Contribution of marine algae to trihalomethane production in chlorinated estuarine water

Three species of marine algae representing major taxonomic groups of phytoplankton, Isochrysis galbana (Chrysophyceae), Carteria sp. (Chlorophyceae), and Thalassiosira pseudonana (Bacillariophyceae), were utilized to investigate the potential of naturally occurring chlorophyll a of living algae to produce trihalomethanes during the chlorination of saline waters. Chlorination of filtered natural estuarine water (salinity=23 p.p.t.) from the North Edisto River, South Carolina, results in rapid formation of 201–221 μg 1⁻¹ trihalomethanes comprised mainly of bromoform (CHBr₃) and chlorodibromomethane (CHBr₂Cl). In the presence of 10⁶ cells ml⁻¹ Isochrysis galbana, chlorination of filtered estuarine water with sodium hypochlorite (NaOCl) to a nominal 10 mg 1⁻¹ chlorine increased the total trihalomethane concentration by an average of 41% (N = 6). The presence of Thalassiosira pseudonana resulted in an average 24% decrease (N = 6) while Carteria sp. did not produce a statistically significant effect upon the total trihalomethane concentration formed.

The absence of any significant statistical correlations between the chlorophyll a content of algal cultures and trihalomethane concentrations causes us to discount chlorine-chlorophyll a interactions as a source of these compounds. However, trihalomethane concentrations produced from the chlorination of algal culture media, after removal of algal populations, suggests instead that the observed trends in trihalomethane production are mainly due to chlorines reaction with the by-products of algal metabolism.