Effects of hardness, alkalinity and pH on the toxicity of pentachlorophenol to selenastrum capricornutum (printz)

The toxicity of pentachlorophenol (PCP) to Selenastrum capricornutum was examined in three different culture media: a hard and a soft form of Freeman's reference water and the algal assay bottle test (AABT) medium (a soft water). The 96‐h growth potentials of the media were equal (28–29 mg/L dry wt.) but 96‐h EC50s ranged sevenfold: 0.11 mg/L (AABT), 0.15 mg/L (Freeman's soft water) and 0.76 mg/L (Freeman's hard water). Culture media equilibrium pH and 96‐h EC50 were strongly correlated ( r = 1.00). Evidence is presented that supports the hypothesis that the toxicity of PCP, a weak acid, is due primarily to the concentration of the undissociated species.