The effect of anthracene and phenanthrene on the growth, photosynthesis, and SOD activity of the green alga Scenedesmus armatus depends on the PAR irradiance and CO2 level

Short-term (24-h) experiments were performed to examine the effect of phenanthrene (PHE) and anthracene (ANT) on algae grown in a batch culture system at irradiances of 12, 33, 48, and 64 W m(-2) of the PAR range. Cultures were aerated (0.1 or 2% CO2) or nonaerated. As a result of aeration the concentration of ANT dropped from 0.45 mg L-1 at the beginning of the experiment (to) to an undetectable value after 10 h. The PHE concentration dropped from 9.36 mg L-1 at to to 0.17 mg L-1 after 24 h. ANT at nominal concentrations exceeding 0.05 mg L-1 inhibited the growth of the algae in a concentration- and irradiance-dependent manner. The algistatic effect of ANT observed at 64 and 48 W m(-2) was independent of the CO2 level, whereas the growth inhibition at 33 and 12 W m- 2 was much greater in cultures aerated with 2% than with 0.1 % CO2. PHE inhibited the growth only at a concentration of 10 mg L-1 (about 50% of the control) regardless of the irradiance or the CO2 concentration. The toxicity of both PHE and ANT was similar in aerated (0.1% CO2) and nonaerated cultures. ANT and PHE had a distinct effect on the photosynthesis. At 0.1% CO2, the irradiance-dependent inhibition (ANT) and stimulation (PHE) of the photosynthesis was observed. The inhibitory effect of ANT was enhanced when algae were grown at 2% CO2, but at the same CO2 concentration PHE did not affect the photosynthesis. ANT stimulated the total superoxide dismutase (SOD) activity in the cells, this effect being generally more pronounced at elevated CO2 levels and increasing with the irradiance. The total SOD activity was 250-300% higher in cells treated with PHE aerated with 0.1% CO2. At 2% CO2 no effect of PHE on the enzyme's activity was noted. The results obtained indicate that ANT acts as a photosensitizer causing an oxidative damage of cells, while PHE seems to affect the macromolecular synthesis.