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 (<i>Raphidocelis subcapitata</i>, <i>Escherichia coli</i>, and <i>Saccharomyces cerevisiae</i>) 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.