CHAPTER 6 - Effects of pH on Prymnesium parvum Cell Viability and Toxicity

Toxic water obtained from E. V. Spence Reservoir during an ongoing Prymnesium parvum-related fish kill was used to evaluate the effect of lower pH levels on P. parvum cell integrity and toxicity. Hydrochloric and sulfuric acids were used separately to lower pH in toxic water to see if the P. parvum cells and ichthyotoxin would be destroyed or deactivated. The treatments ranged from pH 5.5 to pH 7.0 in 0.5-SU increments. Untreated water (control) had a pH of 8.3. The acidic pH levels were effective in reducing the density of viable P. parvum cells, and the percent reduction in density increased as the pH decreased. Reductions in density were 23.6% and 87.6 % for pH 6 and 5.5, respectively, 3 hours after treatment and 41.6% and 94%, respectively, 28 hours after treatment with hydrochloric acid. Sulfuric acid treatments reduced cell density by 38.3% and 61.7% for pH 6.5 and 6, respectively 1 hour after treatment and 35.8% and 82.3% 18 hours after treatment. A bioassay demonstrated that at pH 6 and 6.5, toxicity was reduced but not completely eliminated.