The effects of pH on the growth ofChlorella vulgaris and its interactions with cadmium toxicity

The effects of pH alone, and in combination with exposure to 0.89 M cadmium, on the growth response of the green algaChlorella vulgaris were evaluated. Acidic (3.0–6.2) and alkaline (8.3–9.0) pH values retarded the growth of this alga. Optimal growth occurred when the pH of the medium was adjusted to values of 7.5 and 8.0. When the cells were exposed to pH adjusted medium plus the presence of 0.89 M Cd, a value known to reduce population growth by 50% at the control pH of 6.9, the affects were additive at the acidic (3.0–5.0) pH ranges. At alkaline pH values of 8.3–9.0 all toxicity responses could be explained by pH adjustment alone, indicating that additional cadmium toxicity was absent. At pH values of 7.5 and 8.0, cadmium toxicity was mitigated against, and resultant growth at pH 8.0 was at the same enhanced rate as this pH without cadmium.