green algae in the OECD201 medium (EC50 14-15 mg l-1). TiO2 NPs also did not significantly inhibit Fv/Fm up to 100 mg l-1, suggesting a general lack of effect on photosynthesis. Adverse effects of TiO2 NPs were at least in part due to cell-NP heteroagglomeration. Our data are informative for the complete risk assessment of engineered NPs by filling data gaps about NP effects in environmentally realistic conditions.

Potency of (doped) rare earth oxide particles and their constituent metals to inhibit algal growth and induce direct toxic effects.

Use of rare earth elements (REEs) has increased rapidly in recent decades due to technological advances. It has been accompanied by recurring rare earth element anomalies in water bodies. In this work we (i) studied the effects of eight novel doped and one non-doped rare earth oxide (REO) particles (aimed to be used in solid oxide fuel cells and gas separation membranes) on algae, (ii) quantified the individual adverse effects of the elements that constitute the (doped) REO particles and (iii) attempted to find a discernible pattern to relate REO particle physicochemical characteristics to algal growth inhibitory properties. Green algae Raphidocelis subcapitata (formerly Pseudokirchneriella subcapitata) were used as a test species in two different formats: a standard OECD201 algal growth inhibition assay and the algal viability assay (a 'spot test') that avoids nutrient removal effects. In the 24h 'spot' test that demonstrated direct toxicity, algae were not viable at REE concentrations above 1mgmetal/L. 72-hour algal growth inhibition EC50 values for four REE salts (Ce, Gd, La, Pr) were between 1.2 and 1.4mg/L, whereas the EC50 for REO particles ranged from 1 to 98mg/L. The growth inhibition of REEs was presumably the result of nutrient sequestration from the algal growth medium. The adverse effects of REO particles were at least in part due to the entrapment of algae within particle agglomerates. Adverse effects due to the dissolution of constituent elements from (doped) REO particles and the size or specific surface area of particles were excluded, except for La2NiO4. However, the structure of the particles and/or the varying effects of oxide composition might have played a role in the observed effects. As the production rates of these REO particles are negligible compared to other forms of REEs, there is presumably no acute risk for aquatic unicellular algae.

Multilaboratory evaluation of 15 bioassays for (eco)toxicity screening and hazard ranking of engineered nanomaterials: FP7 project NANOVALID.

Within EU FP7 project NANOVALID, the (eco)toxicity of 7 well-characterized engineered nanomaterials (NMs) was evaluated by 15 bioassays in 4 laboratories. The highest tested nominal concentration of NMs was 100 mg/l. The panel of the bioassays yielded the following toxicity order: Ag > ZnO > CuO > TiO2 > MWCNTs > SiO2 > Au. Ag, ZnO and CuO proved very toxic in the majority of assays, assumingly due to dissolution. The latter was supported by the parallel analysis of the toxicity of respective soluble metal salts. The most sensitive tests/species were Daphnia magna (towards Ag NMs, 24-h EC50 = 0.003 mg Ag/l), algae Raphidocelis subcapitata (ZnO and CuO, 72-h EC50 = 0.14 mg Zn/l and 0.7 mg Cu/l, respectively) and murine fibroblasts BALB/3T3 (CuO, 48-h EC50 = 0.7 mg Cu/l). MWCNTs showed toxicity only towards rat alveolar macrophages (EC50 = 15.3 mg/l) assumingly due to high aspect ratio and TiO2 towards R. subcapitata (EC50 = 6.8 mg Ti/l) due to agglomeration of TiO2 and entrapment of algal cells. Finally, we constructed a decision tree to select the bioassays for hazard ranking of NMs. For NM testing, we recommend a multitrophic suite of 4 in vitro (eco)toxicity assays: 48-h D. magna immobilization (OECD202), 72-h R. subcapitata growth inhibition (OECD201), 30-min Vibrio fischeri bioluminescence inhibition (ISO2010) and 48-h murine fibroblast BALB/3T3 neutral red uptake in vitro (OECD129) representing crustaceans, algae, bacteria and mammalian cells, respectively. Notably, our results showed that these assays, standardized for toxicity evaluation of "regular" chemicals, proved efficient also for shortlisting of hazardous NMs. Additional assays are recommended for immunotoxicity evaluation of high aspect ratio NMs (such as MWCNTs).