Deciphering the toxicity mechanism of haloquinolines on Chlorella pyrenoidosa using QSAR and metabolomics approaches

The hazardous potential of haloquinolines (HQLs) is becoming an issue of great concern due to its wide and long-term usage in many personal care products. We examined the growth inhibition, structure-activity relationship, and toxicity mechanism of 33 HQLs on Chlorella pyrenoidosa using the 72-h algal growth inhibition assay, three-dimensional quantitative structure–activity relationship (3D-QSAR), and metabolomics. We found that the IC50 (half maximal inhibitory concentration) values for 33 compounds ranged from 4.52 to > 150 mg·L−1, most tested compounds were toxic (1 mg·L−1 < IC50 < 10 mg·L−1) or harmful (10 mg·L−1 < IC50 < 100 mg·L−1) for the aquatic ecosystem. Hydrophobic properties of HQLs dominate their toxicity. Halogen atoms with large volume appear at the 2, 3, 4, 5, 6, and 7-positions of the quinoline ring to significantly increase the toxicity. In algal cells, HQLs can block diverse carbohydrates, lipids, and amino acid metabolism pathways, thereby resulting in energy usage, osmotic pressure regulation, membrane integrity, oxidative stress disorder, thus fatally damaging algal cells. Therefore, our results provide insight into the toxicity mechanism and ecological risk of HQLs. [Display omitted] •Algal toxicity data for 33 haloquinolines was provided for the first time.•Most haloquinolines are either harmful or toxic to the aquatic systems.•Toxicity of haloquinolines is mainly related to their hydrophobic properties.•Osmotic pressure, membrane integrity and energy usage were damaged in algal cells.