The Effect of the Antidepressant Citalopram on the Bioconcentration and Biomarker Response of Daphnia magna at Environmentally Relevant Concentrations

The widespread use and pseudo-persistent occurrence of the antidepressant citalopram (CIT) could pose a potential ecological risk in the aquatic environment. The message about the bioconcentration and sensitive biomarker identification of CIT at the environmentally relevant concentrations is limited. In this study, an integral evaluation of the phenotypic and biochemical effects of CIT on Daphnia magna (D. magna) was conducted at 0.5 and 10 µg/L. The biomarker screening includes energy metabolism, phototactic behavior, feeding dysfunction, and antioxidant stress responses. The carbohydrate, lipid, and protein content was determined using the assay of anthrone with glucose as standard, thiophosphorate-Vaniline with cholesterol as standard, and Coomassie brilliant blue with serum albumin as standard, respectively. The results showed the bioconcentration equilibrium of CIT reached at the exposure duration of 48 h during the uptake process. At the exposure concentrations of 0.5 and 10 µg/L, the bioconcentration factor of CIT was 571.2 and 67.4 L/kg, respectively. Both protein and lipid content significantly increased at 0.5 µg/L with a 1.78-fold elevation in total energy. Comparatively, the lipid content showed a significant increase at 10 µg/L, while the available total energy rose by 1.25-fold relative to the control group. The phototactic behavior of D. magna exposed to 0.5 µg/L CIT was markedly reduced at 48 h relative to control. In contrast, a significant decrease in phototaxis was observed after 6 h and then a significant increase at 12 h with a continuously obvious decline at 10 µg/L. The filtration rates were increased by 32% compared to controls at 0.5 µg/L, while the stimulatory effects disappeared at 10 µg/L. With regarding to the antioxidant enzyme activities, CIT exposure significantly inhibited the catalase activity both at 0.5 and 10 µg/L, while the glutathione S-transferase activity was obviously induced at 0.5 µg/L and inhibited at 10 µg/L. The expression level of 18s gene was significantly decreased at 10 µg/L. Only the gst gene expression level was significantly increased at 0.5 µg/L, while the 18s and cat gene expression level was obviously inhibited and induced at 10 µg/L. Comprehensively, the responses of the phenotypic traits and energy metabolism of D. magna at various environmental concentrations were sensitive for CIT. This study provided basic data for the risk estimation of CIT in the real freshwater environment.