Bromoform Toxicity to Marine Microalgae: Studies using the Diatom Chaetoceros lorenzianus as a Model Organism.

Bromoform is the most prominent, relatively long-lived chlorination by-product in condenser effluents from seawater-based power plant cooling systems. There are few reports on the potential toxicity of this trihalomethane to marine phytoplankton. We investigated this using a marine diatom, Chaetoceros lorenzianus as the model organism. The study was conducted by exposing the diatom to bromoform concentrations 0, 50, 100, 150, 250, 500 and 1000 µg/L for exposure time of 3 and 24 h. The mode of action of bromoform was examined using endpoints which include chlorophyll a fluorescence, cell viability by SYTOX® green stain and genotoxicity by comet assay. The relative fluorescence unit and percent viability changed significantly at all concentrations in duration of study. The 24-h IC for viability and chlorophyll was estimated to be 255.6 µg/L and 343.5 µg/L, respectively. The tail DNA of 5-20% observed by comet assay indicated low-level DNA damage. Bromoform manages to target cell membrane and internal machinery, DNA and chlorophyll molecule of cell, leading to cause damage at multiple physiological levels. Based on the present data, the current discharge levels of bromoform 50-250 µg/L cause significant impact on the phytoplankton under investigation. However, the impact can be limited under actual field conditions wherein mixing of cooling water with natural water bodies is considered. Nevertheless, more studies are required to understand the toxicological response of organisms to bromoform, so that discharge levels can be continued to be kept within safe levels.