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.