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Feeding behaviour and movement as sublethal endpoints to study the impact of pharmaceuticals on the freshwater amphipod Gammarus pulex

Student thesis: Doctoral Thesis

Pollution of the aquatic environment by pharmaceuticals is a well-established problem that has raised the attention of the scientific and public community since the late 1970s. However, there remain uncertainties about the possible adverse effects that pharmaceuticals compounds may have on non-target organisms.
The following thesis focuses on understanding the impact of pharmaceuticals on the behaviour of the freshwater amphipod Gammarus pulex. In particular, this thesis provides an evaluation of the effectiveness and applicability of G. pulex feeding behaviour as a sublethal endpoint in ecotoxicology.
G. pulex plays an important role in the decomposition of organic matter in lotic environments. Gammarus spp. feeding behaviour has often been studied as a sublethal endpoint in ecotoxicology. Currently, there is no official standardised methodology and differences in the method can be encountered in several steps of the experimental design: acclimation phase, food preparation and feeding rate calculation. The lack of standardisation for feeding studies can affect the outcome of an experiment and weaken possible comparisons between published literature.
The comparability and applicability of five different feeding equations were determined over periods of 24 h and 7 days, and the toxicity of the antidiabetic drug metformin was also investigated. One of the tested feeding equations was found to produce results that did not reflect G. pulex feeding activity and cannot be considered equivalent to the others. G. pulex feeding rate was inhibited after 2 days by a concentration of 10 μg/L of metformin compared to the control, whereas the swimming velocity was not altered. These results further support the necessity of developing a standard feeding assay for Gammarids, but also highlight the ecological impact that metformin might have in freshwater environments.
The indirect impact on G. pulex feeding behaviour of a mixture of antibiotics (sulfamethoxazole and trimethoprim) was assessed. Fungal biomass on the leaves surface and bacterial abundance in the conditioning water were also measured. G. pulex specimens ate significantly less when they were provided with leaf discs that were conditioned in a mixture of the two antibiotics, each at a concentration of 2 and 20 μg/L. No differences were measured in the fungal biomass, whereas bacterial abundance was significantly lower in the presence of the 20 μg/l and 200 μg/L mixture concentrations. The tested mixture could indirectly affect G. pulex feeding behaviour and reduce the bacterial abundance in water, but this was only measured at concentrations that are typical of heavily polluted streams (2 μg/L ) or are at least 10 times higher (20 μg/L) than the highest reported concentration in the environment.
Behavioural analyses, in terms of movement, ventilation, feeding rate and swimming velocity, were determined after exposure to three concentrations of the antidepressant, venlafaxine. Over a period of 11 days, organisms exposed to 0.02 μg/l were found to move significantly more compared to the control, whereas ventilation was not affected. G. pulex feeding activity was found to significantly increased after 24 h and after 2-day exposure to 20 μg/l venlafaxine concentration. A significant increase in swimming velocity was measure after 7 days in organisms that were exposed to 20 μg/l of venlafaxine. Collectively, these results may have implications for the ecological success of G. pulex.
Overall, this research has demonstrated that G. pulex feeding behaviour is a sensitive sublethal endpoint. G. pulex feeding activity was affected by exposure to metformin and venlafaxine, and by indirect exposure to the antibiotic mixture of sulfamethoxazole and trimethoprim. A standardised methodology would allow comparisons between studies and the possibility of feeding behaviour to be included in environmental risk assessments. The current study has also shown how different pharmaceuticals can induce alterations in different behavioural endpoints (movement, swimming velocity, feeding rate) in G. pulex.
Original languageEnglish
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Award dateDec 2019

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