Single and mixture toxicity of pharmaceuticals on atyaephyra desmarestii in global change scenarios

Abstract

Lethal, sublethal and mixture toxicity tests of three pharmaceutical compounds Diclofenac (DF), Ibuprofen (IB) and Carbamazepine (CBZ) were carried out with the freshwater shrimp Atyaephyra desmarestii at two different temperatures (20º and 25ºC). Obtained lethal concentrations (LC50) for each individual compound after 96 hours of exposure were 6.3 mg· L-1, 13.3 mg·L-1 and 94.3 mg· L-1 in organisms exposed at 20ºC and 6.4 mg· L-1, 10.1 mg·L-1 and 66.4 mg·L-1 at 25ºC for DF, IB and CBZ respectively. Based on obtained mortality data, Predictive No Effect Concentration (PNEC) was calculated for each of the compounds and compared with Predicted Environmental Concentrations (PEC) reported in surface waters. Environmental risk of each compound was estimated as the ratio between PEC/PNEC and revealed that IB could represent a medium risk in freshwater environments. Additionally, binary and ternary mixture toxicity assays of the selected compounds were carried out. The obtained data was applied to two predictive toxicity models: Concentration Addition (CA) and Independent Action (IA). Finally, risk assessment was carried by estimating risk quotients (RQ). In this study, the mortality produced by binary mixtures at 20°C is lower than that produced at 25°C and the predictive model that fits best is CA presumably because two of the compounds (DF and IB) present a similar mode of action. The selected sublethal endpoints: food ingestion, osmoregulatory capacity and respiration rates were monitored at environmental relevant concentrations, ranging between 10-70μg· L-1 for the three selected compounds. No significant differences in both ingestion rate and haemolymph osmolality were found between controls and treatment (Dunnett ́s test p>0.05) neither at 20º nor 25ºC. A decrease in the degree of oxygen independence was observed in shrimps exposed to DF at 20ºC under anoxia conditions (1 mg O2·L-1). For respiration rates there was a decrease in the oxygen consumption in organisms exposed to CBZ at 25ºC even in well oxygenated water (5 mg O2·L-1). Ecotoxicological action models can be considered useful tools to assess the expected effects of complex mixtures of pollutants in the environment. The results obtained provide relevant information on the combined effect of contamination and temperature variation in aquatic organisms in scenarios subject to global warming.