Table 4.
The toxicity (EC50) of magnetite nanoparticles (MNP)s, humic acids (HA), Fe2+ and Fe3+ ions and their complexes with HAs to ciliates P. caudatum and plants S. alba.
| Sample | EC50 ± SD (mg/L) |
|---|---|
| Toxicity to ciliates P. caudatum (24 h EC50) | |
| Fe2+ a | 1.15 ± 1.4 |
| Fe3+ a | 3.27 ± 0.8 |
| Fe2+/Fe3+ c | 0.48 |
| Fe3O4 | >33 |
| HA | >33 |
| Fe(II)HA | >33 |
| Fe(III)HA | 24.6 ± 9.3 |
| Fe(II,III)HA b,c | >15.1 |
| Fe3O4/HA b | 32 ± 3.1 |
| Toxicity to plants S. alba (96 h EC50) | |
| Fe2+ | 35.92 ± 18.6 |
| Fe3+ | 58.71 ± 21.2 |
| Fe2+/Fe3+ | 75.21 ± 44.4 |
| Fe3O4 c | >3300 |
| HA | 900.65 ± 106.2 |
| Fe(II)HA | 1402.3 ± 135.1 |
| Fe(III)HA | 256.18 ± 50.4 |
| Fe(II,III)HA | 910.43 ± 270.1 |
| Fe3O4/HA | 902.71 ± 211.5 |
All concentrations are nominal (mg of compound L−1). Average values ± SD of triplicate; a Values calculated with IBM SPSS Statistica using the probit method; b Values calculated with R using ANOVA. a-c indicate statistical significance. Values with the same letters (a or b) are not significantly different (p > 0.05). Samples with letter “c” have no significantly different at concentrations. EC50 values are calculated as mg/L for Fe3O4, HAs and Fe3O4/HA and as mg Fe/L for Fe-ions; Color code: ≤1 mg/L (red )= very toxic; >1–10 mg/L (orange ) = toxic; >10–100 mg/L (yellow ) = harmful; >100 mg/L (green ) = “not classified/not harmful”. EC50 data not allowing ranking are on white background.