Evaluation of the Multi-Level Ecological Responses of Freshwater Organisms to Selected Human Pharmaceuticals

  • Adeolu Olabode Aderemi

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


The increasing use of human pharmaceuticals and subsequent discharge majorly via wastewater into the aquatic environment have become an ongoing concern due to the threat they pose to non-target organisms. Many of the studies on the ecotoxic effects of pharmaceuticals are focused on the higher levels of biological organization such as growth. However, since the first level of interaction of any pollutant with an organism is at the molecular-cellular level, the integration of the more sensitive suborganismal responses into the ecotoxicity of pharmaceuticals will not only elucidate their mechanisms of toxicity but also allow the prediction of adverse effects before they are detected at the level relevant to risk assessment. This study was therefore carried out to assess the multi-level responses of freshwater organisms namely: unicellular green microalgae (Raphidocelis subcapitata and Chlorella vulgaris) and zebrafish (Danio rerio) embryos to selected human pharmaceuticals.There are no multi-level effect studies carried out yet on the toxicity of the anaesthetic, lidocaine, on zebrafish. In addition, the measurement of energy status in microalgae as well as the evaluation of changes in the chloroplast encoded gene expression of R. subcapitata following exposure to pharmaceuticals is unique.

The risk assessment studies demonstrated that R. subcapitata was generally more sensitive than C. vulgaris to the pharmaceuticals and a link between algal growth and photosynthesis inhibition were observed. Erythromycin and clarithromycin showed high toxicity towards R. subcapitata at environmentally realistic concentrations and thereby represent a significant risk to the phytoplankton community.

In the multi-level effects study with zebrafish larvae, in agreement with its adverse effects in mammals, lethal concentration of lidocaine (> LCio) was noted as neurotoxic and cardiotoxic and this observation was linked to ROS induction due to significant decreases in both catalase (CAT) activity and the amounts of transcripts of antioxidant enzymes, superoxide dismutases (SOD1 and SOD2), and CAT. Cyclophosphamide and sulfamethoxazole elicited cardiotoxic and neurotoxic responses in exposed larvae and their significant upregulation of CAT and SOD1 (cyclophosphamide only) genes is most likely an indication that the antioxidant capacity was not enough to counteract ROS accumulation. A significant upregulation of the CAT activity and/or gene expressions of CAT, SOD1 and SOD2 at non-toxic levels of ifosfamide, lidocaine, cyclophosphamide, atenolol and erythromycin suggests that these antioxidants may play a role in the prevention of teratogenic effects in zebrafish. However, the prolonged or continuous exposure of zebrafish to non-toxic levels may eventually provoke significant oxidative stress responses.

Cell yield inhibitory concentrations of sulfamethoxazole, clarithromycin, erythromycin and ciprofloxacin were found to elicit a considerable increase in the energy consumption in R. subcapitata thereby causing a significant decline in the cellular energy allocation (CEA).However, at the lowest concentration of ciprofloxacin, a stimulatory effect on growth was observed (up to 16%), which was also highly correlated with the increase in the net energy budget (CEA). The elevated cellular respiration rate reported at some of the inhibitory levels of the antibiotics including the non-toxic ciprofloxacin concentration may be attributed to the need for the microalgae to respond to oxidative stress under these conditions, given the significant increase in SOD activity. However, with sulfamethoxazole and erythromycin, the antioxidant responses do not seem to be enough to cope with the reactive oxygen species and prevent oxidative damage, given the elevated LPO levels observed. In this study, Ec, SOD and CEA were more sensitive than growth rate for the test antibiotics and strong correlations occurred between the classical and biochemical parameters. CEA also interestingly yielded a similar ECio as growth yield and a lower ECio values than the growth rate for all the antibiotics.Consequently, in addition to revealing effects of antibiotic stress on R. subcapitata at the cellular level, this present study suggests CEA as a reliable indicator of the organisms’physiological status.

Ultimately, the early detection of pharmaceutical effects in aquatic organisms before they become more obvious and detrimental will allow preventive measures to be put in place. For better understanding and to avoid the underestimation of pharmaceutical effects in the aquatic ecosystem, relevant regulatory bodies such as the Scottish Environmental Protection Agency (SEPA) should consider the integration of the more sensitive, proactive and informative evaluation tools established in this thesis into the risk assessment o f pharmaceuticals. This will go a long way in achieving a good ecological status for our surface water bodies.
Date of Award2018
Original languageEnglish
Awarding Institution
  • Glasgow Caledonian University
SupervisorColin Hunter (Supervisor), Ole Pahl (Supervisor) & Xinhua Shu (Supervisor)

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