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

Abstract

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 (t₀) to an undetectable value after 10 h. The PHE concentration dropped from 9.36 mg L^–1 at t0 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.