Table 5.
The toxicity (EC50 a) of humic acids (HA), as prepared and aged Fe2+/Fe3+ ions to P. caudatum and S. alba.
| Sample | EC50 ± SD (mg Fe/L) |
|---|---|
| Toxicity to ciliates P. caudatum (24 h EC50) | |
| HA * | >33 |
| HA * (90 days) | 1.93 ± 0.55 |
| Fe2+/Fe3+ | 0.48 ± 0.02 |
| Fe2+/Fe3+ (90 days) | 0.67 ± 0.02 |
| Fe(II,III)HA | >15.1 |
| Fe(II,III)HA (90 days) | 1.4 ± 0.4 |
| Toxicity to plants S. alba (96 h EC50) | |
| HA * | 900.65 ± 106.2 |
| HA * (90 days) | 880.1 ± 123.1 |
| Fe2+/Fe3+ | 75.21 ± 44.4 |
| Fe2+/Fe3+ (90 days) | 231.41 ± 97.46 |
| Fe(II,III)HA | 910.43 ± 270.1 |
| Fe(II,III)HA (90 days) | 915.23 ± 145.2 |
All concentrations are nominal (mg of weighed 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; * EC50 values for HA are calculated as mg/L; Color code: ≤ 1 mg/L (red ) = very toxic; > 1–10 mg/L ( ) = toxic; >10–100 mg/L (yellow ) = harmful; > 100 mg/L (green ) = “not classified/not harmful”. EC50 data not allowing ranking are on white background.