Toxicokinetic modeling of octylphenol bioconcentration in Chlorella vulgaris and its trophic transfer to Daphnia magna

Bioconcentration of 4-tert-Octylphenol (OP) in freshwater algae Chlorella vulgaris was investigated by considering the effects of algal growth and exudate excretion. The OP uptake in algae was approximately 113 mg kg⁻¹ after 24 h, and the uptake rate constant was estimated as 2.4 × 10⁴ L kg⁻¹ d⁻¹. The OP sorption onto exudates reduced OP bioavailability to C. vulgaris to 11% after 24 h, with a sorption coefficient of 9.7 × 10³ L kg⁻¹. The elimination of OP by algae growth (0.80 d⁻¹) was dominant over real elimination (0.60 d⁻¹). The calculated bioconcentration factor of OP in C. vulgaris following uptake and elimination rate constants was 4.0 × 10⁴ L kg⁻¹. Further, bioaccumulation of OP in Daphnia magna was investigated by considering both aqueous and dietary (C. vulgaris) exposures. Uptake and elimination rates of OP via water were 1.6 × 10⁴ L kg⁻¹ d⁻¹ and 0.95 d⁻¹, respectively, while ingestion rate and assimilation efficiency via diet were 0.41 d⁻¹ and 58%, respectively. The OP accumulation in D. magna predominantly occurred via water (63%) relative to diet (37%), resulting in a bioaccumulation factor of 2.7 × 10⁴ L kg⁻¹. The estimated trophic transfer factor was 0.25, suggesting that OP biomagnification was unlikely in the C. vulgaris-D. magna trophic relationship.