Comparative Evaluation of Toxicity End Points in Unicellular Bioassays for Environmental Pollutant Assessment

Aquatic environments contain mixtures of contaminants, of which many cannot be detected through conventional chemical monitoring. Effect-directed analysis (EDA) uses bioassays to detect bioactive compounds and relies on sensitive small volume assays. The aim of this study was to evaluate the sensitivity of three unicellular species (Raphidocelis subcapitata, Escherichia coli, and Saccharomyces cerevisiae) and five vertebrate cell lines to 21 chemicals with diverse modes of action. The algae assay exhibited the highest sensitivity, detecting toxicity in >80% of the chemicals, while yeast was the least responsive. Subsequently, 279 wastewater samples were screened using algae and three cell lines. Algae detected toxicity in >92% of the samples, while the cell line viability assays responded to 21-53% of the samples. Bioavailability modeling revealed that medium composition significantly influenced chemical partitioning. Algae assays that performed in protein- and lipid-free medium were more sensitive to lipophilic compounds than assays using heterotrophic cells. We hypothesize that medium-driven differences in bioavailability contribute to the higher sensitivity of algae, even to pharmaceuticals with no known algal targets. Combining algae and DR-EcoScreen cell assays captured 96.4% of detected toxicities in environmental samples. This combination offers a high-throughput, cost-effective strategy for screening environmental samples for bioactive substances.