Acute Toxicities of Bromophenols to Alga and Daphina: Comparative Species Sensitivity Distribution Between Standard and Dietary Supplementation Tests

Bromophenols are synthesized chemicals that are widely used in various industrial activities and are also naturally produced by marine algae as secondary metabolites, including 2,4-dibromophenol (2,4-DBP), 2,6-dibromophenol (2,6-DBP), and 2,4,6-tribromophenol (2,4,6-TBP). However, the toxicological profiles and toxicity data of these bromophenols remain largely unreported, necessitating further investigation. Acute toxicity tests of 2,4-DBP, 2,6-DBP, and 2,4,6-TBP were conducted in this study using <i>Scenedesmus quadricauda</i> and <i>Daphnia magna</i> (standard tests). Furthermore, a modified acute toxicity test of <i>D. magna</i> was proposed, which further evaluates the dietary supplementation effects (1.0 × 10⁴ cells/mL of <i>S. quadricauda</i>) on the toxicities of these three bromophenols (modified tests). The median effect concentrations (EC₅₀s) of <i>D. magna</i> increased significantly when <i>S. quadricauda</i> was supplied as the dietary supplement. The EC₅₀ values of 2,4-DBP increased from 2.17 to 4.47 mg/L, 2,6-DBP from 2.78 to 6.75 mg/L and 2,4,6-TBP from 1.57 to 3.28 mg/L. Moreover, the web-based interspecies correlation estimation platform coupled with the species sensitivity distribution model (Web-ICE-SSD) was used to calculate the fifth percentile hazard concentrations (HC₅s) for 2,4-DBP, 2,6-DBP, and 2,4,6-TBP. The HC₅ values when using standard test data for 2,4-DBP, 2,6-DBP, and 2,4,6-TBP were 0.55, 0.71, and 0.43 mg/L, respectively. In contrast, the HC₅ values when using modified test data increased to 1.20, 1.80, and 0.88 mg/L. These results indicated that dietary supplementation during acute toxicity tests may provide more environment-related risk assessment.