Uptake of microalgae as sublethal biomarker reveals phototoxicity of oxytetracycline to the crustacean Daphnia magna

• Published in: Water research (Oxford) 2021-01, Vol.188, p.116556, Article 116556
• Main Authors: Peroti, Luis, Huovinen, Pirjo, Orellana, Sandra, Muñoz, Marcelo, Fuentes, Romina, Gómez, Iván
• Format: Article
• Language: English
• Subjects: Animals; Antibiotics; Biomarkers; Daphnia; Daphnia magna; Humans; Microalgae; Oxytetracycline - toxicity; Phototoxicity; Raphidocelis subcapitata; Sublethality; UV radiation; Water Pollutants, Chemical - toxicity
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2020.116556

•Oxytetracycline is uptaken by Daphnia, leading to sublethal toxic effects.•UV radiation induces lethality via photosensibilization of OTC in tissues of Daphnia.•OTC adsorbs rapidly on cell surface of microalga, without toxic effects.•UV-induced phototoxicity of OTC impairs physiological status of microalga.•Chlorophyll fluorescence method allows observing feeding rate as sublethal response in Daphnia. Antibiotics are considered emerging pollutants as their presence in the environment is increasingly common. Although their environmental concentrations are generally low, they can pose risk to organisms through bioaccumulation, causing sublethal effects. Furthermore, solar radiation can trigger reactions in certain compounds after their accumulation within organisms or in the environment. Toxicity and photoinduced toxicity of oxytetracycline (OTC, widely used antibiotic in salmon aquaculture) on Daphnia magna (Crustacea, Cladocera) and microalgae Raphidocelis subcapitata (Chlorophyceae) as its food source was assessed via aqueous exposure. Also, the impact via diet (microalga) to the crustacean was examined. In addition to lethal (immobility) effect, in vivo chlorophyll fluorescence techniques were used to determine food ingestion (gut content as a biomarker of physiological health) in D. magna and physiological status of microalgae. OTC (≤10 mg L − 1) was not acutely (24 h) toxic to R. subcapitata when measured as maximum quantum yield (Fv/Fm) in darkness. However, under short (1 h) UV exposure OTC caused irreversible decrease of Fv/Fm (50%) at ≥0.5 mg L − 1. OTC was not acutely lethal to D. magna (≤10 mg L − 1), however, sublethal effects (43% decrease in food ingestion) at 10 mg L − 1 were demonstrated. UV exposure (4.5 h) strongly exacerbated toxicity of OTC, leading to lethal (87% immobility) and sublethal (81% decrease of feeding in survived individuals) effects. Uptake of OTC (aqueous exposure) and its photosensitization in tissues of D. magna under UV exposure was confirmed. On the other hand, rapid bioadsorption of OTC on cell surface was evident in R. subcapitata. Uptake of OTC in D. magna through diet could not be confirmed at short-term. Photomodification of OTC under UV exposure was observed through changes in its absorption spectrum. The results show that short exposure to summer UV levels of southern Chile can rapidly induce phototoxicity of OTC, suggesting a potential risk to aquatic organisms. [Display omitted]