Influence of Environmental Water on the Growth Phases of Freshwater Raphidophytes and Their Disinfection Byproducts

Freshwater raphidophytes occasionally proliferate and release high concentrations of trichloroacetic acid (TCAA) precursors into drinking water sources, which have been identified as phenolic glycosides. However, the environmental factors driving the production of these precursors remain unclear. This study investigated the growth behavior and disinfection byproduct formation potentials, including TCAA formation potential (TCAAFP), of three raphidophyte species (Merotricha bacillata, Gonyostomum latum, and Gonyostomum semen) under different cultivation conditions (i.e., a standard culture medium (AF-6) and environmental water supplemented with the same nutrients as AF-6 (AF-6-Env)). Algal growth was similar across all tested species, with no large differences observed between AF-6-Env and AF-6 media. However, TCAAFPs were consistently higher in AF-6-Env than in AF-6, suggesting that dissolved components in environmental water promote the production of TCAA precursors. Furthermore, the addition of dissolved organic matter (DOM) extracted from the environmental water using solid-phase extraction (SPE) cartridges to G. latum cultures in AF-6 medium resulted in increased TCAAFP. In contrast, no algal growth was observed in AF-6 medium containing the fraction not retained by the SPE cartridges. These results indicate that DOM in environmental waters plays a critical role in TCAA precursors production by raphidophytes.